Lennox ML180DF045P24A, ML180DF090P36B, ML180DF045P36A, ML180DF110P60C, ML180DF090P48B Installation Instructions Manual
...
© 2017 Lennox Industries Inc.
DOWNFLOW
Dallas, Texas USA
INSTALLATION
INSTRUCTIONS
ML180DF
MERIT® SERIES GAS FURNACE
DOWNFLOW AIRDISCHARGE
507326-02
11/2017
Supersedes 05/2016
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
CAUTION
As with any mechanical equipment, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves and
protective clothing.
AIR FLOW
Contents
Unit Dimensions .............................................................2
ML180DF Gas Furnace .................................................. 3
Shipping and Packing List ..............................................3
Safety Information ..........................................................3
Use of Furnace as Construction Heater .........................4
General ........................................................................... 4
Combustion, Dilution & Ventilation Air ............................5
Setting Equipment .........................................................9
Filters ............................................................................ 10
Duct System ................................................................. 11
Venting..........................................................................11
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer or
equivalent, service agency, or the gas supplier.
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
Repait Parts .................................................................. 28
Page 1
Unit Dimensions - inches (mm)
A
B
AIR FLOW
9/16
(14)
FLUE OUTLET
(Top)
3/4 (19)
Front Panel
3-1/8
(79)
D
9/16
(14)
RETURN AIR
OPENING
B
19-7/16
(494)
9/16
(14)
TOP VIEW
27-3/4
(705)
19-7/16
(494)
9/16
(14)
9/16
(14)
ELECTRICAL INLET
(Either Side)
GAS PIPING INLET
(Either Side)
19-1/4
Supply
(489)
Air
3/4
(19)
C
Supply
Air
33
(838)
5-3/8 (137) Right
2-3/16 (56) Left
6-5/8 (168) Right
7-1/8 (181) Left
3/4
(19)
FRONT VIEW SIDE VIEW
Model No.
A B C D
in mm in mm in mm in mm
ML180DF045P24A
ML180DF045P36A
14-1/2 368 13-3/8 340 13 330 4-3/4 121
ML180DF070P36A
ML180DF090P36B
ML180DF090P48B
ML180DF110P60C 21 533 19-7/8 504 19-1/2 495 8 203
17-1/2 446 16-3/8 416 16 406 6-1/4
3/4
(19)
159
Page 2
ML180DF Gas Furnace
The ML180DF gas furnace is shipped ready for installation in the downow position fueled by natural gas. A conversion kit (ordered separately) is required for use in LP/
Propane 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 ooring base
1 - High altitude kit
Check equipment for shipping damage. If you nd 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 oor and may be
difcult 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, personal
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, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves
and protective clothing.
Certications
ML180DF units are CSA International certied.
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 openings 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 certied for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in gure 13. Accessibility and
service clearances must take precedence over re 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
oor. 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 atmosphere, the furnace must be installed according to recommended good practice requirements and
current National Fuel Gas Code.
NOTE - Furnace must be adjusted to obtain a temperature
rise within the range(s) specied 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 electrical
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 ow arrangement, a damper (or other
means to control the ow of air) must adequately prevent
chilled air from entering the furnace (see gure 1). If the
damper is manually operated, it must be equipped to prevent operation of either the heating or the cooling.
Page 3
• The return air duct must be provided and sealed
to the furnace.
• Return air temperature range between 60°F (16°C)
and 80°F (27°C) must be maintained.
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 address:
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
operation down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The ML180DF furnace may be installed in alcoves, closets, attics, basements, garages, and utility rooms in the
downow position.
This furnace design has not been CSA International
certied for installation in mobile homes, recreational
vehicles, or outdoors.
Safety Information
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
operation of the unit with clogged or misplaced lters will
damage the unit.
ML180DF units may be used for heating of buildings or
structures under construction, if the following conditions
are met:
• The vent system must be permanently installed per
these installation instructions.
• A room thermostat must control the furnace. The
use of xed jumpers that will provide continuous
heating is not allowed.
• Air lters must be installed in the system and must
be maintained during construction.
• Air lters must be replaced upon construction com-
pletion.
• The input rate and temperature rise must be set per
the furnace rating plate.
• One hundred percent (100%) outdoor air must be
provided for combustion air requirements during
construction. Temporary ducting may supply 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 conned space with air
from outside.
• The furnace heat exchanger, components, duct
system, air lters and evaporator coils must be
thoroughly cleaned following nal construction
clean-up.
• All furnace operating conditions (including ignition,
input rate, temperature rise and venting) must be
veried 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
following general recommendations must be considered
when installing a ML180DF furnace:
• Place the furnace as close to the center of the air
distribution system as possible. The furnace should
also be located close to the chimney or vent termination point.
• Do not install the furnace where drafts might blow
directly into it. This could cause improper combustion and unsafe operation.
