INSTALLATION
INSTRUCTIONS
ML193UH
E 2013 Lennox Industries Inc.
Dallas, Texas, USA
®
MERIT SERIES GAS FURNACE
UPFLOW / HORIZONTAL AIR DISCHARGE
507121-01
08/2013
Supersedes 06/2013
Litho U.S.A.
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is a safety alert symbol and should never be ignored.
When you see this symbol on labels or in manuals, be alert
to the potential for personal injury or death.
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
AIR FLOW
UPFLOW
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person-
al injury or loss of life. Installation and service must
be performed by a licensed professional HVAC in-
staller (or equivalent), service agency or the gas sup-
plier.
HORIZONTAL RIGHT
HORIZONTAL LEFT
Table of Contents
Unit Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
ML193UH Gas Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Shipping and Packing List . . . . . . . . . . . . . . . . . . . . . . . . 3
Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Use of Furnace as a Construction Heater . . . . . . . . . . . 4
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Combustion, Dilution, Ventilation Air . . . . . . . . . . . . . . . 5
Setting Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Pipe and Fittings Specifications . . . . . . . . . . . . . . . . . . . 13
Joint Cementing Procedure . . . . . . . . . . . . . . . . . . . . . . . 15
Venting Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Vent Piping Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Integrated Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Unit Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Gas Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . 41
Proper Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
High Altitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Testing For Combustion Air Non-Direct Vents . . . . . . . 44
Other Unit Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Twinning the ML193UH . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Repair Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Start Up Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
08/13
507121-01
Page 1
*P507121-01*
*2P0813*
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ML193UH Gas Furnace
Shipping and Packing List
Package 1 of 1 contains
The ML193UH Category IV gas furnace is shipped ready
for installation in the upflow or horizontal position. The fur-
nace is shipped with the bottom panel in place. The bottom
panel must be removed if the unit is to be installed in hori-
zontal or upflow applications with bottom return air.
1 - Assembled ML193UH unit
1 - Bag assembly containing the following:
1 -Snap bushing
1 -Snap plug
The ML193UH can be installed as either a Direct Vent
or a Non-Direct Vent gas central furnace.
1 - Wire tie
1 -Condensate trap
The furnace is equipped for installation in natural gas ap-
plications. A conversion kit (ordered separately) is required
for use in propane/LP gas applications.
1 -Condensate trap cap
1 -Condensate trap clamp
1 -2” diameter debris screen
1 -3/4” Threaded street elbow
Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.
NOTE - In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors. In
Non-Direct Vent installations, combustion air is taken from
indoors or ventilated attic or crawlspace and flue gases are
involving roof termination.
The following items may also be ordered separately:
1 - Thermostat
1 - Propane/LP changeover kit
1 - Return air base kit
DIRECT VENT INSTALLATION
EXHAUST OUTLET
COMBUSTION
NON-DIRECT VENT
INSTALLATION
EXHAUST
OUTLET
1 - Horizontal suspension kit
AIR INTAKE OUTSIDE
OF HOUSE
Safety Information
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage,
personal injury or loss of life. Installation and service
must be performed by a licensed professional in-
staller (or equivalent), service agency or the gas sup-
plier.
COMBUSTION
AIR INTAKE
INSIDE
OF HOUSE
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
FIGURE 1
NON-DIRECT VENT
INSTALLATION
NON-DIRECT VENT
INSTALLATION
EXHAUST
OUTLET
EXHAUST
OUTLET
DANGER
Danger of explosion.
There are circumstances in which odorant used with
LP/propane gas can lose its scent. In case of a leak,
LP/propane gas will settle close to the floor and may
be difficult to smell. An LP/propane leak detector
should be installed in all LP applications.
COMBUSTION
AIR INTAKE INSIDE
VENTILATED
COMBUSTION
AIR INTAKE INSIDE
VENTILATED
CRAWL SPACE
Use only the type of gas approved for use with this furnace.
Refer to unit nameplate.
ATTIC SPACE
ML193UH units are CSA International certified to ANSI
Z21.47 and CSA 2.3 standards.
Building Codes
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI‐Z223.1/NFPA 54). The National Fuel
FIGURE 2
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Gas Code is available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
In Canada, all electrical wiring and grounding for the unit
must be installed according to the current regulations of the
Canadian Electrical Code Part I (CSA Standard C22.1)
and/or local codes.
New York, NY 10036
In Canada, installation must conform with current National
Standard of Canada CSA‐B149 Natural Gas and Propane
Installation Codes, local plumbing or waste water codes
and other applicable local codes.
Heating Unit Installed Parallell to Air Handler Unit
Dampers
(open during heating operation only)
In order to ensure proper unit operation in non-direct vent
applications, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code
or CSA‐B149 standard.
Gas Unit
AIR FLOW
AIR FLOW
Installation Locations
Air Handler Unit
This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
service clearances must take precedence over fire protec-
tion clearances.
Dampers
(open during cooling operation only)
Heating Unit Installed Upstream of Cooling Coil
NOTE - For installation on combustible floors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood flooring.
AIR FLOW
AIR FLOW
Gas Unit
Cooling Coil
For installation in a residential garage, the furnace must be
installed so that the burner(s) and the ignition source are
located no less than 18 inches (457 mm) above the floor.
The furnace must be located or protected to avoid physical
damage by vehicles. When a furnace is installed in a public
garage, hangar, or other building that has a hazardous at-
mosphere, the furnace must be installed according to rec-
ommended good practice requirements and current Na-
tional Fuel Gas Code or CSA B149 standards.
FIGURE 3
NOTE - This furnace is designed for a minimum continuous
return air temperature of 60°F (16°C) or an intermittent op-
eration down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The ML193UH furnace may be installed in alcoves, clos-
ets, attics, basements, garages, crawl spaces and utility
rooms in the upflow or horizontal position.
NOTE - Furnace must be adjusted to obtain a temperature
rise within the range specified on the unit nameplate. Fail-
ure to do so may cause erratic limit operation and prema-
ture heat exchanger failure.
This furnace design has not been CSA certified for installa-
tion in mobile homes, recreational vehicles, or outdoors.
This ML193UH furnace must be installed so that its electri-
cal components are protected from water.
Use of Furnace as Construction Heater
Lennox does not recommend the use of ML193UH units as
a construction heater during any phase of construction.
Very low return air temperatures, harmful vapors and op-
eration of the unit with clogged or misplaced filters will dam-
age the unit.
Installed in Combination with a Cooling Coil
shall be installed in parallel with, or on the upstream side of,
cooling coils to avoid condensation in the heating compart-
ment. With a parallel flow arrangement, a damper (or other
means to control the flow of air) must adequately prevent
chilled air from entering the furnace. If the damper is manu-
ally operated, it must be equipped to prevent operation of
either the heating or the cooling unit, unless it is in the full
HEAT or COOL setting.
ML193UH units may be used for heating of buildings or
structures under construction, if the following conditions
are met:
D The vent system must be permanently installed per
these installation instructions.
D A room thermostat must control the furnace. The use of
fixed jumpers that will provide continuous heating is not
allowed.
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National Electric
Code, ANSI/NFPA No. 70. The National Electric Code
(ANSI/NFPA No. 70) is available from the following ad-
dress:
D The return air duct must be provided and sealed to the
furnace.
D Return air temperature range between 60°F (16°C) and
80°F (27°C) must be maintained.
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
D Air filters must be installed in the system and must be
maintained during construction.
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D Air filters must be replaced upon construction comple-
tion.
WARNING
Product contains fiberglass wool.
D The input rate and temperature rise must be set per the
furnace rating plate.
Disturbing the insulation in this product during
installation, maintenance, or repair will expose you
to fiberglass wool. Breathing this may cause lung
cancer. (Fiberglass wool is known to the State of Cal-
ifornia to cause cancer.)
D One hundred percent (100%) outdoor air must be pro-
vided for combustion air requirements during construc-
tion. Temporary ducting may supply outdoor air to the
furnace. Do not connect duct directly to the furnace.
Size the temporary duct following these instructions in
section for Combustion, Dilution and Ventilation Air in a
confined space with air from outside.
Fiberglass wool may also cause respiratory, skin,
and eye irritation.
To reduce exposure to this substance or for further
information, consult material safety data sheets
available from address shown below, or contact your
supervisor.
D The furnace heat exchanger, components, duct sys-
tem, air filters and evaporator coils must be thoroughly
cleaned following final construction clean-up.
D All furnace operating conditions (including ignition, in-
put rate, temperature rise and venting) must be verified
according to these installation instructions.
Lennox Industries Inc.
P.O. Box 799900
Dallas, TX 75379-9900
• The “A” coil drain pan is high quality engineering poly-
mer with a maximum service temperature of 500° F.
However, adequate space must be provided between
the drain pan and the furnace heat exchanger. At least
2” space is required for sectionalized heat exchanger
and and 4” for drum-type or oil-fired furnace exchanger.
Closer spacing may damage the drain pan and cause
leaking.
WARNING
Insufficient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in rust-
ing and premature heat exchanger failure. Excessive
exposure to contaminated combustion air will result
in safety and performance related problems. Avoid
exposure to the following substances in the com-
bustion air supply:
General
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the fol-
lowing general recommendations must be considered
when installing a ML193UH furnace:
• Place the furnace as close to the center of the air dis-
tribution system as possible. The furnace should also be
located close to the vent termination point.
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
• When the furnace is installed in non-direct vent applica-
tions, do not install the furnace where drafts might blow
directly into it. This could cause improper combustion
and unsafe operation.
Combustion, Dilution & Ventilation Air
If the ML193UH is installed as a Non-Direct Vent Fur-
• When the furnace is installed in non-direct vent applica-
tions, do not block the furnace combustion air opening
with clothing, boxes, doors, etc. Air is needed for proper
combustion and safe unit operation.
nace, follow the guidelines in this section.
NOTE - In Non-Direct Vent installations, combustion air is
taken from indoors or ventilated attic or crawlspace and
flue gases are discharged out-doors.
• When the furnace is installed in an attic or other insu-
lated space, keep insulation away from the furnace.
In the past, there was no problem in bringing in sufficient
outdoor air for combustion. Infiltration provided all the air
that was needed. In today's homes, tight construction prac-
tices make it necessary to bring in air from outside for com-
bustion. Take into account that exhaust fans, appliance
vents, chimneys, and fireplaces force additional air that
could be used for combustion out of the house. Unless out-
side air is brought into the house for combustion, negative
pressure (outside pressure is greater than inside pressure)
• When the furnace is installed in an unconditioned
space, consider provisions required to prevent freezing
of condensate drain system.
CAUTION
ML193UH unit should not be installed in areas nor-
mally subject to freezing temperatures.
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will build to the point that a downdraft can occur in the fur-
nace vent pipe or chimney. As a result, combustion gases
enter the living space creating a potentially dangerous situ-
ation.
infiltration. If the furnace is located in a building of tight
construction with weather stripping and caulking around
the windows and doors, follow the procedures in the Air
from Outside section.
In the absence of local codes concerning air for combus-
tion and ventilation, use the guidelines and procedures in
this section to install ML193UH furnaces to ensure efficient
and safe operation. You must consider combustion air
needs and requirements for exhaust vents and gas piping.
A portion of this information has been reprinted with per-
mission from the National Fuel Gas Code (ANSI-
Z223.1/NFPA 54). This reprinted material is not the com-
plete and official position of the ANSI on the referenced
subject, which is represented only by the standard in its en-
tirety.
Confined Space
A confined space is an area with a volume less than 50 cu-
3
bic feet (1.42 m ) per 1,000 Btu (.29 kW) per hour of the
com-bined input rating of all appliances installed in that
space. This definition includes furnace closets or small
equipment rooms.
When the furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space con-
taining the furnace, the return airmust be handled by ducts
which are sealed to the furnace casing and which terminate
outside the space containing the furnace. This is especially
important when the furnace is mounted on a platform in a
confined space such as a closet or small equipment room.
Even a small leak around the base of the unit at the platform
or at the return air duct connection can cause a potentially
dangerous negative pressure condition. Air for combustion
and ventilation can be brought into the confined space ei-
ther from inside the building or from outside.
In Canada, refer to the CSA B149 installation codes.
CAUTION
Do not install the furnace in a corrosive or contami-
nated atmosphere. Meet all combustion and ventila-
tion air requirements, as well as all local codes.
All gas‐fired appliances require air for the combustion pro-
cess. If sufficient combustion air is not available, the fur-
nace or other appliance will operate inefficiently and un-
safely. Enough air must be provided to meet the needs of
all fuel-burning appliances and appliances such as ex-
haust fans which force air out of the house. When fire-
places, exhaust fans, or clothes dryers are used at the
same time as the furnace, much more air is required to en-
sure proper combustion and to prevent a downdraft. Insuf-
ficient air causes incomplete combustion which can result
in carbon monoxide.
Air from Inside
If the confined space that houses the furnace adjoins a
space categorized as unconfined, air can be brought in by
providing two permanent openings between the two
spaces. Each opening must have a minimum free area of 1
2
square inch (645 mm ) per 1,000 Btu (.29 kW) per hour of
total input rating of all gas-fired equipment in the confined
space. Each opening must be at least 100 square inches
2
(64516 mm ). One opening shall be within 12 inches (305
mm) of the top of the enclosure and one opening within 12
In addition to providing combustion air, fresh outdoor air di-
lutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace compo-
nents.
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM INSIDE
ROOF TERMINATED
EXHAUST PIPE
The requirements for providing air for combustion and ven-
tilation depend largely on whether the furnace is installed in
an unconfined or a confined space.
OPENINGS
(To Adjacent
Unconfined
Space)
Unconfined Space
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
ML193UH
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 50 cubic
3
feet (1.42 m ) per 1,000 Btu (.29 kW) per hour of the com-
bined input rating of all appliances installed in that space.
This space also includes adjacent rooms which are not
separated by a door. Though an area may appear to be un-
confined, it might be necessary to bring in outdoor air for
combustion if the structure does not provide enough air by
NOTE - Each opening shall have a free area of at least one square inch
2
per 1,000 Btu (645mm per .29kW) per hour of the total input rating of
all equipment in the enclosure, but not less than 100 square inches
2).
(64516mm.
FIGURE 4
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Air from Outside
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Crawlspace and Outlet Air to Outside)
If air from outside is brought in for combustion and ventila-
tion, the confined space shall be provided with two perma-
nent openings. One opening shall be within 12” (305mm) of
the top of the enclosure and one within 12” (305mm) of the
bottom. These openings must communicate directly or by
ducts with the outdoors or spaces (crawl or attic) that freely
communicate with the outdoors or indirectly through verti-
cal ducts. Each opening shall have a minimum free area of
Roof Terminated
Exhaust Pipe
2
1 square inch per 4,000 Btu (645mm per 1.17kW) per hour
of total input rating of all equipment in the enclosure. When
communicating with the outdoors through horizontal ducts,
each opening shall have a minimum free area of 1 square
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
Ventilation
Louvers
(Crawl space)
Furnace
2
inch per 2,000 Btu (645mm per .59kW) per total input rat-
permissible to bring in air for combustion from a ventilated
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE
(Inlet Air from Crawl Space and Outlet Air to Ouside)
Coupling or
*Intake Debris Screen Provided)
3 in. to 2 in.
