Lennox ML180UHT Installation Instructions Manual
INSTALLATION
2015 Lennox Industries Inc.
Dallas, Texas, USA
AIR FLOW
UPFLOW
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.
Litho U.S.A.
AIR FLOW
AIR FLOW
HORIZONTAL LEFT
HORIZONTAL RIGHT
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.
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........................................
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
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...................................
Page 1
Unit Dimensions - mm
1
NOTE - 60C and 60D units that require air volumes
over 1800 cfm (850 L/s) must have one of the following:
1. Single side return air with 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.
2
Flue outlet may be horizontal but furnace must be
vented vertically
3
Optional external side return air filter kit cannot be used
with the optional RAB Return Air Base.
D
FLUE OUTLET
(Top)
3
OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
79
SUPPLY AIR
OPENING
603
635
TOP VIEW
19
A
B
C
1
Bottom Return
Air Opening
FRONT VIEW
14
3
OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
375
406
16
19
838
19
Front Panel
76 Right
171 Left
232 Right
219 Left
137 Right
40 Left
ELECTRICAL
INLET (Either Side)
(Either Side)
83
38
83
2
FLUE OUTLET
(Either Side)
GAS PIPING INLET
(Either Side)
1
Side Return
Air Opening
(Either Side)
1
Bottom Return
Air Opening
SIDE VIEW
584
597
705
494
14
38
356
49
ML180UHT Model No.
070TP36A
090TP48B
110TP36C
110TP60C
135TP60D
A B C D
mm mm mm mm
368 340 330 121
446 416 406 159
533 504 495 203
622 546 584 248
Page 2
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*
Gas Properties 101.3 kPa, 15° C Dry bulb
* Wobbe number = heating value square root of specific
gravity
Min Normal Max
46.95 mj / m
(1260 Btu / ft3)
(14.73 psia, 60° F Dry Bulb)
3
50.15 mj / m
(1346 Btu / ft3)
3
53.28 mj / m
(1430 Btu / ft3)
3
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 / m
3
(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 3
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 4
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 m
(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
3
m
(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
WATER
FURNACE
NOTE - Each opening shall have a free area of at least 645 mm
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 mm
square inches).
HEATER
OPENINGS
(To Adjacent
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
3
spaces. Each opening must have a minimum free area of
645 mm
2
(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 mm
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
Room)
2 (
one
2
1(00
2
(100
Page 5
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 mm
2
(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 mm
2
(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
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)
CHIMNEY OR
GAS VENT
VENTILATION LOUVERS
(Each end of attic)
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
OUTLET
FURNACE
VENTILATION
LOUVERS
(For unheated crawl space)
NOTE-The inlet and outlet air openings shall each have a free area of at least 645 mm
square inch) per 1.17 kW (4,000 Btu) per hour of the total input rating of all equipment in the enclo
sure.
AIR
WATER
HEATER
INLET
AIR
2
(one
FIGURE 2
Page 6
CHIMNEY
OR GAS
VENT
FURNACE
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR
INLET AIR
(Ends 12 in.
above bottom)
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.
WATER
HEATER
NOTE-The inlet and outlet air openings shall each have a
free area of at least 645 mm
kW (4,000 Btu) per hour of the total input rating of all
equipment in the enclosure.
2 (
one square inch) per 1.17
FIGURE 3
EQUIPMENT IN
CONFINED SPACE
ALL AIR FROM
OUTSIDE
OUTLET AIR
INLET AIR
FURNACE
CHIMNEY
OR GAS
VENT
WATER
HEATER
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.
ML180UH110TP36C and
ML180UH090TP48B with 1/2 HP
BLOWER MOTOR
RIGID LEG
remove shipping bolt and washer
NOTE - Each air duct opening shall have a free area of at least 645
2 (
mm
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 mm
hour of the total input rating of all other equipment in the enclosure.
2
(one square inch) per 1.17 kW (4,000 Btu) per
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.
FIGURE 5
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 7
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
Left Side
Bottom
Type of Vent
Connector
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.
Type C Type B1
Right Side
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 -
L/s (1800cfm) must have one of the following:
1 - Single side return air with transition to accommodate
2 - Single side return air with optional return airbase. See
3 - Bottom return air.
4 - Return air from both sides.
5 - Bottom and one side return air.
60C and 60D units that require air volumes over 850
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.
figure 8.
Refer to Product Specifications bulletin for additional infor
mation.
Single Side Return Air
(with transition and filter)
508mm X 635mm X 25mm
(20” X 25” X 1”)
Cleanable Filter
Return Air
Plenum
AIR FLOW
Transition
FIGURE 7
Page 8
Optional Return Air Base
(Upflow Applications Only -- For use with A, B, C and D cabinets)
FURNACE
FRONT
IF BASE
IS USED
INDOOR AIR
QUALITY
CABINET
AIR FLOW
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)
NOTE- Optional Side Return Air Filter Kits are not for use with Optional Return Air Base.
1
Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.
(PCO, FILTER
CABINET, ETC
OPTIONAL
RETURN
AIR BASE
WITHOUT
IAQ CABINET,
A SINGLE
RETURN AIR
PLENUM
MUST
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
83 (3−1/4)
184 (7−1/4)
1
584 (26)
Overall
(Maximum)
1
Unit side return air
Opening
143
(5−5/8)
SIDE RETURN
AIR OPENINGS
(Either Side)
683
(26−7/8)
SIDE VIEW
584
(23)
1
Minimum
279 (11)
2
Maximum
356 (14)
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.
2
To minimize pressure drop, the largest opening height possible [up to 356 mm (14 in.)] is preferred.
FIGURE 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.
1
570
(22)
Overall
(Maximum)
19
(3/4)
Page 9
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