Lennox ML193DF User Manual

INSTALLATION

 2010 Lennox Industries Inc.

Dallas, Texas, USA

INSTRUCTIONS
ML193DF

®

MERIT
DOWNFLOW AIR DISCHARGE

506475−01
01/2011
Supersedes 10/2010

SERIES GAS FURNACE

Litho U.S.A.

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

DOWNFLOW

AIR FLOW

Table of Contents

Unit Dimensions 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ML193DF Parts Arrangement 3. . . . . . . . . . . . . . . . . . . . .

ML193DF Gas Furnace 4. . . . . . . . . . . . . . . . . . . . . . . . . .

Shipping and Packing List 4. . . . . . . . . . . . . . . . . . . . . . . .

Safety Information 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Use of Furnace as a Construction Heater 5. . . . . . . . . . .

General 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Combustion, Dilution and Ventilation Air 6. . . . . . . . . . . .

Setting Equipment 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Filters 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Duct System 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Pipe and Fittings Specifications 12. . . . . . . . . . . . . . . . . . .

Joint Cementing Procedure 14. . . . . . . . . . . . . . . . . . . . . .

Venting Practices 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.

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.

Vent Piping Guidelines 15. . . . . . . . . . . . . . . . . . . . . . . . . .

Gas Piping 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electrical 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Unit Start Up 36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gas Pressure Measurement 38. . . . . . . . . . . . . . . . . . . . .

Proper Combustion 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

High Altitude 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Testing Non Direct Appliances for Proper Air 39. . . . . . .

Other Unit Adjustments 40. . . . . . . . . . . . . . . . . . . . . . . . . .

Blower Motor Performance 41. . . . . . . . . . . . . . . . . . . . . . .

Service 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Planned Service 44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Integrated Control Diagnostic Codes 44. . . . . . . . . . . . . .

Troubleshooting 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Repair Parts List 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Start Up Checklist 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

01/11

*2P0111*

Page 1

506475−01

*P506475-01*

ML193DF Unit Dimensions − inches (mm)

COMBUSTION

AIR INTAKE

EXHAUST AIR

OUTLET

2−1/16 (52)

5

(127)

2−1/4

(57)

9/16

(14)

RETURN AIR

B

OPENING

9/16
(14)

TOP VIEW

3/4

(19)

AIR

C

A

B

FLOW

Supply

Air

9/16
(14)

3/4

(19)

33

(838)

1 (25)

Front Panel

2 (51)

Either Side

GAS PIPING INLET

(Either Side)

9−1/8 (232) Right
6−9/16 (167) Left

27−3/4

(705)

19−7/16

(494)

ELECTRICAL INLET

(Either Side)

CONDENSATE

TRAP CONNECTION

(Either Side)

6−1/2 (165)
Either Side

19−1/4

(489)

Supply

Air

9/16
(14)

3/4

(19)

ML193DF

Model No.

04536B
07036B

09048C
11060C

FRONT VIEW SIDE VIEW

A B C

in. mm in. mm in. mm

17−1/2 446 16−3/8 416 16 406

21 533 19−7/8 504 19−1/2 495

Page 2

ML193DF Parts Arrangement

CONTROL BOX

(Includes integrated control,

transformer and door switch)

BLOWER MOTOR

(hidden)

BLOWER

ACCESS

PANEL

BAG ASSEMBLY

BURNER
ACCESS

PANEL

COMBUSTION
AIR INDUCER

BLOWER DECK

PRIMARY LIMIT

COLD END HEADER BOX

HEAT EXCHANGER

GAS VALVE

BURNER BOX ASSEMBLY

(includes sensor, rollout switches and ignitor)

FIGURE 1

Page 3

ML193DF Gas Furnace

The ML193DF Category IV gas furnace is shipped ready
for installation in the downflow position.

The furnace is equipped for installation in natural gas ap­plications. A conversion kit (ordered separately) is re­quired for use in propane/LP gas applications.

The ML193DF can be installed as a Direct Vent or Non−
Direct Vent gas central furnace.

NOTE − In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors. In
Non−Direct Vent installations, combustion air is taken from
indoors and flue gases are discharged outdoors. See figure
2 for applications involving roof termination.

Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.

