Lennox Merit Series User manual
Page 1
INSTALLATION
INSTRUCTIONS
ML180UHE
507103-03
03/2022
Supersedes 08/2019
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 man-
uals, be alert to the potential for personal injury or death.
CAUTION
As with any mechanical equipment, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves and
protective clothing.
IMPORTANT
DO NOT use the heat exchanger bracket to lift, drag
or pull the furnace to its installation location. Doing so
will loosen the bracket causing noise and or unsafe
operation.
Bracket
© 2022 Lennox Industries Inc.
Dallas, Texas USA
MERIT®SERIES GAS FURNACE
UPFLOW / HORIZONTAL AIR DISCHARGE
Contents
Unit Dimensions - inches (mm) ......................................2
ML180UHE Gas Furnace ...............................................3
Shipping and Packing List ..............................................3
Safety .............................................................................3
Use of Furnace as a Construction Heaterl .....................4
General...........................................................................4
Combustion, Dilution, Ventilation Air...............................5
Setting Equipment ..........................................................8
Filters............................................................................ 11
Duct System .................................................................12
Venting..........................................................................13
Gas Piping....................................................................20
Electrical.......................................................................22
Integrated Control.........................................................26
Unit Start-Up.................................................................28
Gas Pressure Measurement.........................................29
Proper Combustion.......................................................29
High Altitude .................................................................29
Other Unit Adjustements...............................................30
Service..........................................................................31
Start-Up Checklist.........................................................35
Blower Data..................................................................37
AIR FLOW
UPFLOW
AIR FLOW
AIR FLOW
HORIZONT
AL RIGHT
HORIZON
TAL LEFT
Page 2
Unit Dimensions - inches (mm)
2Flue outlet may be horizontal but furnace must be
vented vertically
3Optional external side return air filter kit cannot be used
with the optional RAB Return Air Base.
1NOTE - 60C and 60D units that require air volumes
over 1800 cfm must have one of the following:
1. Single side return air and Optional Return Air Base
with transition that must accommodate required
20 x 25 x 1 in. (508 x 635 x 25 mm) air
filter to maintain proper air velocity.)
2. Bottom return air.
3. Return air from both sides.
4. Bottom and one side return air.
See Blower Performance Tables for additional information.
23
(584)
(19)
3/4
(19) 1
Bottom Return
Air Opening
GAS PIPING INLET
(Either Side)
Side Return
Air Opening
(Either Side)
1Bottom Return
Air Opening
FLUE OUTLET
(Top)
ELECTRICAL INLET
(Either Side)
SUPPLY AIR
OPENING
FRONT VIEW
SIDE VIEW
TOP VIEW
A
B9/16 (14)
C
D
3/4
27−3/4
(705)
19−7/16
(494)
23−1/2
(597)
1−1/2
(38)
9−1/8 (232) Right
8−5/8 (219) Left
5−3/8 (137) Right
1−9/16 (40) Left
33
(838)
3−1/8 (79)
1−15/16 (49)
14
(356)
9/16
(14)
3 (76) Right
6−3/4 (171) Left
2FLUE OUTLET
(Either Side)
3OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
16
(406)
14−3/4
(375)
3
OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
3−1/4 (83)
5/8
(16)
1
3−1/4
(83)
23−3/4
(603)
25
(635)
3/4(19)
Front Panel
ELECTRICAL
INLET (Either Side)
(Either Side)
ML180UHE
Model
A B C D
in mm in mm in mm in mm
045(X)E36A
070(X)E36A 14-1/2 368 13-3/8 340 13 330 4-3/4 121
070(X)E36B
090(X)E48B 17-1/2 446 16-3/8 416 16 406 6-1/4 159
090E60C
110(X)E60C 21 533 19-7/8 504 19-1/2 495 8 203
135E60D 24-1/2 622 23-3/8 546 23 584 9-3/4 248
Page 3
ML180UHE Gas Furnace
The ML180UHE unit is shipped ready for installation in the up-
combustion air pressure switch must be moved) fueled by natu-
ral gas. A conversion kit (ordered separately) is required for use
in LP/Propane gas applications. The furnace is shipped with the
bottom panel in place. The bottom panel must be removed if the
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled ML180UHE unit
1 - Bag assembly containing the following:
2 - Screws
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 -Vent warning label
1 - Owner’s manual and warranty card
The following items may be ordered separately:
1 - Thermostat
1 - LP/Propane changeover kit
1 - Return air base
1 - High altitude kit
damage, immediately contact the last carrier.