Transition
VENTILATION LOUVERS
(Each end of attic)
(Field Provided)
ROOF TERMINATED
EXHAUST PIPE
NOTE-The inlet and outlet air openings shall each have a free area
2
of at least one square inch per 4,000 Btu (645mm per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
OUTLET
AIR
FIGURE 7
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
FURNACE
VENTILATION
LOUVERS
INLET
AIR
(For unheated
crawl space)
If air from outside is brought in for combustion and ventila-
tion, the confined space must have two permanent open-
ings. One opening shall be within 12 inches (305 mm) of the
top of the enclosure and one opening within 12 inches (305
mm) of the bottom. These openings must communicate di-
rectly or by ducts with the outdoors or spaces (crawl or at-
tic) that freely communicate with the outdoors or indirectly
through vertical ducts. Each opening shall have a minimum
NOTE-The inlet and outlet air openings shall each have a free area
2
of at least one square inch per 4,000 Btu (645mm per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
FIGURE 5
2
free area of 1 square inch (645 mm ) per 4,000 Btu (1.17
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Attic and Outlet Air to Outside)
kW) per hour of total input rating of all equipment in the en-
the outdoors through horizontal ducts, each opening shall
have a minimum free area of 1 square inch (645 mm ) per
2,000 Btu (.56 kW) per total input rating of all equipment in
the enclosure. See figure 9.
Ventilation Louvers
2
Inlet Air
Roof Terminated
Exhaust Pipe
(Minimum
12 in.(305mm) Above
attic floor)
When ducts are used, they shall be of the same cross-sec-
tional area as the free area of the openings to which they
connect. The minimum dimension of rectangular air ducts
shall be no less than 3 inches (75 mm). In calculating free
area, the blocking effect of louvers, grilles, or screens must
be considered. If the design and free area of protective cov-
ering is not known for calculating the size opening required,
it may be assumed that wood louvers will have 20 to 25 per-
cent free area and metal louvers and grilles will have 60 to
75 percent free area. Louvers and grilles must be fixed in
the open position or interlocked with the equipment so that
they are opened automatically during equipment opera-
tion.
*Intake Debris
Screen
(Provided)
Furnace
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
2
FIGURE 6
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leg). See figure 10. The bolt and washer must be re-
moved before the furnace is placed into operation. Af-
ter the bolt and washer have been removed, the rigid leg
will not touch the blower housing.
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
ROOF TERMINATED
EXHAUST PIPE
VENTILATION LOUVERS
(Each end of attic)
ML193UH090P48C
and ML193UH110P48C
with 1/2 HP Blower Motor
OUTLET
AIR
RIGID LEG
(Remove shipping bolt
and washer)
INLET AIR
(Ends 12” above
bottom)
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
FURNACE
NOTE-The inlet and outlet air openings shall each have a free area of
2
FIGURE 10
at least one square inch per 4,000 Btu (645mm per 1.17kW) per hour
of the total input rating of all equipment in the enclosure.
Installation - Setting Equipment
FIGURE 8
EQUIPMENT IN CONFINED SPACE -
ALL AIR FROM OUTSIDE
WARNING
Do not connect the return air duct to the back of the
furnace. Doing so will adversely affect the operation
of the safety control devices, which could result in
personal injury or death.
ROOF TERMINATED
EXHAUST PIPE
OUTLET AIR
WARNING
Blower access panel must be securely in place when
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into
living space resulting in personal injury or death.
FURNACE
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
INLET AIR
Upflow Applications
NOTE-Each air duct opening shall have a free area of at least one
2
The ML193UH gas furnace can be installed as shipped in
lect a location that allows for the required clearances that
are listed on the unit nameplate. Also consider gas supply
connections, electrical supply, vent connection, conden-
sate trap and drain connections, and installation and ser-
vice clearances [24 inches (610 mm) at unit front]. The unit
must be level from side to side. Unit may be positioned from
level to 1/2” toward the front to aid in draining. See figure
square inch per 2,000 Btu (645mm per .59kW) per hour of the total
input rating of all equipment in the enclosure. If the equipment room
is located against an outside wall and the air openings communi-
cate directly with the outdoors, each opening shall have a free area
of at least 1 square inch per 4,000 Btu (645mm per 1.17kW) per
hour of the total input rating of all other equipment in the enclosure.
2
FIGURE 9
Shipping Bolt Removal
Units with 1/2 hp blower motor are equipped with three flex-
ible legs and one rigid leg. The rigid leg is equipped with a
shipping bolt and a flat white plastic washer (rather than the
rubber mounting grommet used with a flexible mounting
Allow for clearances to combustible materials as indicated
on the unit nameplate.
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SETTING EQUIPMENT
UPFLOW APPLICA-
TION
UNIT
FRONT
UNIT
FRONT
AIR FLOW
AIR FLOW
1/2”
max.
FRONT VIEW
SIDE VIEW
SIDE VIEW
HORIZONTAL APPLICATION
UNIT
FRONT
AIR FLOW
1/2”
max.
END VIEW
FRONT VIEW
Unit must be level side-to-side. Unit may be positioned from level to 1/2” toward the front to aid in draining.
FIGURE 11
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Return Air Guidelines
WARNING
Return air can be brought in through the bottom or either
side of the furnace installed in an upflow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.
Improper installation of the furnace can result in per-
sonal injury or death. Combustion and flue products
must never be allowed to enter the return air system
or air in the living space. Use sheet metal screws and
joint tape to seal return air system to furnace.
In platform installations with furnace return, the fur-
nace should be sealed airtight to the return air ple-
num. A door must never be used as a portion of the
return air duct system. The base must provide a
stable support and an airtight seal to the furnace. Al-
low absolutely no sagging, cracks, gaps, etc.
Markings are provided on both sides of the furnace cabinet
for installations that require side return air. Cut the furnace
cabinet at the maximum dimensions shown on page 2.
For no reason should return and supply air duct sys-
tems ever be connected to or from other heating de-
vices such as a fireplace or stove, etc. Fire, explo-
sion, carbon monoxide poisoning, personal injury
and/or property damage could result.
Refer to Engineering Handbook for additional information.
ML193UH applications which include side return air
and a condensate trap installed on the same side of the
cabinet (trap can be installed remotely within 5 ft.) re-
quire either a return air base or field-fabricated transi-
tion to accommodate an optional IAQ accessory taller
Installation Clearances
Top
Side Return Air
(with transition and filter)
Left Side
Right Side
20” X 25” X 1”
(508mmX635mmX25mm)
Bottom (Floor)
1−1/2”
Air Filter
Top/Plenum
*Front
Back
1 in. (25 mm)
0
0
Sides
0†
0
Return
Air
Vent
Plenum
Floor
0‡
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
†Allow proper clearances to accommodate condensate trap.
‡For installations on a combustible floor, do not install the fur-
nace directly on carpeting, tile or other combustible materials oth-
er than wood flooring.
Transition
FIGURE 13
FIGURE 12
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Optional Return Air Base
(Upflow Applications Only)
CONDENSATE
TRAP
FURNACE
FRONT
1 23 (584)
Overall
IF BASE
IS USED
3−1/4
(83)
1 Minimum
11 (279)
Maximum
WITHOUT
IAQ CABINET,
A SINGLE
RETURN AIR
PLENUM
(Maximum)
INDOOR AIR
QUALITY
CABINET
(PCO, Filter
Cabinet, etc.)
2
1 22−7/16
(570)
Overall
1 Unit side return air
Opening
14 (356)
MUST
AIR FLOW
(Maximum)
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
SIDE RETURN
AIR OPENINGS
(Either Side)
5−5/8
(143)
7−1/4
(184)
23
(584)
OPTIONAL
RETURN
AIR BASE
3/4
(19)
17−1/2 (446) B Width (50W98)
21 (533) C Width (50W99)
26−7/8
(683)
24−1/2 (622) D Width (51W00)
SIDE VIEW
FRONT VIEW
NOTE- Optional side return air filter kits are not for use with return air base.
1
Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.
Minimum unit side return air opening dimensions for units requiring 1800 cfm of air and over (W x H): 23 x 11 in. (584 x 279 mm).
The opening can be cut as needed to accommodate plenum or IAQ cabinet while maintaining dimensions shown.
Side return air openings must be cut in the field. There are cutting guides stenciled on the cabinet for the side return air
opening. The size of the opening must not extend beyond the markings on the furnace cabinet.
2
To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.
FIGURE 14
Removing the Bottom Panel
Removing the Bottom Panel
Remove the two screws that secure the bottom cap to the
furnace. Pivot the bottom cap down to release the bottom
panel. Once the bottom panel has been removed, reinstall
Horizontal Applications
WARNING
Do not install the furnace on its front or back.
Screw
Bottom Cap
Bottom Panel
FIGURE 15
FIGURE 16
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The ML193UH furnace can be installed in horizontal ap-
HORIZONTAL SUSPENSION KIT
plications with either right- or left-hand air discharge.
Internal Brace
(provided with kit)
Metal Strap
(typical)
Horizontal Application
Installation Clearances
Bracket
(typical)
Right-Hand Discharge
Left End
Right End
Air
Flow
Air
Flow
Air
Flow
Bottom (Floor)**
Left-Hand Discharge
Top
FIGURE 18
Left End
Right End
Air
Flow
Air
Flow
Bottom (Floor)**
NOTE - When the furnace is installed on a platform or with
the horizontal suspension kit in a crawlspace, it must be
elevated enough to avoid water damage, accommodate
drain trap and to allow the evaporator coil to drain.
Top
0
0
0
0
0
Front*
Back
Ends
Vent
Platform Installation of Horizontal Unit
1 - Select location for unit keeping in mind service and
Floor
0‡
2 - Construct a raised wooden frame and cover frame
with a plywood sheet. If unit is installed above finished
space, fabricate an auxiliary drain pan to be installed
Leave 8 inches for service clearance below unit for
condensate trap.
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
**An 8” service clearance must be maintained below the unit to
provide for servicing of the condensate trap.
‡For installations on a combustible floor, do not install the fur-
nace directly on carpeting, tile or other combustible materials oth-
er than wood flooring.
FIGURE 17
3 - Provide a service platform in front of unit. When instal-
ling the unit in a crawl space, a proper support platform
may be created using cement blocks.
Suspended Installation of Horizontal Unit
This furnace may be installed in either an attic or a crawl-
space. Either suspend the furnace from roof rafters or floor
form, as shown in figure 19. A horizontal suspension kit
(51W10) may be ordered from Lennox or use equivalent.
4 - Route auxiliary drain line so that water draining from
this outlet will be easily noticed by the homeowner.
5 - If necessary, run the condensate line into a conden-
sate pump to meet drain line slope requirements. The
pump must be rated for use with condensing furnaces.
Protect the condensate discharge line from the pump
to the outside to avoid freezing.
NOTE - Heavy-gauge sheet metal straps may be used to
suspend the unit from roof rafters or ceiling joists. When
straps are used to suspend the unit in this way, support
must be provided for both the ends. The straps must not in-
terfere with the plenum or exhaust piping installation. Cool-
ing coils and supply and return air plenums must be
supported separately.
6 - Continue with exhaust, condensate and intake piping
installation according to instructions.
Page 12
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Duct System
*GAS CONNECTION
INTAKE PIPE
Use industry‐approved standards to size and install the
supply and return air duct system. Refer to ACCA Manual
D. This will result in a quiet and low‐static system that has
uniform air distribution.
EXHAUST PIPE
NOTE - This furnace is not certified for operation in heating
mode (indoor blower operating at selected heating speed)
with an external static pressure which exceeds 0.5 inches
w.c. Operation at these conditions may result in improper
limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel should be installed in the supply air duct. The
access panel should be large enough to permit inspection
of the heat exchanger. The furnace access panel must al-
ways be in place when the furnace is operating and it must
not allow leaks.
RAISED
PLATFORM
SERVICE PLATFORM
FIGURE 19
Return Air -- Horizontal Applications
Return air may be brought in only through the end of a fur-
nace installed in the horizontal position. The furnace is
equipped with a removable bottom panel to facilitate instal-
Return Air Plenum
NOTE - Return air must not be drawn from a room
where this furnace, or any other gas-fueled appliance
(i.e., water heater), or carbon monoxide-producing de-
vice (i.e., wood fireplace) is installed.
Filters
When return air is drawn from a room, a negative pressure
is created in the room. If a gas appliance is operating in a
room with negative pressure, the flue products can be
pulled back down the vent pipe and into the room. This re-
verse flow of the flue gas may result in incomplete com-
bustion and the formation of carbon monoxide gas. This
raw gas or toxic fumes might then be distributed throughout
the house by the furnace duct system.
This unit is not equipped with a filter or rack. A field-pro-
vided high velocity rated filter is required for the unit to oper-
A filter must be in place whenever the unit is operating.
IMPORTANT
If a high-efficiency filter is being installed as part of
this system to ensure better indoor air quality, the fil-
ter must be properly sized. High-efficiency filters
have a higher static pressure drop than standard-ef-
ficiency glass/foam filters. If the pressure drop is too
great, system capacity and performance may be re-
duced. The pressure drop may also cause the limit to
trip more frequently during the winter and the indoor
coil to freeze in the summer, resulting in an increase
in the number of service calls.
Return air can be brought in through the bottom or either
side of the furnace (return air brought into either side fur-
nace allowed in upflow applications only). If a furnace with
bottom return air is installed on a platform, make an airtight
seal between the bottom of the furnace and the platform to
ensure that the unit operates properly and safely. Use fi-
berglass sealing strips, caulking, or equivalent sealing
method between the plenum and the furnace cabinet to en-
sure a tight seal. If a filter is installed, size the return air duct
to fit the filter frame.
Before using any filter with this system, check the
specifications provided by the filter manufacturer
against the data given in the appropriate Lennox
Product Specifications bulletin. Additional informa-
tion is provided in Service and Application Note
ACC-00-2 (August 2000).
Pipe & Fittings Specifications
All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the Ameri-
can Society for Testing and Materials (ANSI/ASTM) stan-
dards. The solvent shall be free flowing and contain no
lumps, undissolved particles or any foreign matter that ad-
versely affects the joint strength or chemical resistance of
the cement. The cement shall show no gelation, stratifica-
tion, or separation that cannot be removed by stirring. Re-
terials.
TABLE 1
Filter Size
Furnace
Cabinet Width
Side Return
Bottom Return
16 X 25 X 1 (1)
20 X 25 X 1 (1)
24 X 25 X 1 (1)
17-1/2”
21”
16 X 25 X 1 (1)
16 X 25 X 1 (1)
16 X 25 X 1 (2)
24-1/2”
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CAUTION
IMPORTANT
Solvent cements for plastic pipe are flammable liq-
uids and should be kept away from all sources of
ignition. Do not use excessive amounts of solvent
cement when making joints. Good ventilation should
be maintained to reduce fire hazard and to minimize
breathing of solvent vapors. Avoid contact of ce-
ment with skin and eyes.
