Lennox ML180UHA User manual

Page 1
2018 Lennox Industries Inc.
Dallas, Texas, USA
AIR FLOW
UPFLOW
AIR FLOW
AIR FLOW
HORIZONTAL RIGHT
HORIZONTAL LEFT
Certified by SAI Global
GSCS20254
INSTALLATION
INSTRUCTIONS
ML180UHA
MERIT®SERIES GAS FURNACE
UPFLOW / HORIZONTAL AIR DISCHARGE
507407-03
10/2018
Supersedes 507407-02
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 HVAC in
staller (or equivalent), service agency or the gas sup
plier.
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
Table of Contents
Unit Dimensions 2................................
ML180UHA Gas Furnace 3.........................
Shipping and Packing List 3........................
Requirements 3...............................
General 4........................................
Combustion, Dilution & Ventilation Air 4..............
Setting Equipment 7...............................
Filters 11..........................................
Duct System 11....................................
Venting 12........................................
Gas Piping 14.....................................
Electrical 16.......................................
Integrated Control 17...............................
Unit Start-Up 19...................................
Gas Pressure Adjustment 20........................
High Altitude 20....................................
Proper Combustion 20..............................
Other Unit Adjustments 21..........................
Service 22........................................
Repair Parts 23...................................
Specifications 24..................................

Page 2
Unit Dimensions - 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 Return Air Base.
1NOTE - 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 transition to accommodate
508 x 635 x 25 mm cleanable air
filter. (Required to maintain proper air velocity.)
2. Single side return with optional return air base.
3. Bottom return air.
4. Return air from both sides.
5. Bottom and one side return air.
See Blower Performance Tables for additional information.
1
Bottom Return
Air Opening
GAS PIPING INLET
(Either Side)
Side Return
Air Opening
(Either Side)
1Bottom Return
Air Opening
FLUE OUTLET
(Top)
SUPPLY AIR
OPENING
FRONT VIEW SIDE VIEW
TOP VIEW
A
B
C
D
2FLUE OUTLET
(Either Side)
3OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
3
OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
1
Front Panel
ELECTRICAL
INLET (Either Side)
(Either Side)
79
76 Right
171 Left
137 Right
40 Left
19
16
19
406
375
838
597
38
38
584
49
356
219 Left
232 Right
14
705
19
494
14
635
603
83
ML180UHA Model No. A B C D
mm mm mm mm
070AP36A 368 340 330 121
090AP48B 446 416 406 159
110AP36C
110AP60C 533 504 495 203
135AP60D 622 546 584 248