Safety Information
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/
installed in all LP applications.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer or
equivalent, service agency, or the gas supplier.
Certications
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:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036
Clearances
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.
Vent installations must be consistent with the National
Fuel Gas Code venting tables (in this instruction) and ap-
plicable provisions of local building codes.
clearances to combustible material as listed on the unit
-
bility and service clearances must take precedence over
NOTE - For installation on combustible oors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood ooring.
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
physical damage by vehicles. When a furnace is installed
in a public garage, hangar, or other building that has a
-
cording to recommended good practice requirements and
current National Fuel Gas Code.
Temperature Rise
NOTE - Furnace must be adjusted to obtain a tempera-
ture rise within the range specied on the unit nameplate.
Failure to do so may cause erratic limit operation and may
result in premature heat exchanger failure.
This ML180UHE furnace must be installed so that its elec-
trical components are protected from water.
Installed in Combination with a Cooling Coil
When this furnace is used with cooling units, it shall be in-
stalled in parallel with, or on the upstream side of, cooling
units to avoid condensation in the heating compartment.
Page 4
chilled air from entering the furnace. If the damper is man-
ually 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.
Gas Unit
Heating Unit Installed Upstream of Cooling Unit
Gas Unit
Dampers
(open during heating operation only)
Dampers
(open during cooling operation only)
Heating Unit Installed Parallell to Air Handler Unit
Air Handler Unit
Evaporator
Figure 1
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:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
NOTE - This furnace is designed for a minimum continu-
ous return air temperature of 60°F (16°C) or an intermittent
operation down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The ML180UHE furnace may be installed in alcoves, clos-
ets, attics, basements, garages, crawl spaces and utility
This furnace design has not been CSA International
certied for installation in mobile homes, recreational
vehicles, or outdoors.
Use of Furnace as Construction Heater
Lennox does not recommend the use of ML180UHE units
as a construction heater during any phase of construc-
tion. Very low return air temperatures, harmful vapors and
damage the unit.
ML180UHE units may be used for heating of buildings or
structures under construction, if the following conditions
are met:
• The vent system must be permanently installed per
these installation instructions.
• A room thermostat must control the furnace. The
heating is not allowed.
• The return air duct must be provided and sealed to
the furnace.
• Return air temperature range between 60°F (16°C)
and 80°F (27°C) must be maintained.
•
be maintained during construction.
• -
pletion.
• The input rate and temperature rise must be set per
the furnace rating plate.
• One hundred percent (100%) outdoor air must be
provided for combustion air requirements during
construction. Temporary ducting may supply out-
door air to the furnace. Do not connect duct directly
these instructions in section for Combustion, Dilu-
from outside.
• The furnace heat exchanger, components, duct
clean-up.
• All furnace operating conditions (including ignition,
input rate, temperature rise and venting) must be
General
These instructions are intended as a general guide and
do not supersede local codes in any way. Consult author-
ities having jurisdiction before installation. In addition to
the requirements outlined previously, the following general
recommendations must be considered when installing a
ML180UHE furnace:
• Place the furnace as close to the center of the air
distribution system as possible. The furnace should
also be located close to the chimney or vent termi-
nation point.
Page 5
• Do not install the furnace where drafts might blow
directly into it. This could cause improper combus-
tion and unsafe operation.
• Do not block the furnace combustion air openings
with clothing, boxes, doors, etc. Air is needed for
proper combustion and safe unit operation.
• When the furnace is installed in an attic or other
insulated space, keep insulation away from the fur-
nace.
NOTE - The Commonwealth of Massachusetts stipu-
lates these additional requirements:
• Gas furnaces shall be installed by a licensed
plumber or tter only.
• The gas cock must be “T handle” type.
• When a furnace is installed in an attic, the pas-
sageway to and service area surrounding the
equipment shall be oored.
Combustion, Dilution & Ventilation Air
that was needed. In today’s homes, tight construction
practices make it necessary to bring in air from outside for
combustion. Take into account that exhaust fans, appli-
that could be used for combustion out of the house. Un-
less 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 oc-
cur in the furnace vent pipe or chimney. As a result, com-
bustion gases enter the living space creating a potentially
dangerous situation.