ML193UH exhaust and intake connections are made
of PVC. Use PVC primer and solvent cement when
using PVC vent pipe. When using ABS vent pipe, use
transitional solvent cement to make connections to
the PVC fittings in the unit.
Use PVC primer and solvent cement or ABS solvent ce-
alternate, use all purpose cement, to bond ABS, PVC, or
CPVC pipe when using fittings and pipe made of the same
materials. Use transition solvent cement when bonding
ABS to either PVC or CPVC.
TABLE 2
PIPING AND FITTINGS SPECIFICATIONS
Schedule 40 PVC (Pipe)
D1785
F891
Schedule 40 PVC (Cellular Core Pipe)
Schedule 40 PVC (Fittings)
D2466
F441
Low temperature solvent cement is recommended during
cooler weather. Metal or plastic strapping may be used for
vent pipe hangers. Uniformly apply a liberal coat of PVC
primer for PVC or use a clean dry cloth for ABS to clean in-
side socket surface of fitting and male end of pipe to depth
of fitting socket.
Schedule 40 CPVC (Pipe)
Schedule 40 CPVC (Fittings)
SDR-21 PVC or SDR-26 PVC (Pipe)
SDR-21 CPVC or SDR-26 CPVC (Pipe)
Schedule 40 ABS Cellular Core DWV (Pipe)
Schedule 40 ABS (Pipe)
F438
D2241
F442
F628
D1527
D2468
Canadian Applications Only - Pipe, fittings, primer and
solvent cement used to vent (exhaust) this appliance must
be certified to ULC S636 and supplied by a single
manufacturer as part of an approved vent (exhaust) sys-
tem. In addition, the first three feet of vent pipe from the fur-
nace flue collar must be accessible for inspection.
Schedule 40 ABS (Fittings)
ABS-DWV (Drain Waste & Vent)
(Pipe & Fittings)
D2661
D2665
PVC-DWV (Drain Waste & Vent)
Pipe & Fittings)
ASTM
SPECIFICATION
PRIMER & SOLVENT CEMENT
PVC & CPVC Primer
PVC Solvent Cement
CPVC Solvent Cement
ABS Solvent Cement
F656
D2564
F493
D2235
PVC/CPVC/ABS All Purpose Cement For
Fittings & Pipe of the same material
D2564, D2235, F493
D3138
ABS to PVC or CPVC Transition Solvent
Cement
CANADA PIPE & FITTING & SOLVENT
CEMENT
MARKING
PVC & CPVC Pipe and Fittings
PVC & CPVC Solvent Cement
ULCS636
ABS to PVC or CPVC Transition Cement
Page 14
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TABLE 3
OUTDOOR TERMINATION USAGE*
STANDARD
CONCENTRIC
Flush-
Mount
Kit
Wall Kit
Wall Ring Kit
2 inch
1-1/2 inch
2 inch
3 inch
Vent
Pipe
Dia. in.
2 inch
3 inch
Input Size
Field
Fabricated
51W11
(US)
51W12
(CA)
71M80
(US)
69M29
(US)
44W92
(CA)
44J40
(US)
81J20 (CA)
22G44 (US)
30G28 (CA)
60L46 (US)
44W93 (CA)
15F74
4
4
4
4
44W92
(CA)
4
3
1
1
5
2
2
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
3
1
1
5
2
2-1/2
YES
YES
YES
YES
YES
045
070
090
3
1
1
5
2
3
YES
YES
YES
YES
YES
3
1
1
5
2
2
YES
YES
YES
YES
YES
3
1
1
5
2
2-1/2
YES
YES
YES
YES
YES
3
1
1
5
2
3
YES
YES
YES
YES
YES
3
5
2
2-1/2
3
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
3
5
YES
YES
3
5
YES
YES
5
2
YES
YES
YES
YES
YES
5
2-1/2
3
YES
110
135
5
YES
YES
YES
5
3
YES
NOTE - Standard Terminations do not include any vent pipe or elbows external to the structure. Any vent pipe or elbows external to the structure must be included in total vent length
calculations. See vent length tables.
* Kits must be properly installed according to kit instructions.
1
Requires field-provided outdoor 1-1/2” exhaust accelerator.
Concentric kits 71M80 and 44W92 include 1-1/2” outdoor accelerator, when uses with 045 and 070 input models.
2
3
Flush mount kits 51W11 and 51W12 includes 1-1/2 in. outdoor exhaust accelerator, required when used with 045, 070 and 090 input models.
Termination kits 30G28, 44W92, 4493 and 81J20 are certified to ULC S636 for use in Canada only.
See table 8 for vent accelerator requirements.
4
5
4 - Test fit joint and mark depth of fitting on outside of
pipe.
Joint Cementing Procedure
All cementing of joints should be done according to the
5 - Uniformly apply a liberal coat of PVC primer for PVC or
use a clean dry cloth for ABS to clean inside socket
specifications outlined in ASTM D 2855.
surface of fitting and male end of pipe to depth of fitting
socket.
NOTE - A sheet metal screw may be used to secure the in-
take pipe to the connector, if desired. Use a drill or self tap-
ping screw to make a pilot hole.
NOTE - Time is critical at this stage. Do not allow prim-
er to dry before applying cement.
6 - Promptly apply solvent cement to end of pipe and in-
side socket surface of fitting. Cement should be ap-
plied lightly but uniformly to inside of socket. Take care
to keep excess cement out of socket. Apply second
coat to end of pipe.
DANGER
DANGER OF EXPLOSION!
Fumes from PVC glue may ignite during system
check. Allow fumes to dissipate for at least 5 minutes
before placing unit into operation.
7 - Immediately after applying last coat of cement to pipe,
and while both inside socket surface and end of pipe
are wet with cement, forcefully insert end of pipe into
socket until it bottoms out. Turn PVC pipe 1/4 turn dur-
ing assembly (but not after pipe is fully inserted) to dis-
tribute cement evenly. DO NOT turn ABS or cellular
core pipe.
1 - Measure and cut vent pipe to desired length.
2 - Debur and chamfer end of pipe, removing any ridges
or rough edges. If end is not chamfered, edge of pipe
may remove cement from fitting socket and result in a
leaking joint.
3 - Clean and dry surfaces to be joined.
Page 15
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NOTE - Assembly should be completed within 20 sec-
onds after last application of cement. Hammer blows
should not be used when inserting pipe.
REPLACING FURNACE THAT
WAS PART OF A COMMON
VENT SYSTEM
CHIMNEY
OR GAS
VENT
(Check sizing
for water
heater only)
8 - After assembly, wipe excess cement from pipe at end
of fitting socket. A properly made joint will show a bead
around its entire perimeter. Any gaps may indicate an
improper assembly due to insufficient solvent.
FURNACE
(Replaced
by ML193)
WATER
HEATER
9 - Handle joints carefully until completely set.
Venting Practices
OPENINGS
(To Adjacent
Room)
Piping Suspension Guidelines
SCHEDULE 40
PVC - 5'
all other pipe* - 3'
If an ML193UH furnace replaces a furnace which
was commonly vented with another gas appliance,
the size of the existing vent pipe for that gas ap-
pliance must be checked. Without the heat of the
original furnace flue products, the existing vent pipe
is probably oversized for the single water heater or
other appliance. The vent should be checked for
proper draw with the remaining appliance.
NOTE - Isolate piping at the point where it exits the outside wall or
roof in order to prevent transmission of vibration to the structure.
FIGURE 21
Wall Thickness Guidelines
24” maximum
3/4” minimum
Route piping to outside of structure. Continue with installa-
tion following instructions given in piping termination sec-
tion.
Wall
inside
outside
CAUTION
Do not discharge exhaust into an existing stack or
stack that also serves another gas appliance. If verti-
cal discharge through an existing unused stack is re-
quired, insert PVC pipe inside the stack until the end
is even with the top or outlet end of the metal stack.
FIGURE 20
1 - In areas where piping penetrates joists or interior
walls, hole must be large enough to allow clearance on
all sides of pipe through center of hole using a hanger.
CAUTION
The exhaust vent pipe operates under positive pres-
sure and must be completely sealed to prevent leak-
age of combustion products into the living space.
2 - When furnace is installed in a residence where unit is
shut down for an extended period of time, such as a
vacation home, make provisions for draining conden-
sate collection trap and lines.
Page 16
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Use the following steps to correctly size vent pipe diameter.
Vent Piping Guidelines
The ML193UH can be installed as either a Non-Direct
Vent or a Direct Vent gas central furnace.
Piping Size Process
NOTE - In Non‐Direct Vent installations, combustion air is
taken from indoors and flue gases are discharged out-
doors. In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors.
What is the
furnace capacity?
045, 070, 090,
110 or 135?
Intake and exhaust pipe sizing -- Size pipe according to
1
2
Regardless of the diameter of pipe used, the standard roof
and wall terminations described in section Exhaust Piping
Terminations should be used. Exhaust vent termination
pipe is sized to optimize the velocity of the exhaust gas as it
Which style termination
being used?
Standard or concentric?
In some applications which permit the use of several differ-
ent sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox' Application Department for assis-
tance in sizing vent pipe in these applications.
Which needs
most elbows?
Intake or
3
exhaust?
NOTE - The exhaust collar on all models is sized to accom-
modate 2” Schedule 40 vent pipe. In horizontal applica-
tions, any transition to exhaust pipe larger than 2” must be
made in vertical runs of the pipe. Therefore a 2” elbow must
be added before the pipe is transitioned to any size larger
than 2”. This elbow must be added to the elbow count used
to determine acceptable vent lengths. Contact the Applica-
tion Department for more information concerning sizing of
vent systems which include multiple pipe sizes.
How many elbows?
Count all elbows inside
and outside house.
4
5
Desired pipe size?
2”, 2-1/2”, 3”
Exhaust Pipe
Exhaust Pipe
What is the altitude of
the furnace installation?
6
12” Min.
Horizontal
Gas Furnace
12” max
max intake or exhaust pipe
length. Includes all vent
pipe and elbows inside
and outside the house.
Of straight pipe
7
NOTE - All horizontal runs of exhaust pipe must slope back to-
ward unit. A minimum of 1/4” (6mm) drop for each 12” (305mm)
of horizontal run is mandatory for drainage.
NOTE - Exhaust pipe MUST be glued to furnace exhaust fittings.
NOTE - Exhaust piping should be checked carefully to make
sure there are no sags or low spots.
FIGURE 23
FIGURE 22
TABLE 4
MINIMUM VENT PIPE LENGTHS
ML193UH
MODEL
MIN. VENT LENGTH*
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups
and may block the terminations.
15 ft. or
5 ft plus 2 elbows or
10 ft plus 1 elbow
045, 070, 090, 110
135
*Any approved termination may be added to the minimum length listed.
Page 17
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TABLE 5
Maximum Allowable Intake or Exhaust Vent Length in Feet
NOTE - Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be
same pipe size.
NOTE - Additional vent pipe and elbows used to terminate the vent pipe outside the structure must be included in the total vent length calculation.
Standard Termination at Elevation 0 - 10,000
2” Pipe
Model
090
44
2-1/2” Pipe
3” Pipe
Model
090
118
113
108
103
98
Number Of
90° Elbows
Used
Model
090
68
045
81
76
71
66
61
56
51
46
41
36
070
66
61
56
51
46
41
36
31
26
21
110
24
135
045
115
110
105
100
95
070
100
95
90
85
80
75
70
65
60
55
110
43
38
33
28
23
18
13
135
045
137
132
127
122
117
112
107
102
97
070
137
132
127
122
117
112
107
102
97
110
118
113
108
103
98
135
114
109
104
99
1
2
39
19
63
3
34
14
58
4
29
53
5
24
48
94
n/a
n/a
6
19
90
43
93
93
89
7
14
85
38
88
88
84
n/a
8
80
33
83
83
79
9
75
28
78
78
74
n/a
n/a
10
70
23
92
92
73
73
69
Concentric Termination Elevation 0 - 10,000
2” Pipe
Model
090
42
2-1/2” Pipe
3” Pipe
Model
090
114
109
104
99
Number Of
90° Elbows
Usedl
Model
045
73
68
63
58
53
48
43
38
33
28
070
58
53
48
43
38
33
28
23
18
13
110
22
135
045
105
100
95
070
90
85
80
75
70
65
60
55
50
45
090
64
59
54
49
44
39
34
29
24
19
110
39
34
29
24
19
14
135
045
121
116
111
106
101
96
070
121
116
111
106
101
96
110
114
109
104
99
135
105
100
95
1
2
37
17
3
32
12
4
27
90
90
5
22
85
94
94
85
n/a
n/a
6
17
80
89
89
80
7
12
75
91
91
84
84
75
n/a
8
70
86
86
79
79
70
n/a
9
65
81
81
74
74
65
n/a
10
60
76
76
69
69
60
TABLE 6
Maximum Allowable Exhaust Vent Lengths With Furnace Installed in a Closet or Basement Using Ventilated
Attic or Crawl Space For Intake Air in Feet
NOTE - Additional vent pipe and elbows used to terminate the vent pipe outside the structure must be included in the total vent length calculation.
Standard Termination at Elevation 0 - 10,000
2” Pipe
Model
090
34
2-1/2” Pipe
3” Pipe
Model
090
98
Number Of
90° Elbows
Used
Model
090
53
045
71
66
61
56
51
46
41
36
31
070
56
51
46
41
36
31
26
21
16
110
14
9
135
045
100
95
90
85
80
75
70
65
60
070
95
80
75
70
65
60
55
60
45
110
28
23
18
13
8
135
045
117
112
107
102
97
070
117
112
107
102
97
110
98
93
88
83
78
73
68
63
58
135
94
89
84
79
74
69
64
59
54
1
2
3
4
5
6
7
8
9
29
48
93
24
4
43
88
19
38
83
14
33
78
n/a
n/a
9
28
3
92
92
73
n/a
4
23
87
87
68
18
82
82
63
n/a
n/a
13
77
77
58
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TYPICAL EXHAUST PIPE CONNECTIONS IN UPFLOW DIRECT OR
NON-DIRECT VENT APPLICATIONS
2”
3”
2”
2”
2”
2”
TRANSITION
or
or
EXHAUST
*2”
DO NOT transition
from smaller to larger
pipe in horizontal runs
of exhaust pipe.
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE − Exhaust pipe and intake pipe must be the same diameter.
FIGURE 24
TYPICAL EXHAUST PIPE CONNECTIONS IN HORIZONTAL DIRECT OR
NON-DIRECT VENT APPLICATIONS
(RIGHT HAND DISCHARGE SHOWN)
12” max.
