Lennox Merit Series User manual

Page 1
INSTALLATION
INSTRUCTIONS
ML180UHV
507945-01
01/2021
Superseds 08/2019
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 man-
uals, be alert to the potential for personal injury or death.
IMPORTANT
DO NOT use the bracket securing the heat exchanger
to lift, drag or pull the furnace to its installation
location. Doing so will loosen the bracket causing
noise and or unsafe operation.
Bracket
© 2021 Lennox Industries Inc.
Dallas, Texas USA
MERIT® SERIES GAS FURNACE
HORIZONTAL AIR DISCHARGE
Contents
Unit Dimensions - inches (mm........................................2
ML180UHV Gas Furnace ...............................................3
Shipping and Packing List ..............................................3
Safety .............................................................................3
Use of Furnace as a Construction Heaterl .....................4
General...........................................................................4
Combustion, Dilution, Ventilation Air...............................5
Setting Equipment ..........................................................8
Filters............................................................................ 11
Duct System .................................................................12
Venting .........................................................................13
Gas Piping....................................................................20
Electrical.......................................................................22
Integrated Control.........................................................25
Unit Start-Up.................................................................29
Gas Pressure Measurement.........................................30
Proper Combustion.......................................................30
High Altitude .................................................................30
Other Unit Adjustments.................................................32
Service..........................................................................32
Blower Data..................................................................35
WARNING
Improper installation, adjustment, alteration,
service or maintenance can cause property damage,
personal injury or loss of life. Installation and service
must be performed by a licensed professional HVAC
installer (or equivalent), service agency or the gas
supplier.

Page 2
Unit Dimensions - inches (mm)
23
(584)
(19)
3/4
(19)
1Bottom Return
Air Opening
GAS PIPING INLET
(Either Side)
Side Return
Air Opening
(Either Side)
1
Bottom Return
Air Opening
FLUE OUTLET
(Top)
ELECTRICAL INLET
(Either Side)
SUPPLY AIR
OPENING
FRONT VIEW SIDE VIEW
TOP VIEW
A
B9/16 (14)
C
D
3/4
27-3/4
(705)
19-7/16
(494)
23-1/2
(597)
1-1/2
(38)
9-1/8 (232) Right
8-5/8 (219) Left
5-3/8 (137) Right
2-3/16 (56) Left
33
(838)
3-1/8 (79)
1-15/16 (49)
14
(356)
9/16
(14)
3 (76) Right
6-3/4 (171) Left
2
FLUE OUTLET
(Either Side)
3OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
16
(406)
14-3/4
(375)
3OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
2
Flue outlet may be horizontal but furnace must be
vented vertically
3
Optional External Side Return Air Filter Kit is not for use
with the optional Return Air Base.
1
NOTE - 60C size units that require air volumes over
1800 cfm must have one of the following:
1. Single side return air and Optional Return Air Base
with transition that must accommodate required
20 x 25 x 1 inch (508 x 635 x 25 mm) air filter to
maintain proper velocity.
2. Bottom return air.
3. Return air from both sides.
4. Bottom and one side return air.
See Blower Performance Tables for additional information.
3-1/4 (83)
5/8
(16)
1
3-1/4
(83)
23-3/4
(603)
25
(635)
3/4(19)
Front Panel
ELECTRICAL
INLET (Either Side)
ML180UHV
Model
A B C D
in mm in mm in mm in mm
030V36A
045V36A
070V36A
14-1/2 368 13-3/8 340 13 330 4-3/4 121
070V36B
070V48B
090V48B
17-1/2 446 16-3/8 416 16 406 6-1/4 159
110V60C 21 533 19-7/8 504 19-1/2 495 8 203