Page 3
ML180UHA Gas Furnace
The ML180UHA unit is shipped ready for use with Natural
gas (LP/Propane changeover kits available), and for instal
lation in the upflow or horizontal right position (for horizon
tal left position the combustion air pressure switch must
be moved). The furnace is shipped with the bottom panel
in place. The bottom panel must be removed if the unit is to
be installed in a horizontal application. The panel may
also be removed in upflow applications with bottom return
air.
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled ML180UHA 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
1 - Bag assembly containing the following:
1 - 2.5 m Power cord
The following items may be ordered separately:
1 - Thermostat
1 - Suspension kit (for horizontal installations)
1 - Propane/LP changeover kit
1 - Return air base
1 - High altitude kit
1 - Side filter kit
Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.
Requirements
The ML180UHA furnace is approved for installation for in
side of building only, with clearances as listed in figure 6.
(Accessibility and service clearances must NOT take pre
cedence over fire protection clearances). Installation of
Lennox forced air central furnaces must be in accordance
with these instructions, local gas fitting regulations, munici
pal building codes, electrical wiring regulations and the cur
rent edition of the Australian Gas Installation Code (AS/
NZS5601).
The acceptable natural gas Wobbe number values for use
with Lennox furnaces are shown in Table 1.
TABLE 1
Wobbe
Number*
Min Normal Max
46.95 mj / m3
(1260 Btu / ft3)
50.15 mj / m3
(1346 Btu / ft3)
53.28 mj / m3
(1430 Btu / ft3)
Gas Properties 101.3 kPa, 15° C Dry bulb
(14.73 psia, 60° F Dry Bulb)
* Wobbe number = heating value square root of specific
gravity
If you need to know whether a gas is acceptable, request
the Wobbe number from your gas supplier and compare to
the chart. If the number is within the ranges listed for Natu
ral gas, the gas is acceptable to use. If the Wobbe number
is outside the acceptable ranges, the gas is not acceptable
to use.
As LP (Propane) is a regulated/manufactured gas, a
Wobbe number is not required to determine acceptability.
For propane installations, the acceptable heating value
range is 93.2 MJ / m3(2500 btu/ft3) +/- 5%.
NOTE - Lennox does not recommend using unrefined or
”well head” gas on Lennox gas-fired furnaces. The quality
of gas is not controlled and may have contaminants which
may lead to corrosion, premature heat exchanger failure or
may void the equipment warranty. The information pro
vided above is intended for evaluating fuel gases available
commercially through gas utilities or LP (propane) suppli
ers.
Adequate clearance must be made around the air open
ings into the vestibule area. Provisions shall be made for
proper operation and for combustion air and ventilation air
supply according to the current edition of the Australian
Gas Installation Code (AS/NZS5601).
NOTE - For installation on combustible floors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood flooring.
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 457 mm (18 in) above the floor.
The furnace must be located or protected to avoid physi
cal damage by vehicles. When a furnace is installed in a
public garage, hangar, or other building that has a hazard
ous atmosphere, the furnace must be installed according
to recommended good practice requirements and current
edition of the Australian Gas Installation Code (AS/
NZS5601).
Unit must be adjusted to obtain a temperature rise within
the range specified on appliance rating plate.
This ML180UHA furnace must be installed so that its elec
trical components are protected from water.

Page 4
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.
With a parallel flow arrangement, a damper (or other means
to control the flow of air) must adequately prevent chilled air
from entering the furnace. If the damper is manually oper
ated, 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.
When installed, this furnace must be electrically
grounded according to local codes.
All field wiring must comply with the current edition of
Australian Standard AS3000.
When furnace is installed so that supply ducts carry air cir
culated by furnace to areas outside of space containing
ufurnace, return air shall be handled by a duct(s) sealed to
a furnace casing and terminating outside space containing
furnace.
NOTE - ML180UHA series units must not be used as a
“construction heater” during any phase of construction.
Very low temperatures, harmful vapors and misplacement
of the filters will damage the unit and its efficiency.
The ML180UHA furnace may be installed in alcoves, clos
ets, attics, basements, garages, crawl spaces and utility
rooms in any of its approved installation positions.
This furnace design has not been certified for installa
tion in mobile homes, recreational vehicles, or out
doors.
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.
General
WARNING
Do not place articles on or against this appliance.
Do not store flammable materials near this appli
ance.
Do not spray aerosols in the vicinity of this appliance
while in operation.
Do not modify this appliance.
Refer to the unit serial / data badge located in the
electrical compartment for gas type and gas con
sumption information.
These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the fol
lowing general recommendations must be considered
when installing a ML180UHA furnace:
Place the furnace as close to the center of the air dis
tribution system as possible. The furnace should also be
located close to the chimney or vent termination point.
Do not install the furnace where drafts might blow direct
ly into it. This could cause improper combustion and un
safe 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 insu
lated space, keep insulation away from the furnace.
•Please consult the manufacturer of your evaporator coil
for their recommendations on distance required
between the heat exchanger and their drain pan. Ad
equate space must be provided between the drain pan
and the furnace heat exchanger.
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.
Refer to and comply with the current edition of the
Australian Gas Installation Code (AS/NZS5601) for ap
pliance combustion air requirements.
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.

