Lennox ML180DF Installation Instructions Manual
INSTALLATION
E 2015 Lennox Industries Inc.
Dallas, Texas, USA
DOWNFLOW
INSTRUCTIONS
ML180DF
MERIT® SERIES GAS FURNACE
DOWNFLOW AIR DISCHARGE
507326-01
06/2015
Supersedes 507057-01
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.
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
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
Table of Contents
Unit Dimensions 2................................
ML180DF Gas Furnace 3..........................
Shipping and Packing List 3........................
Safety Information 3...............................
Use of Furnace as a Construction Heater 4...........
General 4........................................
Combustion, Dilution & Ventilation Air 5..............
Setting Equipment 9...............................
Filters 10..........................................
Duct System 11....................................
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
Venting 11........................................
Gas Piping 16.....................................
Electrical 18.......................................
Integrated Control 21...............................
Unit Start-Up 22...................................
Gas Pressure Adjustment 23........................
Proper Combustion 23..............................
High Altitude 23....................................
Other Unit Adjustments 24..........................
Service 26........................................
Repair Parts 28....................................
Page 1
Unit Dimensions - inches (mm)
3−1/8
(79)
9/16
(14)
D
RETURN AIR
OPENING
B
FLUE OUTLET
(Top)
9/16
(14)
19−7/16
(494)
9/16
(14)
TOP VIEW
A
B
9/16
(14)
3/4 (19)
Front Panel
27−3/4
(705)
19−7/16
(494)
9/16
(14)
ELECTRICAL INLET
(Either Side)
GAS PIPING INLET
(Either Side)
19−1/4
Supply
(489)
Air
3/4
(19)
3/4
(19)
C
Supply
Air
(838)
3/4
(19)
33
5−3/8 (137) Right
2−1/8 (54) Left
6−5/8 (168) Right
7−1/8 (181) Left
FRONT VIEW SIDE VIEW
Model No.
ML180DF045P24A
ML180DF045P36A
ML180DF070P36A
ML180DF090P36B
ML180DF090P48B
ML180DF110P60C 21 533 19-7/8 504 19-1/2 495 8 203
14-1/2 368 13-3/8 340 13 330 4-3/4 121
17-1/2 446 16-3/8 416 16 406 6-1/4 159
A B C D
in. mm in. mm in. mm in. mm
Page 2
ML180DF Gas Furnace
The ML180DF gas furnace is shipped ready for installation
in the downflow position fueled by natural gas. A conver
sion kit (ordered separately) is required for use in LP/Pro
pane gas applications.
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled ML180DF unit
1 - Bag assembly containing the following:
2 - Screws
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 - Vent warning label
1 - Owner's manual and warranty card
The following items may be ordered separately:
1 - Thermostat
1 - LP/Propane changeover kit
1 - Combustible flooring base
1 - High altitude kit
Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.
Safety Information
DANGER
Danger of explosion.
There are circumstances in which odorant used with
LP/propane gas can lose its scent. In case of a leak,
LP/propane gas will settle close to the floor and may
be difficult to smell. An LP/propane leak detector
should be installed in all LP applications.
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.
Certifications
ML180DF units are CSA International certified.
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI‐Z223.1). The National Fuel Gas Code is
available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036
Clearances
Adequate clearance must be made around the air open
ings into the vestibule area. In order to ensure proper unit
operation, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code.
Vent installations must be consistent with the National Fuel
Gas Code venting tables (in this instruction) and applicable
provisions of local building codes.
This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in figure 13. Accessibility and
service clearances must take precedence over fire protec
tion clearances.
Installed Locations
For installation in a residential garage, the furnace must be
installed so that the burner(s) and the ignition source are
located no less than 18 inches (457 mm) above the floor.
The furnace must be located or protected to avoid physical
damage by vehicles. When a furnace is installed in a public
garage, hangar, or other building that has a hazardous at
mosphere, the furnace must be installed according to rec
ommended good practice requirements and current Na
tional Fuel Gas Code.
NOTE - Furnace must be adjusted to obtain a temperature
rise within the range(s) specified on the unit nameplate.
Failure to do so may cause erratic limit operation and may
also result in premature heat exchanger failure.
This ML180DF furnace must be installed so that its electri
cal components are protected from water.