45°
MAX
45°
MAX
3”
2”
or
TRANSITION
2”
*2”
2”
2”
2”
*2”
SIDE VIEW
EXHAUST
DO NOT transition
from smaller to larger
pipe in horizontal runs
of exhaust pipe.
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE − Exhaust pipe and intake pipe must be the same diameter.
FIGURE 25
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TYPICAL AIR INTAKE PIPE CONNECTIONS IN UPFLOW DIRECT VENT
APPLICATIONS
3”
2”
or
TRANSITION
2”
2”
AIR INTAKE
*2”
2”
2”
or
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE − Intake and exhaust pipe must be the same diameter.
FIGURE 26
TYPICAL AIR INTAKE PIPE CONNECTIONS IN HORIZONTAL DIRECT VENT APPLICATIONS
(RIGHT HAND DISCHARGE SHOWN)
3”
2”
or
2”
TRANSITION
*2”
2”
2”
2”
*2”
AIR
INTAKE
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE − Intake and exhaust pipe must be the same diameter.
FIGURE 27
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Intake Piping
TYPICAL AIR INTAKE PIPE CONNECTIONS
HORIZONTAL NON−DIRECT VENT APPLICATIONS
(Horizontal Right−Hand Air Discharge Application Shown)
The ML193UH furnace may be installed in either direct
vent or non-direct vent applications. In non-direct vent
applications, when intake air will be drawn into the furnace
from the surrounding space, the indoor air quality must be
considered and guidelines listed in Combustion, Dilution
and Ventilation Air section must be followed.
PVC pipe
coupling
Follow the next two steps when installing the unit in Direct
Vent applications, where combustion air is taken from
outdoors and flue gases are discharged outdoors. The
provided air intake screen must not be used in direct
vent applications (outdoors).
OR
1 - Use transition solvent cement or a sheet metal screw
to secure the intake pipe to the inlet air connector.
INTAKE
DEBRIS
SCREEN
(Provided)
2 - Route piping to outside of structure. Continue with
installation following instructions given in general
guide lines for piping terminations and intake and ex-
haust piping terminations for direct vent sections. Re-
NOTE - Debris screen may be positioned straight out
(preferred) or with an elbow rotated to face down.
TYPICAL AIR INTAKE PIPE CONNECTIONS
UPFLOW NON−DIRECT
FIGURE 29
VENT APPLICATIONS
Follow the next two steps when installing the unit in Non‐
Direct Vent applications where combustion air is taken
from indoors and flue gases are discharged outdoors.
INTAKE
DEBRIS
SCREEN
(Provided)
1 - Use field-provided materials and the factory-provided
air intake screen to route the intake piping as shown in
(76mm) around the air intake opening. The air intake
opening (with the protective screen) should always be
directed forward or to either side in the upflow position,
and either straight out or downward in the horizontal
position.
The air intake piping must not terminate too close
to the flooring or a platform. Ensure that the intake
air inlet will not be obstructed by loose insulation
or other items that may clog the debris screen.
ameter pipe is used, reduce to 2” diameter pipe at the
termination point to accommodate the debris
screen.Use a sheet metal screw to secure the intake
pipe to the connector, if desired.
NOTE - Debris screen and elbow may be rotated, so that
screen may be positioned to face forward or to either side.
3 - Use a sheet metal screw to secure the intake pipe to
the connector, if desired.
FIGURE 28
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General Guidelines for Vent Terminations
CAUTION
In Non‐Direct Vent applications, combustion air is taken
from indoors and the flue gases are discharged to the out-
doors. The ML193UH is then classified as a non‐direct
vent, Category IV gas furnace.
If this unit is being installed in an application with
combustion air coming in from a space serviced by
an exhaust fan, power exhaust fan, or other device
which may create a negative pressure in the space,
take care when sizing the inlet air opening. The in-
let air opening must be sized to accommodate the
maximum volume of exhausted air as well as the
maximum volume of combustion air required for
all gas appliances serviced by this space.
In Direct Vent applications, combustion air is taken from
outdoors and the flue gases are discharged to the out-
doors. The ML193UH is then classified as a direct vent,
Category IV gas furnace.
In both Non‐Direct Vent and Direct Vent applications, the
vent termination is limited by local building codes. In the ab-
sence of local codes, refer to the current National Fuel Gas
Code ANSI Z223-1/NFPA 54 in U.S.A., and current CSA-
B149 Natural Gas and Propane Installation Codes in Can-
ada for details.
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Attic and Outlet Air to Outside)
Ventilation Louvers
Inlet Air
Roof Terminated
Exhaust Pipe
(Minimum
12 in.(305mm) Above
attic floor)
obstructions and 12” above the average snow accumula-
tion.
*Intake Debris
Screen
(Provided)
At vent termination, care must be taken to maintain
protective coatings over building materials (prolonged
exposure to exhaust condensate can destroy protective
coatings). It is recommended that the exhaust outlet not be
located within 6 feet (1.8m) of an outdoor AC unit because
the condensate can damage the painted coating.
Furnace
NOTE-The inlet and outlet air openings shall each have a free area
2
of at least one square inch per 4,000 Btu (645mm per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
length without insulation in unconditioned space during
winter design temperatures below 32°F (0°C). If required
exhaust pipe should be insulated with 1/2” (13mm) Arma-
flex or equivalent. In extreme cold climate areas, 3/4”
(19mm) Armaflex or equivalent may be necessary. Insula-
tion must be protected from deterioration. Armaflex with
UV protection is permissable. Basements or other en-
closed areas that are not exposed to the outdoor ambient
temperature and are above 32 degrees F (0°C) are to be
considered conditioned spaces.
FIGURE 30
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Crawlspace and Outlet Air to Outside)
Roof Terminated
Exhaust Pipe
Inlet Air
(Minimum
IMPORTANT
Do not use screens or perforated metal in exhaust
terminations. Doing so will cause freeze-ups and
may block the terminations.
12 in.(305mm)
Above crawl
space floor)
Ventilation
Louvers
(Crawl space)
Furnace
Coupling or
*Intake Debris Screen Provided)
3 in. to 2 in.
Transition
IMPORTANT
For Canadian Installations Only:
(Field Provided)
In accordance to CSA International B149 installation
codes, the minimum allowed distance between the
combustion air intake inlet and the exhaust outlet of
other appliances shall not be less than 12 inches
(305mm).
NOTE-The inlet and outlet air openings shall each have a free area
2
of at least one square inch per 4,000 Btu (645mm per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
FIGURE 31
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TABLE 7
Maximum Allowable Exhaust Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space For
Winter Design Temperatures Single - Stage High Efficiency Furnace
Unit Input Size
Winter Design
1
Vent Pipe
Diameter
Temperatures °F (°C)
045
PVC
26
18
14
16
12
9
070
PVC
44
090
PVC
44
110
PVC
24
135
PVC
N/A
N/A
60
2 in.
2-1/2 in.
3 in.
32 to 21
(0 to -6)
32
50
58
26
38
55
2 in
28
40
24
N/A
N/A
40
20 to 1
(-7 to -17)
2-1/2 in.
3 in.
20
30
44
16
26
32
2 in.
10
8
20
30
24
N/A
N/A
30
0 to -20
(-18 to -29)
2-1/2 in.
3 in.
14
20
32
4
10
16
26
1
Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
NOTE - Maximum unisulated vent lengths listed may include the termination(vent pipe exterior to the structure) and cannot exceed 5 linear feet or the
Conditioned
Space
Exhaust
Pipe
Pipe Insulation
Intake
Pipe
Conditioned
Space
Unconditioned
Space
FIGURE 32
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VENT TERMINATION CLEARANCES
FOR NON-DIRECT VENT INSTALLATIONS IN THE USA AND CANADA
INSIDE CORNER
DETAIL
G
H
A
D
E
B
L
B
Fixed
Closed
B
B
I
C
Operable
Fixed
Closed
M
F
Operable
K
J
A
B
AREA WHERE TERMINAL
IS NOT PERMITTED
AIR SUPPLY INLET
VENT TERMINAL
1
2
US Installations
Canadian Installations
A =
Clearance above grade, veranda,
porch, deck or balcony
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
B =
Clearance to window or
door that may be opened
6 inches (152mm) for appliances <10,000
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
4 feet (1.2 m) below or to side of opening;
1 foot (30cm) above opening
C =
D =
Clearance to permanently
closed window
* 12”
* 12”
Vertical clearance to ventilated soffit
located above the terminal within a
horizontal distance of 2 feet (610 mm)
from the center line of the terminal
* Equal to or greater than soffit depth.
* Equal to or greater than soffit depth.
* Equal to or greater than soffit depth.
* No minimum to outside corner
E =
F =
Clearance to unventilated soffit
Clearance to outside corner
* Equal to or greater than soffit depth.
* No minimum to outside corner
*
*
*
*
G = Clearance to inside corner
H = Clearance to each side of center line ex-
tended above meter / regulator assembly
3 feet (.9m) within a height 15 feet (4.5m) 3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
*
above the meter / regulator assembly
I =
Clearance to service regulator
vent outlet
3 feet (.9m)
* 3 feet (.9m)
J =
Clearance to non-mechanical air
supply inlet to building or the com-
bustion air inlet to any other ap-
pliance
6 inches (152mm) for appliances <10,000
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
4 feet (1.2 m) below or to side of opening;
1 foot (30 cm) above opening
K =
L =
Clearance to mechanical air sup-
ply inlet
3 feet (.9m) above if within 10 feet
(3m) horizontally
6 feet (1.8m)
Clearance above paved sidewalk or
paved driveway located on public property
7 feet (2.1m)†
7 feet (2.1m)†
M = Clearance under veranda, porch, deck or balcony
12 inches (305mm)‡
*12 inches (305mm)‡
1
2
In accordance with the current ANSI Z223.1/NFPA 54 Natural Fuel Gas Code
In accordance with the current CSA B149.1, Natural Gas and Propane Installation Code
*For clearances not specified in ANSI Z223.1/NFPA 54 or CSA
B149.1, clearance will be in accordance with local installation
codes and the requirements of the gas supplier and these instal-
lation instructions.”
† A vent shall not terminate directly above a sidewalk or paved driveway that is
located between two single family dwellings and serves both dwellings.
‡ Permitted only if veranda, porch, deck or balcony is fully open
on a minimum of two sides beneath the floor. Lennox recommends
avoiding this location if possible.
FIGURE 33
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VENT TERMINATION CLEARANCES
FOR DIRECT VENT INSTALLATIONS IN THE USA AND CANADA
INSIDE CORNER
DETAIL
G
H
A
D
E
B
L
B
Fixed
Closed
B
B
I
C
Operable
Fixed
Closed
M
F
Operable
K
J
A
B
AREA WHERE TERMINAL
IS NOT PERMITTED
AIR SUPPLY INLET
VENT TERMINAL
1
2
US Installations
Canadian Installations
A =
Clearance above grade, veranda,
porch, deck or balcony
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
B =
Clearance to window or
door that may be opened
6 inches (152mm) for appliances <10,000 6 inches (152mm) for appliances <10,000
Btuh (3kw), 9 inches (228mm) for ap-
pliances > 10,000 Btuh (3kw) and <50,000
Btuh (15 kw), 12 inches (305mm) for ap-
pliances > 50,000 Btuh (15kw)
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
* 12”
C =
D =
Clearance to permanently
closed window
* 12”
Vertical clearance to ventilated soffit
located above the terminal within a
horizontal distance of 2 feet (610mm)
from the center line of the terminal
* Equal to or greater than soffit depth
* Equal to or greater than soffit depth
* Equal to or greater than soffit depth
* Equal to or greater than soffit depth
* No minimum to outside corner
E =
F =
G =
Clearance to unventilated soffit
Clearance to outside corner
Clearance to inside corner
* No minimum to outside corner
*
*
H = Clearance to each side of center line ex-
tended above meter / regulator assembly
3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
I =
Clearance to service regulator
vent outlet
3 feet (.9m)
* 3 feet (.9m)
J =
Clearance to non-mechanical air
supply inlet to building or the com-
bustion air inlet to any other ap-
pliance
6 inches (152mm) for appliances <10,000 6 inches (152mm) for appliances <10,000
Btuh (3kw), 9 inches (228mm) for ap-
pliances > 10,000 Btuh (3kw) and <50,000
Btuh (15 kw), 12 inches (305mm) for ap-
pliances > 50,000 Btuh (15kw)
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
K =
L =
Clearance to mechanical air sup-
ply inlet
3 feet (.9m) above if within 10 feet
(3m) horizontally
6 feet (1.8m)
Clearance above paved sidewalk or
paved driveway located on public property
7 feet (2.1m)†
* 7 feet (2.1m)
M = Clearance under veranda, porch, deck or balcony
*12 inches (305mm)‡
12 inches (305mm)‡
1
2
In accordance with the current ANSI Z223.1/NFPA 54 Natural Fuel Gas Code
*For clearances not specified in ANSI Z223.1/NFPA 54 or CSA
B149.1, clearance will be in accordance with local installation
codes and the requirements of the gas supplier and these
installation instructions.”
In accordance with the current CSA B149.1, Natural Gas and Propane Installation Code
† A vent shall not terminate directly above a sidewalk or paved driveway that is located
between two single family dwellings and serves both dwellings.
‡ Permitted only if veranda, porch, deck or balcony is fully open on a minimum of
two sides beneath the floor. Lennox recommends avoiding this location if possible.
FIGURE 34
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Details of Intake and Exhaust Piping Terminations for
Direct Vent Installations
TABLE 8
EXHAUST PIPE TERMINATION SIZE REDUCTION
ML193UH
MODEL
Termination
Pipe Size
NOTE - In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged to outdoors.
1-1/2” (38mm)
*045 and 070
*090
110
2” (51mm)
2” (51mm)
2” (51mm)
NOTE - Flue gas may be slightly acidic and may adversely
affect some building materials. If any vent termination is
used and the flue gasses may impinge on the building ma-
terial, a corrosion-resistant shield (minimum 24 inches
square) should be used to protect the wall surface. If the
optional tee is used, the protective shield is recommended.
The shield should be constructed using wood, plastic,
sheet metal or other suitable material. All seams, joints,
cracks, etc. in the affected area should be sealed using an
135
*ML193UH-045, -070 and -090 units with the flush mount termination
must use the 1-1/2” accelerator supplied with the kit unless a tee is used
3”(76mm) MAX.
SIZE TERMINATION
Inches(mm)
UNCONDITIONED
ATTIC SPACE
8” (203mm) MIN
Intake and exhaust pipes may be routed either horizontally
through an outside wall or vertically through the roof. In at-
tic or closet installations, vertical termination through the
terminations.
12” (305mm) ABOVE
AVERAGE SNOW
ACCUMULATION
1 - Intake and exhaust terminations are not required to be
in the same pressure zone. You may exit the intake on
one side of the structure and the exhaust on another
3” (76mm) OR
2” (51mm) PVC
PROVIDE SUPPORT
FOR INTAKE AND
EXHAUST LINES
DIRECT VENT ROOF TERMINATION KIT
(15F75 or 44J41)
NOTE - When venting in different pressure zones,
maximum separation of intake and exhaust pipe DO
NOT apply.
