Lennox ML180UHT User manual

Page 1
2015 Lennox Industries Inc.
Dallas, Texas, USA
AIR FLOW
UPFLOW
AIR FLOW
AIR FLOW
HORIZONTAL RIGHT
HORIZONTAL LEFT
Los calefactores están
aprobados por el Instituto
del Gas Argentino (IGA)
para funcionar con gas
natural y no se pueden
convertir para funcionar
con gas licuado.
INSTALLATION
INSTRUCTIONS
ML180UHT
MERIT®SERIES GAS FURNACE
UPFLOW / HORIZONTAL AIR DISCHARGE
507408-01
06/2015 Supersedes 507061-01
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is a safety alert symbol and should never be ignored.
When you see this symbol on labels or in manuals, be alert
to the potential for personal injury or death.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person
al injury or loss of life. Installation and service must
be performed by a licensed professional installer (or
equivalent), service agency or the gas supplier.
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................................
ML180UHT 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 19.....................................
Electrical 21.......................................
Integrated Control 22...............................
Unit Start-Up 24...................................
Gas Pressure Adjustment 25........................
Proper Combustion 25..............................
High Altitude 26....................................
Other Unit Adjustments 26..........................
Service 27........................................
Repair Parts 28...................................
Litho U.S.A.

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 RAB 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 informa
tion.
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
83
38
584
49
356
219 Left
232 Right
14
705
19
494
14
635
603
83
ML180UHT Model No. A B C D
mm mm mm mm
070TP36A 368 340 330 121
090TP48B 446 416 406 159
110TP36C
110TP60C 533 504 495 203
135TP60D 622 546 584 248

Page 3
ML180UHT Gas Furnace
The ML180UHT unit is shipped ready for installation in the
upflow or horizontal right position (for horizontal left posi
tion the combustion air pressure switch must be moved).
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 ML180UHT 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
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 ML180UHT furnace is approved for installation for in
side of building only, with clearances as listed in figure 6.
(Accessibility and service clearances must take prece
dence over fire protection clearances). Installation of Len
nox forced air central furnaces must be in accordance with
these instructions, local gas fitting regulations, municipal
building codes and electrical wiring regulations
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 local codes or these instructions.
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 physical
damage by vehicles. When a furnace is installed in a public
garage, hangar, or other building that has a hazardous at
mosphere, the furnace must be installed according to local
codes.
Unit must be adjusted to obtain a temperature rise within
the range specified on appliance rating plate.
This ML180UHT furnace must be installed so that its elec
trical components are protected from water.
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 manu
ally operated, it must be equipped to prevent operation of
either the heating or the cooling unit, unless it is in the full
HEAT or COOL setting.
When installed, this furnace must be electrically
grounded according to local codes.

Page 4
All field wiring must comply with local codes or what is
listed in these instructions.
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 - ML180UHT 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 ML180UHT 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 approved for instal
lation 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
These instructions are intended as a general guide and
do not supersede local codes in any way. Consult au
thorities having jurisdiction before installation.
In addition to the requirements outlined previously, the fol
lowing general recommendations must be considered
when installing a ML180UHT 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.
WARNING
The State of California has determined that this prod
uct may contain or produce a chemical or chemicals,
in very low doses, which may cause serious illness
or death. It may also cause cancer, birth defects or
reproductive harm.
Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in sufficient
outdoor air for combustion. Infiltration provided all the air
that was needed. In today's homes, tight construction prac
tices make it necessary to bring in air from outside for com
bustion. Take into account that exhaust fans, appliance
vents, chimneys, and fireplaces force additional air that
could be used for combustion out of the house. Unless out
side air is brought into the house for combustion, negative
pressure (outside pressure is greater than inside pressure)
will build to the point that a downdraft can occur in the fur
nace vent pipe or chimney. As a result, combustion gases
enter the living space creating a potentially dangerous situ
ation.
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 com
bustion 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 ex
haust fans which force air out of the house. When fire
places, exhaust fans, or clothes dryers are used at the
same time as the furnace, much more air is necessary to
ensure proper combustion and to prevent a downdraft. In
sufficient air causes incomplete combustion which can re
sult in carbon monoxide.
In addition to providing combustion air, fresh outdoor air di
lutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace compo
nents.
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 con
taining 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 ei
ther 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.
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

Page 6
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 opera
tion.
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 enclo
sure.
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 ML180UHT 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
(ML180UH110TP36C and ML180UH090TP48B)are
equipped with three flexible legs and one rigid leg. See fig
ure 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 re
moved, the rigid leg will not touch the blower housing.
NOTE - ML180UH090TP48B, & ML180UH110TP36C
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
ML180UH110TP36C and
ML180UH090TP48B with 1/2 HP
BLOWER MOTOR
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 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
figure 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 infor
mation.
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.

