Lenox Furnace Lennox Merit Series Gas Furnace Upflow Horizontal air discharge User Manual

INSTALLATION  
INSTRUCTIONS  
E 2011 Lennox Industries Inc.  
Dallas, Texas, USA  
ML180UHE  
®
MERIT SERIES GAS FURNACE  
UPFLOW / HORIZONTAL AIR DISCHARGE  
506810−01  
06/2011  
Supersedes 506732−01  
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.  
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 installer (or  
equivalent), service agency or the gas supplier.  
AIR FLOW  
UPFLOW  
CAUTION  
As with any mechanical equipment, personal injury  
can result from contact with sharp sheet metal  
edges. Be careful when you handle this equipment.  
HORIZONTAL RIGHT  
HORIZONTAL LEFT  
Table of Contents  
Unit Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2  
Parts Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3  
ML180UHE Gas Furnace . . . . . . . . . . . . . . . . . . . . . . . . . 4  
Shipping and Packing List . . . . . . . . . . . . . . . . . . . . . . . . 4  
Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4  
Use of Furnace as a Construction Heater . . . . . . . . . . . 5  
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5  
Combustion, Dilution & Ventilation Air . . . . . . . . . . . . . . 6  
Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23  
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25  
Integrated Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28  
Unit Start−Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29  
Gas Pressure Adjustment . . . . . . . . . . . . . . . . . . . . . . . . 30  
High Altitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30  
Proper Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30  
Other Unit Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . 31  
Blower Performance Data . . . . . . . . . . . . . . . . . . . . . . . . 33  
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35  
Planned Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37  
Repair Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37  
Integrated Control Diagnostic Codes . . . . . . . . . . . . . . . 38  
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39  
Setting Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9  
Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12  
Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12  
Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13  
06/11  
506810−01  
Page 1  
*2P0611*  
*P506810-01*  
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Parts Arrangement  
Make−Up Box  
Heat Exchanger  
Combustion Air Inducer  
Combustion Air Inducer  
Pressure Switch  
Burner Box  
(includes sensor, ignitor  
and rollout switches)  
Gas Valve  
Primary Limit  
(under  
combustion  
air inducer)  
Control Box  
(includes integrated control,  
interlock switch and transformer)  
Upper Access Panel  
Secondary Limits  
Blower Assembly  
Blower Access Panel  
Power Choke  
(4 and 5 Ton Only)  
FIGURE 1  
Page 3  
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ML180UHE Gas Furnace  
CAUTION  
The ML180UHE unit is shipped ready for installation in the  
upflow or horizontal right position (for horizontal left posi-  
tion the combustion air pressure switch must be moved)  
fueled by natural gas. A conversion kit (ordered separate-  
ly) is required for use in LP/Propane gas applications. The  
furnace is shipped with the bottom panel in place. The bot-  
tom panel must be removed if the unit is to be installed in a  
horizontal application. The panel may also be removed in  
upflow applications.  
As with any mechanical equipment, personal injury  
can result from contact with sharp sheet metal  
edges. Be careful when you handle this equipment.  
Certifications  
ML180UHE units are CSA International certified to ANSI  
Z21.47.  
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). The National Fuel Gas Code is  
available from the following address:  
Shipping and Packing List  
American National Standards Institute, Inc.  
11 West 42nd Street  
Package 1 of 1 contains  
1 − Assembled ML180UHE unit  
1 − Bag assembly containing the following:  
2 Screws  
New York, NY 10036  
Clearances  
1 Snap bushing  
Adequate clearance must be made around the air open-  
ings into the vestibule area. In order to ensure proper unit  
operation, combustion and ventilation air supply must be  
provided according to the current National Fuel Gas Code.  
1 Snap plug  
1 − Wire tie  
1 Vent warning label  
1 Owner’s manual and warranty card  
Vent installations must be consistent with the National Fuel  
Gas Code venting tables (in this instruction) and applicable  
provisions of local building codes.  
The following items may be ordered separately:  
1 − Thermostat  
1 − Suspension kit (for horizontal installations)  
1 − LP/Propane changeover kit  
1 − Return air base  
This furnace is CSA International certified for installation  
clearances to combustible material as listed on the unit  
nameplate and in the tables in figures 8 and 12. Accessibility  
and service clearances must take precedence over fire  
protection clearances.  
1 − High altitude kit  
1 − Side filter kit  
NOTE − For installation on combustible floors, the furnace  
shall not be installed directly on carpeting, tile, or other  
combustible material other than wood flooring.  
Check equipment for shipping damage. If you find any  
damage, immediately contact the last carrier.  
Safety Information  
Installed Locations  
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 apublic garage, hangar, or other building that has a haz-  
ardous atmosphere, the furnace must be installed accord-  
ing to recommended good practice requirements and cur-  
rent National Fuel Gas Code.  
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.  
Temperature Rise  
NOTE − Furnace must be adjusted to obtain a temperature  
rise within the range specified on the unit nameplate. Failure  
to do so may cause erratic limit operation and may result in  
premature heat exchanger failure.  
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 installer (or  
equivalent), service agency or the gas supplier.  
This ML180UHE furnace must be installed so that its elec-  
trical components are protected from water.  
Page 4  
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Installed in Combination with a Cooling Coil  
This furnace design has not been CSA International  
certified for installation in mobile homes, recreational  
vehicles, or outdoors.  
When this furnace is used with cooling units, it shall be  
installed in parallel with, or on the upstream side of, cooling  
units to avoid condensation in the heating compartment.  
See figure 2. With a parallel flow arrangement, a damper (or  
other means to control the flow of air) must adequately pre-  
vent chilled air from entering the furnace. If the damper is  
manually 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. See figure 2.  
Use of Furnace as Construction Heater  
Lennox does not recommend the use of ML180UHE 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.  
ML180UHE units may be used for heating of buildings or  
structures under construction, if the following conditions  
are met:  
Heating Unit Installed Parallel to Cooling Coil  
D The vent system must be permanently installed per  
these installation instructions.  
Dampers  
(open during heating operation only)  
D A room thermostat must control the furnace. The use of  
fixed jumpers that will provide continuous heating is not  
allowed.  
Gas Unit  
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.  
Cooling Coil  
D Air filters must be installed in the system and must be  
maintained during construction.  
Dampers  
(open during cooling operation only)  
D Air filters must be replaced upon construction comple-  
tion.  
Heating Unit Installed Upstream of Cooling Coil  
D The input rate and temperature rise must be set per the  
furnace rating plate.  
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.  
Gas Unit  
Cooling Coil  
FIGURE 2  
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 Elec-  
tric Code, ANSI/NFPA No. 70. The National Electric Code  
(ANSI/NFPA No. 70) is available from the following ad-  
dress:  
D The furnace heat exchanger, components, duct system,  
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.  
National Fire Protection Association  
1 Battery March Park  
General  
Quincy, MA 02269  
These instructions are intended as a general guide and do  
not supersede local codes in any way. Consult authorities  
having jurisdiction before installation.  
NOTE − This furnace is designed for a minimum continu-  
ous return air temperature of 60°F (16°C) or an intermit-  
tent operation down to 55°F (13°C) dry bulb for cases  
where a night setback thermostat is used. Return air tem-  
perature must not exceed 85°F (29°C) dry bulb.  
In addition to the requirements outlined previously, the fol-  
lowing general recommendations must be considered  
when installing a ML180UHE furnace:  
The ML180UHE furnace may be installed in alcoves, clos-  
ets, attics, basements, garages, crawl spaces and utility  
rooms in the upflow or horizontal position.  
D 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 chimney or vent termination point.  
Page 5  
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D Do not install the furnace where drafts might blow direct-  
ly into it. This could cause improper combustion and un-  
safe operation.  
information has been reprinted with permission from the  
National Fuel Gas Code (ANSI-Z223.1). This reprinted ma-  
terial is not the complete and official position of the ANSI on  
the referenced subject, which is represented only by the  
standard in its entirety.  
D Do not block the furnace combustion air openings with  
clothing, boxes, doors, etc. Air is needed for proper  
combustion and safe unit operation.  
D When the furnace is installed in an attic or other insu-  
lated space, keep insulation away from the furnace.  
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.  
NOTE − The Commonwealth of Massachusetts stipu-  
lates these additional requirements:  
D Gas furnaces shall be installed by a licensed plumb-  
er or fitter only.  
D The gas cock must be ꢀT handle" type.  
D When a furnace is installed in an attic, the passage-  
way to and service area surrounding the equipment  
shall be floored.  
CAUTION  
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 combus-  
tion air supply:  
WARNING  
Product contains fiberglass wool.  
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.)  
Permanent wave solutions  
Chlorinated waxes and cleaners  
Chlorine base swimming pool chemicals  
Water softening chemicals  
De-icing salts or chemicals  
Fiberglass wool may also cause respiratory, skin,  
and eye irritation.  
Carbon tetrachloride  
Halogen type refrigerants  
To reduce exposure to this substance or for further  
information, consult material safety data sheets  
available from address shown below, or contact your  
supervisor.  
Cleaning solvents (such as perchloroethylene)  
Printing inks, paint removers, varnishes, etc.  
Hydrochloric acid  
Cements and glues  
Antistatic fabric softeners for clothes dryers  
Masonry acid washing materials  
Lennox Industries Inc.  
P.O. Box 799900  
Dallas, TX 75379−9900  
All gas-fired appliances require air for the combustion pro-  
cess. If sufficient combustion air is not available, the fur-  
nace or other appliances will operate inefficiently and un-  
safely. Enough air must be provided to meet the needs of all  
fuel-burning appliances and appliances such as exhaust  
fans which force air out of the house. When fireplaces, ex-  
haust fans, or clothes dryers are used at the same time as  
the furnace, much more air is necessary to ensure proper  
combustion and to prevent a downdraft. Insufficient air  
causes incomplete combustion which can result in carbon  
monoxide.  
Combustion, Dilution & Ventilation Air  
In the past, there was no problem in bringing in sufficient out-  
door air for combustion. Infiltration provided all the air that  
was needed. In today’s homes, tight construction practices  
make it necessary to bring in air from outside for combus-  
tion. 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 outside air is  
brought into the house for combustion, negative pressure  
(outside pressure is greater than inside pressure) will build  
to the point that a downdraft can occur in the furnace vent  
pipe or chimney. As a result, combustion gases enter the liv-  
ing space creating a potentially dangerous situation.  
In addition to providing combustion air, fresh outdoor air  
dilutes contaminants in the indoor air. These contami-  
nants may include bleaches, adhesives, detergents, sol-  
vents and other contaminants which can corrode furnace  
components.  
In the absence of local codes concerning air for combus-  
tion and ventilation, use the guidelines and procedures in  
this section to install ML180UHE furnaces to ensure effi-  
cient and safe operation. You must consider combustion air  
needs and requirements for exhaust vents. A portion of this  
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.  
Page 6  
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Unconfined Space  
Air from Inside  
An unconfined space is an area such as a basement or  
large equipment room with a volume greater than 50 cubic  
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  
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  
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.  
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  
Air from Outside  
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  
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  
combined 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 contain-  
ing the furnace, the return air must 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 either  
from inside the building or from outside.  
2
free area of 1 square inch (645 mm ) per 4,000 Btu (1.17  
kW) per hour of total input rating of all equipment in the en-  
the outdoors through horizontal ducts, each opening shall  
2
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 6.  
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 operation.  
EQUIPMENT IN CONFINED  
SPACE ALL AIR FROM INSIDE  
CHIMNEY  
OR GAS  
VENT  
WATER  
HEATER  
FURNACE  
OPENINGS  
(To Adjacent  
Room)  
NOTE − Each opening shall have a free area of at least one square  
2
inch (645 mm ) per 1,000 Btu (.29 kW) per hour of the total input rat-  
ing of all equipment in the enclosure, but not less than 100 square  
2
inches (64516 mm ).  
FIGURE 3  
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EQUIPMENT IN CONFINED SPACE  
ALL AIR FROM OUTSIDE  
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)  
CHIMNEY OR  
GAS VENT  
VENTILATION LOUVERS  
(Each end of attic)  
OUTLET  
AIR  
WATER  
HEATER  
FURNACE  
INLET  
AIR  
VENTILATION  
LOUVERS  
(For unheated crawl space)  
NOTE−The inlet and outlet air openings shall each have a free area of at least one square inch (645  
2
mm ) per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.  
FIGURE 4  
EQUIPMENT IN  
CONFINED SPACE  
ALL AIR FROM  
OUTSIDE  
EQUIPMENT IN CONFINED SPACE  
ALL AIR FROM OUTSIDE  
(All Air Through Ventilated Attic)  
CHIMNEY  
OR GAS  
VENT  
CHIMNEY  
OR GAS  
VENT  
WATER  
HEATER  
VENTILATION LOUVERS  
(Each end of attic)  
OUTLET AIR  
OUTLET  
AIR  
FURNACE  
FURNACE  
INLET AIR  
(Ends 12 in.  
above bottom)  
INLET AIR  
WATER  
HEATER  
NOTE − Each air duct opening shall have a free area of at least one  
2
square inch (645 mm ) per 2,000 Btu (.59 kW) per hour of the total  
NOTE−The inlet and outlet air openings shall each have a  
2
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 one square inch (645 mm ) per 4,000 Btu (1.17 kW) per  
hour of the total input rating of all other equipment in the enclosure.  
free area of at least one square inch (645 mm ) per 4,000  
Btu (1.17 kW) per hour of the total input rating of all equip-  
ment in the enclosure.  