In the absence of local codes concerning air for combus-
tion and ventilation, use the guidelines and procedures in
-
cient and safe operation. You must consider combustion
air needs and requirements for exhaust vents. A portion of
this information has been reprinted with permission from
the National Fuel Gas Code (ANSI-Z223.1). This reprint-
ANSI on the referenced subject, which is represented only
by the standard in its entirety.
CAUTION
Do not install the furnace in a corrosive or contaminated
atmosphere. Meet all combustion and ventilation air
requirements, as well as all local codes.
CAUTION
excess water in the heat exchanger resulting in rusting
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 combustion
air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
unsafely. Enough air must be provided to meet the needs
of all fuel-burning appliances and appliances such as ex-
-
places, exhaust 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.
result in carbon monoxide.
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace com-
ponents.
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is in-
Unconned Space
large equipment room with a volume greater than 50 cubic
feet (1.42 m3) 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
for combustion if the structure does not provide enough air
construction with weather stripping and caulking around
the windows and doors, follow the procedures in the air
from outside section.
Page 6
Conned Space
cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of
the combined input rating of all appliances installed in that
equipment rooms.
When the furnace is installed so that supply ducts carry
air circulated by the furnace to areas outside the space
containing 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
equipment room.
Even a small leak around the base of the unit at the plat-
form or at the return air duct connection can cause a po-
tentially dangerous negative pressure condition. Air for
combustion and ventilation can be brought into the con-
.
EQUIPMENT IN CONFINED
SPACE ALL AIR FROM INSIDE
CHIMNEY
OR GAS
VENT
FURNACE
WATER
HEATER
OPENINGS
(To Adjacent
Room)
NOTE - Each opening shall have a free area of at least one square
inch (645 mm2
ing of all equipment in the enclosure, but not less than 100 square
inches (64516 mm2).
AIR FLOW
Figure 2
Air from Inside
providing two permanent openings between the two spac-
es. Each opening must have a minimum free area of 1
square inch (645 mm2) per 1,000 Btu (.29 kW) per hour of
space. Each opening must be at least 100 square inches
(64516 mm2). 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-
-
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 communi-
cate directly or by ducts with the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors or in-
directly through vertical ducts. Each opening shall have a
minimum free area of 1 square inch (645 mm2) per 4,000
Btu (1.17 kW) per hour of total input rating of all equipment
-
opening shall have a minimum free area of 1 square inch
(645 mm2) per 2,000 Btu (.56 kW) per total input rating of
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
must be considered. If the design and free area of protec-
required, it may be assumed that wood louvers will have
20 to 25 percent free area and metal louvers and grilles
will have 60 to 75 percent free area. Louvers and grilles
equipment so that they are opened automatically during
equipment operation.
Page 7
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)
NOTE-The inlet and outlet air openings shall each have a free area of at least one square inch (645
mm2)per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR WATER
HEATER
INLET
AIR
CHIMNEY OR
GAS VENT
FURNACE
VENTILATION
LOUVERS
(For unheated crawl space)
AIR FLOW
Figure 3
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
NOTE-The inlet and outlet air openings shall each have a
free area of at least one square inch (645 mm2) per 4,000
ment in the enclosure.
CHIMNEY
OR GAS
VENT
WATER
HEATER
OUTLET
AIR
VENTILATION LOUVERS
(Each end of attic)
INLET AIR
(Ends 12 in.
above bottom)
FURNACE
AIR FLOW
Figure 4
EQUIPMENT IN
CONFINED SPACE
ALL AIR FROM
OUTSIDE
OUTLET AIR
INLET AIR
WATER
HEATER
CHIMNEY
OR GAS
VENT
NOTE - Each air duct opening shall have a free area of at least
one square inch (645 mm2) per 2,000 Btu (.59 kW) per hour of
the total input rating of all equipment in the enclosure. If the
equipment room is located against an outside wall and the air
openings
ing shall have a free area of at least one square inch (645 mm2)
per 4,000 Btu (1.17 kW) per hour of the total input rating of all
other equipment in the enclosure.
FURNACE
AIR FLOW
Figure 5
Page 8
Setting Equipment
WARNING
Do not install the furnace on its front or its back. Do not
connect the return air ducts to the back of the furnace.
control devices, which could result in personal injury or
death.
