Lennox ML195UH045XP24B, ML195UH090XP36C, ML195UH045XP36B, ML195UH070XP36B, ML195UH090XP48C Installation Instructions Manual

Page 1

07/11

*2P0711*

506723−01

*P506723-01*

E 2011 Lennox Industries Inc.

Dallas, Texas, USA

AIR FLOW

UPFLOW

AIR FLOW

AIR FLOW

HORIZONTAL RIGHT

HORIZONTAL LEFT

INSTALLATION
INSTRUCTIONS
ML195UH

MERIT

®

SERIES GAS FURNACE

UPFLOW / HORIZONTAL AIR DISCHARGE

506723−01
07/2011
Supersedes 506533−01

THIS MANUAL MUST BE LEFT WITH THE

HOMEOWNER FOR FUTURE REFERENCE

This is a safety alert symbol and should never be ignored.
When you see this symbol on labels or in manuals, be alert
to the potential for personal injury or death.

CAUTION

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.

Table of Contents

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

ML195UH Parts Arrangement 3. . . . . . . . . . . . . . . . . . . . .

ML195UH Gas Furnace 4. . . . . . . . . . . . . . . . . . . . . . . . . .

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

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

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

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

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

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

Filters 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Duct System 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Pipe and Fittings Specifications 13. . . . . . . . . . . . . . . . . . .

Joint Cementing Procedure 15. . . . . . . . . . . . . . . . . . . . . . .

Venting Practices 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vent Piping Guidelines 17. . . . . . . . . . . . . . . . . . . . . . . . . . .

Gas Piping 34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electrical 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Unit Start Up 40. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Gas Pressure Measurement 42. . . . . . . . . . . . . . . . . . . . . .

Proper Combustion 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

High Altitude 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other Unit Adjustments 44. . . . . . . . . . . . . . . . . . . . . . . . . .

Blower Motor Performance 45. . . . . . . . . . . . . . . . . . . . . . .

Service 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Planned Service 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Integrated Control Diagnostic Codes 49. . . . . . . . . . . . . . .

Troubleshooting 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Repair Parts List 53. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Start Up Checklist 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Litho U.S.A.

Page 2

ML195UH Unit Dimensions − inches (mm)

6−9/16 (167)

Left

9 (229)

Right

23

(584)

(19)

3/4

(19)

1

Bottom Return

Air Opening

GAS PIPING INLET

(Either Side)

Side Return
Air Opening
(Either Side)

1

Bottom Return

Air Opening

EXHAUST AIR

OUTLET

ELECTRICAL

INLET

(Either Side)

SUPPLY AIR

OPENING

FRONT VIEW

SIDE VIEW

TOP VIEW

A

B

9/16 (14)

C

3/4

27−3/4

(705)

19−7/16

(494)

23−1/2

(597)

1−1/2

(38)

6−1/2 (165)
(Either Side)

33

(838)

3−3/8

(86)

1−15/16 (49)

14

(356)

9/16

(14)

12−5/8 (321)
(Either Side)

2

OPTIONAL

SIDE RETURN

AIR FILTER KIT

(Either Side)

16

(406)

14−3/4

(375)

2

OPTIONAL

SIDE RETURN

AIR FILTER KIT

(Either Side)

5/8

(16)

1

3−1/4

(83)

23−3/4

(603)

25

(635)

D

1 (25)

Front Panel

COMBUSTION

AIR INTAKE

2 (51)
(Either Side)

2 (51)

CONDENSATE
TRAP CONNECTION
(Either Side)

2−7/8

(73)

AIR FLOW

2

Optional External Side Return Air Filter Kit is not for use

with the optional Return Air Base.

1. Single side return air with transition, to accommodate
20 x 25 x 1 in. (508 x 635 x 25 mm) cleanable air

filter. Required to maintain proper air velocity.

2. Single side return air with optional Return Air Base

3. Bottom return air.

4. Return air from both sides.

5. Bottom and

one side return air.

See Blower Performance

tables for additional information.

1

NOTE − 60C size units that require air volumes

1800 cfm or over (850 L/s) must have one of the
following

mm in.