FIGURE 35
2 - Intake and exhaust pipes should be placed as close
together as possible at termination end (refer to il-
lustrations). Maximum separation is 3” (76mm) on roof
terminations and 6” (152mm) on side wall termina-
tions.
Exiting Exhaust and Intake Vent
(different pressure zones)
NOTE - When venting in different pressure zones, the
maximum separation requirement of intake and ex-
haust pipe DOES NOT apply.
Inlet Air
3 - On roof terminations, the intake piping should termi-
nate straight down using two 90° elbows (See figure
Exhaust
Pipe
Furnace
(Minimum 12 in.
305 MM) above
grade or snow
accumulation
4 - Exhaust piping must terminate straight out or up as
shown. A reducer may be required on the exhaust pip-
ing at the point where it exits the structure to improve
the velocity of exhaust away from the intake piping.
FIGURE 36
Exiting Exhaust and Intake Vent
(different pressure zones)
5 - On field supplied terminations for side wall exit, ex-
haust piping may extend a maximum of 12 inches
(305mm) for 2” PVC and 20 inches (508mm) for 3”
(76mm) PVC beyond the outside wall. Intake piping
should be as short as possible.
Roof T
erminated
Exhaust Pipe
6 - On field supplied terminations, a minimum distance
between the end of the exhaust pipe and the end of the
intake pipe without a termination elbow is 8” and a
minimum distance of 6” with a termination elbow.
Inlet Air
(Minimum 12 in.
305 MM) above
grade or snow
accumulation
Furnace
NOTE - Care must be taken to avoid recirculation of
FIGURE 37
exhaust back into intake pipe.
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7 - If intake and exhaust piping must be run up a side wall
to position above snow accumulation or other ob-
structions, piping must be supported. At least one
bracket must be used within 6” from the top of the el-
bow and then every 24” (610mm) as shown in figure
exhaust and intake piping must be run up an outside
wall, the exhaust piping must be terminated with pipe
with a 90° elbow turndown. Using turndown will add 5
feet (1.5m) to the equivalent length of the pipe.
8 - A multiple furnace installation may use a group of up to
four terminations assembled together horizontally, as
12”
(305mm)
5-1/2”
(140mm)
EXHAUST
VENT
5”
(127mm)
INTAKE
AIR
18” MAX.
(457mm)
Front View
EXHAUST VENT
12” (305mm) Min.
above grade or
average snow
accumulation.
Inches (mm)
INTAKE
AIR
optional intake elbow
Side View
1 1/2” (38mm) accelerator
provided on 71M80 & 44W92
kits for ML193UH045P24B,
070P24B & 070P36B
OPTIONAL VENT TERMINATION FOR MULTIPLE UNIT
INSTALLATION OF DIRECT VENT WALL TERMINATION KIT
(30G28 or 81J20)
EXHAUST
VENT
FIGURE 40
FLASHING
12” (305mm)
INTAKE
AIR
(Not Furnished)
Minimum
Above Average
Snow
2” EXTENSION FOR 2” PVC
PIPE1” EXTENSION FOR 3”
PVC PIPE
Accumulation
FURNACE
EXHAUST
PIPE
4''
FURNACE
INTAKE
PIPE
SHEET METAL STRAP
(Clamp and sheet metal strap
must be field installed to support
the weight of the termination kit.)
CLAMP
GLUE EXHAUST
END FLUSH INTO
TERMINATION
FIELD-PROVIDED
REDUCER MAY BE REQUIRED
TO ADAPT LARGER VENT
PIPE SIZE TO TERMINATION
FLAT
SIDE
1-1/2” ACCELERATOR
DIRECT VENT CONCENTRIC ROOFTOP TERMINATION
71M80, 69M29 or 60L46 (US)
44W92 or 44W93 (Canada)
(all -45, -070 and -090 units)
FLUSH-MOUNT SIDE WALL TERMINATION KIT
51W11 (US) or 51W12 (Canada)
FIGURE 38
FIGURE 41
FIELD-PROVIDED
REDUCER MAY BE REQUIRED
TO ADAPT LARGER VENT
PIPE SIZE TO TERMINATION
1-1/2” (38mm) accelerator
provided on 71M80 & 44W92
kits for ML193UH045P24B,
070P24B & 070P36B
OUTSIDE
INTAKE
WALL
AIR
EXHAUST
VENT
EXHAUST
VENT
12” (305mm) Min.
above grade or
average snow
accumulation.
INTAKE
AIR
INTAKE
AIR
CLAMP
(Not Furnished)
GRADE
DIRECT VENT CONCENTRIC WALL TERMINATION
71M80, 69M29 or 60L46 (US)
44W92 or 44W93 (Canada)
FIGURE 39
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FIELD FABRICATED WALL TERMINATION
NOTE − FIELD−PROVIDED
REDUCER MAY BE
REQUIRED TO ADAPT
LARGER VENT PIPE SIZE
TO TERMINATION
2” (51mm) 3” (76mm)
Vent Pipe Vent Pipe
A− Minimum clearance
above grade or average
snow accumulation
12” (305 mm) 12” (305 mm)
D
D
B− Maximum horizontal
separation between
intake and exhaust
6” (152 mm)
6” (152 mm)
8” (203 mm)
C1 -Minimum from end of
exhaust to inlet of intake
B
B
8” (203 mm)
6” (152 mm)
12” (305 mm)
Intake
Elbow
C1
C2
C2 -Minimum from end of
exhaust to inlet of intake
A
A
6” (152 mm)
STRAIGHT
APPPLICATION
D− Maximum exhaust
20” (508 mm)
pipe length
E− Maximum wall support
distance from top of each
pipe (intake/exhaust)
* WALL
SUPPORT
6” (152 mm)
6” (152 mm)
D
B
D
with this arrangement.
E
E
* Use wall support every 24” (610 mm). Use two
wall supports if extension is greater than
B
24” (610 mm) but less than 48” (1219 mm).
NOTE − One wall support must be within 6” (152 mm)
from top of each pipe (intake and exhaust) to prevent
movement in any direction.
A
A
C1
C2
EXTENDED
APPLICATION
ALTERNATE TERMINATIONS (TEE & FORTY−FIVE DEGREE ELBOWS ONLY)
3” (76MM)
Vent Pipe
2” (51MM)
Vent Pipe
B
D
B
A− Clearance above
grade or average snow
accumulation
Exhaust
12” (305 mm) Min. 12” (305 mm) Min.
D
1
B− Horizontal
separation between
intake and exhaust
6” (152 mm) Min.
24” (610 mm) Max.
6” (152 mm) Min.
24” (610 mm) Max.
C
3
C
Intake
Elbow
2
C− Minimum from
end of exhaust to
inlet of intake
A
A
9” (227 mm) Min.
9” (227 mm) Min.
12” (305 mm) Min. 12” (305 mm) Min.
16” (405 mm) Max. 20” (508 mm) Max.
D− Exhaust pipe length
Front View of
Intake and Exhaust
D
E− Wall support distance
from top of each pipe
(intake/exhaust)
6” (152 mm) Max. 6” (152 mm) Max.
1
E
Intake
Exhaust
B
12”
1
2
The exhaust termination tee should be connected to the 2” or 3” PVC flue pipe as shown in the illustration.
Do not use an accelerator in applications that include an exhaust termination tee.
The accelerator is not required.
As required. Flue gas may be acidic and may adversely affect some building materials. If a side wall vent
termination is used and flue gases will impinge on the building materials, a corrosion−resistant shield
(24 inches square) should be used to protect the wall surface. If optional tee is used, the protective shield
is recommended. The shield should be constructed using wood, sheet metal or other suitable material.
All seams, joints, cracks, etc. in affected area, should be sealed using an appropriate sealant.
Exhaust pipe 45° elbow can be rotated to the side away from the combustion air inlet to direct exhaust
away from adjacent property. The exhaust must never be directed toward the combustion air inlet.
C
2
A
3
FIGURE 42
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SIZE TERMINATION
ML193UH DIRECT VENT APPLICATION
USING EXISTING CHIMNEY
12” (305mm)
ABOVE AVE.
SNOW
STRAIGHT-CUT OR
ANGLE-CUT IN DIRECTION
OF ROOF SLOPE *
ACCUMULATION
3”-8”
(76mm-203mm)
8” - 12”
(203mm - 305mm)
3” (76mm) OR
2” (51mm) PVC
UNCONDITIONED
ATTIC SPACE
SHOULDER OF FITTINGS
PROVIDE SUPPORT
OF PIPE ON TOP PLATE
Minimum 12” (305MM)
INTAKE PIPE
INSULATION (optional)
PROVIDE SUPPORT
FOR EXHAUST LINES
above chimney top
plate or average snow
accumulation
SHEET
METAL TOP
PLATE
ALTERNATE
INTAKE PIPE
3” - 8”
(76mm-
203mm)
NON-DIRECT VENT ROOF TERMINATION KIT
(15F75 or 44J41)
INSULATE
TO FORM
SEAL
EXTERIOR
PORTION OF
CHIMNEY
FIGURE 44
3 - If exhaust piping must be run up a side wall to position
above snow accumulation or other obstructions, pip-
ing must be supported every 24 inches (610mm).
When exhaust piping must be run up an outside wall,
any reduction in exhaust pipe size must be done after
the final elbow.
*SIZE TERMINATION
NOTE - Do not discharge exhaust gases directly into any chimney or vent stack. If ver-
tical discharge through an existing unused chimney or stack is required, insert piping
inside chimney until the pipe open end is above top of chimney and terminate as illus-
trated. In any exterior portion of chimney, the exhaust vent must be insulated.
4 - Distance between exhaust pipe terminations on mul-
tiple furnaces must meet local codes.
FIGURE 43
Details of Exhaust Piping Terminations for Non‐Direct
Vent Applications
ML193UH NON-DIRECT VENT APPLICATION
USING EXISTING CHIMNEY
Exhaust pipes may be routed either horizontally through an
outside wall or vertically through the roof. In attic or closet
installations, vertical termination through the roof is pre-
STRAIGHT-CUT OR
ANGLE-CUT IN DIRECTION
OF ROOF SLOPE
SIZE TERMINATION
Minimum 12” (305MM)
above chimney top
plate or average snow
1 - Exhaust piping must terminate straight out or up as
shown. The termination pipe must be sized as listed in
ity required to move the exhaust gases away from the
building.
SHOULDER OF FITTINGS
PROVIDE SUPPORT
OF PIPE ON TOP PLATE
accumulation
SHEET
METAL TOP
PLATE
2 - On field supplied terminations for side wall exit, ex-
haust piping may extend a maximum of 12 inches
(305mm) for 2” PVC and 20 inches (508mm) for 3”
(76mm) PVC beyond the outside wall.
INSULATE
TO FORM
SEAL
EXTERIOR
PORTION OF
CHIMNEY
NOTE - Do not discharge exhaust gases directly into any chimney or vent stack. If ver-
tical discharge through an existing unused chimney or stack is required, insert piping
inside chimney until the pipe open end is above top of chimney and terminate as illus-
trated. In any exterior portion of chimney, the exhaust vent must be insulated.
FIGURE 45
Condensate Piping
This unit is designed for either right‐ or left‐side exit of con-
densate piping in upflow applications. In horizontal applica-
tions, the condensate trap must extend below the unit. An
8” service clearance is required for the condensate trap.
Refer to figures 46 and 48 for condensate trap locations.
PVC.
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NOTE - If necessary the condensate trap may be installed
up to 5’ away from the furnace. Use PVC pipe to connect
trap to furnace condensate outlet. Piping from furnace
must slope down a minimum of 1/4” per ft. toward trap.
tions the field provided vent must be a minimum 1” to a
maximum 2” length above the condensate drain outlet
connection. Any length above 2” may result in a
flooded heat exchanger if the combined primary drain
line were to become restricted.
1 - Determine which side condensate piping will exit the
unit, location of trap, field-provided fittings and length
of PVC pipe required to reach available drain.
Horizontal furnace (figure 53) - In horizontal furnace
applications the field provided vent must be a mini-
mum 4” to a maximum 5” length above the condensate
drain outlet connection. Any length above 5” may re-
sult in a flooded heat exchanger if the combined pri-
mary drain line were to become restricted.
2 - Use a large flat head screw driver or a 1/2” drive socket
end header box at the appropriate location on the side
of the unit. Install provided 3/4 NPT street elbow fitting
into cold end header box. Use Teflon tape or appropri-
ate pipe dope.
NOTE - In horizontal applications it is recommended to
install a secondary drain pan underneath the unit and
trap assembly.
3 - Install the cap over the clean out opening at the base
NOTE - Appropriately sized tubing and barbed fitting
may be used for condensate drain. Attach to the drain
4 - Install drain trap using appropriate PVC fittings, glue
all joints. Glue the provided drain trap as shown in fig-
Condensate line must maintain a 1/4” downward slope
from the furnace to the drain.
6 - If unit will be started immediately upon completion of
installation, prime trap per procedure outlined in Unit
Start-Up section.
CONDENSATE TRAP AND PLUG LOCATIONS
(Unit shown in upflow position)
Field Provided Drain Components
Trap
(same on
right side)
1-1/2 in.
Elbow
Plug
(same on left side)
Barbed Fitting
Tubin
g
Hose Clamp
FIGURE 47
CAUTION
Donot use copper tubing or existing copper conden-
sate lines for drain line.
NOTE - In upflow applications where side return
air filter is installed on same side as the conden-
sate trap, filter rack must be installed beyond
condensate trap or trap must be re-located to
avoid interference.
Condensate line must slope downward away from the
trap to drain. If drain level is above condensate trap,
condensate pump must be used. Condensate drain
line should be routed within the conditioned space to
avoid freezing of condensate and blockage of drain
line. If this is not possible, a heat cable kit may be used
on the condensate trap and line. Heating cable kit is
available from Lennox in various lengths; 6 ft. (1.8m) -
kit no. 26K68; 24 ft. (7.3m) - kit no. 26K69; and 50 ft.
(15.2m) - kit no. 26K70.
FIGURE 46
coil using a separate drain. If necessary the conden-
sate line from the furnace and evaporator coil can
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CONDENSATE TRAP LOCA-
(Unit shown in upflow position with remote trap)
TIONS
Condensate Trap With Optional Overflow Switch
From Evaporator Coil
Horizontal Furnace4” Min.to 5” Max. above
condensate drain connection)
FieldProvidedVent
Min.1” AboveCondensate
DrainConnection
1” Min.
2” Max.
Furnace Condensate
DrainConnection
*5’ max.
PVCPipeOnly
Optional
To Drain
*Piping from furnace must slope down a minimum of
1/4” per ft. toward trap.