The ML180UHE gas furnace can be installed as shipped
-
lect a location that allows for the required clearances that
are listed on the unit nameplate. Also consider gas supply
connections, electrical supply, vent connection, and instal-
lation and service clearances [24 inches (610 mm) at unit
front]. The unit must be level.
NOTE - Units with 1/2 or 3/4 hp blower motors are equipped
with three exible legs and one rigid leg. See gure 6. The
rigid leg is equipped with a shipping bolt and a at white
plastic washer (rather than the rubber mounting grommet
used with a exible mounting leg). The bolt and washe
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.
RIGID LEG
remove shipping bolt and washe
Units with 1/2 or 3/4 HP Blower Motor
Figure 6
Upow Applications
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
Upflow Application Installation Clearances
Top
Bottom
Left Side Right Side
Type of Vent
Connector Type CType B1
Top1 in. (25 mm)1 in. (25 mm)
*Front 2-1/4 in. (57 mm)** 2-1/4 in. (57 mm)
Back 0 0
Sides 0†0
Vent 6 in. (152 mm)1 in. (25 mm)
Floor 0‡0‡
*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 installation on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other
than wood flooring.
†Left side requires 3 inches if a single wall vent is used on 14-1/2
in. cabinets, or 2inches if a single wall vent pipe is used on 17-1/2
in. cabinets.
Figure 7
Page 9
Return Air -- Upow Applications
Return air can be brought in through the bottom or either
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.
Markings are provided on both sides of the furnace cab-
inet 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:
1 - Single side return air with optional return air base
with transition that must accommodate required 20
2 - Bottom return air.
3 - Return air from both sides.
4 - Bottom and one side return air.
Refer to Product Specications for additional information.
Return Air
Plenum
Transition
20” X 25” X 1”
(508mm X 635mm X 25mm)
Cleanable Filter
AIR FLOW
Single Side Return Air
(with transition and filter)
Figure 8
Optional Return Air Base
(Upflow Applications Only -- For use with A, B, C and D cabinets)
NOTE- Optional Side Return Air Filter Kits are not for use with Optional Return Air Base.
1Both 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.
2To minimize pressure drop, the largest opening height possible (up to 14 inches 356 mm) is preferred.
FURNACE
FRONT
AIR FLOW
14−1/2 (368) A Width (65W75)
17−1/2 (446) B Width (50W98)
21 (533) C Width (50W99)
24−1/2 (622) D Width (51W00)
1Unit side return air
Opening
SIDE VIEW
3−1/4
(83)
1
23 (584)
Overall
(Maximum)
(584)
23
3/4
(19)
122−7/16
(570)
Overall
(Maximum)
SIDE RETURN
AIR OPENINGS
(Either Side)
5−5/8
(143)
1Minimum
11 (279)
2Maximum
14 (356)
(683)
26−7/8
7−1/4
(184)
IF BASE
IS USED
WITHOUT
IAQ CABINET,
A SINGLE
RETURN AIR
PLENUM
MUST
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
INDOOR AIR
QUALITY
CABINET
(PCO, Filter
Cabinet, etc.)
AIR BASE
OPTIONAL
RETURN
Figure 9
Page 10
Removing the Bottom Panel
Remove the two screws that secure the bottom cap to the
furnace. Pivot the bottom cap down to release the bottom
panel. Once the bottom panel has been removed, reinstall
Removing the Bottom Panel
Screw
Bottom Panel
Bottom Cap
Figure 10
Horizontal Application
Installation Clearances
Top
Bottom
Left
End
Right
End
AIR FLOW
Vent Connector
Type Type CType B1
Top 0 0
*Front 2-1/4 in. (57 mm)**2-1/4 in. (57 mm)
Back 0 0
Ends 2 in. (51 mm)2 in. (51 mm)
Vent 6 in. (152 mm) 1 in. (25 mm)
Floor 0‡0‡
*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 singlewall 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 11
Horizontal Applications
-
Lennox, or use equivalent suspension method.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
This furnace may be installed in either an attic or a crawl-
space. Either suspend the furnace from roof rafters or
Typical Horizontal Application
Unit Suspended in Attic or Crawlspace
Bracket
Bottom Cap
Metal Strap
3/16 inch
Air Flow
Figure 12
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.
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.
Return Air -- Horizontal Applications
Return air must be brought in through the end of a fur-
equipped with a removable bottom panel to facilitate in-
Page 11
Horizontal Application
Unit Installed on Platform
clearances.