ABCD

in. mm in. mm in. mm

17−1/2 446 16−3/8 416 16 406 7−5/8 194

21 533 19−7/8 505 19−1/2 495 9−3/8 238

24−1/2 622 23−3/8 594 23 584 11−1/8 283

ML195UH045XP24B
ML195UH045XP36B
ML195UH070XP36B

ML195UH090XP36C
ML195UH090XP48C
ML195UH110XP48C
ML195UH110XP60C

ML195UH135XP60D

ML195UH Model

Page 3

ML195UH Parts Arrangement

ML195UH PARTS IDENTIFICATION

FIGURE 1

TOP CAP

CABINET

BURNER BOX

ASSEMBLY

SIGHT

GLASS

DuralokPlus

TM

HEAT EXCHANGER

ASSEMBLY

CONTROL BOX

(includes integrated control, transformer and interlock switch)

COMBUSTION AIR

INDUCER

BLOWER

ACCESS

DOOR

BURNER
ACCESS

PANEL

COMBUSTION

AIR PRESSURE

SWITCH

PRIMARY LIMIT

GAS VALVE

BLOWER

ASSEMBLY

FLEXIBLE NO−HUB
EXHAUST COLLAR

MANIFOLD

COLD END

HEADER BOX

BAG ASSEMBLIES

(shipping location)

Page 4

ML195UH Gas Furnace

The ML195UH Category IV gas furnace is shipped ready
for installation in the upflow or horizontal position. The fur­nace is shipped with the bottom panel in place. The bot­tom panel must be removed if the unit is to be installed in
horizontal or upflow applications with bottom return air.

The ML195UH can be installed as either a Direct Vent or
a Non−Direct Vent gas central furnace.

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

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.

FIGURE 2

DIRECT VENT INSTALLATION NON−DIRECT VENT

INSTALLATION

EXHAUST
OUTLET

ML195UH

COMBUSTION

AIR INTAKE INSIDE

OF HOUSE

EXHAUST
OUTLET

COMBUSTION
AIR INTAKE
OUTSIDE OF
HOUSE

ML195UH

Shipping and Packing List

Package 1 of 1 contains

1 − Assembled ML195UH unit
1 − Bag assembly containing the following:

1 − Snap bushing
1 − Snap plug
1 − Wire tie
1 − Condensate trap
1 − Condensate trap cap
1 − Condensate trap clamp
1 − 2" diameter debris screen

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
1 − Return air base kit
1 − Horizontal suspension 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.

CAUTION

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

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.

Use only the type of gas approved for use with this furnace.
Refer to unit nameplate.

ML195UH 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.

Page 5

Installation Locations

This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
nameplate and in the table in figure 10. Accessibility and ser­vice clearances must take precedence over fire protection
clearances.

NOTE − For installation on combustible floors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood flooring.

For installation in a residential garage, the furnace must
be installed so that the burner(s) and the ignition source
are located no less than 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.

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 ML195UH 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 coils (figure 3), it shall
be installed in parallel with, or on the upstream side of, cool­ing coils 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.

FIGURE 3

Gas Unit

Heating Unit Installed Upstream of Cooling Coil

Gas Unit

Dampers

(open during heating operation only)

Dampers

(open during cooling operation only)

Heating Unit Installed Parallel to Air Handler Unit

Air Handler Unit

Cooling Coil

AIR FLOWAIR FLOW

AIR FLOW AIR FLOW

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 ML195UH furnace may be installed in alcoves, clos­ets, attics, basements, garages, crawl spaces and utility
rooms in the upflow or horizontal position.

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

Use of Furnace as Construction Heater

Lennox does not recommend the use of ML195UH 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.

ML195UH 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.

Page 6

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 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.

D The furnace heat exchanger, components, duct system,

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 fol­lowing general recommendations must be considered
when installing a ML195UH 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 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

ML195UH 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

Combustion, Dilution & Ventilation Air

If the ML195UH 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 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 combus-

Page 7

tion, 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 ML195UH furnaces to ensure effi­cient and safe operation. You must consider combustion
air needs and requirements for exhaust vents and gas
piping. 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.

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.

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 m

3

) 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 m

3

) 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 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 4.

FIGURE 4

EQUIPMENT IN CONFINED SPACE − ALL AIR FROM INSIDE

OPENINGS

(To Adjacent

Unconfined

Space)

NOTE − Each opening shall have a free area of at least one square inch
per 1,000 Btu (645mm

2

per .29kW) per hour of the total input rating of

all equipment in the enclosure, but not less than 100 square inches
(64516mm.

2).

ROOF TERMINATED

EXHAUST PIPE

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

ML195UH

Page 8

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

2

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

2

per .59kW) per total input rating of all equipment in the en­closure (See figure 5).

FIGURE 5

EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE

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

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

2

per 1.17kW) per

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

OUTLET

AIR

INLET

AIR

VENTILATION

LOUVERS

(For unheated

crawl space)

FURNACE

ROOF TERMINATED

EXHAUST PIPE

VENTILATION LOUVERS

(Each end of attic)

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

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 mm

2

) 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
mm

2

) 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.