2
FIGURE 5  
FIGURE 6  
Page 8  
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Upflow Applications  
Setting Equipment  
Allow for clearances to combustible materials as indicated  
on the unit nameplate. Minimum clearances for closet or al-  
cove installations are shown in figure 8.  
WARNING  
Do not install the furnace on its front or its back. Do  
not connect the return air ducts to the back of the fur-  
nace. Doing so will adversely affect the operation of  
the safety control devices, which could result in per-  
sonal injury or death.  
Upflow Application Installation Clearances  
Top  
The ML180UHE gas furnace can be installed as shipped  
in either the upflow position or the horizontal position.  
Select a location that allows for the required clearances  
that are listed on the unit nameplate. Also consider gas  
supply connections, electrical supply, vent connection,  
and installation and service clearances [24 inches (610  
mm) at unit front]. The unit must be level.  
Left Side  
Right Side  
NOTE − Units with 1/2 or 3/4 hp blower motors are equipped  
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 leg). The bolt and washer  
must be removed before the furnace is placed into op-  
eration. After the bolt and washer have been removed, the  
rigid leg will not touch the blower housing.  
Bottom  
Type C  
Type of Vent  
Connector  
Type B1  
Top  
*Front  
Back  
Sides  
Vent  
1 in. (25 mm)  
1 in. (25 mm)  
2−1/4 in. (57 mm)**  
2−1/4 in. (57 mm)  
0
0
0†  
6 in. (152 mm)  
0‡  
0
1 in. (25 mm)  
0‡  
Units with 1/2 or 3/4 HP Blower Motor  
Floor  
*Front clearance in alcove installation must be 24 in. (610 mm).  
Maintain a minimum of 24 in. (610 mm) for front service access.  
** 4−1/2" if single wall vent pipe is used.  
For installation on a combustible floor, do not install the furnace  
directly on carpeting, tile or other combustible materials other  
than wood flooring.  
RIGID LEG  
remove shipping bolt and washer  
Left side requires 3 inches if a single wall vent is used on 14−1/2  
inch cabinets, or 2 inches if a single wall vent pipe is used on  
17−1/2 inch cabinets.  
FIGURE 8  
FIGURE 7  
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Return Air −− Upflow Applications  
Single Side Return Air  
(with transition and filter)  
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.  
20” X 25” X 1”  
(508mm X 635mm X 25mm)  
Cleanable Filter  
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.  
NOTE 60C and 60D units that require air volumes over 1800  
cfm (850 L/s) must have one of the following:  
Return Air  
Plenum  
1 − Single side return air with transition to accommodate 20  
x 25 x 1 in. (508 x 635 x 25 mm) cleanable air filter. (Re-  
quired to maintain proper air velocity.) See figure 9.  
AIR FLOW  
2 − Single side return air with optional return airbase. See fig-  
Transition  
3 − Bottom return air.  
4 − Return air from both sides.  
5 − Bottom and one side return air.  
Refer to Engineering Handbook for additional information.  
FIGURE 9  
Optional Return Air Base  
(Upflow Applications Only −− For use with A, B, C and D cabinets)  
FURNACE  
FRONT  
1 23 (584)  
IF BASE  
31/4  
(83)  
IS USED  
WITHOUT  
IAQ CABINET,  
A SINGLE  
RETURN AIR  
PLENUM  
Overall  
1 Minimum  
11 (279)  
(Maximum)  
INDOOR AIR  
QUALITY  
CABINET  
(PCO, Filter  
Cabinet, etc.)  
2
1 227/16  
(570)  
Maximum  
1 Unit side return air  
Opening  
14 (356)  
Overall  
AIR FLOW  
MUST  
(Maximum)  
COVER BOTH  
UNIT AND  
RETURN  
AIR BASE  
OPENINGS  
SIDE RETURN  
55/8  
(143)  
71/4  
(184)  
AIR OPENINGS  
(Either Side)  
23  
OPTIONAL  
RETURN  
AIR BASE  
3/4  
(19)  
(584)  
267/8  
141/2 (368) A Width (65W75)  
171/2 (446) B Width (50W98)  
21 (533) C Width (50W99)  
(683)  
241/2 (622) D Width (51W00)  
SIDE VIEW  
NOTE− Optional Side Return Air Filter Kits are not for use with Optional 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 or more of air (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 356 mm) is preferred.  
FIGURE 10  
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Removing the Bottom Panel  
Horizontal Applications  
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  
The ML180UHE furnace can be installed in horizontal ap-  
plications. Order horizontal suspension kit (51W10) from  
Lennox, or use equivalent suspension method.  
Allow for clearances to combustible materials as indicated  
on the unit nameplate. Minimum clearances for closet or al-  
cove installations are shown in figure 12.  
Removing the Bottom Panel  
This furnace may be installed in either an attic or a crawl-  
space. Either suspend the furnace from roof rafters or  
floor joists, as shown in figure13, or install the furnace on a  
platform, as shown in figure 14.  
Typical Horizontal Application  
Unit Suspended in Attic or Crawlspace  
Metal  
Strap  
Bracket  
3/16"  
Screw  
Air  
Flow  
Bottom Cap  
Bottom Panel  
FIGURE 11  
FIGURE 13  
Horizontal Application  
Installation Clearances  
Top  
NOTE − Heavy−gauge perforated 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 interfere with the plenum or exhaust pip-  
ing installation. Cooling coils and supply and return air  
plenums must be supported separately.  
Left  
End  
Right  
End  
Bottom  
Type C  
NOTE − When the furnace is installed on a platform in a  
crawlspace, it must be elevated enough to avoid water  
damage and to allow the evaporator coil to drain.  
Vent Connector  
Type  
Type B1  
Return Air −− Horizontal Applications  
Top  
*Front  
Back  
Ends  
Vent  
0
2−1/4 in. (57 mm)**  
0
0
2−1/4 in. (57 mm)  
0
Return air must be brought in through the end of a furnace  
installed in a horizontal application. The furnace is  
equipped with a removable bottom panel to facilitate  
installation. See figure 11.  
2 in. (51 mm)  
6 in. (152 mm)  
0‡  
2 in. (51 mm)  
1 in. (25 mm)  
0‡  
Floor  
*Front clearance in alcove installation must be 24 in. (610 mm).  
Maintain a minimum of 24 in. (610 mm) for front service access.  
** 4−1/2 in. if single wall vent pipe is used.  
For installations on a combustible floor, do not install the furnace  
directly on carpeting, tile or other combustible materials other  
than wood flooring.  
FIGURE 12  
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TABLE 1  
Horizontal Application  
Unit Installed on Platform  
Filter Size  
Furnace  
Cabinet Width  
Line contact is permissible but not preferred  
See the unit nameplate for  
Side Return  
Bottom Return  
clearances.  
A − 14−1/2"  
B − 17−1/2"  
C − 21"  
16 X 25 X 1 (1)  
16 X 25 X 1 (1)  
16 X 25 X 1 (1)  
16 X 25 X 1 (2)  
14 X 25 X 1 (1)  
16 X 25 X 1 (1)  
20 X 25 X 1 (1)  
24 X 25 X 1 (1)  
D − 24−1/2"  
GAS  
ENTRY  
VENT  
PIPE  
Duct System  
Use industry-approved standards (such as those pub-  
lished by Air Conditioning Contractors of America or Ameri-  
can Society of Heating, Refrigerating and Air Conditioning  
Engineers) to size and install the supply and return air duct  
system. This will result in a quiet and low-static system that  
has uniform air distribution.  
SERVICE PLATFORM  
NOTE − Do not operate the furnace in the heating mode  
with an external static pressure that exceeds 0.5 inches  
w.c. Higher external static pressures may cause erratic lim-  
it operation.  
FIGURE 14  
Supply Air Plenum  
If the furnace is installed without a cooling coil, a removable  
access panel must be installed in the supply air duct. The  
access panel should be large enough to permit inspection  
(either by smoke or reflected light) of the heat exchanger  
for leaks after the furnace is installed. The furnace access  
panel must always be in place when the furnace is operat-  
ing and it must not allow leaks into the supply air duct sys-  
tem.  
WARNING  
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 the living space. Use screws and joint tape to seal  
the return air system to the furnace.  
In platform installations with bottom return air, the  
furnace 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.  
The return and supply air duct systems must never  
be connected to or from other heating devices such  
as a fireplace or stove, etc. Fire, explosion, carbon  
monoxide poisoning, personal injury and/or proper-  
ty damage could result.  
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.  
When return air is drawn from a room, a negative pres-  
sure is created in the room. If agas 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  
reverse flow of the flue gas may result in incomplete com-  
bustion and the formation of carbon monoxide gas. This  
toxic gas might then be distributed throughout the house  
by the furnace duct system.  
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.  
In upflow applications, the return air can be brought in  
through the bottom or either side of the furnace. If a fur-  
nace 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 fiberglass sealing strips, caulking, or equiva-  
lent sealing method between the plenum and the furnace  
cabinet to ensure a tight seal. If a filter is installed, size the  
return air duct to fit the filter frame.  
Filters  
This unit is not equipped with a filter or rack. A field−pro-  
vided high−velocity filter is required for the unit to operate  
properly. Table 1 lists recommended filter sizes.  
A filter must be in place any time the unit is operating.  
Page 12  
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secure the combustion air inducer / pressure switch  
assembly to the orifice plate. Lift the assembly and ro-  
tate it 90 degrees clockwise or counterclockwise to ei-  
ther the 3 o’clock position or to 9 o’clock position. Re−  
secure with four screws. Gasket should be left in place.  
Venting  
A 4−inch diameter flue transition is factory-installed on the  
combustion air inducer outlet of all models. Figure 16  
shows the combustion air inducer as shipped from the  
factory.  
2 − Use tin snips to cut preferred opening on the cabinet  
for repositioning the flue outlet. Use the cut−out piece  
as a cover plate to patch unused opening on cabinet.  
Mounting Screws Location  
Flue Transition  
Mounting Screws  
UPFLOW POSITION  
Left Side Vent Discharge  
Cover Plate  
Collector Box  
Pressure  
Switch  
Make−Up  
Box  
Vent Pipe  
FIGURE 15  
Flue  
Transition  
UPFLOW POSITION  
Top Vent Discharge  
FLOW  
AIR  
Vent Pipe  
Flue  
D Gas supply piping must be brought into the unit from the right  
side in order to accommodate the flue pipe.  
Transition  
Collector Box  
Pressure  
Switch  
D Cut Combustion air inducer tubing from 9" to 8" to avoid inter-  
ference with inducer motor  
D Remove make−up box assembly (2 screws) and cut wire tie to  
free make−up box wires. Re−install make−up box on other side  
of cabinet.  
Make−Up  
Box  
D Re−secure make−up box wires: Either pull excess wires  
through the blower compartment and secure using supplied  
wire tie, or coil excess wire and secure to the gas manifold.  
FIGURE 17  
UPFLOW POSITION  
Right Side Vent Discharge  
Flue Transition  
Vent Pipe  
Cover Plate  
Collector Box  
Pressure  
Switch  
FLOW  
AIR  
FIGURE 16  
IMPORTANT  
The unit will not vent properly with the flue transition  
pointed down in the 6 o’clock position.  
The combustion air inducer may be rotated clock-  
wise or counterclockwise by 90° to allow for top or  
side vent discharge in all applications. When the unit  
is installed, the flue transition must be in the 9  
o’clock, 12 o’clock or 3 o’clock position.  
Make−Up  
Box  
FLOW  
AIR  
D Cut combustion air inducer tubing from 9" to 5" to avoid  
interference with inducer motor  
If necessary, reposition the combustion air inducer, pres-  
sure switch and/or make−up box as needed per the follow-  
FIGURE 18  
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HORIZONTAL RIGHT POSITION  
Top Vent Discharge  
HORIZONTAL LEFT POSITION  
Top Vent Discharge  
Vent Pipe  
Vent Pipe  
Pressure Switch  
Pressure  
Switch  
Flue  
Transition  
Cover Plate  
AIR  
AIR  
Flue  
Transition  
FLOW  
FLOW  
Collector Box  
Make−Up Box  
Cover Plate  
Collector Box  
Make−Up Box  
D Disconnect pressure switch hose from barbed fitting on the  
pressure switch assembly. Remove pressure switch assembly  
(1 screw) and cut wire tie to free pressure switch wires. Re−  
install pressure switch on the other side of orifice plate and re−  
connect pressure switch hose.  