GAS
ENTRY VENT
PIPE
See the unit nameplate for
Line contact is permissible
SERVICE PLATFORM
Figure 13
CAUTION
If this unit is being installed in a space serviced by an
exhaust fan, power exhaust fan, or other device which
may create a negative pressure in the space, take care
of exhausted air as well as the maximum volume of
combustion air required for all gas appliances serviced
by this space.
WARNING
Improper installation of the furnace can result in
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 plenum. 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. Allow 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
poisoning, personal injury and/or property damage could
result.
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 injury or death.
Filters
-
must be in place any time the unit is operating.
TABLE 1
Furnace Cabinet
Width
Side Return Bottom Return
A - 14-1/2” 16 X 25 X 1 (1) 14 X 25 X 1 (1)
B - 17-1/2” 16 X 25 X 1 (1) 16 X 25 X 1 (1)
C - 21” 16 X 25 X 1 (1) 20 x 25 x 1 (1)
D - 24-1/2” 16 X 25 X 1 (2) 24 x 25 x 1 (1)
IMPORTANT
and performance may be reduced. The pressure drop
may also cause the limit to trip more frequently during
resulting in an increase in the number of service calls.
the data given in the appropriate Lennox Product
in Service and Application Note ACC002 (August 2000).
Page 12
Duct System
Use industry-approved standards (such as those pub-
lished by Air Conditioning Contractors of America or Amer-
ican Society of Heating, Refrigerating and Air Conditioning
This will result in a quiet and low-static system that has
uniform air distribution.
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
limit operation.
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
for leaks after the furnace is installed. The furnace access
panel must always be in place when the furnace is oper-
ating and it must not allow leaks into the supply air duct
applications to seal the top cap to the vestibule panel.
Return Air Plenum
NOTE - Return air must not be drawn from a roomwhere
this furnace, or any other gas-fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
replace) is installed.
When return air is drawn from a room, a negative pressure
is created in the room. If a gas appliance is operating in
pulled back down the vent pipe and into the room. This
-
bustion and the formation of carbon monoxide gas. This
toxic gas might then be distributed throughout the house
by the furnace duct system.
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
-
lent sealing method between the plenum and the furnace
HORIZONTAL UNIT
SUPPLY
AIR
SUPPLY
AIR Install self tapping screws
to seal any potential air
leaks
UPFLOW UNIT
Figure 14
Page 13
Venting
the combustion air inducer outlet of all models. Figure 16
shows the combustion air inducer as shipped from the fac-
tory.
Mounting Screws Location
Mounting Screws
Flue Transition
Figure 15
UPFLOW POSITION
Top Vent Discharge
FLOW
AIR
Collector Box
Vent Pipe
Flue
Transition
Pressure
Switch
Make-Up
Box
Figure 16
IMPORTANT
pointed down in the 6 o’clock position. The combustion
air inducer may be rotated clockwise or counterclockwise
by 90° to allow for top or side vent discharge in all
must be in the 9 o’clock, 12 o’clock or 3 o’clock position.
If necessary, reposition the combustion air inducer, pres-
sure switch and/or make-up box as needed per the follow-
1 -
secure the combustion air inducer / pressure switch
rotate it 90 degrees clockwise or counterclockwise
to either the 3 o’clock position or to 9 o’clock
position. Resecure with four screws. Gasket should
be left in place.
2 - Use tin snips to cut preferred opening on the cabinet
as a cover plate to patch unused opening on cabinet
.
UPFLOW POSITION
Left Side Vent Discharge
Gas supply piping must be brought into the unit from the right
side in order to accommodate the flue pipe.
ference with inducer motor
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.
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.
FLOW
AIR
Make-Up
Box
Pressure
Switch
Flue
Transition
Vent Pipe
Cover PlateCollector Box
Figure 17
UPFLOW POSITION
Right Side Vent Discharge
FLOW
AIR
Cover PlateFlue Transition
Vent Pipe
Pressure
Switch
Make-Up
Box
Collector Box
Cut combustion air inducer tubing from 9” to 5” to avoid
interference with inducer motor
Figure 18
Page 14
HORIZONTAL LEFT POSITION
Top Vent Discharge
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.
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.