The following items may also be ordered separately:
1 − Thermostat
1 − Propane/LP changeover kit

Safety Information

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.

DIRECT VENT INSTALLATION NON−DIRECT VENT

EXHAUST
COMBUSTION
AIR INTAKE
OUTSIDE OF
HOUSE

ML193DF

OUTLET

INSTALLATION

ML193DF

EXHAUST
OUTLET

COMBUSTION

AIR INTAKE INSIDE

OF HOUSE

FIGURE 2

Shipping and Packing List

Package 1 of 1 contains

1 − Assembled ML193DF unit
1 − Bag assembly containing the following:

3 − Wire nuts
1 − Snap bushing
1 − Snap plug
1 − Wire tie
1 − Condensate trap
1 − Condensate trap cap
1 − Condensate trap clamp
1 − 2" diameter Air intake screen

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.

CAUTION

As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.

Use only the type of gas approved for use with this furnace.
Refer to unit nameplate.
ML193DF units are CSA International certified to ANSI
Z21.47 and CSA 2.3 standards.

Building Codes

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/NFPA 54). The National Fuel Gas Code is
available from the following address:

American National Standards Institute, Inc.
11 West 42nd Street

New York, NY 10036
In Canada, installation must conform with current National
Standard of Canada CSA-B149 Natural Gas and Propane

Installation Codes, local plumbing or waste water codes
and other applicable local codes.
In order to ensure proper unit operation in non−direct vent
applications, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code
or CSA-B149 standard.

Locations and Clearances

This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
nameplate and in the table in figure 11. Accessibility and ser­vice clearances must take precedence over fire protection
clearances.

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 atmosphere, the furnace must be installed accord­ing to recommended good practice requirements and cur­rent National Fuel Gas Code or CSA B149 standards.

Page 4

NOTE − Furnace must be adjusted to obtain a temperature
rise within the range specified on the unit nameplate. Failure
to do so may cause erratic limit operation and premature heat
exchanger failure.

This ML193DF furnace must be installed so that its electri­cal components are protected from water.

Installation in Combination with a Cooling Coil

When this furnace is used with cooling units (figure 3), it
shall be installed in parallel with, or on the upstream side of,
cooling units to avoid condensation in the heating compart­ment. With a parallel flow arrangement, a damper (or other
means to control the flow of air) must adequately prevent
chilled air from entering the furnace. If the damper is manu­ally 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. 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

In Canada, all electrical wiring and grounding for the unit
must be installed according to the current regulations of the
Canadian Electrical Code Part I (CSA Standard C22.1)
and/or local codes.

Heating Unit Installed Parallell to Air Handler Unit

GAS UNIT

Dampers

(open during heating

operation only)

AIR HANDLER

Dampers

(open during cooling

operation only)

FIGURE 3

NOTE − This furnace is designed for a minimum continu­ous return air temperature of 60°F (16°C) or an intermit-

tent 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 ML193DF furnace may be installed in alcoves, closets,
attics, basements, garages, utility rooms and crawl
spaces.

This furnace design has not been CSA certified for installa­tion in mobile homes, recreational vehicles, or outdoors.

Never use an open flame to test for gas leaks. Check all
connections using a commercially available soap solution
made specifically for leak detection.

Use of Furnace as Construction Heater

Lennox does not recommend the use of ML193DF 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 filters will dam­age the unit.

ML193DF 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
fixed jumpers that will provide continuous heating is not
allowed.

• 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.

• Air filters must be installed in the system and must be
maintained during construction.

• Air filters must be replaced upon construction comple­tion.

• 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
confined space with air from outside.

• The furnace heat exchanger, components, duct system,
air filters and evaporator coils must be thoroughly
cleaned following final construction clean−up.

• All furnace operating conditions (including ignition, in­put rate, temperature rise and venting) must be verified
according to these installation instructions.

Page 5

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 ML193DF 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.

• When the furnace is installed in non−direct vent applica­tions, do not install the furnace where drafts might blow
directly into it. This could cause improper combustion
and unsafe operation.

• When the furnace is installed in non−direct vent applica­tions, do not block the furnace combustion air opening
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 furnace.

• When the furnace is installed in an unconditioned
space, consider provisions required to prevent freezing
of condensate drain system.