D Gas supply piping must be brought into the unit from the bot-  
tom in order to accommodate the flue pipe.  
D Cut combustion air inducer tubing from 9" to 8" to avoid inter-  
ference with inducer motor  
D Re−secure pressure switch wires: Either pull excess wires  
through the blower compartment and secure using supplied  
wire tie, or coil excess wire and secure to the gas manifold.  
D Remove make−up box assembly (2 screws) and cut wire tie to  
free make−up box wires. Re−install make−up box on other side  
of cabinet.  
FIGURE 19  
D Re−secure make−up box wires: Either pull excess wires through  
the blower compartment and secure using supplied wire tie, or  
coil excess wire and secure to the gas manifold.  
HORIZONTAL LEFT POSITION  
Side Vent Discharge  
FIGURE 21  
Pressure Switch  
HORIZONTAL RIGHT POSITION  
Side Vent Discharge − no modifications necessary  
AIR  
Make−Up Box  
Pressure Switch  
FLOW  
Vent Pipe  
Vent Pipe  
AIR  
Make−Up Box  
Collector Box  
FLOW  
D Cut combustion air inducer tubing from 9" to 7" to avoid inter-  
ference with inducer motor  
Flue Transition  
D Disconnect pressure switch hose from barbed fitting on the  
pressure switch assembly. Remove pressure switch assembly  
(1 screw) and cut wire tie to free pressure switch wires. Re−  
install pressure switch on the other side of orifice plate and re−  
connect pressure switch hose.  
Collector Box  
D Re−secure pressure switch wires: Either pull excess wires  
through the blower compartment and secure using supplied  
wire tie, or coil excess wire and secure to the gas manifold.  
FIGURE 22  
FIGURE 20  
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The ML180UHE series units are classified as fan−assisted  
Category I furnaces when vertically vented according to  
the latest edition of National Fuel Gas Code (NFPA 54 /  
ANSI Z223.1) in the USA. A fan−assisted Category I fur-  
nace is an appliance equipped with an integral mechanical  
means to either draw or force combustion products through  
the combustion chamber and/or heat exchanger. The  
ML180UHE is not approved for use with horizontal venting.  
lining system or dedicated gas vent. Unlined masonry  
mon venting.  
A chimney with one or more sides exposed to the outside of  
the structure is considered to be an exterior chimney.  
An exterior masonry chimney that is not tile−lined must be  
lined with B1 vent or a listed insulated flexible metal vent.  
An exterior tile−lined chimney that is sealed and capped  
may be lined with a listed uninsulated flexible metal vent.  
NOTE − Use these instructions as a guide. They do not su-  
persede local codes. This furnace must be vented accord-  
ing to all local codes these installation instructions, and the  
provided venting tables in these instructions  
If the existing chimney will not accommodate a listed metal  
liner, either the chimney must be rebuilt to accommodate  
one of these liners or an alternate approved venting meth-  
od must be found.  
The venting tables in this manual were extracted from the  
National Fuel Gas Code (NFPA 54 / ANSI Z223.1) and are  
provided as a guide for proper vent installation. Proper ap-  
plication, termination, construction and location of vents  
must conform to local codes having jurisdiction. In the ab-  
sence of local codes, the NFGC serves as the defining doc-  
ument.  
Insulation for the flexible vent pipe must be an encapsu-  
lated fiberglass sleeve recommended by the flexible vent  
pipe manufacturer. See figure 24.  
Refer to the tables and the venting information contained in  
these instructions to properly size and install the venting  
system.  
Use self−drilling sheet metal screws or a mechanical fas-  
tener to firmly secure the vent pipe to the round collar of the  
flue transition. If self−drilling screws are used to attach the  
vent pipe, it is recommended that three be used. Drive one  
self−drilling screw through the front and one through each  
side of the vent pipe and collar. See figure 23.  
IMPORTANT  
Once the venting system is installed, attach the ꢀDis-  
connected Vent" warning sticker to a visible area of  
warning sticker is provided in the bag assembly. Or-  
der kit 66W04 for additional stickers.  
Install the first vent connector elbow at a minimum of six  
inches (152 mm) from the furnace vent outlet. See figure  
Venting Using a Masonry Chimney  
WARNING  
Asphyxiation hazard. The exhaust vent for this fur-  
nace must be securely connected to the furnace flue  
transition at all times.  
The following additional requirements apply when a lined  
masonry chimney is used to vent this furnace.  
Masonry chimneys used to vent Category I central fur-  
naces must be either tile-lined or lined with a listed metal  
VENT CONNECTION UPFLOW AND HORIZONTAL POSITION  
“DISCONNECTED VENT”  
WARNING  
STICKER  
VENT PIPE  
(min. 6" length)  
“DISCONNECTED VENT”  
WARNING  
STICKER  
FLUE TRANSITION  
COLLAR  
FLUE  
TRANSITION  
COLLAR  
VENT PIPE  
(min. 6" length)  
FIGURE 23  
Page 15  
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When inspection reveals that an existing chimney is not  
safe for the intended purpose, it shall be rebuilt to conform  
to nationally recognized standards, lined or relined with  
suitable materials, or replaced with a gas vent or chimney  
suitable for venting ML180UHE series units. The chimney  
passageway must be checked periodically to ensure that it  
is clear and free of obstructions.  
Common Venting Using Metal−Lined Masonry Chimney  
SEALED  
MAX. LENGTH  
−− SEE NOTE 1  
BELOW.  
5 ft. (1.5 m)  
minimum  
MIN. LENGTH −− AS  
SHORT AS PRACTICAL  
EXTERIOR  
CHIMNEY WITH  
METAL  
Do not install a manual damper, barometric draft regulator,  
or flue restrictor between the furnace and the chimney.  
LINER  
VENT CONNECTOR  
Never connect a Category I appliance to a chimney that is  
servicing a solid−fuel appliance. If a fireplace chimney flue  
is used to vent this appliance, the fireplace opening must  
be permanently sealed.  
4 in. (102 mm)  
minimum  
FURNACE  
A type B or listed chimney lining system that passes  
through an unused masonry chimney flue is not considered  
to be exposed to the outdoors.  
OTHER  
APPLIANCE  
PERMANENTLY  
SEALED FIREPLACE  
OPENING  
General Venting Requirements  
Vent all ML180UHE furnaces according to these instruc-  
tions:  
NOTE 1 − Refer to the provided venting tables for installations. Refer  
to the capacity requirements shown in the provided venting tables.  
1 − Vent diameter recommendations and maximum allow-  
able piping runs are found in the provided venting  
tables.  
FIGURE 24  
DO NOT insulate the space between the liner and the  
chimney wall with puffed mica or any other loose gran-  
ular insulating material.  
2 − In no case should the vent or vent connector diameter  
be less than the diameter specified in the provided  
venting tables.  
3 − The minimum vent capacity determined by the sizing  
tables must be less than the low fire input rating and the  
maximum vent capacity must be greater than the high  
fire input rating.  
IMPORTANT  
SINGLE appliance venting of a fan-assisted furnace  
into a tile-lined masonry chimney (interior or outside  
wall) is PROHIBITED. The chimney must first be lined  
with either type B1 vent or an insulated single wall  
flexible vent lining system which has been sized ac-  
cording to the provided venting tables and the vent  
pipe manufacturer’s instructions.  
4 − Single appliance vents − If the vertical vent or tile-lined  
chimney has a larger diameter or flow area than the  
vent connector, use the vertical vent diameter to de-  
termine the minimum vent capacity and the vent  
connector diameter to determine the maximum vent  
capacity. The flow area of the vertical vent, however,  
shall not exceed 7 times the flow area of the listed ap-  
pliance categorized vent area, drafthood outlet area or  
flue collar area unless designed according to approved  
engineering methods.  
A fan−assisted furnace may be commonly vented into an  
existing lined masonry chimney if the following conditions  
are met:  
S The chimney is currently serving at least one drafthood−  
equipped appliance;  
S The vent connectors and chimney are sized according  
to the provided venting tables.  
5 − Multiple appliance vents − The flow area of the largest  
section of vertical vent or chimney shall not exceed 7  
times the smallest listed appliance categorized vent  
area, drafthood outlet area or flue collar area unless de-  
signed according to approved engineering methods.  
If type B1 double-wall vent is used inside a chimney, no oth-  
er appliance can be vented into the chimney. The outer wall  
of type B1 vent pipe must not be exposed to flue products.  
A type B1 vent or masonry chimney liner shall terminate  
above the roof surface with a listed cap or a listed roof as-  
sembly according to the terms of their respective listings  
and the vent manufacturer’s instructions.  
Page 16  
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Common Venting Using Tile−Lined Interior Masonry Chimney and Combined Vent Connector  
MINIMUM LENGTH = AS SHORT AS PRACTICAL.  
FOR MAXIMUM LENGTH SEE NOTE TO LEFT  
INTERIOR TILE−LINED  
MASONRY CHIMNEY  
NOTE− Refer to provided venting  
tables for installations.  
NOTE − the chimney must be properly  
sized per provided venting tables or  
lined with listed metal lining system.  
VENT  
CONNECTOR  
OTHER  
APPLIANCE  
PERMANENTLY  
SEALED FIREPLACE  
OPENING  
FURNACE  
FIGURE 25  
6 − The entire length of single wall metal vent connector  
shall be readily accessible for inspection, cleaning,  
and replacement.  
1-1/2 feet (.46 m) for each inch (25 mm) of common  
vent diameter.  
10 − The vent pipe should be as short as possible with the  
least number of elbows and angles required to com-  
plete the job. Route the vent connector to the vent us-  
ing the shortest possible route.  
7 − Single appliance venting configurations with zero lat-  
elbows in the vent system. For all other vent configura-  
tions, the vent system is assumed to have two 90° el-  
bows. For each additional 90° elbow or equivalent (for  
example two 45° elbows equal one 90° elbow) beyond  
two, the maximum capacity listed in the venting table  
should be reduced by 10% (0.90 x maximum listed ca-  
pacity).  
11 − A vent connector shall be supported without any dips  
or sags and shall slope a minimum of 1/4 inch (6.4 mm)  
per linear foot (305 mm) of connector, back toward the  
appliance.  
12 − Vent connectors shall be firmly attached to the furnace  
flue collar by self−drilling screws or other approved  
means, except vent connectors of listed type B vent  
material which shall be assembled according to the  
manufacturer’s instructions. Joints between sections  
of single wall connector piping shall be fastened by  
screws or other approved means.  
8 − The common venting tables (5, 6, 7, and 8) were gen-  
erated using a maximum horizontal vent connector  
length of 1−1/2 feet (.46 m) for each inch (25 mm) of  
connector diameter as follows:  
TABLE 2  
13 − When the vent connector used for Category I ap-  
pliances must be located in or pass through a crawl-  
space, attic or other areas which may be cold, that por-  
tion of the vent connector shall be constructed of listed  
double-wall type B vent material or material having  
equivalent insulation qualities.  
Maximum Horizontal  
Connector Length feet (m)  
Connector Diameter  
inches (mm)  
3 (76)  
4 (102)  
5 (127)  
6 (152)  
7 (178)  
4−1/2 (1.37)  
6 (1.83)  
7−1/2 (2.29)  
9 (2.74)  
14 − All venting pipe passing through floors, walls, and ceil-  
ings must be installed with the listed clearance to com-  
bustible materials and be fire stopped according to lo-  
cal codes. In absence of local codes, refer to NFGC  
(Z223.1).  
10−1/2 (3.20)  
9 − If the common vertical vent is offset, the maximum  
common vent capacity listed in the common venting  
tables should be reduced by 20%, the equivalent of two  
90° elbows (0.80 x maximum common vent capacity).  
The horizontal length of the offset shall not exceed  
15 − No portion of the venting system can extend into, or pass  
through any circulation air duct or plenum.  
Page 17  
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16 − Vent connectors serving Category I appliances shall  
not be connected to any portion of mechanical draft  
systems operating under positive pressure such as  
Category III or IV venting systems.  
two consecutive table size diameters over the size of  
the draft hood outlet or flue collar outlet.  
20 − Do not install a manual damper, barometric draft regu-  
lator or flue restrictor between the furnace and the  
chimney.  
17 − If vent connectors are combined prior to entering the  
common vent, the maximum common vent capacity  
listed in the common venting tables must be reduced by  
10%, the equivalent of one 90° elbow (0.90 x maximum  
common vent capacity).  
21 − When connecting this appliance to an existing dedi-  
cated or common venting system, you must inspect the  
venting system’s general condition and look for signs  
of corrosion. The existing vent pipe size must conform  
to these instructions and the provided venting tables. If  
the existing venting system does not meet these re-  
quirements, it must be resized.  
18 − The common vent diameter must always be at least as  
large as the largest vent connector diameter.  