Pressure
Switch
Vent Pipe
Flue
Transition
Cover Plate
Make-Up BoxCollector Box
FLOW
AIR
Figure 19
Make-Up Box Collector Box
Vent Pipe
Pressure Switch
HORIZONTAL LEFT POSITION
Side Vent Discharge
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.
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.
FLOW
AIR
ference with inducer motor
Figure 20
HORIZONTAL RIGHT POSITION
Top Vent Discharge
Gas
supply piping must be brought into the unit from the bottom
in order to accommodate the flue pipe.
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.
Re-secure make-up box wires by either pulling excess wire
s
through the blower compartment and securing with supplie
d
wire tie, or coil excess wire and secure to the gas manifold.
FLOW
AIR
flue transition
vent pipe
pressure switch
cover plate
make-up box
collector box
Figure 21
HORIZONTAL RIGHT POSITION
Side Vent Discharge - no modifications necessary
FLOW
AIR
Pressure Switch
Flue Transition
Collector Bo
x
Make-Up Box
Vent Pipe
Figure 22
Page 15
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 mechan-
ical means to either draw or force combustion products
through the combustion chamber and/or heat exchanger.
venting.
NOTE - Use these instructions as a guide. They do not
supersede local codes. This furnace must be vented ac-
cording to all local codes these installation instructions,
and the provided venting tables in these instructions
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
application, termination, construction and location of vents
must conform to local codes having jurisdiction. In the ab-
document.
Use self-drilling sheet metal screws or a mechanical fas-
the vent pipe, it is recommended that three be used. Drive
one self-drilling screw through the front and one through
23.
Venting Using a Masonry Chimney
The following additional requirements apply when a lined
masonry chimney is used to vent this furnace. Masonry
chimneys used to vent Category I central furnaces must
be either tile-lined or lined with a listed metal
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
An exterior tile-lined chimney that is sealed and capped
If the existing chimney will not accommodate a listed met-
al liner, either the chimney must be rebuilt to accommo-
date one of these liners or an alternate approved venting
method must be found.
-
the venting information contained in these instructions to
IMPORTANT
Once the venting system is installed, attach the
“Disconnected Vent” warning sticker to a visible area
warning sticker is provided in the bag assembly. Order
Kit 66W04 for additional stickers.
WARNING
at all times..
FLUE TRANSITION
COLLAR
VENT PIPE
(min. 6” length)
“DISCONNECTED VENT”
WARNING
STICKER
FLUE
TRANSITION
COLLAR
VENT CONNECTION UPFLOW AND HORIZONTAL POSITION
VENT PIPE
(min. 6” length)
“DISCONNECTED VENT”
WARNING
STICKER
Figure 23
Page 16
Common Venting Using Metal-Lined Masonry Chimney
4 in. (102 mm)
minimum
MIN. LENGTH -- AS
SHORT AS PRACTICAL
MAX. LENGTH
-- SEE NOTE 1
BELOW.
SEALED
PERMANENTLY
SEALED FIREPLACE
OPENING
EXTERIOR
CHIMNEY WITH
METAL
LINER
VENT CONNECTOR
NOTE 1 - Refer to the provided venting tables for installations. Refer
to the capacity requirements shown in the provided venting tables.
OTHER
APPLIANCE
FURNACE
5 ft. (1.5 m)
minimum
AIR FLOW
Figure 24
DO NOT insulate the space between the liner and
the chimney wall with pued mica or any other loose
granular insulating material.
IMPORTANT
SINGLE appliance venting of a fan-assisted furnace into
a tile-lined masonry chimney (interior or outside wall)
provided venting tables and the vent pipe manufacturer’s
instructions.
A fan-assisted furnace may be commonly vented into an
existing lined masonry chimney if the following conditions
are met:
• The chimney is currently serving at least one draft-
hoodequipped appliance;
• -
ing o the provided venting tables.
If type B1 double-wall vent is used inside a chimney, no
other appliance can be vented into the chimney. The outer
-
ucts. A type B1 vent or masonry chimney liner shall termi-
nate above the roof surface with a listed cap or a listed
roof assembly according to the terms of their respective
listings and the vent manufacturer’s instructions.
When inspection reveals that an existing chimney is not
safe for the intended purpose, it shall be rebuilt to conform
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.
Do not install a manual damper, barometric draft regulator,
Never connect a Category I appliance to a chimney that is
be permanently sealed.