FIGURE 6

EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE

(All Air Through Ventilated Attic)

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

2

per 1.17kW) per hour

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

OUTLET

AIR

VENTILATION LOUVERS

(Each end of attic)

INLET AIR

(Ends 12" above

bottom)

ROOF TERMINATED

EXHAUST PIPE

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

FURNACE

FIGURE 7

EQUIPMENT IN CONFINED SPACE −

ALL AIR FROM OUTSIDE

OUTLET AIR

INLET AIR

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

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.

ROOF TERMINATED

EXHAUST PIPE

SIDE WALL

TERMINATED

EXHAUST PIPE

(ALTERNATE

LOCATION)

FURNACE

Page 9

Shipping Bolt Removal

Units with 1/2 hp blower motor are equipped with 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.

FIGURE 8

RIGID LEG

(Remove shipping bolt

and washer)

ML195UH090P48C
ML195UH110P48C

with 1/2 HP Blower Motor

Installation − Setting Equipment

WARNING

Do not connect the return air duct 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.

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.

Upflow Applications

The ML195UH gas furnace can be installed as shipped
in the upflow position. Refer to figure 10 for clearances.
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.

Allow for clearances to combustible materials as indicated
on the unit nameplate.

FIGURE 9

SETTING EQUIPMENT

UPFLOW APPLICATION

HORIZONTAL APPLICATION

FRONT VIEW

SIDE VIEW

FRONT VIEW

END VIEW

UNIT

FRONT

AIR FLOW

UNIT

FRONT

1/2"

max.

1/2"

max.

AIR FLOW

AIR FLOW

SIDE VIEW

UNIT

FRONT

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

Page 10

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.

Installation Clearances

Top

Bottom (Floor)

Left Side

Right Side

Top/Plenum 1 in. (25 mm)

*Front 0

Back 0

Sides 0†

Vent 0

Floor 0‡

*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.
‡For installations on a combustible floor, do not install the furnace

directly on carpeting, tile or other combustible materials other
than wood flooring.

FIGURE 10

Return Air Guidelines

Return air can be brought in through the bottom or either
side of the furnace installed in an upflow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.

Markings are provided on both sides of the furnace cabinet
for installations that require side return air. Cut the furnace
cabinet at the maximum dimensions shown on page 2.

Refer to Engineering Handbook for additional information.

ML195UH applications which include side return air
and a condensate trap installed on the same side of the
cabinet (trap can be installed remotely within 5 ft.) re­quire either a return air base or field−fabricated transi­tion to accommodate an optional IAQ accessory taller
than 14.5". See figure 11.

Side Return Air

(with transition and filter)

FIGURE 11

Return

Air

Plenum

Transition

20” X 25” X 1”

(508mmX635mmX 25mm)

Air Filter

1−1/2”

Page 11

FIGURE 12

Optional Return Air Base

(Upflow Applications Only)

NOTE− Optional side return air filter kits are not for use with return air base.

1

Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.
Minimum unit side return air opening dimensions for units requiring 1800 cfm of air and over (W x H): 23 x 11 in. (584 x 279 mm).
The opening can be cut as needed to accommodate plenum or IAQ cabinet while maintaining dimensions shown.
Side return air openings must be cut in the field. There are cutting guides stenciled on the cabinet for the side return air
opening. The size of the opening must not extend beyond the markings on the furnace cabinet.

2

To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.

FRONT VIEW

1

Unit side return air

Opening

SIDE VIEW

3−1/4

(83)

1

23 (584)

Overall

(Maximum)

(584)

23

3/4

(19)

1

22−7/16

(570)

Overall

(Maximum)

SIDE RETURN

AIR OPENINGS

(Either Side)

5−5/8

(143)

1

Minimum

11 (279)

2

Maximum

14 (356)

(683)

26−7/8

7−1/4

(184)

FURNACE

FRONT

AIR FLOW

IF BASE

IS USED

WITHOUT

IAQ CABINET,

A SINGLE

RETURN AIR

PLENUM

MUST

COVER BOTH

UNIT AND

RETURN

AIR BASE

OPENINGS

INDOOR AIR

QUALITY
CABINET

(PCO, Filter

Cabinet, etc.)