19 − In no case, shall the vent connector be sized more than  
TABLE 3  
Capacity of Type B Double−Wall Vents with Type B Double−Wall Connectors  
Serving a Single Category I Appliance  
Vent and Connector Diameter − D (inches)  
Height  
H
(feet)  
Lateral  
L
(feet)  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
MIN  
0
MAX  
78  
51  
49  
46  
84  
57  
53  
49  
88  
61  
57  
51  
94  
69  
65  
59  
53  
97  
75  
71  
64  
58  
52  
100  
81  
77  
70  
64  
58  
NA  
MIN  
0
MAX  
152  
97  
MIN  
0
MAX  
251  
157  
153  
149  
276  
178  
171  
164  
295  
194  
187  
176  
327  
226  
219  
206  
195  
349  
250  
242  
229  
217  
206  
374  
283  
275  
262  
249  
237  
214  
MIN  
0
MAX  
375  
232  
227  
223  
415  
263  
255  
247  
447  
289  
280  
267  
502  
339  
330  
315  
301  
540  
377  
367  
351  
337  
322  
587  
432  
421  
405  
389  
374  
346  
0
2
13  
21  
25  
0
18  
30  
36  
0
27  
39  
47  
0
32  
50  
59  
0
6
8
4
94  
6
91  
0
165  
109  
103  
98  
2
12  
23  
28  
0
16  
32  
39  
0
25  
42  
51  
0
28  
53  
64  
0
5
8
0
175  
118  
113  
104  
191  
136  
130  
121  
112  
202  
149  
143  
133  
124  
116  
213  
166  
160  
150  
141  
132  
113  
2
12  
23  
30  
0
17  
32  
41  
0
23  
41  
54  
0
26  
52  
67  
0
10  
5
10  
0
2
11  
22  
29  
35  
0
15  
30  
40  
48  
0
20  
39  
51  
61  
0
22  
49  
64  
76  
0
5
15  
10  
15  
0
2
10  
21  
28  
34  
48  
0
14  
29  
38  
46  
55  
0
18  
38  
50  
59  
69  
0
20  
47  
62  
73  
84  
0
5
20  
10  
15  
20  
0
2
9
13  
28  
37  
44  
53  
73  
14  
36  
48  
57  
66  
88  
18  
45  
59  
70  
80  
104  
5
21  
27  
33  
56  
NA  
10  
15  
20  
30  
30  
NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other  
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°  
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi-  
mum listed capacity).  
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TABLE 4  
Capacity of Type B Double−Wall Vents with Single−Wall Metal Connectors  
Serving a Single Category I Appliance  
Vent and Connector Diameter − D (inches)  
Height  
H
(feet)  
Lateral  
L
(feet)  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
MIN  
38  
MAX  
77  
MIN  
59  
60  
74  
83  
58  
59  
77  
90  
57  
59  
76  
97  
56  
57  
75  
95  
NA  
54  
56  
73  
93  
NA  
NA  
53  
55  
72  
91  
115  
NA  
NA  
MAX  
151  
96  
MIN  
85  
MAX  
249  
156  
152  
147  
273  
176  
168  
161  
293  
193  
185  
171  
325  
225  
216  
201  
186  
346  
248  
239  
223  
208  
192  
372  
281  
271  
255  
239  
223  
NA  
MIN  
126  
123  
146  
163  
123  
121  
151  
175  
120  
119  
148  
188  
116  
115  
144  
182  
220  
114  
113  
141  
177  
216  
254  
110  
109  
136  
171  
208  
246  
NA  
MAX  
373  
231  
225  
220  
412  
261  
252  
243  
444  
287  
277  
261  
499  
337  
326  
308  
290  
537  
375  
363  
344  
325  
306  
584  
429  
417  
397  
377  
357  
NA  
0
2
39  
51  
85  
6
8
4
NA  
NA  
37  
NA  
NA  
83  
92  
102  
114  
83  
6
89  
0
164  
108  
102  
95  
2
39  
56  
83  
5
NA  
NA  
37  
NA  
NA  
87  
107  
122  
82  
8
0
174  
117  
111  
100  
190  
136  
128  
116  
NA  
2
39  
61  
82  
10  
5
52  
56  
105  
132  
80  
10  
0
NA  
36  
NA  
93  
2
38  
69  
80  
5
51  
63  
102  
128  
158  
78  
15  
10  
15  
0
NA  
NA  
35  
NA  
NA  
96  
200  
148  
140  
129  
NA  
2
37  
74  
78  
5
50  
68  
100  
125  
155  
186  
76  
20  
10  
15  
20  
0
NA  
NA  
NA  
34  
NA  
NA  
NA  
99  
NA  
211  
164  
157  
144  
131  
NA  
2
37  
80  
76  
5
49  
74  
98  
10  
15  
20  
30  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
122  
151  
181  
NA  
30  
NA  
NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other  
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°  
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi-  
mum listed capacity).  
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TABLE 5  
Vent Connector Capacity  
Type B Double−Wall Vents with Type B Double−Wall Connectors  
Serving Two or More Category I Appliances  
Vent and Connector Diameter − D (inches)  
Vent  
Height  
H
Connector  
Rise  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
R
(feet)  
Appliance Input Rating in Thousands of Btu Per Hour  
(feet)  
MIN  
22  
23  
24  
22  
23  
24  
22  
23  
24  
21  
22  
24  
21  
22  
23  
20  
21  
22  
MAX  
37  
41  
44  
40  
44  
47  
43  
47  
50  
50  
53  
55  
54  
57  
60  
62  
64  
66  
MIN  
35  
37  
38  
35  
36  
37  
34  
36  
37  
33  
35  
36  
33  
34  
35  
31  
33  
34  
MAX  
66  
MIN  
46  
48  
49  
49  
51  
53  
49  
51  
52  
47  
49  
51  
46  
48  
50  
45  
47  
48  
MAX  
106  
121  
132  
114  
128  
139  
123  
136  
146  
142  
153  
163  
157  
167  
176  
181  
190  
198  
MIN  
58  
60  
62  
64  
66  
67  
65  
67  
69  
64  
66  
68  
62  
64  
66  
60  
62  
64  
MAX  
164  
183  
199  
176  
195  
210  
189  
206  
220  
220  
235  
248  
246  
259  
271  
288  
299  
309  
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
75  
6
81  
72  
80  
8
87  
78  
86  
10  
15  
20  
30  
92  
89  
96  
102  
99  
105  
110  
113  
118  
123  
TABLE 6  
Common Vent Capacity  
Type B Double−Wall Vents with Type B Double−Wall Connectors  
Serving Two or More Category I Appliances  
Common Vent Diameter − D (inches)  
Vent  
Height  
H
4 Inch  
5 Inch  
6 Inch  
7 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
(feet)  
FAN + FAN  
92  
FAN + NAT  
FAN + FAN  
140  
FAN + NAT  
116  
FAN + FAN  
204  
FAN + NAT  
161  
FAN + FAN  
309  
FAN + NAT  
248  
6
81  
90  
8
101  
155  
129  
224  
178  
339  
275  
10  
15  
20  
30  
110  
97  
169  
141  
243  
194  
367  
299  
125  
112  
123  
138  
195  
164  
283  
228  
427  
352  
136  
215  
183  
314  
255  
475  
394  
152  
244  
210  
361  
297  
547  
459  
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TABLE 7  
Vent Connector Capacity  
Type B Double−Wall Vents with Single−Wall Metal Connectors  
Serving Two or More Category I Appliances  
Vent and Connector Diameter − D (inches)  
Height  
H
(feet)  
Lateral  
L
(feet)  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
MIN  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
49  
MAX  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
56  
MIN  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
84  
MAX  
NA  
NA  
NA  
NA  
NA  
NA  
NA  
85  
MIN  
NA  
MAX  
NA  
MIN  
NA  
MAX  
NA  
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
NA  
NA  
168  
175  
NA  
182  
198  
NA  
6
121  
NA  
131  
NA  
125  
130  
119  
124  
129  
116  
121  
127  
115  
120  
125  
112  
117  
122  
126  
138  
121  
134  
144  
138  
150  
160  
152  
163  
172  
175  
185  
193  
184  
191  
182  
189  
197  
177  
185  
193  
175  
182  
190  
169  
177  
185  
193  
208  
186  
203  
217  
214  
230  
243  
238  
252  
264  
278  
290  
300  
8
10  
15  
20  
30  
89  
91  
79  
87  
83  
94  
87  
100  
97  
78  
52  
59  
82  
103  
107  
110  
115  
119  
55  
62  
87  
47  
60  
77  
51  
62  
81  
54  
64  
85  
NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other  
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°  
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi-  
mum listed capacity).  
TABLE 8  
Common Vent Capacity  
Type B Double−Wall Vents with Single−Wall Metal Connectors  
Serving Two or More Category I Appliances  
Common Vent Diameter − D (inches)  
Vent  
4 Inch  
5 Inch  
6 Inch  
7 Inch  
Height  
H
(feet)  
Appliance Input Rating in Thousands of Btu Per Hour  
FAN + FAN  
FAN + NAT  
FAN + FAN  
NA  
FAN + NAT  
113  
FAN + FAN  
200  
FAN + NAT  
158  
FAN + FAN  
FAN + NAT  
244  
6
NA  
NA  
78  
87  
304  
331  
357  
416  
463  
533  
8
NA  
126  
218  
173  
269  
10  
15  
20  
30  
NA  
94  
163  
137  
237  
189  
292  
121  
131  
145  
108  
118  
132  
189  
159  
275  
221  
343  
208  
177  
305  
247  
383  
236  
202  
350  
286  
446  
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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  
properly 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  
venting 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 burner have 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 horizontal  
pitch. Determine that there is no blockage, restriction,  
leakage, corrosion, or other deficiencies which could  
cause an unsafe condition.  
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4 − The piping should be sloped 1/4 inch (6.4 mm) per 15  
feet (4.57 m) upward toward the meter from the fur-  
nace. The piping must be supported at proper intervals  
[every 8 to 10 feet (2.44 to 3.01 m)] with suitable hang-  
ers or straps. Install a drip leg in vertical pipe runs to the  
unit.  
Gas Piping  
Gas supply piping should not allow more than 0.5"W.C. drop  
in pressure between gas meter and unit. Supply gas pipe  
must not be smaller than unit gas connection.  
CAUTION  
5 − A 1/8" N.P.T. plugged tap or pressure post is located  
on the gas valve to facilitate test gauge connection.  
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.  
6 − In some localities, codes may require the installation of  
a manual main shut-off valve and union (furnished by  
the installer) external to the unit. The union must be of  
the ground joint type.  
Gas Supply  
1 − This unit is shipped standard for left or right side instal-  
lation of gas piping (or top entry in horizontal applica-  
tions). Connect the gas supply to the piping assembly.  
2 − When connecting the gas supply piping, consider fac-  
tors such as length of run, number of fittings, and fur-  
nace rating to avoid excessive pressure drop. Table 9  
lists recommended pipe sizes for typical applications.  
3 − The gas piping must not run in or through air ducts,  
clothes chutes, gas vents or chimneys, dumb waiters,  
or elevator shafts.  
IMPORTANT  
Compounds used on threaded joints of gas piping  
must be resistant to the actions of liquified petro-  
leum gases.  
NOTE − If emergency shutoff is necessary, shut off the main  
manual gas valve and disconnect main power to the fur-  
nace. The installer should properly label these devices.  
TABLE 9  
3
3
Gas Pipe Capacity − ft /hr (m /hr)  
Nominal  
Iron Pipe  
Size  
inches  
(mm)  
Length of Pipe − feet (m)  
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)  
172  
(4.87)  
118  
(3.34)  
95  
(2.69)  
81  
(2.29)  
72  
(2.03)  
65  
(1.84)  
60  
(1.69)  
56  
(1.58)  
52  
(1.47)  
50  
(1.42)  
3/4  
(19.05)  
.824  
(20.930)  
360  
(10.19)  
247  
(7.00)  
199  
(5.63)  
170  
(4.81)  
151  
(4.28)  
137  
(3.87)  
126  
(3.56)  
117  
(3.31)  
110  
(3.11)  
104  
(2.94)  
1
(25.4)  
1.049  
(26.645)  
678  
(19.19)  
466  
(13.19)  
374  
(10.59)  
320  
(9.06)  
284  
(8.04)  
257  
(7.27)  
237  
(6.71)  
220  
(6.23)  
207  
(5.86)  
195  
(5.52)  
1−1/4  
(31.75)  
1.380  
(35.052)  
1350  
(38.22)  
957  
(27.09)  
768  
(22.25)  
657  
(18.60)  
583  
(16.50)  
528  
(14.95)  
486  
(13.76)  
452  
(12.79)  
424  
(12.00)  
400  
(11.33)  
1−1/2  
(38.1)  
1.610  
(40.894)  
2090  
(59.18)  
1430  
(40.49)  
1150  
(32.56)  
985  
(27.89)  
873  
(24.72)  
791  
(22.39)  
728  
(20.61)  
677  
(19.17)  
635  
(17.98)  
600  
(17.00)  
2
(50.8)  
2.067  
(52.502)  
4020  
(113.83)  
2760  
(78.15)  
2220  
(62.86)  
1900  
(53.80)  
1680  
(47.57)  
1520  
(43.04)  
1400  
(39.64)  
1300  
(36.81)  
1220  
(34.55)  
1160  
(32.844)  
2−1/2  
(63.5)  
2.469  
(67.713)  
6400 4400  
(181.22) (124.59)  
3530  
(99.95)  
3020  
(85.51)  
2680  
(75.88)  
2480  
(70.22)  
2230  
(63.14)  
2080  
(58.89)  
1950  
(55.22)  
1840  
(52.10)  
3
(76.2)  
3.068  
(77.927)  
11300 7780  
6250  
5350  
4740  
4290  
3950  
3670  
(319.98) (220.30) (176.98) (151.49) (134.22) (121.47) (111.85) (103.92)  
3450  
(97.69)  
3260  
(92.31)  
3
NOTE − Capacity given in cubic feet (m ) of gas per hour and based on 0.60 specific gravity gas.  