FIGURE 50
FIGURE 48
ML193UH With Evaporator
Coil Using A Separate Drain
Evaporator drain
line required
(Trap at coil is optional)
Field Provided Vent
(1” min. 2” max. above
condensate connec-
tion)
Condensate
DrainConnection
FIGURE 49
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ML193UH with Evaporator Coil Using a Separate Drain
(Unit shown in horizontal left-hand discharge position)
Field Provided Vent
(4” min. to 5” max. above
condensate connection)
Evaporator
Coil
4”min
5”max
5’ max.
PVC Pipe Only
Condensate
DrainConnection
(Trap at coil is optional)
*Piping from furnace and evaporator coil must
slope down a minimum 1/4” per ft. toward trap
Drain Pan
FIGURE 51
.
ML193UH with Evaporator
Coil Using a Common Drain
IMPORTAN-
T
Evaporator drain
line required
When combining the furnace and evaporator
coil drains together, the A/C condensate drain
outlet must be vented to relieve pressure in or-
der for the furnace pressure switch to operate
properly.
(Trap at coil is optional)
(1”min. to 2” Max.above
condensate drain connection)
Condensate
DrainConnection
FIGURE 52
ML193UH with Evaporator Coil Using a Common Drain
(Unit shown in horizontal left−hand discharge position)
(4”min. to 5” Max.above
condensate drain connection)
Evaporator
Coil
4”min
5”max
5’ max.
PVC Pipe Only
Condensate
DrainConnection
(Trap at coil is optional)
Drain Pan
*Piping from furnace and evaporator coil must
slope down a minimum 1/4” per ft. toward trap
FIGURE 53
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TRAP / DRAIN ASSEMBLY USING 1/2” PVC OR 3/4” PVC
Optional Condensate Drain Connection
Adapter 3/4 inch slip X
3/4 inch mpt (not furnished)
90° Street Elbow
3/4 inch PVC
(not furnished)
Adapter 3/4 inch slip X
3/4 inch mpt (not furnished)
Condensate Drain
Connection In Unit
1 (25 mm) Min.
2 (50 mm) Max.
Above Top Of
Condensate Drain
Connection In Unit
Vent
5 Feet
Maximum
Condensate Drain
Connection In Unit
90° Street Elbow
3/4 inch PVC
( furnished)
90° Elbow 3/4 inch PVC
(Not Furnished)
To
Trap
3/4 inch PVC Pipe
(Not Furnished)
1/2 inch PVC Pipe
(Not Furnished)
OptionalDrainPipingFromTrap
Coupling 3/4 inch slip X slip
(Not Furnished)
Drain Assembly for 1/2 inch Drain Pipe
1/2 inch PVC Pipe
(Not Furnished)
Drain Trap
Assembly
(Furnished)
90° Elbow
1/2 inch PVC
(Not Furnished)
To
Drain
Drain Assembly for 3/4 inch Drain Pipe
Drain Trap
Clean Out
90° Elbow
90° Elbow
3/4 inch PVC
(Not Furnished)
3/4 inch PVC
(Not Furnished)
To
Drain
To
Drain
Coupling 3/4 inch slip X slip
(Not Furnished)
DrainTrap Assembly with 3/4 inch Piping
DrainTrap Assembly with 1/2 inch Piping
1 (25 mm) Min. 2 (50 mm) Max. Above Top
Of Condensate Drain Connection In Unit
1 (25 mm) Min. 2 (50 mm) Max. Above Top
Of Condensate Drain Connection In Unit
Vent
DrainTrapAssembly
(Furnished)
Vent
3/4 inch
1/2 inch
7
Condensate Drain
Connection In Unit
Condensate Drain
Connection In Unit
(178)
To
Drain
To
Drain
FIGURE 54
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4 - Piping should be sloped 1/4 inch per 15 feet (6mm per
5.6m) upward toward the gas meter from the furnace.
The piping must be supported at proper intervals, ev-
ery 8 to 10 feet (2.44 to 3.05m), using suitable hangers
or straps. Install a drip leg in vertical pipe runs to serve
as a trap for sediment or condensate.
Gas Piping
CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet. The flexible connector can then
be added between the black iron pipe and the gas
supply line.
5 - A 1/8” N.P.T. plugged tap or pressure post is located
on the gas valve to facilitate test gauge connection.
6 - In some localities, codes may require installation of a
manual main shut‐off valve and union (furnished by in-
staller) external to the unit. Union must be of the
ground joint type.
WARNING
Do not exceed 600 in-lbs (50 ft-lbs) torque when at-
taching the gas piping to the gas valve.
IMPORTANT
Compounds used on threaded joints of gas piping
must be resistant to the actions of liquified petro-
leum gases.
1 - Gas piping may be routed into the unit through either
the left‐ or right‐hand side. Supply piping enters into
the gas valve from the side of the valve as shown in
line enters. Ensure opposite gas line hole is plugged
with supplied plug.
Leak Check
After gas piping is completed, carefully check all piping
connections (factory- and field-installed) for gas leaks. Use
a leak detecting solution or other preferred means.
Never use an open flame to test for gas leaks. Check all
connections using a commercially available soap solution
made specifically for leak detection.
IMPORTANT
When converting the ML193 unit from natural gas to
LP/propane install the field provided low pressure
The furnace must be isolated from the gas supply system
by closing its individual manual shut‐off valve during any
pressure testing of the gas supply system at pressuresless
than or equal to 1/2 psig (3.48 kPa, 14 inches w.c.).
LOW INLET PRESSURE SWITCH
(S145) LOCATION
Orange
MANUAL MAIN SHUT-OFF
VALVE WILL NOT HOLD
NORMAL TEST PRESSURE
FURNACE
ISOLATE
GAS VALVE
1/8” N.P.T.
PLUGGED TAP
White
Orange
CAP
FIGURE 56
IMPORTANT
Yellow
Gas Valve Shown In Off Position
When testing pressure of gas lines, gas valve must
valves can be damaged if subjected to pressures
greater than 1/2 psig (3.48 kPa).
FIGURE 55
2 - When connecting gas supply, factors such as length of
run, number of fittings and furnace rating must be con-
recommended pipe sizes for typical applications.
WARNING
FIRE OR EXPLOSION HAZARD
NOTE - Use two wrenches when connecting gas pip-
ing to avoid transferring torque to the manifold.
Failure to follow the safety warnings exactly could
result in serious injury, death, or property damage.
Never use an open flame to test for gas leaks. Check
all connections using a commercially available soap
solution made specifically for leak detection. Some
soaps used for leak detection are corrosive to cer-
tain metals. Carefully rinse piping thoroughly after
leak test has been completed.
3 - Gas piping must not run in or through air ducts, clothes
chutes, chimneys or gas vents, dumb waiters or eleva-
tor shafts. Center gas line through piping hole. Gas
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AUTOMATIC
GAS VALVE
(with manual
shut-off valve)
Left Side Piping
(Standard)
Right Side Piping
(Alternate)
Bellows Grommet
MANUAL
MAIN SHUT-OFF
VALVE
MANUAL
MAIN SHUT-OFF
VALVE
Plug
Plug
GROUND
JOINT
UNION
GROUND
JOINT
UNION
DRIP LEG
Gas Valve
Gas Valve
Bellows Grommet
DRIP LEG
FIELD
PROVIDED
AND INSTALLED
NOTE - BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET
FIGURE 57
Horizontal Applications
Possible Gas Piping Configurations
MANUAL
MAIN SHUT-OFF
VALVE
Horizontal Application
Left-Side Air Discharge
MANUAL
MAIN SHUT-OFF
VALVE
GROUND
JOINT
UNION
Bellows Grommet
GROUND
JOINT
UNION
DRIP LEG
Bellows Grommet
DRIP LEG
Gas Valve
Horizontal Application
Right-Side Air Discharge
MANUAL
MAIN SHUT-OFF
VALVE
Gas Valve
GROUND
JOINT
UNION
Bellows Grommet
FIELD
PROVIDED
AND INSTALLED
DRIP LEG
NOTE - BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET
Plug
FIGURE 58
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TABLE 9
GAS PIPE CAPACITY - FT3/HR (kL/HR)
Length of Pipe-Feet(m)
Nominal
Iron Pipe Size
-Inches(mm)
Internal
Diameter
-Inches(mm)
10
(3.048)
20
(6.096)
30
(9.144)
40
50
60
70
80
90
100
(12.192) (15.240) (18.288) (21.336) (24.384) (27.432) (30.480)
1/2
(12.7)
.622
(17.799)
175
(4.96)
120
(3.40)
97
(2.75)
82
(2.32)
73
(2.07)
66
(1.87)
61
(1.73)
57
(1.61)
53
(1.50)
50
(1.42)
3/4
(19.05)
.824
(20.930)
360
(10.19)
250
(7.08)
200
(5.66)
170
(4.81)
151
(4.28)
138
(3.91)
125
(3.54)
118
(3.34)
110
(3.11)
103
(2.92)
1
(25.4)
1.049
(26.645)
680
(19.25)
465
(13.17)
375
(10.62)
320
(9.06)
285
(8.07)
260
(7.36)
240
(6.80)
220
(6.23)
205
(5.80)
195
(5.52)
1-1/4
(31.75)
1.380
(35.052)
1400
(39.64)
950
(26.90)
770
(21.80)
660
(18.69)
580
(16.42)
530
(15.01)
490
(13.87)
460
(13.03)
430
(12.18)
400
(11.33)
1-1/2
(38.1)
1.610
(40.894)
2100
(59.46)
460
(41.34)
1180
(33.41)
990
(28.03)
900
(25.48)
810
(22.94)
750
(21.24)
690
(19.54)
650
(18.41)
620
(17.56)
2
(50.8)
2.067
(52.502)
3950
(111.85)
2750
(77.87)
2200
(62.30)
1900
(53.80)
1680
(47.57)
1520
(43.04)
1400
(39.64)
1300
(36.81)
1220
(34.55)
1150
(32.56)
2-1/2
(63.5)
2.469
(67.713)
6300
(178.39)
4350
(123.17)
3520
(99.67)
3000
(84.95)
2650
(75.04)
2400
(67.96)
2250
(63.71)
2050
(58.05)
1950
(55.22)
1850
(52.38)
3
(76.2)
3.068
(77.927)
11000
(311.48)
7700
(218.03)
6250
(176.98)
5300
(150.07)
4750
(134.50)
4300
(121.76)
3900
(110.43)
3700
(104.77)
3450
(97.69)
3250
(92.03)
4
(101.6)
4.026
(102.260)
23000
(651.27)
15800
(447.39)
12800
(362.44)
10900
(308.64)
9700
(274.67)
8800
(249.18)
8100
(229.36)
7500
(212.37)
7200
(203.88)
6700
(189.72)
NOTE - Capacity given in cubic feet of gas per hour (kilo liters of gas per hour) and based on 0.60 specific gravity gas.
Removal of the Furnace from Common Vent
3 - Close all building doors and windows and all doors be-
tween the space in which the appliances remaining
connected to the common venting system are located
and other spaces of the building. Turn on clothes dry-
ers and any appliances not connected to the common
venting system. Turn on any exhaust fans, such as
range hoods and bathroom exhausts, so they will oper-
ate at maximum speed. Do not operate a summer ex-
haust fan. Close fireplace dampers.
In the event that an existing furnace is removed from a
venting system commonly run with separate gas ap-
pliances, the venting system is likely to be too large to prop-
erly vent the remaining attached appliances.
Conduct the following test while each appliance is operat-
ing and the other appliances (which are not operating) re-
main connected to the common venting system. If the vent-
ing system has been installed improperly, you must
correct the system as indicated in the general venting re-
quirements section.
4 - Follow the lighting instructions. Turn on the appliance
that is being inspected. Adjust the thermostat so that
the appliance operates continuously.
5 - After the main burner has operated for 5 minutes, test
for leaks of flue gases at the draft hood relief opening.
Use the flame of a match or candle.
WARNING
CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon mon-
oxide poisoning or death.
The following steps shall be followed for each ap-
pliance connected to the venting system being
placed into operation, while all other appliances
connected to the venting system are not in
operation:
6 - After determining that each appliance connected to the
common venting system is venting properly, (step 3)
return all doors, widows, exhaust fans, fireplace damp-
ers, and any other gas-burning appliances to their pre-
vious mode of operation.
7 - If a venting problem is found during any of the preced-
ing tests, the common venting system must be modi-
fied to correct the problem.
1 - Seal any unused openings in the common venting sys-
tem.
Resize the common venting system to the minimum
vent pipe size determined by using the appropriate
tables in Appendix G. (These are in the current stan-
dards of the National Fuel Gas Code ANSI Z223.1.
2 - Inspect the venting system for proper size and horizon-
tal pitch. Determine that there is no blockage, restric-
tion, leakage, corrosion, or other deficiencies which
could cause an unsafe condition.
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Complete the wiring connections to the equipment. Use the
provided unit wiring diagram and the field wiring shown in
Class II rating for thermostat connections.
Electrical
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
Electrically ground the unit according to local codes or, in
the absence of local codes, according to the current Na-
tional Electric Code (ANSI/NFPA No. 70) for the USA and
current Canadian Electric Code part 1 (CSA standard
C22.1) for Canada. A green ground wire is provided in the
field make-up box.
CAUTION
Electrostatic discharge can affect elec-
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
NOTE - The ML193UH furnace contains electronic compo-
nents that are polarity sensitive. Make sure that the furnace
is wired correctly and is properly grounded.
INTERIOR MAKE-UP BOX INSTALLATION
remove and relocate
plug to unused
opening on left side
Accessory Terminals
One line voltage “EAC” 1/4” spade terminal is provided on
control configuration. This terminal is energized when the
indoor blower is operating. Any accessory rated up to one
amp can be connected to this terminal with the neutral leg
of the circuit being connected to one of the provided neutral
terminals. If an accessory rated at greater than one amp is
connected to this terminal, it is necessary to use an exter-
nal relay.
MAKE-UP
BOX
Right Side
One line voltage “HUM” 1/4” spade terminal is provided on
control configuration. This terminal is energized in the
heating mode when the combustion air inducer is operat-
ing. Any humidifier rated up to one amp can be connected
to this terminal with the neutral leg of the circuit being con-
nected to one of the provided neutral terminals. If a humidi-
fier rated at greater than one amp is connected to this termi-
nal, it is necessary to use an external relay relay.
FIGURE 59
The unit is equipped with a field make-up box. The make-
up box may be moved to the right side of the furnace to fa-
cilitate installation. Seal unused openings on left side with
plugs removed from right side. Secure the excess wire to
the existing harness to protect it from damage.
Thermostat
bleshooting.
Install the room thermostat according to the instructions
designations. If the furnace is being matched with a heat
pump, refer to the FM21 installation instruction or appropri-
ate dual fuel thermostat instructions.
The power supply wiring must meet Class I restrictions.
Protected by either a fuse or circuit breaker, select circuit
protection and wire size according to unit nameplate.
NOTE - Unit nameplate states maximum current draw.