AIR BASE

OPTIONAL
RETURN

CONDENSATE

TRAP

17−1/2 (446) B Width (50W98)
21 (533) C Width (50W99)

24−1/2 (622) D Width (51W00)

Removing the Bottom Panel

FIGURE 13

Screw

Bottom Panel

Bottom Cap

Removing the Bottom Panel

Remove the two screws that secure the bottom cap to the
furnace. Pivot the bottom cap down to release the bottom
panel. Once the bottom panel has been removed, reinstall
the bottom cap. See figure 13.

Horizontal Applications

FIGURE 14

WARNING

Do not install the furnace on its front or back.
See figure 14.

Front

Back

Page 12

The ML195UH furnace can be installed in horizontal ap­plications with either right− or left−hand air discharge.

Refer to figure 15 for clearances in horizontal applications.

Horizontal Application

Installation Clearances

Left End Right End

Right−Hand Discharge

Left−Hand Discharge

Top

Bottom (Floor)**

Bottom (Floor)**

Left End Right End

Air

Flow

Air

Flow

Air

Flow

Air

Flow

Top 0

Front* 0

Back 0

Ends 0

Vent 0

Floor 0‡

*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
**An 8" service clearance must be maintained below the unit to
provide for servicing of the condensate trap.
‡For installations on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other
than wood flooring.

FIGURE 15

Suspended Installation of Horizontal Unit

This furnace may be installed in either an attic or a crawl­space. Either suspend the furnace from roof rafters or
floor joists, as shown in figure 16, or install the furnace on a
platform, as shown in figure 17. A horizontal suspension
kit (51W10) may be ordered from Lennox or use equiva­lent.

NOTE − Heavy−gauge sheet metal straps may be used to
suspend the unit from roof rafters or ceiling joists. When
straps are used to suspend the unit in this way, support
must be provided for both the ends. The straps must not
interfere with the plenum or exhaust piping installation.

Cooling coils and supply and return air plenums must
be supported separately.

FIGURE 16

HORIZONTAL SUSPENSION KIT

Bracket
(typical)

Metal Strap

(typical)

Air

Flow

Internal Brace

(provided with kit)

NOTE − When the furnace is installed on a platform or with
the horizontal suspension kit in a crawlspace, it must be
elevated enough to avoid water damage, accommodate
drain trap and to allow the evaporator coil to drain.

Platform Installation of Horizontal Unit

1 − Select location for unit keeping in mind service and

other necessary clearances. See figure 15.

2 − Construct a raised wooden frame and cover frame

with a plywood sheet. If unit is installed above finished
space, fabricate an auxiliary drain pan to be installed
under unit. Set unit in drain pan as shown in figure 17.
Leave 8 inches for service clearance below unit for
condensate trap.

3 − Provide a service platform in front of unit. When instal-

ling the unit in a crawl space, a proper support platform
may be created using cement blocks.

4 − Route auxiliary drain line so that water draining from

this outlet will be easily noticed by the homeowner.

Page 13

5 − If necessary, run the condensate line into a conden-

sate pump to meet drain line slope requirements. The
pump must be rated for use with condensing furnaces.
Protect the condensate discharge line from the pump
to the outside to avoid freezing.

6 − Continue with exhaust, condensate and intake piping

installation according to instructions.

FIGURE 17

*Gas connector may be
used for Canadian
installation if accept­able by local authority
having jurisdiction.

*GAS CONNECTION

RAISED

PLATFORM

SERVICE PLATFORM

INTAKE PIPE

EXHAUST PIPE

Return Air −− Horizontal Applications

Return air may be brought in only through the end of a fur­nace installed in the horizontal position. The furnace is
equipped with a removable bottom panel to facilitate
installation. See figure 13.

Filters

This unit is not equipped with a filter or rack. A field−pro­vided high velocity rated filter is required for the unit to oper­ate properly. Table 1 lists recommended filter sizes.
A filter must be in place whenever the unit is operating.

TABLE 1

Furnace

Cabinet Width

Filter Size

Side Return Bottom Return

17−1/2" 16 X 25 X 1 (1) 16 X 25 X 1 (1)

21" 16 X 25 X 1 (1) 20 X 25 X 1 (1)

24−1/2" 16 X 25 X 1 (2) 24 X 25 X 1 (1)

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 0.8 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.

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.

Return air can be brought in through the bottom or either
side of the furnace. If a furnace with bottom return air is
installed on a platform, make an airtight seal between the
bottom of the furnace and the platform to ensure that the
unit operates properly and safely. 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.

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 2 below for approved piping and fitting ma­terials.

Page 14

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.