Page 3
ML180UHV Gas Furnace
The ML180UHV unit is shipped ready for installation in the
upow or horizontal right position (for horizontal left posi-
tion the combustion air pressure switch must be moved)
fueled by natural gas. A conversion kit (ordered separate-
ly) is required for use in LP/Propane gas applications. The
furnace is shipped with the bottom panel in place. The bot-
tom panel must be removed if the unit is to be installed in
a horizontal application. The panel may also be removed
in upow applications.
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled ML180UHV unit
1 - Bag assembly containing the following:
2 - Screws
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 -Vent warning label
1 - Owner’s manual and warranty card
The following items may be ordered separately:
1 - Thermostat
1 - Suspension kit (for horizontal installations)
1 - LP/Propane changeover kit
1 - Return air base
1 - High altitude kit
1 - Side lter kit
Check equipment for shipping damage. If you nd any
damage, immediately contact the last carrier.
Safety Information
DANGER
Danger of explosion.
There are circumstances in which odorant used with
LP/propane gas can lose its scent. In case of a leak,
LP/propane gas will settle close to the oor and may
be di󰀩cult to smell. An LP/propane leak detector
should be installed in all LP applications.
CAUTION
As with any mechanical equipment, contact with
sharp sheet metal edges can result in personal
injury. Take care while handling this equipment and
wear gloves and protective clothing.
Certications
ML180UHV units are CSA International certied to ANSI
Z21.47.
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI-Z223.1). The National Fuel Gas Code is
available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036
Clearances
Adequate clearance must be made around the air open-
ings into the vestibule area. In order to ensure proper unit
operation, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code.
Vent installations must be consistent with the National Fu-
elGas Code venting tables (in this instruction) and appli
cable provisions of local building codes.
This furnace is CSA International certied for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in gures 7 and 11. Accessi-
bility and service clearances must take precedence over
re protection clearances.
NOTE - For installation on combustible oors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood ooring.
Installed Locations
For installation in a residential garage, the furnace must
be installed so that the burner(s) and the ignition source
are located no less than 18 inches (457 mm) above the
oor. The furnace must be located or protected to avoid
physical damage by vehicles. When a furnace is installed
in a public garage, hangar, or other building that has a
hazardous atmosphere, the furnace must be installed ac-
cording to recommended good practice requirements and
current National Fuel Gas Code.
Temperature Rise
NOTE - Furnace must be adjusted to obtain a tempera-
ture rise within the range specied on the unit nameplate.
Failure to do so may cause erratic limit operation and may
result in premature heat exchanger failure.
This ML180UHV furnace must be installed so that its elec-
trical components are protected from water.
Installed in Combination with a Cooling Coil
When this furnace is used with cooling units, it shall be in-
stalled in parallel with, or on the upstream side of, cooling
units to avoid condensation in the heating compartment.
See gure 1.

Page 4
With a parallel ow arrangement, a damper (or other
means to control the ow of air) must adequately prePage
4 vent chilled air from entering the furnace. If the damper
is manually operated, it must be equipped to prevent op-
eration of either the heating or the cooling unit, unless it is
in the full HEAT or COOL setting. See gure 1.
Gas Unit
Heating Unit Installed Upstream of Cooling Unit
Gas Unit
Dampers
(open during heating operation only)
Dampers
(open during cooling operation only)
Heating Unit Installed Parallell to Air Handler Unit
Air Handler Unit
Evaporator
FIGURE 1
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National Elec-
tric Code, ANSI/NFPA No. 70. The National Electric Code
(ANSI/NFPA No. 70) is available from the following ad-
dress:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
NOTE - This furnace is designed for a minimum continu-
ous 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 ML180UHV furnace may be installed in alcoves, clos-
ets, attics, basements, garages, crawl spaces and utility
rooms in the upow or horizontal position.
This furnace design has not been CSA International
certied for installation in mobile homes, recreational
vehicles, or outdoors.
Use of Furnace as Construction Heater
Lennox does not recommend the use of ML180UHV units
as a construction heater during any phase of construc-
tion. Very low return air temperatures, harmful vapors and
operation of the unit with clogged or misplaced lters will
damage the unit.
ML180UHV units may be used for heating of buildings or
structures under construction, if the following conditions
are met:
• The vent system must be permanently installed per
these installation instructions.
• A room thermostat must control the furnace. The
use of xed jumpers that will provide continuous
heating is not allowed.
• 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 lters must be installed in the system and must
be maintained during construction.
• Air lters must be replaced upon construction com-
pletion.
• The input rate and temperature rise must be set per
the furnace rating plate.
• One hundred percent (100%) outdoor air must be
provided for combustion air requirements during
construction. Temporary ducting may supply out-
door air to the furnace. Do not connect duct directly
to the furnace. Size the temporary duct following
these instructions in section for Combustion, Dilu-
tion and Ventilation Air in a conned space with air
from outside.
• The furnace heat exchanger, components, duct
system, air lters and evaporator coils must be
thoroughly cleaned following nal construction
clean-up.
• All furnace operating conditions (including ignition,
input rate, temperature rise and venting) must be
veried according to these installation instructions.
General
These instructions are intended as a general guide and
do not supersede local codes in any way. Consult author-
ities having jurisdiction before installation. In addition to
the requirements outlined previously, the following general
recommendations must be considered when installing a
ML180UHV 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 termi-
nation point.