Installed in Combination with a Cooling Coil
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 (see figure 1). If the
damper is manually operated, it must be equipped to pre
vent operation of either the heating or the cooling unit, un
less it is in the full HEAT or COOL setting.
Page 3
GAS UNIT
Dampers
(open during heating
operation only)
AIR HANDLER
Dampers
(open during cooling
operation only)
FIGURE 1
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National Electric
Code, ANSI/NFPA No. 70. The National Electric Code
(ANSI/NFPA No. 70) is available from the following ad
dress:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
NOTE - This furnace is designed for a minimum continuous
return air temperature of 60°F (16°C) or an intermittent op
eration down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The ML180DF furnace may be installed in alcoves, closets,
attics, basements, garages, and utility rooms in the down
flow position.
This furnace design has not been CSA International
certified for installation in mobile homes, recreational
vehicles, or outdoors.
Use of Furnace as Construction Heater
Lennox does not recommend the use of ML180DF units as
a construction heater during any phase of construction.
Very low return air temperatures, harmful vapors and op
eration of the unit with clogged or misplaced filters will dam
age the unit.
ML180DF units may be used for heating of buildings or
structures under construction, if the following conditions
are met:
D The vent system must be permanently installed per
these installation instructions.
D A room thermostat must control the furnace. The use of
fixed jumpers that will provide continuous heating is not
allowed.
D The return air duct must be provided and sealed to the
furnace.
D Return air temperature range between 60°F (16°C) and
80°F (27°C) must be maintained.
D Air filters must be installed in the system and must be
maintained during construction.
D Air filters must be replaced upon construction comple
tion.
D The input rate and temperature rise must be set per the
furnace rating plate.
D One hundred percent (100%) outdoor air must be pro
vided for combustion air requirements during construc
tion. Temporary ducting may supply outdoor air to the
furnace. Do not connect duct directly to the furnace.
Size the temporary duct following these instructions in
section for Combustion, Dilution and Ventilation Air in a
confined space with air from outside.
D The furnace heat exchanger, components, duct sys
tem, air filters and evaporator coils must be thoroughly
cleaned following final construction clean-up.
D All furnace operating conditions (including ignition, in
put rate, temperature rise and venting) must be verified
according to these installation instructions.
General
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 ML180DF furnace:
D Place the furnace as close to the center of the air dis
tribution system as possible. The furnace should also be
located close to the chimney or vent termination point.
D Do not install the furnace where drafts might blow direct
ly into it. This could cause improper combustion and un
safe operation.
D Do not block the furnace combustion air openings with
clothing, boxes, doors, etc. Air is needed for proper
combustion and safe unit operation.
D When the furnace is installed in an attic or other insu
lated space, keep insulation away from the furnace.
NOTE - The Commonwealth of Massachusetts stipu
lates these additional requirements:
D Gas furnaces shall be installed by a licensed plumb
er or fitter only.
D The gas cock must be “T handle” type.
D When a furnace is installed in an attic, the passage
way to and service area surrounding the equipment
shall be floored.
Page 4
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
combustion. Take into account that exhaust fans, ap
pliance 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, nega
tive pressure (outside pressure is greater than inside pres
sure) will build to the point that a downdraft can occur in the
furnace vent pipe or chimney. As a result, combustion
gases enter the living space creating a potentially danger
ous situation.
In the absence of local codes concerning air for combus
tion and ventilation, use the guidelines and procedures in
this section to install ML180DF furnaces to ensure efficient
and safe operation. You must consider combustion air
needs and requirements for exhaust vents. A portion of this
information has been reprinted with permission from the
National Fuel Gas Code (ANSI‐Z223.1). This reprinted ma
terial is not the complete and official position of the ANSI on
the referenced subject, which is represented only by the
standard in its entirety.
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.
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.
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
combustion air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De‐icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
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 50 cubic
feet (1.42 m
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 50 cu
bic feet (1.42 m
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
containing the furnace, the return air must be handled by
ducts which are sealed to the furnace casing and which ter
minate outside the space containing the furnace. This is
3
) per 1,000 Btu (.29 kW) per hour of the com
3
) per 1,000 Btu (.29 kW) per hour of the
Page 5
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 condi
tion. Air for combustion and ventilation can be brought into
the confined space either from inside the building or from
outside.