Page 5
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:
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
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.
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.
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.
Unconfined Space
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 1.42 m3
(50 cubic feet) per .29 kW (1,000 Btu) 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.
Confined Space
A confined space is an area with a volume less than 1.42
m3(50 cubic feet) per .29 kW (1,000 Btu) 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.
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 645 mm2(one
square inch) per .29 kW (1,000 Btu) per hour of the total input rating
of all equipment in the enclosure, but not less than 64516 mm21(00
square inches).
FIGURE 1
Air from Inside
If the confined space that houses the furnace adjoins a
space categorized as unconfined, air can be brought in by
providing two permanent openings between the two
spaces. Each opening must have a minimum free area of
645 mm2(1 square inch) per .29 kW (1,000 Btu) per hour of
total input rating of all gas-fired equipment in the confined
space. Each opening must be at least 64516 mm2(100
square inches). One opening shall be within 305 mm (12
inches) of the top of the enclosure and one opening within
305 mm (12 inches) of the bottom. See figure 1.

Page 6
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 305 mm (12 inches) of the
top of the enclosure and one opening within 305 mm (12
inches) of the bottom. These openings must communicate
directly or by ducts with the outdoors or spaces (crawl or
attic) that freely communicate with the outdoors or indirect
ly through vertical ducts. Each opening shall have a mini
mum free area of 645 mm2(1 square inch) per 1.17 kW
(4,000 Btu) per hour of total input rating of all equipment in
the enclosure. See figures 2 and 3. When communicating
with the outdoors through horizontal ducts, each opening
shall have a minimum free area of 645 mm2(1 square inch)
per .56 kW (2,000 Btu) per total input rating of all equipment
in the enclosure. See figure 4.
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 75 mm (3 inches). 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 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 645 mm2(one square
inch) per 1.17 kW (4,000 Btu) 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)
FIGURE 2

Page 7
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 645 mm2(one square inch) per 1.17
kW (4,000 Btu) per hour of the total input rating of all
equipment 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
FIGURE 3
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 645
mm2(one square inch) per .59 kW (2,000 Btu) per hour of the total
input rating of all equipment in the enclosure. If the equipment room
is located against an outside wall and the air openings communi
cate directly with the outdoors, each opening shall have a free area
of at least 645 mm2(one square inch) per 1.17 kW (4,000 Btu) per
hour of the total input rating of all other equipment in the enclosure.
FURNACE
FIGURE 4
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 fur
nace. Doing so will adversely affect the operation of
the safety control devices, which could result in per
sonal injury or death.
NOTE - As an option, rubberlike pads defined as having an
elastic texture resembling rubber in flexibility or toughness,
may be placed under each corner of the furnace as ap
propriate to the application.
The ML180UHA 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 [610 mm (24
inches)] at unit front. The unit must be level.
NOTE - Units with 1/2 hp blower motors
(ML180UH110AP36C and ML180UH090AP48B) are
equipped with three flexible legs and one rigid leg. See
figure 5. The rigid leg is equipped with a shipping bolt
and a flat white plastic washer (rather than the rubber
mounting grommet used with a flexible mounting leg).
The bolt and washer must be removed before the
furnace is placed into operation. After the bolt and
washer have been removed, the rigid leg will not touch
the blower housing.
NOTE - ML180UH090AP48B, & ML180UH110AP36C
are also equipped with a shipping pad under the blower
housing. Remove the shipping pad prior to operation.
FIGURE 5
RIGID LEG
remove shipping bolt and washer
ML180UH110AP36C and
ML180UH090AP48B with 1/2 HP
BLOWER MOTOR