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Left Side Piping  
(Standard)  
MANUAL  
MAIN SHUT−OFF  
VALVE  
AUTOMATIC  
GAS VALVE  
MANUAL  
MAIN SHUT−OFF  
VALVE  
(With 1/8 in. NPT  
Plugged Tap Shown)  
(With 1/8 in. NPT  
Plugged Tap  
Shown)  
GROUND  
JOINT  
UNION  
AUTOMATIC  
GAS VALVE  
GROUND  
JOINT  
UNION  
DRIP LEG  
Right Side Piping  
(Alternate)  
FIELD  
PROVIDED  
AND INSTALLED  
DRIP LEG  
NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET  
FIGURE 26  
Horizontal Applications  
Possible Gas Piping Configurations  
MANUAL  
MAIN SHUT−OFF  
VALVE  
MANUAL  
MAIN SHUT−OFF  
VALVE  
Horizontal Application  
Left−Side Air Discharge  
GROUND  
JOINT  
UNION  
GROUND  
JOINT  
UNION  
DRIP LEG  
DRIP LEG  
MANUAL  
MAIN SHUT−OFF  
VALVE  
GROUND  
JOINT  
UNION  
FIELD  
PROVIDED  
AND INSTALLED  
Horizontal Application  
Right−Side Air Discharge  
NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET  
DRIP LEG  
FIGURE 27  
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Leak Check  
The unit is equipped with a field make−up box on the left  
hand side of the cabinet. The make−up box may be moved  
to the right side of the furnace to facilitate installation. If the  
make−up box is moved to the right side, clip the wire ties  
that bundle the wires together. The excess wire must be  
pulled into the blower compartment. Secure the excess  
wire to the existing harness to protect it from damage.  
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.  
NOTE − If emergency shutoff is necessary, shut off the main  
manual gas valve and disconnect the main power to the  
furnace. The installer should properly label these devices.  
INTERIOR MAKE−UP BOX INSTALLATION  
CAUTION  
Right Side  
Some soaps used for leak detection are corrosive to  
certain metals. Carefully rinse piping thoroughly af-  
ter leak test has been completed. Do not use  
matches, candles, flame or other sources of ignition  
to check for gas leaks.  
BOX  
The furnace must be isolated by closing its individual  
manual shut-off valve and disconnecting from from the gas  
supply system during any pressure testing of the gas sup-  
ply system at pressures greater than 1/2 psig (3.48 kPa, 14  
inches w.c.).  
FIGURE 29  
IMPORTANT  
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, 14 inches w.c.).  
INTERIOR MAKE−UP BOX INSTALLATION  
Left side  
MANUAL MAIN  
ISOLATE  
SHUT−OFF VALVE  
WILL NOT HOLD  
NORMAL TEST  
PRESSURE  
GAS VALVE  
BOX  
FURNACE  
1/8 NPT PLUG  
CAP  
FIGURE 28  
Electrical  
ELECTROSTATIC DISCHARGE (ESD)  
Precautions and Procedures  
FIGURE 30  
CAUTION  
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.  
Electrostatic discharge can affect electronic com-  
ponents. Take precautions during furnace installa-  
tion and service to protect the furnace’s electronic  
controls. Precautions will help to avoid control ex-  
posure to electrostatic discharge by putting the fur-  
nace, the control and the technician at the same  
electrostatic potential. Neutralize electrostatic  
charge by touching hand and all tools on an un-  
painted unit surface, such as the gas valve or blower  
deck, before performing any service procedure.  
NOTE − Unit nameplate states maximum current draw.  
Maximum over−current protection allowed is 15 AMP.  
Holes are on both sides of the furnace cabinet to facilitate  
wiring.  
Install a separate (properly sized) disconnect switch near  
the furnace so that power can be turned off for servicing.  
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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.  
Generator Use − Voltage Requirements  
The following requirements must be kept in mind when  
specifying a generator for use with this equipment:  
S
S
S
The furnace requires 120 volts + 10% (Range: 108  
volts to 132 volts).  
Complete the wiring connections to the equipment. Use the  
provided unit wiring diagram and the field wiring diagram  
shown in figure 33. Use 18−gauge wire or larger that is suit-  
able for Class II rating for thermostat connections.  
The furnace operates at 60 Hz + 5% (Range: 57 Hz to  
63 Hz).  
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.  
Generator should have a wave form distortion of less  
than 5% total harmonic distortion.  
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). A green ground  
wire is provided in the field make−up box.  
S
Thermostat  
NOTE − The ML180UHE furnace contains electronic  
components that are polarity sensitive. Make sure that the  
furnace is wired correctly and is properly grounded.  
Install the room thermostat according to the instructions  
provided with the thermostat. See figure 31 for thermostat  
designations. If the furnace is being matched with a heat  
pump, refer to the FM21 installation instruction or appropri-  
ate dual fuel thermostat instructions.  
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.  
ML180UHE and CONDENSING UNIT  
THERMOSTAT DESIGNATIONS  
(Refer to specific thermostat and outdoor unit.)  
Thermostat  
Furnace  
Condensing  
Unit  
*CONDENSING  
UNITꢁ  
POWER  
R
R
W1  
Y
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.  
HEAT  
W
Y
CONDENSING  
UNITꢁ  
COOLING  
INDOOR BLOWER  
G
G
C
CONDENSING  
UNITꢁ COMMON  
COMMON  
C
*NOTE − ꢀR" REQUIRED ON SOME OUTDOOR UNITS  
FIGURE 31  
Indoor Blower Speeds  
One 24V "H" 1/4" spade terminal is provided on the furnace  
integrated control. See figure 34 for integrated control con-  
figuration. The terminal is energized in the heating mode  
when the combustion air inducer is operating and the pres-  
sure switch is closed. Any humidifier rated up to 0.5 amp  
can be connected to this terminal with the ground leg of the  
circuit connected to ground or the "C" terminal.  
1 − When the thermostat is set to ꢀFAN ON," the indoor  
blower will run continuously on the fan speed when  
there is no cooling or heating demand.  
2 − When the ML180UHE is running in the heating mode,  
the indoor blower will run on the heating speed.  
3 − When there is a cooling demand, the indoor blower will  
run on the cooling speed.  
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ML180UHE Schematic Wiring Diagram and Sequence of Operation  
3
10  
1
5
2
7
5
9
4
8
6
1
1 − Line voltage is applied to L1 and N. the T1 low voltage transformer is energized, and line voltage is applied to B3 indoor blower.  
2 − S47 rollout switch(es) must be closed in order for 24V from transformer to be output on integrated control "R" to power thermostat.  
3 − When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.  
4 − A92 integrated control runs a self−check. S10 primary limit and S21 secondary limit contacts are found to be closed. Call for heat can continue.  
5 − A92 integrated control energizes B6 combustion air inducer. S18 combustion air pressure switch closes . Once S18 closes, a 15−second  
pre−purge follows.  
6 − A92 integrated control energizes R33 ignitor. A 20−second warm−up period begins.  
7 − GV1 gas valve opens for a 4−second trial for ignition  
8 − Flame is sensed, gas valve remains open for the heat call.  
9 − After 30−second delay (from flame sensed), A92 integrated control applies 24vVAC to Heat speed of B3 indoor blower.  
10 − When heat demand is satisfied, W1 of the indoor thermostat de−energizes W of A92ignition control which de−energizes GV1 gas valve.  
B6 combustion air inducer continues a 5−second post−purge period, and B3 indoor blower completes a selected OFF time delay.  
FIGURE 32  
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TYPICAL ML180UHE FIELD WIRING DIAGRAM  
FIGURE 33  
TABLE 10  
INTEGRATED CONTROL  
(Automatic Hot Surface Ignition System)  
1/4" QUICK CONNECT TERMINALS  
Humidifier 120VAC  
120HUM  
LINE  
120VAC  
XFMR  
Transformer 120VAC  
CIRC  
Indoor blower 120VAC  
Indoor air quality accessory 120VAC  
Common 120VAC  
EAC  
NEUTRALS  
HUM24  
Humidifier 24VAC  
3/16" QUICK CONNECT TERMINALS  
Cooling tap 24VAC  
COOL  
HEAT  
FAN  
Heating tap 24VAC  
Continuous blower 24 VAC  
PARK (no power)  
FLAME/FS  
Park terminal for speed taps  
Flame sense  
24 COM  
Common 24VAC  
BLOWER OFF DELAY  
RED LED  
RECALL BUTTON  
FIGURE 34  
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4 − This furnace is equipped with an ignition device which  
automatically lights the burners. Do not try to light the  
burners by hand.  
Unit Start−Up  
FOR YOUR SAFETY READ BEFORE LIGHTING  
5 − Remove the upper access panel.  
6 − Move switch on gas valve to OFF. Do not force. See  
figure 35.  
WARNING  
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.  
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 ser-  
vice 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.  
MANIFOLD  
MANIFOLD  
PRESSURE  
PRESSURE  
ADJUSTMENT  
OUTLET  
SCREW  
PORT  
WARNING  
If overheating occurs or if gas supply fails to shut off,  
shut off the manual gas valve to the appliance before  
shutting off electrical supply.  
INLET  
PRESSURE  
PORT  
GAS VALVE SHOWN IN ON POSITION  
FIGURE 35  
8 − Move switch on gas valve to ON. Do not force. See fig-  
CAUTION  
Before attempting to perform any service or mainte-  
nance, turn the electrical power to unit OFF at dis-  
connect switch.  
9 − Replace the upper access panel.  
10− Turn on all electrical power to to the unit.  
11− Set the thermostat to desired setting.  
NOTE − When unit is initially started, steps 1 through 11  
may need to be repeated to purge air from gas line.  
BEFORE LIGHTING smell all around the appliance area for  
gas. Be sure to smell next to the floor because some gas is  
heavier than air and will settle on the floor.  
12− If the appliance will not operate, follow the instructions  
ꢀTurning Off Gas to Unit" and call your service techni-  
cian or gas supplier.  
The gas valve on the ML180UHE unit is equipped with a  
gas control switch. Use only your hand to move the switch.  
Never use tools. If the switch will not turn or if the control  
switch will not move by hand, do not try to repair it.  
Turning Off Gas to Unit  
1 − Set the thermostat to the lowest setting.  
2 − Turn off all electrical power to the unit if service is to be  
performed.  
Placing the furnace into operation:  
3 − Remove the upper access panel.  
4 − Move switch on gas valve to OFF. Do not force.  
ML180UHE units are equipped with an automatic ignition  
system. Do not attempt to manually light burners on these  
furnaces. 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 units with an automatic  
ignition system.  
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 circuit 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?  
WARNING  
If you do not follow these instructions exactly, a fire  
or explosion may result causing property damage,  
personal injury or death.  
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 lock out? If the unit locks out  
again, call the service technician to inspect the unit for  
blockages.  
1 − STOP! Read the safety information at the beginning of  
this section.  
10 − Is pressure switch closed? Obstructed flue will cause  
unit to shut off at pressure switch. Check flue and outlet  
for blockages.  
2 − Set the thermostat to the lowest setting.  
3 − Turn off all electrical power to the unit.  
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11 − Are flame rollout switches tripped? If flame rollout  
switches are tripped, call the service technician for in-  
spection.  
Supply Pressure Measurement  
A threaded plug on the inlet side of the gas valve provides  
access to the supply pressure tap. Remove the threaded  
plug, install a field−provided barbed fitting and connect a  
manometer to measure supply pressure. See table 13 for  
proper line pressure. Replace the threaded plug after mea-  
surements have been taken.  
Heating Sequence Of Operation  
1 − When thermostat calls for heat, combustion air blower  
starts.  
Manifold Pressure Measurement  
2 − Combustion air pressure switch proves blower opera-  
tion. Switch is factory−set and requires no adjustment.  
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.  