EQUIPMENT IN CONFINED
CHIMNEY
OR GAS
VENT
FURNACE
NOTE - Each opening shall have a free area of at least one square
inch (645 mm
ing of all equipment in the enclosure, but not less than 100 square
inches (64516 mm
2
) per 1,000 Btu (.29 kW) per hour of the total input rat
2
).
SPACE ALL AIR FROM INSIDE
WATER
HEATER
OPENINGS
(To Adjacent
Room)
FIGURE 2
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 1
square inch (645 mm
2
) per 1,000 Btu (.29 kW) per hour of
total input rating of all gas-fired equipment in the confined
space. Each opening must be at least 100 square inches
(64516 mm
2
). One opening shall be within 12 inches (305
mm) of the top of the enclosure and one opening within 12
inches (305 mm) of the bottom. See figure 2.
Air from Outside
If air from outside is brought in for combustion and ventila
tion, the confined space must have two permanent open
ings. One opening shall be within 12 inches (305 mm) of the
top of the enclosure and one opening within 12 inches (305
mm) of the bottom. These openings must communicate di
rectly or by ducts with the outdoors or spaces (crawl or at
tic) that freely communicate with the outdoors or indirectly
through vertical ducts. Each opening shall have a minimum
free area of 1 square inch (645 mm
2
) per 4,000 Btu (1.17
kW) per hour of total input rating of all equipment in the en
closure. See figures 3 and 4. When communicating with
the outdoors through horizontal ducts, each opening shall
have a minimum free area of 1 square inch (645 mm
2
) per
2,000 Btu (.56 kW) per total input rating of all equipment in
the enclosure. See figure 5.
When ducts are used, they shall be of the same cross-sec
tional area as the free area of the openings to which they
connect. The minimum dimension of rectangular air ducts
shall be no less than 3 inches (75 mm). In calculating free
area, the blocking effect of louvers, grilles, or screens must
be considered. If the design and free area of protective cov
ering is not known for calculating the size opening required,
it may be assumed that wood louvers will have 20 to 25 per
cent free area and metal louvers and grilles will have 60 to
75 percent free area. Louvers and grilles must be fixed in
the open position or interlocked with the equipment so that
they are opened automatically during equipment opera
tion.
Page 6
CHIMNEY OR
GAS VENT
FURNACE
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)
VENTILATION LOUVERS
(Each end of attic)
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
OUTLET
AIR
WATER
HEATER
CHIMNEY
OR GAS
VENT
FURNACE
VENTILATION
LOUVERS
(For unheated crawl space)
NOTE-The inlet and outlet air openings shall each have a free area of at least one square inch (645
2
mm
) per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
INLET
AIR
FIGURE 3
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)
FURNACE
CHIMNEY
OR GAS
VENT
CONFINED SPACE
WATER
HEATER
OUTLET AIR
INLET AIR
EQUIPMENT IN
ALL AIR FROM
OUTSIDE
NOTE-The inlet and outlet air openings shall each have a
free area of at least one square inch (645 mm
Btu (1.17 kW) per hour of the total input rating of all equip
ment in the enclosure.
FIGURE 4
WATER
HEATER
2
) per 4,000
Page 7
NOTE - Each air duct opening shall have a free area of at least
one square inch (645 mm
2
) per 2,000 Btu (.59 kW) per hour of
the total input rating of all equipment in the enclosure. If the
equipment room is located against an outside wall and the air
openings communicate directly with the outdoors, each open
ing shall have a free area of at least one square inch (645 mm
per 4,000 Btu (1.17 kW) per hour of the total input rating of all
other equipment in the enclosure.
FIGURE 5
2
)
Downflow Installation
Downflow unit installs in three ways: on non-combustible
flooring, on combustible flooring using a downflow com
bustible flooring base, or on a reverse-flow cooling cabinet.
Do not drag the unit across the floor.
Installation on Non-Combustible Flooring (Figure 6)
1 - Cut floor opening keeping in mind clearances listed on
unit rating plate. Also keep in mind gas supply connec
tions, electrical supply, flue and air intake connections
and sufficient installation and servicing clearances.
See table 1 for correct floor opening size.
2 - Flange warm air plenum and lower the plenum into the
opening.
3 - Set the unit over the plenum and seal the plenum to
the unit.
4 - Ensure that the seal is adequate.