Page 8
Upflow Applications
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or al
cove installations are shown in figure 6.
Upflow Application Installation Clearances
Top
Bottom
Left Side Right Side
Type of Vent
Connector Type C Type B1
Top 25 mm (in.) 25 mm (1 in.)
*Front 57 mm (2-1/4 in)** 57 mm (2-1/4 in.)
Back 0 0
Sides 0†0
Vent 152 mm (6 in.) 25 mm (1 in.)
Floor 0‡0‡
*Front clearance in alcove installation must be 610 mm (24 in.).
Maintain a minimum of 610 (24 in.) mm for front service access.
** 114 mm (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 76 mm (3 in.) if a single wall vent is used on 368
mm (14-1/2 in.) cabinets, or 51 mm (2 in.) if a single wall vent pipe
is used on 445 mm (17-1/2 in.) cabinets.
FIGURE 6
Return Air - Upflow Applications
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.
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 850
L/s (1800cfm) must have one of the following:
1 - Single side return air with transition to accommodate
508 x 635 x 25 mm (20 x 25 x 1 in.) cleanable air filter. (Re
quired to maintain proper air velocity.) See figure 7.
2 - Single side return air with optional return airbase. See fig
ure 8.
3 - Bottom return air.
4 - Return air from both sides.
5 - Bottom and one side return air.
Refer to Product Specifications bulletin for additional informa
tion.
FIGURE 7
Return Air
Plenum
Transition
508mm X 635mm X 25mm
(20” X 25” X 1”)
Cleanable Filter
AIR FLOW
Single Side Return Air
(with transition and filter)

Page 9
Optional Return Air Base
(Upflow Applications Only -- For use with A, B, C and D cabinets)
FIGURE 8
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 850 L/s (1800 cfm) or more of air (W x H): 584 x 279
mm. (23 X 11 in.)
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 356 mm (14 in.)] is preferred.
FURNACE
FRONT
AIR FLOW
1Unit side return air
Opening
SIDE VIEW
1
Overall
(Maximum)
1
Overall
(Maximum)
SIDE RETURN
AIR OPENINGS
(Either Side)
1Minimum
2Maximum
IF BASE
IS USED
WITHOUT
IAQ CABINET,
A SINGLE
RETURN AIR
PLENUM
MUST
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
584 (26)
279 (11)
356 (14)
INDOOR AIR
QUALITY
CABINET
(PCO, FILTER
CABINET, ETC
OPTIONAL
RETURN
AIR BASE
368 (14−1/2) A WIDTH (65W75)
446 (17−1/2) B WIDTH (50W89)
533 (21) C WIDTH (50W99)
622 (24−1/2) D WIDTH (51W00)
83 (3−1/4)
184 (7−1/4)
570
(22)
19
(3/4)
584
(23)
683
(26−7/8)
143
(5−5/8)
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
the bottom cap. See figure 9.
Removing the Bottom Panel
FIGURE 9
Screw
Bottom Panel
Bottom Cap

Page 10
Horizontal Application
Installation Clearances
Top
Bottom
Left
End
Right
End
AIR FLOW
Vent Connector
Type Type C Type B1
Top 0 0
*Front 57 mm (2-1/4 in.)** 57 mm (2-1/4 in. )
Back 0 0
Ends 51 mm (2 in.) 51 mm (2 in.)
Vent 152 mm (6 in.) 25 mm (1 in. )
Floor 0‡0‡
*Front clearance in alcove installation must be 610 mm (24 in)
Maintain a minimum of 610 mm (24 in.) for front service access.
** 114 mm (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 10
Horizontal Applications
The ML180UHA 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 10.
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 figure 11, or install the furnace on a
platform, as shown in figure 12.
Typical Horizontal Application
Unit Suspended in Attic or Crawlspace
FIGURE 11
Internal
Brace
Bracket
Metal
Strap
Air Flow
4.8 mm
(3/16 in
)
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 furnace
installed in a horizontal application. The furnace is
equipped with a removable bottom panel to facilitate
installation. See figure 9.
Horizontal Application
Unit Installed on Platform
FIGURE 12
clearances.
GAS
ENTRY VENT
PIPE
See the unit nameplate for
Line contact is permissible but not preferred
SERVICE PLATFORM
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 when sizing the inlet air opening. The in
let air opening must be sized to accommodate the
maximum volume of exhausted air as well as the
maximum volume of combustion air required for
all gas appliances serviced by this space.