3 − After a 15−second prepurge, the hot surface ignitor en-  
ergizes.  
4 − After a 20−second ignitor warm−up period, the gas  
valve solenoid opens. A 4−second trial for ignition peri-  
od begins.  
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.  
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.  
4 − After allowing unit to stabilize for 5 minutes, record  
manifold pressure and compare to value given in table  
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.  
7 − To interrupt the 60−minute ꢀWATCHGUARD" period,  
move thermostat from ꢀHeat" to ꢀOFF" then back to  
ꢀHeat." Heating sequence then restarts at step 1.  
Proper Combustion  
Gas Pressure Adjustment  
Furnace should operate a minimum 15 minutes with cor-  
rect manifold pressure and gas flow rate before checking  
combustion. Take combustion sample beyond the flue out-  
let and compare to the tables below. The maximum car-  
bon monoxide reading should not exceed 50 ppm.  
TABLE 12  
Gas Flow (Approximate)  
TABLE 11  
GAS METER CLOCKING CHART  
Seconds for One Revolution  
CO %  
2
CO %  
2
For  
For  
ML180UHE Unit  
Natural  
LP  
Nat  
L.P.  
ML180UHE Unit  
1 cu ft 2 cu ft 1 cu ft 2 cu ft  
−045  
−070  
−090  
−110  
−135  
Dial  
80  
Dial  
160  
110  
82  
Dial  
200  
136  
102  
82  
DIAL  
400  
272  
204  
164  
136  
−045  
−070  
−090  
−110  
−135  
7.2 − 7.8  
7.5 − 9.0  
55  
41  
33  
66  
27  
54  
68  
High Altitude  
Natural−1000 btu/cu ft  
LP−2500 btu/cu ft  
The manifold pressure may require adjustment and com-  
bustion air pressure switch may need replacing to ensure  
proper combustion at higher altitudes. Refer to table 13 for  
manifold pressure and table 14 for pressure switch change  
and gas conversion kits.  
Furnace should operate at least 5 minutes before check-  
ing gas flow. Determine time in seconds for two revolu-  
tions of gas through the meter. (Two revolutions assures a  
more accurate time.) Divide by two and compare to time  
in table 11. If manifold pressure matches table 13 and rate  
is incorrect, check gas orifices for proper size and restric-  
tion. Remove temporary gas meter if installed.  
IMPORTANT  
For safety, shut unit off and remove manometer as  
soon as an accurate reading has been obtained.  
Take care to replace pressure tap plug.  
NOTE − To obtain accurate reading, shut off all other gas  
appliances connected to meter.  
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TABLE 13  
Manifold Pressure Settings at all Altitudes  
Line Pressure in.wg.  
Model  
Input Size  
Gas  
0−2000 ft  
2001−4500 ft.  
4501−7500 ft  
7501 − 10,000 ft  
Min  
4.5  
Max  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
Nat  
LP/propane  
Nat  
3.5  
10.0  
3.5  
3.2  
10.0  
3.2  
3.0  
10.0  
2.8  
10.0  
2.7  
9.6  
3.0  
9.6  
2.9  
9.6  
3.5  
10.0  
3.5  
045  
070  
090  
110  
135  
11.0  
4.5  
LP/propane  
Nat  
10.0  
3.5  
10.0  
3.2  
10.0  
3.5  
11.0  
4.5  
LP/propane  
Nat  
10.0  
3.5  
10  
10.0  
3.5  
11.0  
4.5  
3.5  
LP/propane  
Nat  
10.0  
3.5  
10.0  
3.5  
10.0  
3.5  
11.0  
4.5  
LP/propane  
10.0  
10.0  
10.0  
11.0  
TABLE 14  
Pressure Switch and Gas Conversion Kits at all Altitudes  
High Altitude  
Natural Gas Burner  
Orifice Kit  
LP/Propane to  
Natural Gas Burner  
Orifice Kit  
Natural Gas to LP/Propane  
Burner Orifice Kit  
High Altitude Pressure Switch Kit  
Model  
Input Size  
0−4500 ft  
4501−7500 ft  
80W52  
7501 − 10,000 ft  
7501 − 10,000 ft  
0 − 7500 ft  
7501 − 10,000 ft  
0 − 7500 ft  
045  
070  
090  
110  
135  
80W51  
80W51  
80W51  
80W52  
80W51  
80W52  
No Change  
80W52  
73W37  
70W89  
76W15  
73W81  
80W57  
80W52  
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.  
air temperatures have been allowed to stabilize, check the  
Other Unit Adjustments  
temperature rise. If necessary, adjust the blower speed to  
Primary and Secondary Limits  
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.  
The primary limit is located on the heating compartment  
vestibule panel. The secondary limits (if equipped) are lo-  
cated in the blower compartment, attached to the back side  
of the blower. These auto reset limits are factory−set and re-  
quire no adjustment.  
Fan Control  
Flame Rollout Switches  
The heat fan−on time of 30 seconds is not adjustable. The  
heat 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  
delay setting of 90 seconds. The fan−off delay affects com-  
fort and is adjustable to satisfy individual applications. Ad-  
just the fan−off delay to achieve a supply air temperature  
between 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-  
These manually reset switches are located on the burner  
box.  
Pressure Switch  
The pressure switch is located in the heating compartment  
adjacent to the combustion air inducer. The switch checks  
for proper combustion air inducer operation before allow-  
ing ignition trial. The switch is factory−set and requires no  
adjustment.  
Temperature Rise  
After the furnace has been started, and supply and return  
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Input Voltage Requirements  
HEAT FAN-OFF TIME IN SECONDS  
The circuit is designed to be operated with AC voltage. A  
voltage of 12 to 33VAC is required to energize the motor.  
Expected current draw will be less than 20mA.  
Blower Speeds  
Follow the steps below to change the blower speeds.  
1 − Turn off electrical power to furnace.  
2 − Remove blower access panel.  
NO JUMPER  
To adjust fan−off timing, reposition jumper across pins to  
achieve desired setting.  
3 − Disconnect existing speed tap at integrated control  
speed terminal.  
60 Second  
off Time  
90 Second  
off Time  
120 Second  
off Time  
180 Second  
off Time  
NOTE − Termination of any unused motor leads must be  
insulated.  
4 − Place unused blower speed tap on integrated control  
ꢀPARK" terminal or insulate.  
5 − Refer to blower speed selection chart on unit wiring dia-  
gram for desired heating or cooling speed. See Blower  
performance data beginning on the next page.  
FIGURE 36  
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.  
Thermostat Heat Anticipation  
Set the heat anticipator setting (if adjustable) according to  
the amp draw listed on the wiring diagram that is attached  
to the unit.  
Electronic Ignition  
The integrated control has an added feature of an internal  
Watchguard control. The feature serves as an automatic re-  
set device for integrated control lockout caused by ignition  
failure. This type of lockout is usually due to low gas line  
pressure. After one hour of continuous thermostat demand  
for heat, the Watchguard will re−set and remake thermostat  
demand to the furnace and automatically reset the inte-  
grated control to begin the ignition sequence.  
Constant Torque Motor  
ML180UHE units are equipped with a constant torque ECM  
motor. It has a DC motor coupled to an electronic control  
module both contained in the same motor housing. The mo-  
tor is programmed to provide constant torque at each of the  
five selectable speeds. The motor has five speed taps.  
Each tap requires 24 volts to energize.  
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BLOWER DATA  
ML180UH045E36A PERFORMANCE (Less Filter)  
External  
Static  
Pressure  
in. w.g.  
Air Volume / Watts at Various Blower Speeds  
Medium-High Medium Medium-Low  
High  
Low  
Low  
Low  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
0.00  
0.10  
0.20  
0.30  
0.40  
0.50  
0.60  
0.70  
0.80  
1380  
1345  
1320  
1290  
1265  
1230  
1190  
1165  
1130  
265  
270  
285  
295  
310  
315  
330  
340  
350  
1155  
1120  
1080  
1055  
1010  
990  
165  
175  
190  
200  
205  
215  
230  
235  
245  
995  
950  
900  
875  
825  
790  
750  
705  
670  
120  
120  
125  
135  
145  
155  
165  
170  
180  
975  
880  
805  
750  
710  
660  
630  
570  
535  
115  
105  
105  
110  
120  
125  
135  
140  
150  
945  
865  
700  
640  
595  
535  
500  
435  
380  
105  
100  
85  
90  
95  
100  
110  
115  
120  
945  
915  
880  
ML180UH070E36B PERFORMANCE (Less Filter)  
External  
Static  
Pressure  
in. w.g.  
Air Volume / Watts at Various Blower Speeds  
Medium-High Medium Medium-Low  
High  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
0.00  
0.10  
0.20  
0.30  
0.40  
0.50  
0.60  
0.70  
0.80  
1415  
1415  
1355  
1330  
1290  
1245  
1225  
1190  
1160  
265  
280  
290  
300  
310  
325  
335  
350  
365  
1330  
1295  
1225  
1190  
1155  
1115  
1045  
1000  
925  
170  
170  
185  
200  
205  
215  
230  
235  
245  
1215  
1145  
1110  
1060  
1015  
980  
135  
145  
150  
160  
175  
180  
190  
205  
205  
1175  
1130  
1080  
1035  
970  
125  
130  
140  
155  
160  
170  
180  
190  
200  
1075  
955  
885  
825  
770  
695  
625  
540  
445  
85  
95  
100  
110  
120  
125  
135  
140  
145  
930  
920  
865  
855  
790  
790  
735  
ML180UH090E48B PERFORMANCE (Less Filter)  
External  
Static  
Pressure  
in. w.g.  
Air Volume / Watts at Various Blower Speeds  
Medium-High Medium Medium-Low  
High  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
cfm  
Watts  
0.00  
0.10  
0.20  
0.30  
0.40  
0.50  
0.60  
0.70  
0.80  
1785  
1755  
1730  
1690  
1645  
1615  
1590  
1545  
N/A  
380  
395  
415  
435  
440  
455  
470  
475  
N/A  
1570  
1535  
1505  
1460  
1435  
1395  
1350  
1300  
1270  
270  
275  
290  
305  
320  
335  
350  
360  
370  
1440  
1420  
1380  
1345  
1310  
1265  
1210  
1175  
1140  
220  
230  
245  
260  
270  
285  
290  
305  
310  
1395  
1350  
1310  
1275  
1240  
1180  
1150  
1095  
1040  
190  
205  
215  
230  
240  
255  
265  
275  
285  
1190  
1140  
1110  
1065  
1010  
955  
120  
130  
145  
155  
165  
180  
185  
200  
210  
915  
860  
820  
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BLOWER DATA  
ML180UH090E60C PERFORMANCE (Less Filter)  
Air Volume / Watts at Different Blower Speeds  
Bottom Return Air, Side Return Air with Optional Return Single Side Return Air − Air volumes in bold require field  
Air Base, Return Air from Both Sides or Return Air from fabricated transition to accommodate 20 x 25 x 1 in. air filter  
External  
Static  
Pressure  
in. w.g.  
Bottom and One Side.  
in order to maintain proper air velocity.  
High  
Med-High Medium Med-Low  
Low  
High Med-High Medium Med-Low  
Low  
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts  
2255 640 1940 420 1750 310 1580 230 1485 185 2290 655 1980 425 1775 310 1605 235 1495 195  
2200 655 1910 440 1705 315 1535 240 1385 190 2250 675 1945 445 1730 320 1555 245 1400 190  
2150 675 1865 450 1655 340 1490 260 1340 205 2210 695 1885 465 1680 340 1510 265 1350 205  
2125 695 1835 475 1635 355 1450 275 1285 215 2165 715 1850 475 1645 355 1470 275 1285 215  
2090 715 1800 495 1585 370 1405 285 1235 230 2135 720 1810 490 1595 370 1410 290 1225 230  
2060 735 1760 510 1545 385 1370 305 1200 245 2070 735 1765 515 1545 390 1370 305 1180 245  
2020 750 1725 525 1515 405 1320 320 1145 255 2030 760 1715 530 1495 405 1325 320 1140 255  
1980 765 1680 540 1465 420 1265 330 1105 270 1990 775 1685 540 1450 425 1265 330 1095 270  
1935 785 1635 560 1420 435 1225 350 1055 285 1950 795 1645 560 1415 435 1225 345 1040 285  
0.00  
0.10  
0.20  
0.30  
0.40  
0.50  
0.60  
0.70  
0.80  
ML180UH110E60C PERFORMANCE (Less Filter)  
Air Volume / Watts at Different Blower Speeds  
Bottom Return Air, Side Return Air with Optional Return Single Side Return Air − Air volumes in bold require field  
Air Base, Return Air from Both Sides or Return Air from fabricated transition to accommodate 20 x 25 x 1 in. air filter  
External  
Static  
Pressure  
in. w.g.  
Bottom and One Side.  
in order to maintain proper air velocity.  