CAUTION

ML193DF unit should not be installed in areas nor­mally subject to freezing temperatures.

WARNING

Product contains fiberglass wool.

Disturbing the insulation in this product during
installation, maintenance, or repair will expose you
to fiberglass wool. Breathing this may cause lung
cancer. (Fiberglass wool is known to the State of Cal­ifornia to cause cancer.)

Fiberglass wool may also cause respiratory, skin,
and eye irritation.

To reduce exposure to this substance or for further
information, consult material safety data sheets
available from address shown below, or contact your
supervisor.

Lennox Industries Inc.
P.O. Box 799900
Dallas, TX 75379−9900

WARNING

Insufficient 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 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
practices make it necessary to bring in air from outside
for combustion. Take into account that exhaust fans, ap­pliance vents, chimneys, and fireplaces force additional
air that could be used for combustion out of the house.
Unless outside air is brought into the house for combus­tion, negative pressure (outside pressure is greater than
inside pressure) will build to the point that a downdraft
can occur in the furnace vent pipe or chimney. As a result,
combustion gases enter the living space creating a po­tentially dangerous situation.

In the absence of local codes concerning air for combus−
tion and ventilation, use the guidelines and procedures in
this section to install ML193DF furnaces to ensure effi­cient and safe operation. You must consider combustion
air needs and requirements for exhaust vents and gas
pip−ing. A portion of this information has been reprinted
with permission from the National Fuel Gas Code (ANSI−
Z223.1/NFPA 54). This reprinted material is not the com­plete and official position of the ANSI on the referenced
subject, which is represented only by the standard in its
entirety.

Combustion, Dilution & Ventilation Air

If the ML193DF is installed as a Non−Direct Vent Fur­nace, follow the guidelines in this section.

NOTE − In Non−Direct Vent installations, combustion air
is taken from indoors and flue gases are discharged out−
doors.

In Canada, refer to the CSA B149 installation codes.

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.

Page 6

All gas-fired appliances require air for the combustion pro­cess. If sufficient combustion air is not available, the fur­nace or other appliance will operate inefficiently 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 fireplaces, ex­haust fans, or clothes dryers are used at the same time as
the furnace, much more air is required to ensure proper
combustion and to prevent a downdraft. Insufficient air
causes incomplete combustion which can result in carbon
monoxide.

In addition to providing combustion air, fresh outdoor air di­lutes contaminants in the indoor air. These 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 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 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 un­confined, 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 cubic
feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the com−
bined 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 terminate
outside the space containing the furnace. This is especially
important when the furnace is mounted on a platform in a
confined space such as a closet or small equipment room.
Even a small leak around the base of the unit at the platform
or at the return air duct connection can cause a potentially

dangerous negative pressure condition. Air for combustion
and ventilation can be brought into the confined space ei­ther from inside the building or from outside.

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 mm2) 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 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 figure 4.

EQUIPMENT IN CONFINED SPACE − ALL AIR FROM INSIDE

ROOF TERMINATED

EXHAUST PIPE

OPENINGS

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

NOTE − Each opening shall have a free area of at least one square
inch per 1,000 Btu (645mm
rating of all equipment in the enclosure, but not less than 100 square
inches (64516mm.

2

per .29kW) per hour of the total input

2).

(To Adjacent

Unconfined

Space)

FIGURE 4

Air from Outside

If air from outside is brought in for combustion and ventila­tion, the confined space shall be provided with two perma­nent openings. One opening shall be within 12" (305mm)
of the top of the enclosure and one within 12" (305mm) 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 per 4,000 Btu (645mm
per 1.17kW) per hour of total input rating of all equipment
in the enclosure. When communicating with the outdoors
through horizontal ducts, each opening shall have a mini­mum free area of 1 square inch per 2,000 Btu (645mm
per .59kW) per total input rating of all equipment in the en­closure (See figure 5).

2

2

Page 7

EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE

(Inlet Air from Crawl Space and Outlet Air to Ventilated Attic)

VENTILATION LOUVERS

OUTLET

AIR

(Each end of attic)

ROOF TERMINATED

EXHAUST PIPE

EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE

(All Air Through Ventilated Attic)

ROOF TERMINATED

EXHAUST PIPE

OUTLET

AIR

VENTILATION LOUVERS

(Each end of attic)

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

INLET

AIR

NOTE−The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm

VENTILATION

LOUVERS

(For unheated

crawl space)

2

per 1.17kW) per

hour of the total input rating of all equipment in the enclosure.