TABLE 2

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)

D2661

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

D2665

PRIMER & SOLVENT CEMENT

ASTM

SPECIFICATION

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

D2564, D2235, F493

ABS to PVC or CPVC Transition Solvent
Cement

D3138

CANADA PIPE & FITTING & SOLVENT

CEMENT

MARKING

PVC & CPVC Pipe and Fittings

ULCS636

PVC & CPVC Solvent Cement

ABS to PVC or CPVC Transition Cement

IMPORTANT

ML195UH 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 2. 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.

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. When bonding the vent system to the fur­nace, use ULC S636 approved One−Step Transition Ce­ment to bond the pipe to the flue collar, or to bond the 90°
elbow or reducing 90° elbow to the flue collar. In addi­tion, the first three feet of vent pipe from the furnace flue
collar must be accessible for inspection.

Page 15

TABLE 3

OUTDOOR TERMINATION KITS USAGE

EL195

UNIT

VENT

PIPE

DIA.

(in.)

STANDARD CONCENTRIC

Outdoor
Exhaust

Accelerator

(Dia. X

Length)

Outdoor
Exhaust

Accelerator

(Dia. X

Length)

2" Wall Plate

Kit

3" Wall Plate

Kit

2" Wall

Ring Kit

Flush­Mount

Kit

1−1/2"

Concentric

Kit

2"

Concentric

Kit

3"

Concentric

Kit

1−1/2" X 12" 2" X 12"

22G44

or 30G28

44J40

or 81J20

15F74 51W11**

71M80

or

44W92

69M29

or

44W92

60L46

or 44W93

045

2 YES YES YES* YES YES YES

2−1/2 YES YES YES* YES YES YES

3 YES YES YES* YES YES YES

070

2 YES YES YES* YES YES YES

2−1/2 YES YES YES* YES YES YES

3 YES YES YES* YES YES YES

090

2 YES YES YES YES YES YES

2−1/2 YES YES YES YES YES YES

3 YES YES YES YES YES YES

110

2 YES YES YES YES YES YES

2−1/2 YES YES YES YES YES YES

3 YES YES YES YES YES YES

135 3 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 ML195UH−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 ML195UH045P24B and

ML195UH070P36B

furnaces.

Joint Cementing Procedure

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

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.

NOTE − Check the inside of vent pipe thoroughly for
any obstruction that may alter furnace operation.

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.

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

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.

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.

Page 16

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.

Venting Practices

FIGURE 18

* See table 2 for allowable pipe.

Piping Suspension Guidelines

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

SCHEDULE 40

PVC − 5’

all other pipe* − 3’

Wall

inside outside

24" maximum
3/4" minimum

Wall Thickness Guidelines

insulation

(if required)

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.

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.

CHIMNEY

OR GAS

VENT

(Check sizing

for water

heater only)

FURNACE

(Replaced

by ML195)

WATER

HEATER

OPENINGS

(To Adjacent

Room)

If an ML195UH 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.

FIGURE 19

REPLACING FURNACE THAT

WAS PART OF A COMMON

VENT SYSTEM

Exhaust Piping (Figures 22 and 23)

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

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.

Page 17

Vent Piping Guidelines

The ML195UH 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 4 and

5. Table 4 lists the minimum vent pipe lengths

permitted. Table 5 lists the maximum pipe lengths per-
mitted.

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 6.

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.

NOTE − The exhaust collar on all models is sized to ac­commodate 2" Schedule 40 vent pipe. When vent pipe
which is larger than 2" must be used in an upflow applica­tion, a transition must be applied at the exhaust collar in
order to properly step to the larger diameter vent pipe.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.

FIGURE 20

Exhaust Pipe

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

NOTE − All horizontal runs of exhaust pipe must slope back to-

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

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

12” ma x

of straight pip

e

Exhaust Pipe

12” Min.

Horizontal

Gas Furnace

TABLE 4

MINIMUM VENT PIPE LENGTHS

ML195UH

MODEL

MIN. VENT LENGTH*

045, 070, 090, 110, 135

15 ft. or

5 ft. plus 2 elbows or

10 ft. plus 1 elbow

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

Use the following steps to correctly size vent pipe diameter.

1

2

3

4

5

6

045, 070,
090, 110
or 135 btuh

Which termination?

Standard or
Concentric?
See table 3

Intake or
exhaust

Which needs
most elbows?

How many?

2", 2 1/2"
or 3"

Desired pipe size?

Use table 5 to find
max. intake or
exhaust pipe length.

FIGURE 21

What is the altitude?

7

Furnace capacity?

IMPORTANT

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