Page 11
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.
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.
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 2 lists recommended filter sizes.
A filter must be in place any time the unit is operating.
IMPORTANT
If a highefficiency filter is being installed as part of
this system to ensure better indoor air quality, the fil
ter must be properly sized. Highefficiency filters
have a higher static pressure drop than standardef
ficiency glass/foam filters. If the pressure drop is too
great, system capacity and performance may be re
duced. The pressure drop may also cause the limit to
trip more frequently during the winter and the indoor
coil to freeze in the summer, resulting in an increase
in the number of service calls.
Before using any filter with this system, check the
specifications provided by the filter manufacturer
against the data given in the appropriate Lennox
Product Specifications bulletin. Additional informa
tion is provided in Service and Application Note
ACC002 (August 2000).
TABLE 2
Furnace
Cabinet
Width
Filter Size mm (in) and Quantity
Side Return Bottom Return
A - 338
(14-1/2”)
406 X 635 X 25 1
(16 X 25 X 1)
356 X 635 X 25 1
(14 X 25 X 1)
B- 446
( 17-1/2”)
406 X 635 X 25 1
(16 X 25 X 1)
406 X 635 X 25 1
(16 X 25 X 1)
C - 533
( 21”)
405 X 635 X 25 1
(16 X 25 X 1)
508 X 635 X 25 1
(20 X 25 X 1)
D - 622
(24-1/2”)
405 X 635 X 25 2
(16 X 25 X 1)
610 X 635 X 25 1
(24 X 25 X 1)
Duct System
Use industry‐approved standards 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.
NOTE - Do not operate the furnace in the heating mode
with an external static pressure that exceeds 125Pa (0.5”
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
(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.
TABLE 3
Unit Capacity Minimum Number of Outlets
ML180UH070AP36A 5
ML180UH090AP48B 7
ML180UH110AP36C 8
ML180UH110AP60C 9
ML180UH135AP60D 10
NOTE - The number of outlets was calculated for the facto
ry set heating speed tap.
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 fireplace) is installed.
When return air is drawn from a room, a negative pres
sure is created in the room. If a gas appliance is operating
in a room with negative pressure, the flue products can
be pulled back down the vent pipe and into the room. This
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.

Page 12
Venting
The ML180UHA is a fan assisted furnace equipped with an
integral mechanical means to either draw or force products
of combustion through the combustion chamber and/or
heat exchanger. When installed in the vertical position and
vented vertically, the furnace operates with a non-positive
vent stack pressure. When installed in the horizontal posi
tion and vented vertically, the furnace operates with a posi
tive stack pressure.
IMPORTANT
The ML180UH is certified for horizontal installation
but DO NOT vent flue horizontally. The ML180UH fur
nace is not certified for horizontal venting. See figure
21.
General Venting Requirements
A 102 mm (4 in.) diameter flue transition is factory‐installed
on the combustion air inducer outlet of all models. Figure
14 shows the combustion air inducer as shipped from
the factory. Refer to the current edition of the Australian
Gas Installation Code (AS/NZS5601) and instructions in
this manual for proper sizing an installation of the venting
system
When flues are terminated vertically, an AGA approved
cowl must be used.
FIGURE 13
Mounting Screws Location
Mounting Screws
Flue Transition
If necessary, reposition the combustion air inducer, pres
sure switch and/or make-up box as needed per the follow
ing steps. See figures 14 through 20.
1 - Remove the four mounting screws (figure 13) which
secure the combustion air inducer / pressure switch
assembly to the orifice plate. Lift the inducer assembly
and rotate it 90 degrees clockwise or counterclockwise
to either the 3 o'clock position or to 9 o'clock position.
Re-secure with four screws. Gasket should be left in
place.
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.
Upflow Position
FIGURE 14
UPFLOW POSITION
Top Vent Discharge
FLOW
AIR
Collector Box
Vent Pipe
Flue
Transition
Pressure
Switch
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.
UPFLOW POSITION
Left Side Vent Discharge
FIGURE 15
 Cut combustion air inducer tubing from 229 mm (9”) to 203 mm
(8”) to avoid interference with inducer motor
FLOW
AIR
Pressure
Switch
Flue
Transition
Vent Pipe
Collector Box
 Gas supply piping must be brought into the unit from the right
side in order to accommodate the flue pipe.