Page 10
Removing the Bottom Panel
FIGURE 9
Screw
Bottom Panel
Bottom Cap
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 fur
nace directly on carpeting, tile or other combustible materials oth
er than wood flooring.
FIGURE 10
Horizontal Applications
The ML180UHT 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 plat
form, 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 piping instal
lation. 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 instal
lation. See figure 9.

Page 11
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
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.
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 0.5 inches
w.c. Higher external static pressures may cause erratic lim
it 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.
Return Air Plenum
NOTE - Return air must not be drawn from a room
where this furnace, or any other gas-fueled appliance
(i.e., water heater), or carbon monoxide producing de
vice (i.e., wood fireplace) is installed.
When return air is drawn from a room, a negative pressure
is created in the room. If a gas appliance is operating in a
room with negative pressure, the flue products can be
pulled back down the vent pipe and into the room. This re
verse flow of the flue gas may result in incomplete combus
tion and the formation of carbon monoxide gas. This toxic
gas might then be distributed throughout the house by the
furnace duct system.
In upflow applications, the return air can be brought in
through the bottom or either side of the furnace. If a furnace
with bottom return air is installed on a platform, make an air
tight seal between the bottom of the furnace and the plat
form to ensure that the unit operates properly and safely.

Page 12
Use fiberglass sealing strips, caulking, or equivalent seal
ing method between the plenum and the furnace cabinet to
ensure a tight seal. If a filter is installed, size the return air
duct to fit the filter frame.
Venting
The ML180UHT 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 ML180UHT is certified for horizontal installation
but DO NOT vent flue horizontally. The ML180UHT
furnace 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.
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
HORIZONTAL RIGHT POSITION
Side Vent Discharge
FIGURE 18
FLOW
AIR
Pressure Switch
Flue Transition
Collector Box
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
 Cut combustion air inducer tubing from 227 mm (9”) to
178 mm (7”) to avoid interference with inducer motor

Page 14
HORIZONTAL RIGHT POSITION
Top Vent Discharge
FIGURE 20
FLOW
AIR
Flue
Transitio
n
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
The ML180UHT series units are classified as fan-assisted
Category I furnaces when vertically vented. according to
the latest edition of National Fuel Gas Code (NFPA 54 /
ANSI Z223.1) in the USA. A fan-assisted Category I fur
nace is an appliance equipped with an integral mechanical
means to either draw or force combustion products through
the combustion chamber and/or heat exchanger. The
ML180UHT is not approved for use with horizontal venting.
NOTE - Use these instructions as a guide. They do not su
persede local codes. This furnace must be vented accord
ing to all local codes these installation instructions, and the
provided venting tables in these instructions
The venting tables in this manual were extracted from the
National Fuel Gas Code (NFPA 54 / ANSI Z223.1) and are
provided as a guide for proper vent installation. Proper ap
plication, termination, construction and location of vents
must conform to local codes having jurisdiction. In the ab
sence of local codes, the NFGC serves as the defining doc
ument.
Refer to the tables and the venting information contained in
these instructions to properly size and install the venting
system.
Use self-drilling sheet metal screws or a mechanical fas
tener to firmly secure the vent pipe to the round collar of the
flue transition. If self-drilling screws are used to attach the
vent pipe, it is recommended that three be used. Drive one
self-drilling screw through the front and one through each
side of the vent pipe and collar. See figure 21.
Install the first vent connector elbow at a minimum of six
inches (152 mm) from the furnace vent outlet. See figure
21.
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 fur
naces must be either tile‐lined or lined with a listed metal
lining system or dedicated gas vent. Unlined masonry
chimneys are prohibited. See figures 22 and 23 for com
mon venting.
A chimney with one or more sides exposed to the outside of
the structure is considered to be an exterior chimney.
An exterior masonry chimney that is not tile-lined must be
lined with B1 vent or a listed insulated flexible metal vent.
An exterior tile-lined chimney that is sealed and capped
may be lined with a listed uninsulated flexible metal vent.
If the existing chimney will not accommodate a listed metal
liner, either the chimney must be rebuilt to accommodate
one of these liners or an alternate approved venting meth
od must be found.
Insulation for the flexible vent pipe must be an encapsu
lated fiberglass sleeve recommended by the flexible vent
pipe manufacturer. See figure 22.
IMPORTANT
Once the venting system is installed, attach the “Dis
connected Vent” warning sticker to a visible area of
the plenum near the vent pipe. See figure 21. The
warning sticker is provided in the bag assembly. Or
der kit 66W04 for additional stickers.
WARNING
Asphyxiation hazard. The exhaust vent for this fur
nace must be securely connected to the furnace flue
transition at all times.
FIGURE 21
VENT CONNECTION UPFLOW AND HORIZONTAL POSITION
“DISCONNECTED
VENT” WARNING
STICKER
VENT PIPE
(min. 6” length)
FLUE
TRANSITION
COLLAR
“DISCONNECTED
VENT” WARNING
STICKER
VENT PIPE
(min. 6” length)
FLUE
TRANSITION
COLLAR