Maximum Over-Current Protection allowed is 15 AMP.
Indoor Blower Speeds
Holes are on both sides of the furnace cabinet to facilitate
wiring.
1 - When the thermostat is set to “FAN ON,” the indoor
blower will run continuously on the heating speed
when there is no cooling or heating demand.
Install a separate (properly sized) disconnect switch near
the furnace so that power can be turned off for servicing.
2 - When the ML193UH is running in the heating mode,
the indoor blower will run on the heating speed.
Before connecting the thermostat check to make sure the
wires will be long enough for servicing at a later date. Make
sure that thermostat wire is long enough to facilitate future
removal of blower for service.
3 - When there is a cooling demand, the indoor blower will
run on the cooling speed.
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Generator Use - Voltage Requirements
D The furnace integrated control requires both polarity
and proper ground. Both polarity and proper grounding
should be checked before attempting to operate the
furnace on either permanent or temporary power
D Generator should have a wave form distortion of less
than 5% THD (total harmonic distortion).
The following requirements must be kept in mind when
specifying a generator for use with this equipment:
D The furnace requires 120 volts + 10% (Range: 108
volts to 132 volts)
D The furnace operates at 60 Hz + 5% (Range: 57 Hz to
63 Hz)
TYPICAL ML193UH WIRING DIAGRAM
FIGURE 60
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Integrated Control
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
Humidifier (120VAC)
HUM
LINE
Input (120VAC)
Transformer (120VAC)
XFMR
EAC
Indoor Air Qality Accessory Air Cleaner (120VAC)
Blower - Cooling Speed (120VAC)
Blower - Heating Speed (120VAC)
Dead terminals to park alternate spd taps
Continuous blower
COOL
HEAT
PARK
CONT
NEUTRALS
Neutral terminals (120VAC)
Twinning Terminal (24VAC)
TWIN
LED
PUSH BUTTON
TWIN
BLOWER OFF
DELAY JUMPER
FIGURE 1
Note - This control is equipped with a push button switch for
diagnostic code recall. The control stores the last 5 fault
codes in non-volatile memory. The most recent fault code
is flashed first, the oldest fault code is flashed last. There is
a 2 second pause between codes. When the push button
switch is pressed for less than 5 seconds, the control will
flash the stored fault codes when the switch is released.
The fault code history may be cleared by pressing the push
button switch for more than 5 seconds.
Integrated Control Diagnostic Codes
DIAGNOSTIC CODES
LED Status
LED Off
LED On
1 Flash
DESCRIPTION
No power to control or control harware
fault detected.
Normal operation.
Flame present with gas vavle
de-energized.
Pressure switch closed with combustion
air inducer de-energized.
2 Flashes
Pressure switch open with combus-
tion air inducer energized.
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
Primary limit switch open.
Rollout switch open.
Pressure switch cycle lockout.
Lockout, burners fail to light.
Lockout, buners lost flame too many
times.
8 Flashes
9 Flashes
Line voltage polarity incorrect.
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5 - Wait for the combustion air inducer to stop. Set the
thermostat to initiate a heating demand and again al-
low the burners to fire for approximately 3 minutes.
6 - Adjust the thermostat to deactivate the heating de-
mand and wait for the combustion air inducer to stop.
At this point, the trap should be primed with sufficient
water to ensure proper condensate drain operation.
Unit Start-Up
FOR YOUR SAFETY READ BEFORE OPERATING
WARNING
Do not use this furnace if any part has been under-
water. A flood-damaged furnace is extremely dan-
gerous. Attempts to use the furnace can result in fire
or explosion. Immediately call a qualified service
technician to inspect the furnace and to replace all
gas controls, control system parts, and electrical
parts that have been wet or to replace the furnace, if
deemed necessary.
WARNING
If you do not follow these instructions exactly, a fire
or explosion may result causing property damage,
personal injury or death.
1 - STOP! Read the safety information at the beginning of
this section.
WARNING
2 - Set the thermostat to the lowest setting.
3 - Turn off all electrical power to the unit.
4 - This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
Danger of explosion. Can cause injury
or product or property damage. Should
the gas supply fail to shut off or if
overheating occurs, shut off the gas
valve to the furnace before shutting off
the electrical supply.
5 - Remove the upper access panel.
7 - Wait five minutes to clear out any gas. If you then smell
gas, STOP! Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's instruc-
tions. If you do not smell gas go to next step.
CAUTION
Before attempting to perform any service or mainte-
nance, turn the electrical power to unit OFF at dis-
connect switch.
MANIFOLD
PRESSURE
OUTLET
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
BEFORE LIGHTING the unit, smell all around the furnace
area for gas. Be sure to smell next to the floor because
some gas is heavier than air and will settle on the floor.
The gas valve on the ML193UH is equipped with a gas con-
trol switch (lever). Use only your hand to move switch. Nev-
er use tools. If the the switch will not move by hand, do not
try to repair it. Force or attempted repair may result in a fire
or explosion.
INLET
PRESSURE
PORT
Placing the furnace into operation:
ML193UH units are equipped with an automatic hot sur-
face ignition system. Do not attempt to manually light burn-
ers on this furnace. Each time the thermostat calls for heat,
the burners will automatically light. The ignitor does not get
hot when there is no call for heat on these units.
GAS VALVE SHOWN IN ON POSITION
FIGURE 61
9 - Replace the upper access panel.
10- Turn on all electrical power to to the unit.
11- Set the thermostat to desired setting.
Priming Condensate Trap
NOTE - When unit is initially started, steps 1 through 11
The condensate trap should be primed with water prior to
start-up to ensure proper condensate drainage. Either pour
10 fl. oz. (300 ml) of water into the trap, or follow these steps
to prime the trap:
may need to be repeated to purge air from gas line.
12- If the appliance will not operate, follow the instructions
“Turning Off Gas to Unit” and call your service techni-
cian or gas supplier.
1 - Follow the lighting instructions to place the unit into op-
eration.
Turning Off Gas to Unit
2 - Set the thermostat to initiate a heating demand.
1 - Set the thermostat to the lowest setting.
3 - Allow the burners to fire for approximately 3 minutes.
2 - Turn off all electrical power to the unit if service is to be
performed.
4 - Adjust the thermostat to deactivate the heating de-
mand.
3 - Remove the upper access panel.
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4 - Move gas valve switch to OFF.
Furnace should operate at least 5 minutes before checking
gas flow. Determine time in seconds for two revolutions of
gas through the meter. (Two revolutions assures a more
accurate time.) Divide by two and compare to time in table
incorrect, check gas orifices for proper size and restriction.
Remove temporary gas meter if installed.
5 - Replace the upper access panel.
Failure To Operate
If the unit fails to operate, check the following:
1 - Is the thermostat calling for heat?
2 - Are access panels securely in place?
3 - Is the main disconnect switch closed?
4 - Is there a blown fuse or tripped breaker?
5 - Is the filter dirty or plugged? Dirty or plugged filters will
cause the limit control to shut the unit off.
6 - Is gas turned on at the meter?
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
Supply Pressure Measurement
When testing supply gas pressure, use the 1/8” N.P.T.
plugged tap or pressure post located on the gas valve to
line pressure with unit firing at maximum rate. Low pres-
sure may result in erratic operation or underfire. High pres-
sure can result in permanent damage to gas valve or over-
fire.
7 - Is the manual main shut‐off valve open?
8 - Is the internal manual shut‐off valve open?
9 - Is the unit ignition system in lockout? If the unit locks
out again, inspect the unit for blockages.
Heating Sequence Of Operation
1 - When thermostat calls for heat, combustion air inducer
starts.
2 - Combustion air pressure switch proves blower opera-
tion. Switch is factory set and requires no adjustment.
3 - After a 15-second prepurge, the hot surface ignitor en-
ergizes.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
Manifold Pressure Measurement
4 - After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second Trial for Ignition peri-
od begins.”
1 - Remove the threaded plug from the outlet side of the
gas valve and install a field-provided barbed fitting.
Connect to a manometer to measure manifold pres-
sure.
5 - Gas is ignited, flame sensor proves the flame, and the
combustion process continues.
6 - If flame is not detected after first ignition trial, the igni-
tion control will repeat steps 3 and 4 four more times
before locking out the gas valve (“WATCHGUARD”
flame failure mode). The ignition control will then auto-
matically repeat steps 1 through 6 after 60 minutes.
To interrupt the 60-minute “WATCHGUARD” period,
move thermostat from “Heat” to “OFF” then back to
“Heat”. Heating sequence then restarts at step 1.
2 - Start unit and allow 5 minutes for unit to reach steady
state.
3 - While waiting for the unit to stabilize, observe the
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
Gas Pressure Adjustment
NOTE - Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
Gas Flow (Approximate)
TABLE 10
GAS METER CLOCKING CHART
Seconds for One Revolution
TABLE 11
Supply Line and Manifold Pressure (inches w.c.)
Natural
LP
ML193
Unit
Manifold
Pressure
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
Unit
Fuel
Line Pressure
All
All
Nat. Gas
L.P. Gas
3.5
4.5 - 10.5
-045
-070
-090
-110
-135
80
160
110
82
200
136
102
82
400
272
204
164
136
55
10.0
11.0 - 13.0
41
33
66
NOTE - A natural to L.P. propane gas changeover kit is
necessary to convert this unit. Refer to the changeover kit
installation instruction for the conversion procedure.
27
54
68
Natural-1000 btu/cu ft
LP-2500 btu/cu ft
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Proper Combustion
High Altitude Information
NOTE - In Canada, certification for installations at eleva-
tions over 4500 feet (1372 m) is the jurisdiction of local au-
thorities.
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustion. Take combustion sample beyond the flue outlet
and compare to the tables below.
ML193UH units require no manifold pressure adjustments
for operation at altitudes up to 10,000 feet (3048 m) above
sea level. Units installed at altitude of 4501 - 10,000 feet
(1373 to 3048m) require a pressure switch change which
can be ordered separately. Table 13 lists conversion kit
and pressure switch requirements at varying altitudes.
The combustion air pressure switch is factory-set and re-
quires no adjustment.
TABLE 12
ML193
CO %
2
CO %
For L.P.
For Nat
2
Unit
-045
-070
-090
-110
-135
7.2 - 7.9
8.6 - 9.3
NOTE - A natural to LP/propane gas changeover kit is nec-
essary to convert this unit. Refer to the changeover kit
installation instruction for the conversion procedure.
The maximum carbon monoxide reading should not exceed 50 ppm.
TABLE 13
Conversion Kit and Pressure Switch Requirements at Varying Altitudes
High Altitude
Natural Burner
Orifice Kit
LP/Propane
to
Natural
High Altitude
LP/Propane
Burner Orifice Kit
Natural to
LP/Propane
High Altitude Pressure Switch
ML193
Unit
0 - 7500 ft
(0 - 2286m)
7501 - 10,000 ft
(2286 - 3038m)
0 - 7500 ft
(0 - 2286m)
7501 - 10,000 ft
(2286 - 3038m)
4501 - 7500 ft 7501 -10,000 ft
(1373 - 2286m) (2286 - 3048m)
-045
-070
-090
-110
-135
*69W73
73W37
*73W81
*68W68
93W87
93W88
* Conversion requires installation of a gas valve manifold spring which is provided with the gas conversion kit.
Pressure switch is factory set. No adjustment necessary. All models use the factory-installed pressure switch from 0-4500 feet (0-1370 m).
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Testing for Proper Venting and Sufficient Combustion Air for Non-Direct Vent Applications
horizontal pitch. Determine there is no blockage or re-
striction, leakage, corrosion, or other deficiencies
which could cause an unsafe condition.
WARNING
CARBON MONOXIDE POISONING HAZARD!
3 - To the extent that it is practical, close all building doors
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon monox-
ide poisoning or death.
and windows and all doors between the space in
which the appliances connected to the venting system
are located and other spaces of the building.
4 - Close fireplace dampers.
The following steps shall be followed for each ap-
pliance connected to the venting system being
placed into operation, while all other appliances con-
nected to the venting system are not in operation.
5 - Turn on clothes dryers and any appliances not con-
nected to the venting system. Turn on any exhaust
fans, such as range hoods and bathroom exhausts, so
they will operate at maximum speed. Do not operate a
summer exhaust fan.
After the ML193UH gas furnace has been started, the fol-
lowing test should be conducted to ensure proper venting
and sufficient combustion air has been provided to the
ML193UH as well as to other gas‐fired appliances which
are separately vented.
6 - Follow the lighting instruction to place the appliance
being inspected into operation. Adjust thermostat so
appliance will operate continuously.
7 - Use the flame of match or candle to test for spillage of
flue gases at the draft hood relief opening after 5 min-
utes of main burner operation.
If a ML193UH furnace replaces a Category I furnace which
was commonly vented with another gas appliance, the size
of the existing vent pipe for that gas appliance must be
checked. Without the heat of the original furnace flue prod-
ucts, the existing vent pipe is probably oversized for the
single water heater or other appliance. The vent should be
checked for proper draw with the remaining appliance.
8 - If improper venting is observed during any of the
above tests, the venting system must be corrected or
sufficient combustion/make‐up air must be provided.
The venting system should be re‐sized to approach
the minimum size as determined by using the ap-
propriate tables in appendix G in the current standards
of the National Fuel Gas Code ANSI-Z223.1/NPFA 54
in the U.S.A., and the appropriate Natural Gas and
Propane appliances venting sizing tables in the cur-
rent standard of the CSA-B149 Natural Gas and Pro-
pane Installation Codes in Canada.
The test should be conducted while all appliances (both in
operation and those not in operation) are connected to the
venting system being tested. If the venting system has
been installed improperly, or if provisions have not been
made for sufficient amounts of combustion air, corrections
must be made as outlined in the previous section.
9 - After determining that each appliance remaining con-
nected to the common venting system properly vents
when tested as indicated in step 3, return doors, win-
dows, exhaust fans, fireplace dampers and any other
gas‐burning appliance to their previous condition of
use.
1 - Seal any unused openings in the venting system.
2 - Visually inspect the venting system for proper size and
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Other Unit Adjustments
HEAT FAN‐OFF TIME IN SECONDS
Primary Limit.
The primary limit is located on the heating compartment
vestibule panel. This limit is factory set and requires no ad-
justment.
NO JUMPER
Flame Rollout Switches (Two)
To adjust fan-off timing, reposition jumper across pins to
achieve desired setting.
These manually reset switches are located on the front of
the burner box.
60 Second
off Time
90 Second
off Time
120 Second
off Time
180 Second
off Time
Pressure Switch
The pressure switch is located in the heating compartment
on the cold end header box. This switch checks for proper
combustion air inducer operation before allowing ignition
trial. The switch is factory-set and must not be adjusted.
Temperature Rise
After the furnace has been started and supply and return
air temperatures have been allowed to stabilize, check the
temperature rise. If necessary, adjust the blower speed to
maintain the temperature rise within the range shown on
the unit nameplate. Increase the blower speed to decrease
the temperature. Decrease the blower speed to increase
the temperature rise. Failure to adjust the temperature rise
may cause erratic limit operation.