Page 13
UPFLOW POSITION
Right Side Vent Discharge
FIGURE 16
FLOW
AIR
Cover Plate Flue Transition
Vent Pipe
Pressure
Switch
Collector Box
 Cut combustion air inducer tubing from 229 mm ( 9” ) to 127 mm
(5”) to avoid interference with inducer motor
HORIZONTAL LEFT POSITION
Top Vent Discharge
FIGURE 17
 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
Collector Box
FLOW
AIR
FIGURE 18
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
 Cut combustion air inducer tubing from 227 mm (9”) to
178 mm (7”) to avoid interference with inducer motor
HORIZONTAL RIGHT POSITION
Top Vent Discharge
FIGURE 19
FLOW
AIR
Flue
Transition
Vent Pipe
Pressure Switch
Cover Plate
Collector Box
 Gas supply piping must be brought into the unit from the
bottom in order to accommodate the flue pipe.
 Cut combustion air inducer tubing from 227 mm (9”) to 203
mm (8”) to avoid interference with inducer motor

Page 14
HORIZONTAL RIGHT POSITION
Side Vent Discharge
FIGURE 20
FLOW
AIR
Pressure Switch
Flue Transition
Collector Box
IMPORTANT
Do not use an unlined masonry chimney as the flue
for this appliance.
FIGURE 21
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
Gas Piping
Refer to the current edition of the Australian Gas Instal
lation Code (AS/NZS5601) for gas piping requirements
and gas pipe sizing tables.
Gas supply piping should not allow more than 125 Pa
(0.5”W.C.) drop in pressure between gas meter and unit.
Supply gas pipe must not be smaller than unit gas connec
tion.
CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet. The flexible connector can then
be added between the black iron pipe and the gas
supply line.

Page 15
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.
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 6.4 mm (1/4 in) per 4.57 m
(15 ft.) upward toward the meter from the furnace. The
piping must be supported at proper intervals every
2.44 to 3.01 m (8 to 10 ft) with suitable hangers or
straps. Install a drip leg in vertical pipe runs to the unit.
5 - A 3 mm (1/8”) N.P.T. plugged tap or pressure port is lo
cated on the gas valve to facilitate test gauge connec
tion. See figure 27.
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.
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.
GROUND
JOINT
UNION
AUTOMATIC
GAS VALVE
FIELD
PROVIDED
AND INSTALLED
GROUND
JOINT
UNION
Left Side Piping
(Standard)
Right Side Piping
(Alternate)
AUTOMATIC
GAS VALVE
DRIP LEG
DRIP LEG
MANUAL
MAIN SHUT-OFF
VALVE
(With 1/8 in. NPT
Plugged Tap Shown)
MANUAL
MAIN SHUT-OFF
VALVE
(With 1/8 in. NPT
Plugged Tap
Shown)
NOTE - BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET
FIGURE 22
GROUND
JOINT
UNION
DRIP LEG
MANUAL
MAIN SHUT-OFF
VALVE
GROUND
JOINT
UNION
DRIP LEG
MANUAL
MAIN SHUT-OFF
VALVE
GROUND
JOINT
UNION
DRIP LEG
MANUAL
MAIN SHUT-OFF
VALVE
Horizontal Application
Left-Side Air Discharge
Horizontal Application
Right-Side Air Discharge NOTE - BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET
FIELD
PROVIDED
AND INSTALLED
FIGURE 23