Page 15
FIGURE 22
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
DO NOT insulate the space between the liner and the
chimney wall with puffed mica or any other loose gran
ular insulating material.
IMPORTANT
SINGLE appliance venting of a fan‐assisted furnace
into a tile‐lined masonry chimney (interior or outside
wall) is PROHIBITED. The chimney must first be lined
with either type B1 vent or an insulated single wall
flexible vent lining system which has been sized ac
cording to the provided venting tables and the vent
pipe manufacturer's instructions.
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 drafthood-
equipped appliance;
The vent connectors and chimney are sized according
to the provided venting tables.
If type B1 double‐wall vent is used inside a chimney, no oth
er appliance can be vented into the chimney. The outer wall
of type B1 vent pipe must not be exposed to flue products.
A type B1 vent or masonry chimney liner shall terminate
above the roof surface with a listed cap or a listed roof as
sembly according to the terms of their respective listings
and the vent manufacturer's instructions.
When inspection reveals that an existing chimney is not
safe for the intended purpose, it shall be rebuilt to conform
to nationally recognized standards, lined or relined with
suitable materials, or replaced with a gas vent or chimney
suitable for venting ML180UHT 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,
or flue restrictor between the furnace and the chimney.
Never connect a Category I appliance to a chimney that is
servicing a solid-fuel appliance. If a fireplace chimney flue
is used to vent this appliance, the fireplace opening must
be permanently sealed.
A type B or listed chimney lining system that passes
through an unused masonry chimney flue is not considered
to be exposed to the outdoors.
General Venting Requirements
Vent all ML180UHT furnaces according to these instruc
tions:
1 - Vent diameter recommendations and maximum allow
able piping runs are found in the provided venting
tables.
2 - In no case should the vent or vent connector diameter
be less than the diameter specified in the provided
venting tables.
3 - The minimum vent capacity determined by the sizing
tables must be less than the low fire input rating and the
maximum vent capacity must be greater than the high
fire input rating.
4 - Single appliance vents - If the vertical vent or tile‐lined
chimney has a larger diameter or flow area than the
vent connector, use the vertical vent diameter to de
termine the minimum vent capacity and the vent
connector diameter to determine the maximum vent
capacity. The flow area of the vertical vent, however,
shall not exceed 7 times the flow area of the listed ap
pliance categorized vent area, drafthood outlet area or
flue collar area unless designed according to approved
engineering methods.
5 - Multiple appliance vents - The flow area of the largest
section of vertical vent or chimney shall not exceed 7
times the smallest listed appliance categorized vent
area, drafthood outlet area or flue collar area unless
designed according to approved engineering meth
ods.