FIGURE 5

If air from outside is brought in for combustion and ventila­tion, the confined 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 figures 5 and 6. 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 figure 7.

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 fixed in the open position or interlocked with the
equipment so that they are opened automatically during
equipment operation.

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

NOTE−The inlet and outlet air openings shall each have a free area of
at least one square inch per 4,000 Btu (645mm

INLET AIR

(Ends 12" above

bottom)

2

per 1.17kW) per

hour of the total input rating of all equipment in the enclosure.

FIGURE 6

EQUIPMENT IN CONFINED SPACE −

ALL AIR FROM OUTSIDE

ROOF TERMINATED

EXHAUST PIPE

OUTLET AIR

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

NOTE−Each air duct opening shall have a free area of at least one
square inch per 2,000 Btu (645mm

2

per .59kW) per hour of the total

INLET AIR

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 opening shall have a free area
of at least 1 square inch per 4,000 Btu (645mm

2

per 1.17kW) per

hour of the total input rating of all other equipment in the enclosure.

FIGURE 7

Shipping Bolt Removal

NOTE − The ML193DF09048C is equipped with a 1/2 hp
blower motor which has three flexible legs and one rigid
leg. 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). See figure 8.

The bolt and washer must be removed before the fur­nace is placed into operation. After the bolt and washer

have been removed, the rigid leg will not touch the blower
housing.

Page 8

ML193DF09048C BLOWER MOTOR

remove shipping bolt and washer

RIGID LEG

FIGURE 8

Installation − Setting Equipment

Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or al­cove installations are shown in figure 11.

WARNING

Blower access panel must be securely in place when
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into
living space resulting in personal injury or death.

WARNING

Do not install the furnace on its front, back or in the
horizontal position. See figure 10. 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.

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,
condensate trap and drain connections, and installation
and service clearances [24 inches (610 mm) at unit
front]. The unit must be level from side to side. Unit may

be positioned from level to 1/2" toward the front to aid in
draining. See figure 9.

SETTING EQUIPMENT

AIR FLOW

FRONT VIEW SIDE VIEW

Unit must be level side−to−side. Unit may be positioned
from level to 1/2" toward the front to aid in draining.

AIR FLOW

FIGURE 9

AIR FLOW

SIDE VIEW

1/2"

max.

Front

Back

NOTE − Do not install the furnace on its front, back or in the horizontal position

FIGURE 10

Page 9

Horizontal

WARNING

Improper installation of the furnace can result in per­sonal injury or death. Combustion and flue products
must never be allowed to enter the return air system
or air in the living space. Use sheet metal screws and
joint tape to seal return air system to furnace.
In platform installations with furnace return, the fur­nace should be sealed airtight to the return air ple­num. 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. Al­low absolutely no sagging, cracks, gaps, etc.
For no reason should return and supply air duct sys­tems ever be connected to or from other heating de­vices such as a fireplace or stove, etc. Fire, explo­sion, carbon monoxide poisoning, personal injury
and/or property damage could result.

The unit may be installed three ways in downflow applica­tions: on non−combustible flooring, on combustible flooring
using an additive base, or on a reverse−flow cooling coil
cabinet. Do not drag the unit across the floor in the

downflow position. Floor and furnace flange damage
will result.
Refer to figure 11 for clearances in downflow applica-

tions.

Installation on Non−Combustible Flooring Figure 12

1 − Cut floor opening keeping in mind clearances listed on

unit rating plate. Also keep in mind gas supply connec­tions, 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.

TABLE 1

NON−COMBUSTIBLE FLOOR OPENING SIZE

Cabinet Width

B Cabinet (17.5") 19 − 3/4 502 16 − 5/8 422

C Cabinet (21") 19 − 3/4 502 20−1/8 511

NOTE − Floor opening dimensions listed are 1/4 inch (6 mm) larger than
the unit opening. See dimension drawing on page 2.