Page 16
Leak Check
After gas piping is completed, carefully check all piping
connections (factory- and field-installed) for gas leaks. Use
a leak detecting solution or other preferred means.
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.
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.
The furnace must be isolated by closing its individual man
ual shut‐off valve and disconnecting from from the gas sup
ply system the during any pressure testing of the gas sup
ply system at pressures greater than 3.48 kPa (1/2 psig, 14
inches w.c.).
IMPORTANT
When testing pressure of gas lines, gas valve must
be disconnected and isolated. See figure 24. Gas
valves can be damaged if subjected to pressures
greater than 1/2 psig (3.48 kPa, 14 inches w.c.).
MANUAL MAIN
SHUT-OFF VALVE
WILL NOT HOLD
NORMAL TEST
PRESSURE
CAP
ISOLATE
GAS VALVE
FURNACE
FIGURE 24
1/8 NPT PLUG
Electrical
CAUTION
Electrostatic discharge can affect elec
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
A power wiring harness is shipped with each ML180UHA
furnace. An IEC receptacle is provided on the right side of
the unit. Plug the harness into the IEC receptacle and into a
properly sized wall plug.
Refer to figure 26 schematic wiring diagram.
1 - Ensure that power connection point is located with 2m
of furnace.
2 - Holes are on both sides of the furnace cabinet to facili
tate thermostat wiring.
3 - Before connecting the thermostat wiring, check to
make sure the wires will be long enough for servicing at
a later date. Remove the blower access panel to check
the length of the wire.
4 - Complete the wiring connections to the equipment.
Use the provided unit wiring diagram shown in figure
26. 18-gauge wire or larger that is suitable for Class II
rating for thermostat connections.
5 - Electrically ground the unit according to local codes.
NOTE - The ML180UHA furnace contains electronic
components that are polarity sensitive. Make sure that
the furnace is wired correctly and is properly grounded.
6 - One line voltage “EAC” spade terminal is provided on
the furnace control board. Any electronic air cleaner
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. See figure 25 for
control board configuration. This terminal is energized
when the indoor blower is operating.
7 - One line voltage “HUM” spade terminal is provided on
the furnace control board. Any humidifier 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. See figure 25 for control
board configuration. This terminal is energized in the
heating mode when the combustion air inducer is oper
ating.
8 - Install the room thermostat according to the instruc
tions provided with the thermostat. See figure 26 for
thermostat designations. If the furnace is being
matched with a heat pump, refer to the instruction
packaged with the dual fuel thermostat.
Indoor Blower Speeds
1 - When the thermostat is set to “FAN ON,” the indoor
blower will run continuously on the heating speed
when there is no cooling or heating demand.
2 - When the ML180UHA 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.
Generator Use - Voltage Requirements
The following requirements must be kept in mind when
specifying a generator for use with this equipment:
The furnace requires 240 volts + 10%.
The furnace operates at 50 Hz + 5% .
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% THD (total harmonic distortion)

Page 17
Integrated Control
FIGURE 25
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
HUM - Humidifier 240VAC
LINE - Input 240VAC
XFMR - Transformer 240VAC
EAC - Electronic Air Cleaner 240VAC
COOL - Cool Speed 240VAC
PARK1, PARK2 - Dead terminals for alternate speed taps
NEUTRALS - Neutral terminals 240VAC
HEAT - Heating Speed 240VAC
FS - Flame Sense