• Do not block the furnace combustion air openings
with clothing, boxes, doors, etc. Air is needed for
proper combustion and safe unit operation.
• When the furnace is installed in an attic or other
insulated space, keep insulation away from the fur-
nace.
NOTE - The Commonwealth of Massachusetts
stipulates these additional requirements:
• Gas furnaces shall be installed by a licensed
plumber or tter only.
• The gas cock must be “T handle” type.
• When a furnace is installed in an attic, the pas-
sageway to and service area surrounding the
equipment shall be oored.
Page 4
WARNING
This prodcut contains a chemical known to the State
of California to cause cancer, birth defects, or other
reproductive harm.
Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in sufcient
outdoor air for combustion. Inltration provided all the air
that was needed. In today’s homes, tight construction
practices make it necessary to bring in air from outside for
combustion. Take into account that exhaust fans, appli-
ance vents, chimneys, and replaces force additional air
that could be used for combustion out of the house. Unless outside air is brought into the house for combustion,
negative pressure (outside pressure is greater than inside
pressure) will build to the point that a downdraft can occur in the furnace vent pipe or chimney. As a result, combustion gases enter the living space creating a potentially
dangerous situation.
In the absence of local codes concerning air for combustion and ventilation, use the guidelines and procedures in
this section to install ML180DF furnaces to ensure efcient and safe operation. You must consider combustion
air needs and requirements for exhaust vents. A portion of
this information has been reprinted with permission from
the National Fuel Gas Code (ANSI-Z223.1). This reprint-
ed material is not the complete and ofcial position of the
ANSI on the referenced subject,
CAUTION
Do not install the furnace in a corrosive or contaminated
atmosphere. Meet all combustion and ventilation air
requirements, as well as all local codes.
All gas-red appliances require air for the combustion
process. If sufcient combustion air is not available, the
furnace or other appliances will operate inefciently and
unsafely. Enough air must be provided to meet the needs
of all fuel-burning appliances and appliances such as exhaust fans which force air out of the house. When replaces, 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.
Insufcient air causes incomplete combustion which can
result in carbon monoxide.
CAUTION
Insufcient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in rusting
and premature heat exchanger failure. Excessive
exposure to contaminated combustion air will result
in safety and performance related problems. Avoid
exposure to the following substances in the combustion
air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace components.
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is in-
stalled in an unconned or a conned space.
Unconned Space
An unconned space is an area such as a basement or
large equipment room with a volume greater than 50 cubic
feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the combined 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
unconned, it might be necessary to bring in outdoor air
for combustion if the structure does not provide enough air
by inltration. 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.
Conned Space
A conned space is an area with a volume less than 50
cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of
the combined input rating of all appliances installed in that
space. This denition includes furnace closets or small
equipment rooms.
Page 5
When the furnace is installed so that supply ducts carry
air circulated by the furnace to areas outside the space
containing the furnace, the return air must be handled by
ducts which are sealed to the furnace casing and which
terminate outside the space containing the furnace. This
is especially important when the furnace is mounted on
a platform in a conned 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 conned space either from inside the building or
from outside.
EQUIPMENT IN CONFINED
CHIMNEY
OR GAS
VENT
FURNACE
AIR FLOW
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
2
).
SPACE ALL AIR FROM INSIDE
WATER
HEATER
OPENINGS
(To Adjacent
Room)
FIGURE 2
Air from Inside
If the conned space that houses the furnace adjoins a
space categorized as unconned, 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 mm2) per 1,000 Btu (.29 kW) per hour of
total input rating of all gas-red equipment in the conned
space. Each opening must be at least 100 square inches
(64516 mm2). One opening shall be within 12 inches (305
mm) of the top of the enclosure and one opening within 12
inches (305 mm) of the bottom. See gure 2.
Air from Outside
If air from outside is brought in for combustion and ventilation, the conned space must have two permanent openings. 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 directly or by ducts with the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors or indirectly through vertical ducts. Each opening shall have a
minimum free area of 1 square inch (645 mm2) per 4,000
Btu (1.17 kW) per hour of total input rating of all equipment
in the enclosure. See gures 3 and 4. When communicating with the outdoors through horizontal ducts, each
opening shall have a minimum free area of 1 square inch
(645 mm2) per 2,000 Btu (.56 kW) per total input rating of
all equipment in the enclosure. See gure 5.
When ducts are used, they shall be of the same cross-sectional 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 covering is not known for calculating the size opening
required, it may be assumed that wood louvers will have
20 to 25 percent free area and metal louvers and grilles
will have 60 to 75 percent free area. Louvers and grilles
must be xed in the open position or interlocked with the
equipment so that they are opened automatically during
equipment operation.
Page 6
CHIMNEY OR
EQUIPMENT IN CONFINED SPACE
ment in the enclosure.