Front to Rear Side to Side

in. mm in. mm

Downflow Application Installation Clearances

Top

Left Side Right Side

Bottom

Top 0

*Front 0

Back 0

Sides 0†

Vent 0

Floor NC‡

*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
†Allow proper clearances to accommodate condensate trap and
vent pipe installation.
‡The furnace may be installed on a combustible wood floor if an op­tional additive base is installed between the furnace and the com­bustible floor.

FIGURE 11

FURNACE

PROPERLY

SIZED FLOOR

OPENING

SUPPLY AIR

PLENUM

FIGURE 12

Installation on Combustible Flooring Figure 13

1 − When unit is installed on a combustible floor, a down-

flow combustible flooring base must be installed be­tween the furnace and the floor. The base must be or­dered separately. See table 2 for opening size to cut in
floor.

CAUTION

The furnace and combustible flooring base shall not
be installed directly on carpeting, tile, or other com­bustible material other than wood flooring.

Page 10

TABLE 2

COMBUSTIBLE FLOORING BASE OPENING SIZE

Cabinet

Width

B Cabinet

(17.5")

Catalog
Number

11M60

Front to Rear Side to Side

in. mm in. mm

22 559 18 − 3/4 476

FURNACE

C Cabinet

(21")

FURNACE

PROPERLY

SIZED FLOOR

OPENING

11M61

22 559 22 − 3/4 578

SUPPLY AIR

PLENUM

COMBUSTIBLE
FLOORING BASE

FIGURE 13

2 − After opening is cut, set the combustible flooring base

into opening.

3 − Check fiberglass strips on the combustible flooring

base to make sure they are properly glued and posi­tioned.

4 − Lower supply air plenum into the combustible flooring

base until plenum flanges seal against fiberglass
strips.

NOTE − Be careful not to damage fiberglass 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 Coil Cabinet Figure 14

NOTE − Downflow combustible flooring kit is not used..

1 − Refer to reverse−flow coil installation instructions for

correctly sized opening in floor and installation of cabi­net.

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.

COOLING COIL

PROPERLY

SIZED FLOOR

OPENING

PLENUM

FIGURE 14

Return Air Opening −− Downflow Units

Return air may be brought in only through the top opening
of a furnace installed in the downflow position. The follow­ing steps should be taken when installing plenum:

1 − Bottom edge of plenum should be flanged with a

hemmed edge (See figure 15 or 16).

2 − Sealing strips should be used to ensure an airtight seal

between the cabinet and the plenum.

3 − In all cases, plenum should be secured to top of fur-

nace using sheet metal screws.

4 − Make certain that an adequate seal is made.

PLENUM

(Field Provided)

SEALING STRIP
(Field Provided)

SECURE FROM

OUTSIDE CABINET

CABINET

SIDE PANEL

Side View

FIGURE 15

PLENUM

(Field Provided)

SECURE FROM

INSIDE CABINET

Side View

SEALING STRIP

(Field Provided)

CABINET

SIDE PANEL

FIGURE 16

Page 11

Filters

This unit is not equipped with a filter or rack. A field−pro­vided filter is required for the unit to operate properly. Table
3 lists recommended filter size.
A filter must be in place whenever the unit is operating.

TABLE 3

Furnace

Cabinet Width

17−1/2"

21"

Filter Size

16 x 25 x 1 (1)

Pipe & Fittings Specifications

All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the Ameri­can Society for Testing and Materials (ANSI/ASTM) stan­dards. The solvent shall be free flowing and contain no
lumps, undissolved particles or any foreign matter that ad­versely affects the joint strength or chemical resistance of
the cement. The cement shall show no gelation, stratifica­tion, or separation that cannot be removed by stirring. Re­fer to the table 4 below for approved piping and fitting ma­terials.

Duct System

Use industry-approved standards to size and install the
supply and return air duct system. Refer to ACCA Manual
D. This will result in a quiet and low-static system that has
uniform air distribution.

NOTE − This furnace is not certified for operation in heating
mode (indoor blower operating at selected heating speed)
with an external static pressure which exceeds 0.5 inches
w.c. Operation at these conditions may result in improper
limit operation.

Supply Air Plenum

If the furnace is installed without a cooling coil, a removable
access panel should be installed in the supply air duct. The
access panel should be large enough to permit inspection
of the heat exchanger. The furnace access panel must al­ways be in place when the furnace is operating and it must
not allow leaks into the supply air duct system.