Page 16
FIGURE 23
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
6 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
7 - Single appliance venting configurations with zero lat
eral lengths (table 4) are assumed to have no elbows in
the vent system. For all other vent configurations, the
vent system is assumed to have two 90° elbows. For
each additional 90° elbow or equivalent (for example
two 45° elbows equal one 90° elbow) beyond two, the
maximum capacity listed in the venting table should be
reduced by 10% (0.90 x maximum listed capacity).
8 - The common venting tables (5 and 6) were generated
using a maximum horizontal vent connector length of
1-1/2 feet (.46 m) for each inch (25 mm) of connector
diameter as follows:
TABLE 3
Connector Diameter
inches (mm)
Maximum Horizontal
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)
9 - If the common vertical vent is offset, the maximum
common vent capacity listed in the common venting
tables should be reduced by 20%, the equivalent of two
90° elbows (0.80 x maximum common vent capacity).
The horizontal length of the offset shall not exceed
1‐1/2 feet (.46 m) for each inch (25 mm) of common
vent diameter.
10 - The vent pipe should be as short as possible with the
least number of elbows and angles required to com
plete the job. Route the vent connector to the vent us
ing the shortest possible route.
11 - A vent connector shall be supported without any dips
or sags and shall slope a minimum of 1/4 inch (6.4 mm)
per linear foot (305 mm) of connector, back toward the
appliance.
12 - Vent connectors shall be firmly attached to the furnace
flue collar by self-drilling screws or other approved
means, except vent connectors of listed type B vent
material which shall be assembled according to the
manufacturer's instructions. Joints between sections
of single wall connector piping shall be fastened by
screws or other approved means.
13 - When the vent connector used for Category I ap
pliances must be located in or pass through a crawl
space, attic or other areas which may be cold, that por
tion of the vent connector shall be constructed of listed
double‐wall type B vent material or material having
equivalent insulation qualities.
14 - All venting pipe passing through floors, walls, and ceil
ings must be installed with the listed clearance to com
bustible materials and be fire stopped according to lo
cal codes. In absence of local codes, refer to NFGC
(Z223.1).
15 - No portion of the venting system can extend into, or
pass through any circulation air duct or plenum.

Page 17
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.
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 maxi
mum common vent capacity).
18 - The common vent diameter must always be at least as
large as the largest vent connector diameter.
19 - In no case, shall the vent connector be sized more than
two consecutive table size diameters over the size of
the draft hood outlet or flue collar outlet.
20 - Do not install a manual damper, barometric draft regu
lator or flue restrictor between the furnace and the
chimney.
21 - When connecting this appliance to an existing dedi
cated or common venting system, you must inspect the
venting system's general condition and look for signs
of corrosion. The existing vent pipe size must conform
to these instructions and the provided venting tables. If
the existing venting system does not meet these re
quirements, it must be resized.
TABLE 4
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
2 11 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
NOTE - Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi
mum listed capacity).

Page 18
TABLE 5
Vent Connector Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)
Connector
Rise
R
(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 22 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 6
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)
Common Vent Diameter - D (inches)
4 Inch 5 Inch 6 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 19
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 ap
pliances, the venting system is likely to be too large to prop
erly vent the remaining attached appliances.
Conduct the following test while each appliance is operat
ing and the other appliances (which are not operating) re
main connected to the common venting system. If the vent
ing system has been installed improperly, you must
correct the system as indicated in the general venting re
quirements section.
WARNING
CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon mon
oxide poisoning or death.
The following steps shall be followed for each ap
pliance connected to the venting system being
placed into operation, while all other appliances
connected to the venting system are not in
operation:
1 - Seal any unused openings in the common venting sys
tem.
2 - Inspect the venting system for proper size and horizon
tal pitch. Determine that there is no blockage, restric
tion, leakage, corrosion, or other deficiencies which
could cause an unsafe condition.
3 - Close all building doors and windows and all doors be
tween the space in which the appliances remaining
connected to the common venting system are located
and other spaces of the building. Turn on clothes dry
ers and any appliances not connected to the common
venting system. Turn on any exhaust fans, such as
range hoods and bathroom exhausts, so they will oper
ate at maximum speed. Do not operate a summer ex
haust fan. Close fireplace dampers.
4 - Follow the lighting instructions. Turn on the appliance
that is being inspected. Adjust the thermostat so that
the appliance operates continuously.
5 - After the burner have operated for 5 minutes, test for
leaks of flue gases at the draft hood relief opening. Use
the flame of a match or candle.
6 - After determining that each appliance connected to the
common venting system is venting properly, (step 3)
return all doors, widows, exhaust fans, fireplace damp
ers, and any other gas-burning appliances to their pre
vious mode of operation.
7 - If a venting problem is found during any of the preced
ing tests, the common venting system must be modi
fied to correct the problem.
Using local codes, resize the common venting system
to the minimum vent pipe size.
Gas Piping
See local codes 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.
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 post is
located on the gas valve to facilitate test gauge con
nection. See figure 29.
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
furnace. The installer should properly label these devices.

Page 20
GROUND
JOINT
UNION
AUTOMAT
IC
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 24
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 25