High  
Med-High Medium Med-Low  
Low  
High Med-High Medium Med-Low  
Low  
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts  
2230 635 1945 430 1715 295 1555 230 1470 185 2315 645 1990 415 1780 300 1610 230 1510 200  
2180 655 1905 445 1690 305 1510 240 1340 175 2260 655 1945 425 1740 315 1550 240 1400 185  
2135 680 1865 465 1630 330 1470 260 1280 190 2210 680 1895 450 1680 335 1510 255 1350 200  
2090 695 1830 480 1595 345 1440 275 1235 200 2165 700 1850 465 1650 355 1455 275 1285 210  
2050 715 1785 495 1550 360 1385 285 1175 210 2130 715 1830 485 1585 365 1395 285 1230 225  
2025 730 1740 520 1500 375 1340 300 1130 225 2095 730 1770 500 1535 385 1365 300 1175 235  
2010 750 1710 535 1470 390 1305 320 1080 240 2055 755 1725 515 1495 400 1305 315 1135 250  
1965 755 1670 555 1420 410 1255 330 1015 255 2000 765 1675 535 1465 410 1255 325 1080 265  
1905 785 1635 560 1380 425 1215 350 975 270 1965 785 1640 555 1400 425 1210 345 1025 275  
0.00  
0.10  
0.20  
0.30  
0.40  
0.50  
0.60  
0.70  
0.80  
ML180UH135E60D PERFORMANCE (Less Filter)  
Air Volume / Watts at Different Blower Speeds  
Bottom Return Air, Side Return Air with Optional Return Single Side Return Air − Air volumes in bold require field  
Air Base, Return Air from Both Sides or Return Air from fabricated transition to accommodate 20 x 25 x 1 in. air filter  
External  
Static  
Pressure  
in. w.g.  
Bottom and One Side.  
in order to maintain proper air velocity.  
High  
Med-High Medium Med-Low  
Low  
High Med-High Medium Med-Low  
Low  
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts  
2495 755 2295 590 2045 435 1845 315 1650 230 2365 725 2295 575 2005 410 1820 300 1635 235  
2440 780 2220 620 2015 445 1820 330 1615 245 2350 745 2210 595 2000 435 1745 320 1530 230  
2390 790 2175 640 1935 470 1735 350 1550 255 2330 775 2175 625 1945 455 1730 330 1490 250  
2360 805 2140 655 1895 490 1720 370 1485 275 2245 785 2135 645 1895 475 1655 355 1425 265  
2285 835 2125 675 1850 510 1660 380 1455 290 2215 810 2085 660 1840 495 1600 375 1385 285  
2240 860 2060 690 1815 535 1610 400 1415 310 2175 825 2045 680 1815 505 1590 390 1340 290  
2225 865 2015 715 1785 550 1535 420 1330 320 2125 845 1995 700 1765 530 1525 405 1300 310  
2160 895 1955 735 1755 570 1500 440 1265 340 2095 865 1950 710 1700 545 1485 420 1260 325  
2105 905 1925 750 1715 580 1435 450 1215 345 2065 880 1890 725 1680 565 1415 445 1205 345  
0.00  
0.10  
0.20  
0.30  
0.40  
0.50  
0.60  
0.70  
0.80  
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3 − Label the wires from gas valve, rollout switches, prima-  
ry limit switch and make−up box then disconnect them.  
4 − Remove the screws that secure the combustion air in-  
ducer/pressure switch assembly to the collector box.  
Carefully remove the combustion air inducer to avoid  
damaging blower gasket. If gasket is damaged, it must  
be replaced to prevent leakage.  
Service  
WARNING  
ELECTRICAL SHOCK, FIRE,  
OR EXPLOSION HAZARD.  
5 − Remove the collector box located behind the combus-  
tion air inducer. Be careful with the collector box gas-  
ket. If the gasket is damaged, it must be replaced to  
prevent leakage.  
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.  
6 − Disconnect gas supply piping. Remove the four screws  
securing the burner manifold assembly to the vestibule  
panel and remove the assembly from the unit.  
7 − NOX units only − Remove screw securing NOX insert.  
Remove NOX insert. See figure 38.  
8 − Remove screws from both sides, top and bottom of  
vestibule panel.  
9 − Remove heat exchanger. It may be necessary to  
spread cabinet side to allow more room. If so, remove  
five screws from the left side or right side of cabinet.  
At the beginning of each heating season, a qualified techni-  
cian should check the system as follows:  
Blower  
10 Backwash using steam. Begin from the burner opening  
on each clam. Steam must not exceed 275°F.  
Check the blower wheel for debris and clean if necessary.  
The blower motors are prelubricated for extended bearing  
life. No further lubrication is needed.  
11 − To clean burners, run a vacuum cleaner with a soft brush  
attachment over the face of burners. Visually inspect in-  
side the burners and crossovers for any blockage  
caused by foreign matter. Remove any blockage. Figure  
37 shows burner detail.  
WARNING  
12 −To clean the combustion air inducer visually inspect and  
using a wire brush clean where necessary. Use com-  
pressed air to clean off debris and any rust.  
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.  
13 −Reinstall heat exchanger in vestibule. (Replace the  
five screws in the cabinet from step 10 if removed).  
14 NOx units only − Replace NOx inserts.  
Filters  
All ML180UHE filters are installed external to the unit. Fil-  
ters should be inspected monthly. Clean or replace the fil-  
ters when necessary to ensure that the furnace operates  
properly. Replacement filters must be rated for high veloc-  
ity airflow. Table 1 lists recommended filter sizes.  
Flue And Chimney  
15 Reinstall collector box and combustion air assembly.  
Reinstall all screws to the collector box and combustion  
air inducer. Failure to replace all screws may cause  
leaks. Inspect gaskets for any damage and replace if  
necessary.  
16 Reinstall burner box and manifold assembly.  
17 Reconnect all wires.  
1 − Check flue pipe, chimney and all connections for tight-  
ness and to make sure there is no blockage.  
2 − Check unit for proper draft.  
18 Reconnect top cap and vent pipe to combustion air in-  
ducer outlet.  
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.  
19 −Reconnect gas supply piping.  
20 −Turn on power and gas supply to unit.  
21 −Set thermostat and check for proper operation.  
22 −Check all piping connections, factory and field, for gas  
leaks. Use a leak detecting solution or other preferred  
means.  
Unit Nameplate__________Actual__________  
Cleaning the Heat Exchanger and Burners  
NOTE − Use papers or protective covering in front of the fur-  
nace during cleaning.  
23 −If a leak is detected, shut gas and electricity off and  
repair leak.  
1 − Turn off both electrical and gas power supplies to fur-  
nace.  
2 − Remove flue pipe and top cap (some applications top  
cap can remain) from the unit.  
24 −Repeat steps 24 and 26 until no leaks are detected.  
25 −Replace access panel.  
Page 35  
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ML180UHE BURNER, COMBUSTION AIR INDUCER ASSEMBLY  
&
HEAT EXCHANGER REMOVAL  
Gasket  
Flue Transition  
Pressure Switch  
Rollout Switches  
(−090, −110 −135 units)  
Heat Exchanger  
Rollout Switches  
(−045 and −070 units)  
Ignitor  
Orifice Plate  
Collector Box  
Combustion Air Inducer  
Sensor  
Retention Rings  
Cross Over  
Manifold And Gas Valve  
FIGURE 37  
Remove 5 screws if necessary  
(either side of cabinet)  
ML180UHE NOx INSERTS  
1
2
3
4
5
NOx Insert  
FIGURE 38  
CAUTION  
Some soaps used for leak detection are corrosive to  
certain metals. Carefully rinse piping thoroughly af-  
ter leak test has been completed. Do not use  
matches, candles, flame or other sources of ignition  
to check for gas leaks.  
FIGURE 39  
Page 36  
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Planned Service  
The following items should be checked during an annual inspection. Power to the unit must be shut off for the service techni-  
cian’s safety.  
Fresh air grilles and louvers (on the unit and in the room  
where the furnace is installed) − Must be open and unob-  
structed to provide combustion air.  
Operating performance − Unit must be observed during  
operation to monitor proper performance of the unit and the  
vent system.  
Combustion gases − Flue products must be analyzed and  
Burners − Must be inspected for rust, dirt, or signs of water.  
compared to the unit specifications. See table 12.  
Vent pipe − Must be inspected for signs of water, damaged  
Problems detected during the inspection may make it nec-  
essary to temporarily shut down the furnace until the items  
can be repaired or replaced.  
or sagging pipe, or disconnected joints.  
Unit appearance − Must be inspected for rust, dirt, signs  
of water, burnt or damaged wires, or components.  
Instruct the homeowners to pay attention to their  
furnace. Situations can arise between annual furnace in-  
spections that may result in unsafe operation. For instance,  
items innocently stored next to the furnace may obstruct  
the combustion air supply. This could cause incomplete  
combustion and the production of carbon monoxide gas.  
Blower access panel − Must be properly in place and pro-  
vide a seal between the return air and the room where the  
furnace is installed.  
Return air duct − Must be properly attached and provide  
an air seal to the unit.  
Repair Parts List  
The following repair parts are available through independent Lennox dealers. When ordering parts, include the complete  
furnace model number listed on the CSA International nameplate −− Example: ML180UHE045P24A−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 panel  
Top cap  
Heat exchanger assembly  
Gas manifold  
Control Panel Parts  
Transformer  
Combustion air inducer  
Gas valve  
Integrated control  
Door interlock switch  
Circuit breaker  
Main burner cluster  
Main burner orifices  
Pressure switch  
Ignitor  
Blower Parts  
Primary limit control  
Flame rollout switch (s)  
Secondary limit  
Blower wheel  
Blower housing  
Motor  
Motor mounting frame  
Motor power choke  
Blower housing cutoff plate  
Page 37  
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Integrated Control Diagnostic Codes  
RED LED  
Flash Code  
Diagnostic Codes / Status of Furnace  
Off  
No power to control or board fault detected  
Board fault detected,  
On  
1
Heartbeat  
Control powered − displayed during all modes of operation if no errors are detected  
Reverse Line Voltage Polarity  
1
2
3
4
5
6
Improper Earth Ground  
Burner failed to light, or lost flame during heat demand  
Low Flame Signal − check flame sensor  
Watchguard − burner failed to light, exceeded maximum number of retries or recycles.  
Not Used  
Primary or Secondary Limit Open or Watchguard Mode − Limit Switch Open longer than 3 min-  
utes  
7
8
Rollout Switch Open  
9
Pressure Switch failed to close or opened during heat demand  
Watchguard − Pressure Switch opened 5 times during one heat demand  
Pressure Switch stuck closed prior to activation of combustion air inducer  
Flame Sensed without gas valve energized  
Low Line Voltage  
10  
11  
12  
13  
Notes  
Note 1  
Note  
A "Heartbeat" is indicated by a "Slow Flash" − 1 sec on 1 sec off, repeating  
Error codes are indicated by a "Rapid Flash" − the LED flashes X times at 1/2 sec on 1/2 sec  
off, remains off for 3 sec, then repeats  
Last 10 error codes are stored in memory including when power is shut off to the unit. − To recall,  
press and release button, most recent will be displayed first, LED off for 3 sec, then next error  
code is displayed, etc. To clear error codes, depress and hold button longer than 5 seconds.  
Note  
Page 38  
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Troubleshooting: Heating Sequence of Operation  
HEATING SEQUENCE OF OPERATION  
ABNORMAL HEATING MODE  
NORMAL HEATING MODE  
POWER ON  
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.  
INDOOR BLOWER DELAY OFF.  
LED SLOW FLASH  
NO  
CONTROL SELF−CHECK OKAY?  
(RESET CONTROL BY TURNING MAIN POWER OFF.)  
YES  
NO  
LED FLASHES CODE 1 − POLARITY REVERSED.  
LED FLASHES CODE 2 − IMPROPER GROUND.  
IS POLARITY CORRECT?  
YES  
NO  
IS THERE A PROPER GROUND?  
YES  
NO  
LED FLASHES CODE 13 − LOW LINE VOLTAGE.  
CONTROL WILL NOT RESPOND TO A CALL FOR  
HEATING UNTIL VOLTAGE RISES ABOVE 75 VOLTS.  
IS VOLTAGE  
ABOVE 70 VOLTS?  
LED FLASHES CODE 8 − ROLLOUT SWITCH OPEN.  
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.  
INDOOR BLOWER ON.  
YES  
NO  
ROLLOUT SWITCH CLOSED?  
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES  
AND POWER IS RESET OR T’STAT IS INTERRUPTED  
FOR MINIMUM OF 1 SECOND.  
YES  
LED FLASHES CODE 12 − FLAME SENSED  
WITHOUT GAS VALVE ENERGIZED.  
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.  
INDOOR BLOWER ON HEATING SPEED.  
NO  
BURNER OFF?  