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 de­vice (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
reverse flow of the flue gas may result in incomplete com­bustion and the formation of carbon monoxide gas. This
raw gas or toxic fumes might then be distributed through­out the house by the furnace duct system.

Use fiberglass sealing strips, caulking, or equivalent seal­ing 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.

CAUTION

Solvent cements for plastic pipe are flammable liq­uids and should be kept away from all sources of
ignition. Do not use excessive amounts of solvent
cement when making joints. Good ventilation should
be maintained to reduce fire hazard and to minimize
breathing of solvent vapors. Avoid contact of cement
with skin and eyes.

PIPING AND FITTINGS SPECIFICATIONS

Schedule 40 PVC (Pipe) D1785
Schedule 40 PVC (Cellular Core Pipe) F891

Schedule 40 PVC (Fittings) D2466

Schedule 40 CPVC (Pipe) F441

Schedule 40 CPVC (Fittings) F438

SDR−21 PVC or SDR−26 PVC (Pipe) D2241

SDR−21 CPVC or SDR−26 CPVC (Pipe) F442

Schedule 40 ABS Cellular Core DWV (Pipe) F628

Schedule 40 ABS (Pipe) D1527

Schedule 40 ABS (Fittings) D2468

ABS−DWV (Drain Waste & Vent)
(Pipe & Fittings)

PVC−DWV (Drain Waste & Vent)
Pipe & Fittings)

PRIMER & SOLVENT CEMENT

PVC & CPVC Primer F656
PVC Solvent Cement D2564

CPVC Solvent Cement F493

ABS Solvent Cement D2235

PVC/CPVC/ABS All Purpose Cement For
Fittings & Pipe of the same material

ABS to PVC or CPVC Transition Solvent
Cement

CANADA PIPE & FITTING & SOLVENT

CEMENT

PVC & CPVC Pipe and Fittings
PVC & CPVC Solvent Cement

ABS to PVC or CPVC Transition Cement

TABLE 4

D2661

D2665

ASTM

SPECIFICATION

D2564, D2235, F493

D3138

MARKING

ULCS636

Page 12

IMPORTANT

ML193DF exhaust and intake connections are made
of PVC. Use PVC primer and solvent cement when
using PVC vent pipe. When using ABS vent pipe, use
transitional solvent cement to make connections to
the PVC fittings in the unit.

Use PVC primer and solvent cement or ABS solvent cement
meeting ASTM specifications, refer to Table 4. As an alter­nate, use all purpose cement, to bond ABS, PVC, or CPVC
pipe when using fittings and pipe made of the same materi­als. Use transition solvent cement when bonding ABS to ei­ther PVC or CPVC.

TABLE 5

ML193

UNIT

OUTDOOR TERMINATION KITS USAGE

STANDARD CONCENTRIC

Outdoor

VENT

PIPE

DIA.
(in.)

2 YES YES YES* YES YES YES

Exhaust

Accelerator

(Dia. X

Length)

1−1/2" X 12" 2" X 12"

Outdoor
Exhaust

Accelerator

(Dia. X

Length)

2" Wall Plate

Kit

22G44

or 30G28

Low temperature solvent cement is recommended during
cooler weather. Metal or plastic strapping may be used for
vent pipe hangers. Uniformly apply a liberal coat of PVC
primer for PVC or use a clean dry cloth for ABS to clean in­side socket surface of fitting and male end of pipe to depth
of fitting socket.

Canadian Applications Only − Pipe, fittings, primer
and solvent cement used to vent (exhaust) this ap­pliance must be certified to ULC S636 and supplied by a
single manufacturer as part of an approved vent (ex­haust) system. In addition, the first three feet of vent
pipe from the furnace flue collar must be accessible for
inspection.