Page 18
FIGURE 26
ML180UHA Schematic Wiring Diagram

Page 19
Unit Start-Up
FOR YOUR SAFETY READ BEFORE LIGHTING
WARNING
Do not use this furnace if any part has been under
water. A flood-damaged furnace is extremely dan
gerous. Attempts to use the furnace can result in
fire or explosion. Immediately call a qualified 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.
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.
CAUTION
Before attempting to perform any service or mainte
nance, turn the electrical power to unit OFF at dis
connect switch.
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.
The gas valve on the ML180UHA unit will be 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.
Placing the furnace into operation:
ML180UHA 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.
WARNING
If you do not follow these instructions exactly, a fire
or explosion may result causing property damage,
personal injury or death.
Gas Valve Operation
1 - STOP! Read the safety information at the beginning of
this section.
2 - Set the thermostat to the lowest setting.
3 - Turn off all electrical power to the unit.
4 - This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
5 - Remove the upper access panel.
6 - Move lever on gas valve to OFF. See figure 27.
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.
FIGURE 27
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
OUTLET
PORT
INLET
PRESSURE
PORT
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
(under cap)
White Rodgers 3600 Gas Valve
8 - Move lever on gas valve to ON. See figure 27.
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.
12- If the appliance will not operate, follow the instructions
“Turning Off Gas to Unit” and call your service techni
cian or gas supplier.
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.
3 - Remove the upper access panel.

Page 20
4 - Move lever on gas valve to OFF. See figure 27.
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?
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.
10 - Is pressure switch closed? Obstructed flue will cause
unit to shut off at pressure switch. Check flue and outlet
for blockages. If no blockage is found call the service
technician.
11 - Are flame rollout switches tripped? If flame rollout
switches are tripped, call the service technician for in
spection.
Heating Sequence Of Operation
(follow steps below or see Figure 26 for more detail)
1 - When thermostat calls for heat, combustion air blower
starts.
2 - Combustion air pressure switch proves blower opera
tion. Switch is factory-set and requires no adjustment.
3 - After a 15-second prepurge, the hot surface ignitor en
ergizes.
4 - After a 20-second ignitor warm-up period, the gas
valve solenoid opens. A 4-second trial for ignition peri
od begins.
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.
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.
Gas Pressure Adjustment
Gas Flow
NOTE - The manufacturer recommended gas orifice size is
1.60 mm for natural gas and 0.86 mm for L.P.
To check for proper flow to combustion chamber, deter
mine MJ/Hr input from appliance rating plate. Divide this in
put rating by the MJ/Hr per cubic meter of available gas.
Result is the required number of cubic meter per hour. De
termine the flow of gas through the gas meter for two min
utes and multiply by 30 to get the hourly flow of gas.
IMPORTANT
The White Rodgers 36G24 gas valve (figure 27) is
equipped with pressure posts for measuring supply
and manifold pressures. The posts provide built-in
7.9mm (5/16”) hose connections and have an inte
gral 2.4mm (3/32”) Allen-head screw. Rotate the
screw counterclockwise one full turn to permit pres
sure measurement. Reseat the screw (rotate one full
turn clockwise) after measurements have been taken
to prevent gas leakage.
Use pressure measurement kit 69M1701 to connect
7.9mm (5/16”) pressure post on gas valve to 6.4mm (1/4”)
hose off the manometer.
Line Pressure Measurement
1 - Check the gas line pressure with the unit firing at maxi
mum rate. See table 5 for maximum and minimum line
pressures.
After the line pressure has been checked and adjusted,
check the manifold pressure per table 5. See figure 27 for
the location of the manifold pressure adjustment screw.
Manifold Pressure Measurement
1 - Connect the outlet side of the gas to a manometer to
measure manifold pressure.
2 - Start unit and allow 5 minutes for unit to reach steady
state.
3 - While waiting for the unit to stabilize, observe the
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
5.
5 - Shut unit off and remove manometer as soon as an ac
curate reading has been obtained. Take care to re
place pressure tap plug.
6 - Start unit and perform leak check. Seal leaks if found.
Proper Combustion
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 100 ppm.
TABLE 4
Unit CO2%For Nat CO2% For L.P.
-070
6.3 - 7.8 7.0 - 9.0
-090
-110
-135