FIGURE 62
NOTE - Termination of any unused motor leads must be in-
sulated.
4 - Place unused blower speed tap on integrated control
“PARK” terminal or insulate.
5 - Refer to blower speed selection chart on unit wiring
diagram for desired heating or cooling speed. See
Product Specifications bulletin for blower perfor-
mance tables.
Fan Control
The fan on time of 30 seconds is not adjustable. The fan off
delay (amount of time that the blower operates after the
heat demand has been satisfied) may be adjusted by
changing the jumper position across the five pins on the
integrated control. The unit is shipped with a factory fan off
setting of 120 seconds. The fan off delay affects comfort
and is adjustable to satisfy individual applications. Adjust
the fan off delay to achieve a supply air temperature be-
tween 90° and 110°F at the moment that the blower is
de-energized. Longer off delay settings provide lower re-
turn air temperatures; shorter settings provide higher re-
6 - Connect selected speed tap at integrated control
speed terminal.
7 - Resecure blower access panel.
8 - Turn on electrical power to furnace.
9 - Recheck temperature rise.
Electronic Ignition
The integrated control has an added feature of an internal
Watchguard control. The feature serves as an automatic
reset device for integrated control lockout caused by igni-
tion failure. This type of lockout is usually due to low gas
line pressure. After one hour of continuous thermostat de-
mand for heat, the Watchguard will break and remake ther-
mostat demand to the furnace and automatically reset the
integrated control to begin the ignition sequence.
Electrical
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating). Correct voltage is 120VAC + 10%
3 - Check amp-draw on the blower motor with blower ac-
cess panel in place.
Exhaust and Air Intake Pipe
Motor Nameplate__________Actual__________
Blower Speeds
1 - Check exhaust and air intake connections for tightness
and to make sure there is no blockage.
2 - Is pressure switch closed? Obstructed exhaust pipe
will cause unit to shut off at pressure switch. Check ter-
mination for blockages.
Follow the steps below to change the blower speeds.
1 - Turn off electrical power to furnace.
2 - Remove blower access panel.
3 - Obstructed pipe or termination may cause rollout
switches to open. Reset manual flame rollout switches
on burner box assembly if necessary.
3 - Disconnect existing speed tap at integrated control
speed terminal.
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between the ”C” and ”Twin” terminals of the two controls.
The 24 VAC secondary of the two systems must be in
phase. All thermostat connections are made to one control
only. Figure 2 show wiring for two-stage and single stage
thermostats.
Twinning the ML193UH
The control board in this furnace is equipped with a provi-
sion to ”twin” (interconnect) two(2) adjacent furnaces with a
common plenum such that they operate as one (1) large
unit.
The twinned furnace without thermostat connections is to
have the call for heat supplied by an external 24VAC isola-
tion relay to prevent its rollout switch from being bypassed
by the other twinned furnace. The coil of the isolation relay
connects from the thermostat ”W” to 24 VAC common. The
contacts of the relay connect ”R” to ”W” on the non-thermo-
stat twin.
When twinned, the circulating blower speeds are synchro-
nized between the furnaces. If either furnace has a need to
run the blower, both furnaces will run the blower on the
same speed. The cooling speed has highest priority, fol-
lowed by heating speed and fan speed.
Field installation of twinning consists of connecting wires
FIELD WIRING FOR TWINNING
TWIN
TWIN
SINGLE STAGE THERMOSTAT
TWO-STAGE THERMOSTAT
R
R
Y
G
R
R
Y
G
Call For Cool
Call For Cool
TWIN 1
TWIN 1
Y
Y
Call For Fan
Call For Fan
G
G
Call For 1st
Stage Heat
Call For Heat
W
W1
W
C
W
Call For 2nd
StageHeat
W2
C
TWIN
TWIN
ISOLATION
RELAY
ISOLATION
RELAY
R
R
Y
G
TWIN 2
TWIN 2
Y
G
W
C
W
C
FIGURE 2
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Electrical
Service
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating).
3 - Check amp-draw on the blower motor.
Motor Nameplate__________Actual__________
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
Winterizing and Condensate Trap Care
1 - Turn off power to the furnace.
Failure to follow safety warnings exactly could result
in dangerous operation, serious injury, death or
property damage.
Improper servicing could result in dangerous opera-
tion, serious injury, death, or property damage.
Before servicing, disconnect all electrical power to
furnace.
When servicing controls, label all wires prior to dis-
connecting. Take care to reconnect wires correctly.
Verify proper operation after servicing.
2 - Have a shallow pan ready to empty condensate water.
3 - Remove the clean out cap from the condensate trap
and empty water. Inspect the trap then reinstall the
clean out cap.
Cleaning the Burner Assembly
1 - Turn off gas and electrical power to the furnace. Re-
move heating compartment access panel.
2 - Disconnect the gas supply line from the gas valve.
3 - Disconnect and label wires from gas valve.
4 - Disconnect ignitor wiring at 2 circuit plug.
5 - Disconnect and label wires from rollout switch.
6 - Disconnect and label flame sensor wire.
At the beginning of each heating season, system should be
checked as follows by a qualified service technician:
Blower
7 - Disconnect and label ground wire from burner/man-
ifold assembly.
Check the blower wheel for debris and clean if necessary.
The blower motors are prelubricated for extended bearing
life. No further lubrication is needed.
8 - Remove four screws that secures burner/manifold as-
sembly to vestibule. Remove the assembly and make
note not to allow ignitor plate to dislodge from the as-
sembly.
9 - Gently clean the face of the burners using the soft
brush attachment on a vacuum cleaner. Visually in-
spect the inside of the burners and crossovers for any
blockage caused by foreign matter. Remove any
blockage
WARNING
The blower access panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal inju-
ry or death.
10 - Reinstall the burner/manifold assembly using the ex-
isting four screws. Burners are self aligning to cen-
ter of clam shells.
Filters
11 - Reconnect ground wire.
12 - Reconnect flame sensor wire.
13 - Reconnect rollout switch wires.
14 - Reconnect ignitor wires.
All air filters are installed external to the unit. Filters should
be inspected monthly. Clean or replace the filters when
recommended filter sizes.
15 - Reconnect gas valve wires.
16 - Reconnect gas supply line to gas valve.
Exhaust and air intake pipes
17 - Refer to instructions on verifying gas and electrical
connections when re-establishing supplies.
Check the exhaust and air intake pipes and all connections
for tightness and to make sure there is no blockage.
18 - Follow instructions to place furnace in operation. Run
furnace 5 minutes to ensure burners are clean and op-
erating correctly.
NOTE - After any heavy snow, ice or frozen fog event the
furnace vent pipes may become restricted. Always check
the vent system and remove any snow or ice that may be
obstructing the plastic intake or exhaust pipes.
19 - Replace heating compartment access panel.
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Repair Parts List
The following repair parts are available through Lennox dealers. When ordering parts, include the complete furnace model
number listed on the CSA nameplate -- Example: ML193UH045XP36B-01. All service must be performed by a licensed
professional installer (or equivalent), service agency, or gas supplier.
Cabinet Parts
Upper access panel
Heating Parts
Flame Sensor
Blower access panel
Top Cap
Heat exchanger assembly
Gas manifold
Control Panel Parts
Transformer
Combustion air inducer
Gas valve
Integrated control board
Door interlock switch
Blower Parts
Main burner cluster
Main burner orifices
Pressure switch
Blower wheel
Ignitor
Motor
Primary limit control
Flame rollout switches
Motor mounting frame
Motor capacitor
Blower housing cutoff plate
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Start-Up & Performance Check List
UNIT SET UP
Furnace:
Model Number_______________
Serial Number_________________
SUPPLY
AIR
Line Voltage
2
4
1
GAS SUPPLY
Natural Gas
LP Propane Gas
3
Piping Connections Tight
Leak Tested
Flter
RETURN AIR
2
Supply Line Pressure “W.C.________
1
Gas Supply Pressure
DUCT SYS-
TEM
SUPPLY AIR DUCT
3
1
Sealed
Insulated (if necessary)
RETURN DUCT
Sealed
2
INTAKE / EXHAUST
PIPE
All Joints Primed and Glued
Filter Installed and Clean
Terminations Installed Properly
Grilles Unobstructed
Horizontal Pipes Sloped (if applicable)
Condensate Trap Primed / Line Sloped
VOLTAGE CHECK
4
Supply Voltage _____
Electrical Connections Tight
Pipes Sup-
ported
Heat Cable Installed and Operable (if applicable)
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UNIT OPERATION
HEATING MODE
COOLING MODE
GAS MANIFOLD PRESSURE “W.C._____
1
2
INDOOR BLOWER
AMPS______
3
4
COMBUSTION SAMPLE CO % CO PPM_______
2 ______
TEMPERATURE DROP
Return Duct Temperature _________
_
INDOOR BLOWER
AMPS______
3
4
Supply Duct Temperature _______
Temperature Drop = _________
TEMPERATURE RISE
5
TOTAL EXTERNAL STATIC (dry coil)
Supply External Static _______
Supply Duct Temperature ________
_
Return Duct Temperature
_____
Return External Static + ______
Total External Static = _______
Temperature Rise = ________
TOTAL EXTERNAL STATIC
5
8
DRAIN LINE
Leak Free
Supply External Static _______
Return External Static + ______
Total External Static = _______
THERMOSTAT
6
7
9
CONDENSATE LINE
Leak Free
Adjusted and Programmed
Explained Operation to Own-
er
VENT PIPE
Leak Free
Combustion CO
2
2
7
SUPPLY
AIR
Thermostat
Temperatures
8
Gas Manifold Pressure
9
4
1
Blower Motor Amps
6
3
Duct Static
5
RETURN AIR
Contractor's: Name_________________________Telephone_____________Checklist Completed____________________
Job Address_____-________________________________Technician's Name___________________________________
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Requirements for Commonwealth of Massachusetts
Modifications to NFPA-54, Chapter 10
4 - INSPECTION. The state or local gas inspector of the
side wall, horizontally vented, gas-fueled equipment
shall not approve the installation unless, upon inspec-
tion, the inspector observes carbon monoxide detec-
tors and signage installed in accordance with the pro-
visions of 248 CMR 5.08(2)(a) 1 through 4.
Revise NFPA-54 section 10.8.3 to add the following re-
quirements:
For all side wall, horizontally vented, gas-fueled equipment
installed in every dwelling, building or structure used in
whole or in part for residential purposes, including those
owned or operated by the Commonwealth and where the
side wall exhaust vent termination is less than seven (7)
feet above the finished grade in the area of the venting, in-
cluding but not limited to decks and porches, the following
requirements shall be satisfied:
EXEMPTIONS: The following equipment is exempt
from 24 CMR 5.08(2)(a) 1 through 4:
1 - The equipment listed in Chapter 10 entitled “Equip-
ment Not Required to Be Vented” in the most current
edition of NFPA 54 as adopted by the Board; and
2 - Product Approved side wall, horizontally vented, gas-
fueled equipment installed in a room or structure sepa-
rate from the dwelling, building or structure used in
whole or in part for residential purposes.
1 - INSTALLATION OF CARBON MONOXIDE DETEC-
TORS. At the time of installation of the side wall, hori-
zontally vented, gas-fueled equipment, the installing
plumber or gasfitter shall observe that a hard-wired
carbon monoxide detector with an alarm and battery
backup is installed on the floor level where the gas
equipment is to be installed. In addition, the installing
plumber or gasfitter shall observe that a battery-oper-
ated or hard-wired carbon monoxide detector with an
alarm is installed on each additional level of the dwell-
ing, building or structure served by the side wall, hori-
zontally vented, gas-fueled equipment. It shall be the
responsibility of the property owner to secure the ser-
vices of qualified licensed professionals for the instal-
lation of hard-wired carbon monoxide detectors.
MANUFACTURER REQUIREMENTS -
GAS EQUIPMENT VENTING SYSTEM PROVIDED.
When the manufacturer of Product Approved side wall,
horizontally vented, gas-fueled equipment provides a vent-
ing system design or venting system components with the
equipment, the instructions provided by the manufacturer
for installation of the equipment and the venting system
shall include:
1 - Detailed instructions for the installation of the venting
system design or the venting system components:
and
a - In the event that the side wall, horizontally vented,
gas-fueled equipment is installed in a crawl space
or an attic, the hard-wired carbon monoxide detec-
tor with alarm and battery back-up may be installed
on the next adjacent floor level.
2 - A complete parts list for the venting system design or
venting system.
MANUFACTURER REQUIREMENTS -
GAS EQUIPMENT VENTING SYSTEM NOT PROVIDED.
b - In the event that the requirements of this subdivi-
sion cannot be met at the time of completion of
installation, the owner shall have a period of thirty
(30) days to comply with the above requirements;
provided, however, that during said thirty (30) day
period, a battery-operated carbon monoxide detec-
tor with an alarm shall be installed.
When the manufacturer of Product Approved side wall,
horizontally vented, gas-fueled equipment does not pro-
vide the parts for venting the flue gases, but identifies “spe-
cial venting systems,” the following requirements shall be
satisfied by the manufacturer:
2 - APPROVED CARBON MONOXIDE DETECTORS.
Each carbon monoxide detector as required in accor-
dance with the above provisions shall comply with
NFPA 720 and be ANSI/UL 2034 listed and IAS certi-
fied.
1 - The referenced “special venting system” instructions
shall be included with the appliance or equipment
installation instructions; and
2
The “special venting systems” shall be Product Ap-
proved by the Board, and the instructions for that sys-
tem shall include a parts list and detailed installation
instructions.
3 - SIGNAGE. A metal or plastic identification plate shall
be permanently mounted to the exterior of the building
at a minimum height of eight (8) feet above grade di-
rectly in line with the exhaust vent terminal for the hori-
zontally vented, gas-fueled heating appliance or
equipment. The sign shall read, in print size no less
than one-half (1/2) inch in size, “GAS VENT DIRECT-
LY BELOW. KEEP CLEAR OF ALL OBSTRUC-
TIONS.”
A copy of all installation instructions for all Product
Approved side wall, horizontally vented, gas-fueled
equipment, all venting instructions, all parts lists for
venting instructions, and/or all venting design instruc-
tions shall remain with the appliance or equipment at
the completion of the installation.
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FOR THE PROVINCE OF ONTARIO, HORIZONTAL SIDEWALL VENT APPLICATIONS ONLY
For exterior horizontal venting applications, the 2” X 1.5”
reducer for 2” venting at the point where the exhaust pipe
exits the structure is not required in direct or non-direct vent
applications in the Province of Ontario. In these applica-
tions, the vent should be oriented such that the exhaust
plume is unobjectionable. If the installation requires more
separation between the flue gases and the building struc-
ture, a reducer may be installed on the exhaust pipe to in-
crease the flue gas velocity.
Page 51
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