3" Wall Plate

Kit

44J40

or 81J20

2" Wall

Ring Kit

15F74 51W11**

Flush­Mount

Kit

1−1/2"

Concentric

Kit

71M80

or

44W92

2"

Concentric

Kit

69M29

or

44W92

3"

Concentric

Kit

60L46

or 44W93

045

070

090

110 3 YES YES YES YES YES YES

*Requires field−provided and installed 1−1/2" exhaust accelerator.
** Kit 51W11 is provided with a 1−1/2" accelerator which must be used for all ML193DF−045, −070 and −090 installations.
 Termination kits 44W92, 44W93, 30G28 and 81J20 approved for use in Canadian installations to meet CSAB149.
 The 44W92 Concentric kit is provided with a 1−1/2" accelerator which must be installed on the exhaust outlet when this kit is used with the ML193DF045P36B and

ML193DF070P36B

2−1/2 YES YES YES* YES YES YES

3 YES YES YES* YES YES YES

2 YES YES YES* YES YES YES

2−1/2 YES YES YES* YES YES YES

3 YES YES YES* YES YES YES

2 YES YES YES YES YES YES

2−1/2 YES YES YES YES YES YES

3 YES YES YES YES YES YES

furnaces.

Page 13

Joint Cementing Procedure

Venting Practices

All cementing of joints should be done according to the
specifications outlined in ASTM D 2855.

NOTE − A sheet metal screw may be used to secure
the intake pipe to the connector, if desired. Use a drill
or self tapping screw to make a pilot hole.

DANGER

DANGER OF EXPLOSION!

Fumes from PVC glue may ignite during system
check. Allow fumes to dissipate for at least 5 minutes
before placing unit into operation.

1 − Measure and cut vent pipe to desired length.

2 − Debur and chamfer end of pipe, removing any ridges

or rough edges. If end is not chamfered, edge of pipe
may remove cement from fitting socket and result in a
leaking joint.

3 − Clean and dry surfaces to be joined.

4 − Test fit joint and mark depth of fitting on outside of pipe.

5 − Uniformly apply a liberal coat of PVC primer for PVC or

use a clean dry cloth for ABS to clean inside socket
surface of fitting and male end of pipe to depth of fitting
socket.

6 − Promptly apply solvent cement to end of pipe and in-

side socket surface of fitting. Cement should be ap­plied lightly but uniformly to inside of socket. Take
care to keep excess cement out of socket. Apply sec­ond coat to end of pipe.

NOTE − Time is critical at this stage. Do not allow prim­er to dry before applying cement.

7 − Immediately after applying last coat of cement to pipe,

and while both inside socket surface and end of pipe
are wet with cement, forcefully insert end of pipe into
socket until it bottoms out. Turn PVC pipe 1/4 turn dur­ing assembly (but not after pipe is fully inserted) to dis­tribute cement evenly. DO NOT turn ABS or cellular
core pipe.

NOTE − Assembly should be completed within 20 sec­onds after last application of cement. Hammer blows
should not be used when inserting pipe.

8 − After assembly, wipe excess cement from pipe at end

of fitting socket. A properly made joint will show a
bead around its entire perimeter. Any gaps may indi­cate an improper assembly due to insufficient sol­vent.

9 − Handle joints carefully until completely set.

Piping Suspension Guidelines

SCHEDULE 40

PVC − 5’

all other pipe* − 3’

* See table 4 for allowable pipe.

NOTE − Isolate piping at the point where it exits the outside wall or
roof in order to prevent transmission of vibration to the structure.

Wall Thickness Guidelines

24" maximum
3/4" minimum

inside outside

Wall

FIGURE 17

REPLACING FURNACE THAT

CHIMNEY

OR GAS

VENT

(Check sizing

for water

heater only)

FURNACE

(Replaced

by ML193)

If an ML193DF furnace replaces a furnace which was com­monly vented with another gas appliance, the size of the ex­isting vent pipe for that gas appliance must be checked.
Without the heat of the original furnace flue products, the
existing vent pipe is probably oversized for the single water
heater or other appliance. The vent should be checked for
proper draw with the remaining appliance.

WAS PART OF A COMMON

VENT SYSTEM

WATER

HEATER

OPENINGS

(To Adjacent

Room)

FIGURE 18

1 − In areas where piping penetrates joists or interior

walls, hole must be large enough to allow clearance on
all sides of pipe through center of hole using a hanger.

Page 14

2 − When furnace is installed in a residence where unit is

shut down for an extended period of time, such as a
vacation home, make provisions for draining conden­sate collection trap and lines.

Exhaust Piping (Figures 20 and 21)

Route piping to outside of structure. Continue with installa­tion following instructions given in piping termination sec­tion.