(Flame sensed without gas valve energized)  
YES  
NO  
NORMAL OPERATION:  
LED SLOW FLASH  
YES  
LED FLASHES CODE 7 − PRIMARY LMIT  
OPEN. COMBUSTION AIR INDUCER  
OFF.INDOOR BLOWER ON  
THERMOSTAT CALLS FOR HEAT:  
LED SLOW FLASH  
NO  
YES  
PRIMARY LIMIT SWITCH. CLOSED?  
LED FLASHES CODE 11 − PRESSURE  
SWITCH CLOSED.  
YES  
GAS VALVE OFF COMBUSTION AIR  
INDUCER OFF. INDOOR BLOWER  
OFF WITH DELAY.  
NO  
IS COMBUSTION AIR  
PRESSURE SWITCH OPEN?  
(Sequence holds until pressure switch  
opens or thermostat resets control.)  
YES  
IS COMBUSTION AIR INDUCER  
ENERGIZED?  
YES  
LED FLASHES CODE 9 − PRESSURE SWITCH FAILED  
TO CLOSE OR OPENED DURING HEAT DEMAND.  
PRESSURE SWITCH IS IN WATCHGUARD MODE. GAS  
VALVE OFF. COMBUSTION AIR INDUCER OFF.  
INDOOR BLOWER OFF WITH DELAY. IS 5-MINUTE  
RESET PERIOD COMPLETE?  
YES  
NO  
HAS COMBUSTION AIR PRESSURE  
SWITCH CLOSED IN 2.5 MINUTES?  
YES  
CONTINUED NEXT PAGE  
Page 39  
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Troubleshooting: Heating Sequence of Operation (Continued)  
HEATING SEQUENCE CONTINUED  
NORMAL HEATING MODE  
ABNORMAL HEATING MODE  
15-SECOND COMBUSTION AIR INDUCER PREPURGE  
INITIATED BY CLOSED PRESSURE SWITCH.  
LED FLASHES CODE 13 −  
LOW LINE VOLTAGE.  
ONCE VOLTAGE IS ABOVE  
75 VOLTS, HEATING  
SEQUENCE RESTARTS.  
YES  
NO  
NO  
IS VOLTAGE ABOVE 70 VOLTS?  
IGNITOR WARM-UP −− 20 SECONDS.  
YES  
YES  
4-SECOND TRIAL FOR IGNITION.  
GAS VALVE OPENS. IGNITOR ENERGIZED FOR  
FIRST 3 SECONDS OF THE TRIAL.  
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.  
INDOOR BLOWER OFF.  
NO  
YES  
HAS CONTROL FAILED TO SENSE FLAME FOR  
FIVE CONSECUTIVE TRIES DURING A SINGLE  
HEAT DEMAND?  
NO  
FLAME STABILIZATION PERIOD.  
4 SECONDS  
YES  
FLAME RECTIFICATION CURRENT  
CHECK. CAN FLAME BE PROVEN WITHIN  
4 SECONDS AFTER GAS VALVE OPENS?  
(0.5 microamps)  
LED SIGNAL WATCHGUARD FAILURE CODE  
WATCHGUARD MODE. GAS VALVE OFF.  
COMBUSTION AIR INDUCER OFF.  
INDOOR BLOWER OFF WITH DELAY  
IS 60-MINUTE RESET PERIOD COMPLETE?  
YES  
YES  
NO  
NO  
YES  
HAS CONTROL RESET IGNITION  
SEQUENCE FOUR TIMES?  
FLAME PRESENT?  
YES  
LED FLASHES CODE  
7 − PRIMARY LIMIT  
OPEN. GAS VALVE,  
COMB. AIR INDUCER  
AND INDOOR BLOW-  
ER OFF. LEDs SIG-  
NAL LIMIT SWITCH  
OPEN UNTIL MAIN  
POWER IS  
NO  
LED FLASHES CODE 4 − LOW FLAME  
SIGNAL.  
(Does not affect operation of control)  
FLAME SIGNAL 1.5 MICROAMPS OR GREATER?  
YES  
INDOOR BLOWER ON  
AFTER 30−SECOND DELAY  
LED FLASHES CODE 7 − PRIMARY LIMIT OPEN  
GAS VALVE DE−ENERGIZED.  
YES  
INTERRUPTED OR  
T’STAT IS CYCLED  
OFF/ON FOR 1 SEC.  
MINIMUM. 60−MINUTE  
WATCHGUARD PE-  
RIOD STARTS AT  
TIME LIMIT CLOSES.  
IS 60−MIN. PERIOD  
COMPLETE?  
COMBUSTION AIR INDUCER DE−ENERGIZED.  
INDOOR BLOWER ON UNTIL SWITCH CLOSES.  
LIMIT SWITCH CLOSED?  
NO  
PRIMARY LIMIT SWITCH CLOSED?  
YES  
YES  
HAS PRIMARY LIMIT RESET  
TIME EXCEEDED 3 MINUTES?  
YES  
NO  
NO  
NO  
LED FLASHES CODE 8 − ROLLOT SWITCH OPEN.  
ROLLOUT SWITCH CLOSED?  
GAS VALVE POWER OFF. COMBUSTION AIR INDUCER POWER  
ON. INDOOR BLOWER ON SEQUENCE HOLDS UNTIL ROLLOUT  
SWITCH IS RESET AND MAIN POWER IS INTERRUPTED OR  
THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.  
YES  
COMBUSTION AIR PRESSURE  
SWITCH CLOSED?  
YES  
HAS PRESSURE SWITCH OPENED 5 TIMES  
LED FLASHES  
IN THE SAME HEAT DEMAND?  
CODE 10  
THERMOSTAT DEMAND SATISFIED.  
1 HR PRESSURE  
SWITCH  
WATCHGUARD  
MODE  
YES  
NO  
YES  
GAS VALVE DE−ENERGIZED. COMBUSTION AIR  
INDUCER ON. INDOOR BLOWER OFF WITH  
DELAY. HAS CAB PRESSURE SWITCH CLOSED  
WITHIN 2.5 MINUTES?  
LED SLOW FLASH.  
YES  
COMB. AIR INDUCER CONTINUES 5-SECOND  
POST PURGE AFTER T’STAT DEMAND IS SATISFIED.  
INDOOR AIR BLOWER COMPLETES SELECTED ꢀOFF"  
DELAY BEFORE SHUTTING OFF.  
YES  
NO  
5-MINUTE PRESSURE SWITCH  
WATCHGUARD MODE.  
Page 40  
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Troubleshooting: Cooling Sequence of Operation  
COOLING SEQUENCE OF OPERATION  
NORMAL COOLING MODE  
ABNORMAL COOLING MODE  
POWER ON  
IGNITION CONTROL MAIN POWER ON.  
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.  
INDOOR BLOWER OFF WITH NORMAL DELAY.  
SIGNAL CIRCUIT BOARD FAILURE AT LED.  
NO  
CONTROL SELF DIAGNOSTIC CHECK.  
IS CONTROL OPERATING NORMALLY?  
INTERRUPT MAIN POWER TO RESET CONTROL.  
YES  
NO  
LED FLASHES CODE 2 IMPROPER GROUND  
CONTROL WILL CONTINUE TO CALL FOR COOLING  
IN THIS CONDITION.  
IS THERE A PROPER GROUND?  
YES  
NO  
LED FLASHES CODE 1 POLARITY REVERSED  
CONTROL WILL CONTINUE TO CALL FOR COOLING IN  
THIS CONDITION.  
IS POLARITY CORRECT?  
YES  
NO  
LED FLASHES CODE 13 LOW VOLTAGE. CONTROL  
WILL CONTINUE TO CALL FOR COOLING  
IN THIS CONDITION.  
IS VOLTAGE  
ABOVE 70 VOLTS?  
YES  
LED FLASHES CODE 8 ROLLOUT SWITCH OPEN. GAS  
VALVE OFF. COMBUSTION AIR INDUCER ON. INDOOR  
BLOWER ON. SEQUENCE HOLDS UNTIL ROLLOUT SWITCH  
CLOSES AND MAIN POWER IS INTERRUPTED OR  
NO  
ROLLOUT SWITCH MONITORED CONTINUOUSLY.  
IS ROLLOUT SWITCH CLOSED?  
THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.  
YES  
LED: SLOW FLASH RATE REMAINS UNCHANGED  
THROUGHOUT COOLING CYCLE.  
THERMOSTAT CALLS FOR COOLING.  
COMPRESSOR CONTACTOR AND SYSTEM FAN  
ENERGIZED WITH 2-SECOND DELAY  
(COOLING SPEED). EAC TERM. ENERGIZED.  
THERMOSTAT OPENS.  
COMPRESSOR OFF.  
SYSTEM FAN AND EAC TERM. OFF  
WITH 45-SECOND DELAY.  
Page 41  
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Troubleshooting: Continuous Fan Sequence of Operation  
CONTINUOUS FAN SEQUENCE OF OPERATION  
LED: SLOW FLASH RATE REMAINS  
UNCHANGED THROUGHOUT SEQUENCE.  
MANUAL FAN SELECTION MADE AT THERMOSTAT.  
CONTROL (G) ENERGIZES SYSTEM FAN AT FAN  
SPEED. EAC TERMINAL IS ENERGIZED.  
THERMOSTAT CALLS FOR HEAT (W).  
YES  
NO  
SYSTEM FAN CONTINUES FAN SPEED WITHOUT  
INTERRUPTION. EAC TERMINAL REMAIN ON.  
HUM TERMINAL IS ENERGIZED WITH COMBUSTION  
AIR BLOWER.  
THERMOSTAT CALLS FOR COOLING.  
YES  
NO  
SYSTEM FAN SWITCHED TO COOL SPEED.  
EAC TERM. REMAINS ON.  
SYSTEM FAN SWITCHES TO HEAT SPEAD AFTER 30  
SECOND DELAY. EAC AND HUM TERMINAL REMAIN ON.  
THERMOSTAT OPENS.  
MANUAL FAN SELECTION MADE AT THERMOSTAT.  
CONTROL (G) ENERGIZES SYSTEM FAN AT FAN  
SPEED. EAC TERM. ENERGIZED.  
THERMOSTAT OPENS.  
HUM. TERMINAL OFF AFTER POST PURGE  
BY COMBUSTION AIR BLOWER. SYTEM FAN  
SWITCHES TO FAN SPEED AFTER BLOWER  
OFF DELAY. EAC CONTINUES WITHOUT  
INTERRUPTION.  
Page 42  
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Start−Up & Performance Check List  
UNIT SET UP  
(typical)  
Unit Model Number_______________  
Serial Number___________________  
2
SUPPLY  
AIR  
Line Voltage  
5
2
upflow furnace shown  
1
3
Gas Supply Pressure  
Filter  
1
RETURN  
AIR  
4
3
DUCT SYSTEM  
GAS SUPPLY  
Natural Gas  
1
SUPPLY AIR DUCT  
Sealed  
LP/Propane Gas  
Piping Connections Tight  
Leak Tested  
Insulated (if necessary)  
Registers Open and Unobstructed  
Supply Line Pressure ꢀ W.C.________  
RETURN DUCT  
Sealed  
VENT / EXHAUST PIPE  
2
Secure to Unit  
Filter Installed and Clean  
Grilles Unobstructed  
Elbows Secured to Pipe  
Roof Flashing (water tight)  
Vent Pipe Supported  
INTEGRATED CONTROL  
4
DIP Switches Set (if applicable)  
Appropriate Links in Place (if applicable)  
5
VOLTAGE CHECK  
Supply Voltage _____  
Electrical Connections Tight  
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UNIT OPERATION  
(typical)  
Combustion CO  
2
2
SUPPLY  
AIR  
7
Thermostat  
Gas Manifold Pressure  
Temperatures  
6
1
upflow furnace shown  
4
Filter  
Blower Motor Amps  
Duct Static  
3
RETURN  
AIR  
5
COOLING MODE  
HEATING MODE  
INDOOR BLOWER AMPS______  
3
4
GAS MANIFOLD PRESSURE ꢀW.C._____  
1
2
TEMPERATURE DROP  
COMBUSTION SAMPLE CO % CO PPM_______  
2 ______  
Return Duct Temperature _________  
_
Supply Duct Temperature _______  
Temperature Drop = _________  
INDOOR BLOWER AMPS______  
TEMPERATURE RISE  
3
4
TOTAL EXTERNAL STATIC (dry coil)  
Supply External Static _______  
5
Supply Duct Temperature ________  
_
Return External Static + ______  
Total External Static = _______  
Return Duct Temperature _____  
Temperature Rise = ________  
DRAIN LINE  
Leak Free  
6
7
TOTAL EXTERNAL STATIC (dry coil)  
Supply External Static _______  
Return External Static + ______  
Total External Static = _______  
5
THERMOSTAT  
Adjusted and Programmed  
Operation Explained to Owner  
Contractor’s: Name_________________________Telephone_____________Checklist Completed____________________  
Job Address_____−________________________________Technician’s Name___________________________________  
Page 44  
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