A type B or listed chimney lining system that passes
-
ered to be exposed to the outdoors.
General Venting Requirements
Vent all ML180UHE furnaces according to these instruc-
tions:
1 - Vent diameter recommendations and maximum
allowable piping runs are found in the provided
venting tables.
2 - In no case should the vent or vent connector diameter
venting tables.
the maximum vent capacity must be greater than the
4 - Single appliance vents - If the vertical vent or tile-
the vent connector, use the vertical vent diameter to
determine the minimum vent capacity and the vent
connector diameter to determine the maximum vent
approved engineering methods.
section of vertical vent or chimney shall not exceed
unless designed according to approved engineering
methods.
6 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
Page 17
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 - the chimney must be properly
sized per provided venting tables or
lined with listed metal lining system.
PERMANENTLY
SEALED FIREPLACE
OPENING
VENT
CONNECTOR
NOTE- Refer to provided venting tables
for installations.
FURNACE
OTHER
APPLIANCE
AIR FLOW
Figure 25
6 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
lateral lengths (tables 3 and 4 are assumed to have
no elbows in the vent system. For all other vent
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% (0.90
x maximum listed capacity).
8 - The common venting tables (4 and 5) were generated
1-1/2 feet (.46 m) for each inch (25 mm) of connector
diameter as follows:
TABLE 2
Connector Diameter
inches (mm)
Connector Length feet (m)
3 (76) 4-1/2 (1.37)
4 (102) 6 (1.83)
5 (127) 7-1/2 (2.29)
6 (152) 9 (2.74)
7 (178) 10-1/2 (3.20)
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
exceed 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
complete the job. Route the vent connector to the
vent using the shortest possible route.
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.
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.
13 - When the vent connector used for Category I
appliances must be located in or pass through
a crawlspace, attic or other areas which may
be cold, that portion of the vent connector shall
be constructed of listed double-wall type B vent
material or material havingequivalent insulation
qualities.
ceilings must be installed with the listed clearance
according to local codes. In absence of local codes,
refer to NFGC (Z223.1).
15 - No portion of the venting system can extend into,
or pass through any circulation air duct or plenum.
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.
Page 18
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).
18 - The common vent diameter must always be at least
as large as the largest vent connector diameter.
20 - Do not install a manual damper, barometric draft
the chimney.
21 - When connecting this appliance to an existing
dedicated or common venting system, you must
inspect the venting system’s general condition
and look for signs of corrosion. The existing vent
the provided venting tables. If the existing venting
system does not meet these requirements, it must
TABLE 3
Capacity of Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving a Single Category I Appliance
Height
H
(feet)
Lateral
L
(feet)
Vent and Connector Diameter - D (inches)
3 inch 4 inch 5 inch 6 inch
Appliance Input Rating in Thousands of Btu Per Hour
Min Max Min Max Min Max Min Max
6
0 0 78 0 152 0 251 0 375
2 13 51 18 97 27 157 32 232
4 21 49 30 94 39 153 50 227
6 25 46 36 91 47 149 59 223
8
0 0 84 0 165 0 276 0 415
2 12 57 16 109 25 178 28 263
5 23 53 32 103 42 171 53 255
8 28 49 39 98 51 164 64 247
10
0 0 88 0 175 0 295 0 447
2 12 61 17 118 23 194 26 289
5 23 57 32 113 41 187 52 280
10 30 51 41 104 54 176 67 267
15
0 0 94 0 191 0 327 0 502
211 69 15 136 20 226 22 339
5 22 65 30 130 39 219 49 330
10 29 59 40 121 51 206 64 315
15 35 53 48 112 61 195 76 301
20
0 0 97 0 202 0 349 0 540
2 10 75 14 149 18 250 20 377
5 21 71 29 143 38 242 47 367
10 28 64 38 133 50 229 62 351
15 34 58 46 124 59 217 73 337
20 48 52 55 116 69 206 84 322
30
0 0 100 0 213 0 374 0 587
2 9 81 13 166 14 283 18 432
5 21 77 28 160 36 275 45 421
10 27 70 37 150 48 262 59 405
15 33 64 44 141 57 249 70 389
20 56 58 53 132 66 237 80 374
30 NA NA 73 113 88 214 104 346
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 maximum listed capacity).