Use the following steps to correctly size vent pipe diameter.

045, 070,

1

Furnace capacity?

090, 110
or 135 btuh

CAUTION

Do not discharge exhaust into an existing stack or
stack that also serves another gas appliance. If verti­cal discharge through an existing unused stack is re­quired, insert PVC pipe inside the stack until the end
is even with the top or outlet end of the metal stack.

CAUTION

The exhaust vent pipe operates under positive pres­sure and must be completely sealed to prevent leak­age of combustion products into the living space.

Vent Piping Guidelines

The ML193DF can be installed as either a Non−Direct
Vent or a Direct Vent gas central furnace.

NOTE − In Non-Direct Vent installations, combustion air is
taken from indoors and flue gases are discharged outdoors.
In Direct Vent installations, combustion air is taken from out­doors and flue gases are discharged outdoors.

Intake and exhaust pipe sizing −− Size pipe according to

tables 6 and 7. Table 6 lists the minimum vent pipe lengths
permitted. Table 7 lists the maximum pipe lengths per-
mitted.

MINIMUM VENT PIPE LENGTHS

ML193DF

MODEL

045, 070, 090, 110

*Any approved termination may be added to the minimum length listed.

Regardless of the diameter of pipe used, the standard roof
and wall terminations described in section Exhaust Piping
Terminations should be used. Exhaust vent termination
pipe is sized to optimize the velocity of the exhaust gas as
it exits the termination. Refer to table 8.

In some applications which permit the use of several differ­ent sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox’ Application Department for assis­tance in sizing vent pipe in these applications.

TABLE 6

MIN. VENT LENGTH*

15 ft. or

5 ft plus 2 elbows or

10 ft plus 1 elbow

Standard or

Which termination?

2

3

4

5

6

7

NOTE − It is acceptable to use any pipe size which fits within
the guidelines allowed in table 7.

NOTE −
toward unit. A minimum of 1/4" (6mm) drop for each 12"
(305mm) of horizontal run is mandatory for drainage.

Which needs
most elbows?

How many?

Desired pipe size?

What is the altitude?

Use table 7 to find
max intake or exhaust
pipe length.

FIGURE 19

All horizontal runs of exhaust pipe must slope back

Concentric?
See table 5

Intake or
exhaust

2", 2−1/2"
or 3"

IMPORTANT

Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze−ups
and may block the terminations.

Page 15

NOTE − Exhaust pipe MUST be glued to furnace exhaust
fittings.

NOTE − Exhaust piping should be checked carefully to
make sure there are no sags or low spots.

Maximum Allowable Intake or Exhaust Vent Length in Feet

TABLE 7

*Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be same pipe size.

Standard Termination at Elevation 0 − 10,000 ft.

Number

Of 90°

Elbows

Used

1 61 46 24

2 56 41 19 95 75 38 122 122 103 103

3 51 36 14 90 70 33 11 7 117 98 98

4 46 31

5 41 26 80 60 23 107 107 88 88

6 36 21 75 55 18 102 102 83 83

7 31 16 70 50 13 97 97 78 78

8 26 11 65 45

9 21

10 16 55 35 82 82 63 63

Number

Of 90°

Elbows

Used

1 53 38 22

2 48 33 17 85 65 34 106 106 99 99

3 43 28 12 80 60 29 101 101 94 94

4 38 23

5 33 18 70 50 19 91 91 84 84

6 28 13 65 45 14 86 86 79 79

7 23

8 18 55 35 76 76 69 69

9 13 50 30 71 71 64 64

10 n/a 45 25 66 66 59 59

045 070 090 110 045 070 090 110 045 070 090 110

045 070 090 110 045 070 090 110 045 070 090 110

2" Pipe 2−1/2" Pipe 3" Pipe

Model Model Model

100 80 43

85 65 28 11 2 112 93 93

n/a

n/a

n/a

Concentric Termination Elevation 0 − 10,000 ft.

2" Pipe 2−1/2" Pipe 3" Pipe

Model Model Model

n/a

n/a

n/a

60 40 87 87 68 68

90 70 39

75 55 24 96 96 89 89

60 40

n/a

n/a

n/a

n/a

127 127 108 108

92 92 73 73

111 111 104 104

81 81 74 74

Page 16