S
other equipment in the enclosure.
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)
AIR FLOW
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
ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
VENTILATION LOUVER
(Each end of attic)
OUTLET
AIR
INLET AIR
(Ends 12 in.
above bottom)
FURNACE
CHIMNEY
OR GAS
VENT
CONFINED SPACE
WATER
HEATER
OUTLET AIR
EQUIPMENT IN
ALL AIR FROM
OUTSIDE
AIR FLOW
NOTE-The inlet and outlet air openings shall each have a
free area of at least one square inch (645 mm
FIGURE 4
WATER
HEATER
2
) per 4,000
Page 7
AIR FLOW
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
INLET AIR
the total input rating of all equipment in the enclosure. If the
equipment room is located against an outside wall and the air
openings
ing shall have a free area of at least one square inch (645 mm
per 4,000 Btu (1.17 kW) per hour of the total input rating of all
FIGURE 5
2
)
Downow Installation
Downow unit installs in three ways: on non-combustible
ooring, on combustible ooring using a downow com-
bustible ooring base, or on a reverse-ow cooling cabinet. Do not drag the unit across the oor.
Installation on Non-Combustible Flooring (Figure 6)
1 - Cut oor opening keeping in mind clearances listed
on unit rating plate. Also keep in mind gas supply
connections, electrical supply, ue and air intake
connections and sufcient installation and servicing
clearances. See table 1 for correct oor 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.
SUPPLY AIR
OPENING
PLENUM
FIGURE 6
TABLE 1
NON-COMBUSTIBLE FLOOR OPENING SIZE
Cabinet
Width
A (14.5”)
B (17.5”) 16-3/4 413
Front to Rear Side to Side
in mm in mm
13-1/4 337
19-3/4 502
C (21”) 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.
Installation on Combustible Flooring (Figure 7)
1 - When unit is installed on a combustible oor,
a downow combustible ooring base must be
installed between the furnace and the oor. The
base must be ordered separately.
See table 2 for opening size to cut in oor.
CAUTION
The furnace and downow combustible ooring base
shall not be installed directly on carpeting, tile, or other
combustible material other than wood ooring.
SUPPLY AIR PLENUM
PROPERLY
SIZED FLOOR
OPENING
FIGURE 7
TABLE 2
COMBUSTIBLE FLOOR OPENING SIZE
Cabinet
Width
Front to Rear Side to Side
in mm in mm
A (14.5”)
B (17.5”) 18-3/4 476
22 569
C (21”) 22-3/4
2 - After opening is cut, set combustible ooring base
into opening.
3 - Check sealing strips on combustible ooring base to
make sure they are properly glued and positioned.
4 - Lower supply air plenum into downow combustible
ooring base until plenum anges 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 s adequate.
Installation on Cooling Cabinet (Figure 8)
1 - Refer to reverse-ow coil installation instructions for
correctly sized opening in oor and installation of
cabinet.
NOTE - Downow combustible ooring 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.
DOWNFLOW
COMBUSTIBLE
FLOORING BASE
15-3/4 400
578
Page 8
PROPERLY
Blower motor with three exible legs and one
SIZED FLOOR
OPENING
FIGURE 8
Return Air Opening -- Downow Units
COOLING COIL
PLENUM
Setting Equipment
WARNING
Do not install the furnace on its front, back or in the
horizontal position. See gure 12. Do not connect the
return air ducts to the back of the furnace. Doing so
will adversely affect the operation of the safety control
devices, which could result in personal injury or death.
Install the ML180DF gas furnace as shipped in the down-
ow position only. Do not install the furnace horizontally.
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.
The following steps should be taken when installing plenum:
1 - Bottom edge of plenum should be anged with a
hemmed edge (See gure 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
anges of furnace with sheet metal screws.
PLENUM
SIDE CABINET
HEMMED EDGE
Side View
NOTE - Units with 1/3HP and 1/2HP blower motors are
equipped with three exible legs and one shipping leg. See
gure 11. In some units with 1/3HP blower motor, the shipping leg is exible with rubber mounting grommets similar
to the other three mounting legs and require no modication. The rest of the units with 1/3HP and 1/2HP blower
motors (these blower motor housings will be tagged) have
a rigid shipping leg equipped with a shipping bolt and at
white plastic washer. The bolt and washer must be re-
moved before the furnace is placed into operation. After the bolt and washer have been removed, the rigid leg
will not touch the blower housing.
rigid shipping leg. Blower motor housings
will be tagged for shipping bolt removal
RIGID LEG
(Remove shipping bolt
and washer)
FIGURE 11
FIBERGLASS
SEALING STRIP
(Field Provided)
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 gure 10).
5 - Make certain that an adequate seal is made.
WARNING
The blower access panel must be securely in place when
the blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into living
space resulting in personal injury or death.
Page 9
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