CAUTION
The furnace and downflow combustible flooring
base shall not be installed directly on carpeting, tile,
or other combustible material other than wood floor
ing.
ML180DF UNIT
SUPPLY AIR PLENUM
PROPERLY
SIZED FLOOR
OPENING
DOWNFLOW
COMBUSTIBLE
FLOORING BASE
ML180DF UNIT
OPENING
SUPPLY AIR
PLENUM
FIGURE 6
TABLE 1
NON-COMBUSTIBLE FLOOR OPENING SIZE
Cabinet Width
A (14.5”) 19-3/4 502 13-1/4 337
B (17.5”) 19-3/4 502 16-1/4 413
C (21”) 19-3/4 502 19-3/4 502
NOTE - Floor opening dimensions listed are 1/4 inch (6 mm) larger than
the unit opening. See unit dimensions on page 2.
Front to Rear Side to Side
in. mm in. mm
Installation on Combustible Flooring (Figure 7)
1 - When unit is installed on a combustible floor, a down
flow combustible flooring base must be installed be
tween the furnace and the floor. The base must be or
dered separately.
See table 2 for opening size to cut in floor.
FIGURE 7
TABLE 2
COMBUSTIBLE FLOOR OPENING SIZE
Cabinet Width
A (14.5”)
B (17.5”)
C (21”)
Front to Rear Side to Side
in. mm in. mm
22 559 15-3/4 400
22 559 18-3/4 476
22 559 22-3/4 578
2 - After opening is cut, set combustible flooring base into
opening.
3 - Check sealing strips on combustible flooring base to
make sure they are properly glued and positioned.
4 - Lower supply air plenum into downflow combustible
flooring base until plenum flanges seal against the
strips.
NOTE - Be careful not to damage sealing strips. Check
for a tight seal.
5 - Set the furnace over the plenum.
6 - Ensure that the seal between the furnace and plenum
is adequate.
Installation on Cooling Cabinet (Figure 8)
1 - Refer to reverse-flow coil installation instructions for
correctly sized opening in floor and installation of cabi
net.
NOTE - Downflow combustible flooring kit is not used
2 - When cooling cabinet is in place, set and secure the
furnace according to the instructions that are provided
with the cooling coil. Secure the furnace to the cabinet.
3 - Seal the cabinet and check for air leaks.
Page 8
Setting Equipment
ML180DF UNIT
COOLING COIL
PROPERLY
SIZED FLOOR
OPENING
PLENUM
FIGURE 8
Return Air Opening -- Downflow Units
The following steps should be taken when installing ple
num:
1 - Bottom edge of plenum should be flanged with a
hemmed edge (See figure 9).
PLENUM
SECURE FROM
OUTSIDE CABINET
Side View
HEMMED EDGE
SEALING STRIP
(Field Provided)
CABINET SIDE PANEL
FIGURE 9
2 - Sealing strip should be used.
3 - In all cases, plenum should be secured to top flanges
of furnace with sheet metal screws.
WARNING
Do not install the furnace on its front, back or in the
horizontal position. See figure 12. Do not connect the
return air ducts to the back of the furnace. Doing so
will adversely affect the operation of the safety con
trol devices, which could result in personal injury or
death.
Install the ML180DF gas furnace as shipped in the down
flow position only. Do not install the furnace hori
zontally.
Select a location that allows for the required clearances
that are listed on the unit nameplate. Also consider gas
supply connections, electrical supply, vent connection, and
installation and service clearances [24 inches (610 mm) at
unit front]. The unit must be level.
NOTE - Units with 1/2 hp blower motors are equipped with
three flexible legs and one rigid leg. See figure 11. 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 opera
tion. After the bolt and washer have been removed, the rig
id leg will not touch the blower housing.
UNITS WITH 1/2 HP BLOWER MOTOR
RIGID LEG
remove shipping bolt and washer
SECURE FROM IN
SIDE CABINET
FIBERGLASS
SEALING STRIP
(Field Provided)
PLENUM
HEMMED EDGE
CABINET SIDE
PANEL
FIGURE 10
4 - In closet installations, it may be impossible to install
sheet metal screws from the outside. In this case,
make plenum with a removable front and install
screws from the inside (See figure 10).
5 - Make certain that an adequate seal is made.
Side View
FIGURE 11
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.
Page 9
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