Page 19
TABLE 4
Vent Connector Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Height
H
(feet)
Lateral
L
(feet)
Vent and Connector Diameter - D (inches)
3 inch 4 inch 5 inch 6 inch
Appliance Input Rating in Thousands of Btu Per Hour
Min Max Min Max Min Max Min Max
6
1 22 37 35 66 46 106 58 164
2 23 41 37 75 48 121 60 183
3 24 44 38 81 49 132 62 199
8
1 22 40 35 72 49 114 64 176
2 23 44 36 80 51 128 66 195
3 24 47 37 87 53 139 67 210
10
1 22 43 34 78 49 123 65 189
2 23 47 36 86 51 136 67 206
3 24 50 37 92 52 146 69 220
15
1 21 50 33 89 47 142 64 220
2 22 53 35 96 49 153 66 235
3 24 55 36 102 51 163 68 248
20
1 21 54 33 99 46 157 62 246
2 2 57 34 105 48 167 64 259
3 23 60 35 110 50 176 66 271
30
1 20 62 31 113 45 181 60 288
2 21 64 33 118 47 190 62 299
3 22 66 34 123 48 198 64 309
TABLE 5
Common Vent Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)
Vent and Connector Diameter - D (inches)
4 inch 5 inch 7 inch 7 inch
Appliance Input Rating in Thousands of Btu Per Hour
FAN + FAN FAN + NAT FAN + FAN FAN + NAT FAN + FAN FAN + NAT FAN + FAN FAN + NAT
6 92 81 140 116 204 161 309 248
8 101 90 155 129 224 178 339 275
10 110 97 169 141 243 194 367 299
15 125 112 195 164 283 228 427 352
20 136 123 215 183 314 255 475 394
30 152 138 244 210 361 297 547 459
Page 20
Removal of the Furnace from Common Vent
In the event that an existing furnace is removed from a
venting system commonly run with separate gas applianc-
es, the venting system is likely to be too large to properly
vent the remaining attached appliances. Conduct the fol-
lowing test while each appliance is operating and the oth-
er appliances (which are not operating) remain 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 requirements section.
IMPORTANT
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 monoxide poisoning
or death. The following steps shall be followed for each
appliance connected to the venting system being placed
into operation, while all other appliances connected to
the venting system are not in operation:
1 - Seal any unused openings in the common venting
system.
which could cause an unsafe condition.
3 - Close all building doors and windows and all
doors between the space in which the appliances
remaining connected to the common venting system
are located and other spaces of the building. Turn on
clothes dryers 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 operate at maximum speed. Do not
dampers.
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
6 - After determining that each appliance connected to
the common venting system is venting properly, (step
dampers, and any other gas-burning appliances to
their previous mode of operation.
7 - If a venting problem is found during any of the
preceding tests, the common venting system must
common venting system to the minimum vent pipe
Appendix G. (These are in the current standards of
the National Fuel Gas Code ANSI Z223.1.
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.
WARNING
Do not over torque (800 in-lbs) or under torque (350 in-
lbs) when attaching the gas piping to the gas valve.
CAUTION
authority that has jurisdiction, black iron pipe shall be
installed at the gas valve and extend outside the furnace
between the black iron pipe and the gas supply line.
Gas Supply
1 - This unit is shipped standard for left or right side
applications). Connect the gas supply piping into the
gas valve. The maximum torque is 800 in lbs and
minimum torque is 350 in lbs when when attaching
the gas piping to the gas valve.
2 - When connecting the gas supply piping, consider
furnace rating to avoid excessive pressure drop.
applications.
3 - The gas piping must not run in or through air ducts,
clothes chutes, gas vents or chimneys, dumb waiters,
or elevator shafts.
4 - The piping should be sloped 1/4 inch (6.4 mm) per
15 feet (4.57 m) upward toward the meter from the
furnace. The piping must be supported at proper
intervals [every 8 to 10 feet (2.44 to 3.01 m)] with
suitable hangers or straps. Install a drip leg in vertical
pipe runs to the unit.
5 - A 1/8” N.P.T. plugged tap or pressure post is located
on the gas valve to facilitate test gauge connection.
6 - In some localities, codes may require the installation
by the installer) external to the unit. The union must
be of the ground joint type.
IMPORTANT
Compounds used on threaded joints of gas piping must
NOTE - If emergency shuto is necessary, shut o the
main manual gas valve and disconnect main power to the
furnace. The installer should properly label these devices
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