Page 5
• Do not install the furnace where drafts might blow
directly into it. This could cause improper combus-
tion and unsafe operation.
• Do not block the furnace combustion air openings
with clothing, boxes, doors, etc. Air is needed for
proper combustion and safe unit operation.
• When the furnace is installed in an attic or other
insulated space, keep insulation away from the fur-
nace.
NOTE - The Commonwealth of Massachusetts
stipulates these additional requirements:
• Gas furnaces shall be installed by a licensed
plumber or tter only.
• The gas cock must be “T handle” type.
• When a furnace is installed in an attic, the pas-
sageway to and service area surrounding the
equipment shall be oored.
Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in su󰀩cient
outdoor air for combustion. Inltration provided all the air
that was needed. In today’s homes, tight construction
practices make it necessary to bring in air from outside for
combustion. Take into account that exhaust fans, appli-
ance vents, chimneys, and replaces force additional air
that could be used for combustion out of the house. Un-
less 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 oc-
cur in the furnace vent pipe or chimney. As a result, com-
bustion 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 ML180UHE furnaces to ensure e󰀩-
cient and safe operation. You must consider combustion
air needs and requirements for exhaust vents. A portion of
this information has been reprinted with permission from
the National Fuel Gas Code (ANSI-Z223.1). This reprint-
ed material is not the complete and o󰀩cial position of the
ANSI on the referenced subject, which is represented only
by the standard in its entirety.
CAUTION
Do not install the furnace in a corrosive or
contaminated atmosphere. Meet all combustion
and ventilation air requirements, as well as all local
codes.
CAUTION
Insu󰀩cient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in
rusting and premature heat exchanger failure.
Excessive exposure to contaminated combustion
air will result in safety and performance related
problems. Avoid exposure to the following
substances in the combustion air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace com-
ponents.
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is in-
stalled in an unconned or a conned space
Unconned Space
An unconned 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 com-
bined input rating of all appliances installed in that space.
This space also includes adjacent rooms which are not
separated by a door. Though an area may appear to be
unconned, it might be necessary to bring in outdoor air
for combustion if the structure does not provide enough air
by inltration. 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.

Page 6
Conned Space
A conned space is an area with a volume less than 50
cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of
the combined input rating of all appliances installed in that
space. This denition 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 conned 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 con-
dition. Air for combustion and ventilation can be brought
into the conned space either from inside the building or
from outside.
EQUIPMENT IN CONFINED
SP
ACE ALL AIR FROM INSIDE
CHIMNEY
OR GAS
VENT
FURNACE
WATER
HEATER
OPENINGS
(To Adjacent
Room)
NOTE - Each opening shall have a free area of at least one square
inch (645 mm2
ing of all equipment in the enclosure, but not less than 100 square
inches (64516 mm2).
AIR FLOW
FIGURE 2
Air from Inside
f the conned space that houses the furnace adjoins a
space categorized as unconned, 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 in-
put rating of all gas-red equipment in the conned space.
Each opening must be at least 100 square inches (64516
mm2). One opening shall be within 12 inches (305 mm) of
the top of the enclosure and one opening within 12 inches
(305 mm) of the bottom. See gure 2.
Air from Outside
If air from outside is brought in for combustion and ventila-
tion, the conned space must have two permanent open-
ings. One opening shall be within 12 inches (305 mm) of
the top of the enclosure and one opening within 12 inches
(305 mm) of the bottom. These openings must communi-
cate directly or by ducts with the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors or in-
directly through vertical ducts. Each opening shall have a
minimum free area of 1 square inch (645 mm2) per 4,000
Btu (1.17 kW) per hour of total input rating of all equipment
in the enclosure. See gures 3 and 4. When communi-
cating with the outdoors through horizontal ducts, each
opening shall have a minimum free area of 1 square inch
(645 mm2) per 2,000 Btu (.56 kW) per total input rating of
all equipment in the enclosure. See gure 5.
When ducts are used, they shall be of the same cross-sec-
tional area as the free area of the openings to which they
connect. The minimum dimension of rectangular air ducts
shall be no less than 3 inches (75 mm). In calculating free
area, the blocking e󰀨ect of louvers, grilles, or screens
must be considered. If the design and free area of protec-
tive covering is not known for calculating the size opening
required, it may be assumed that wood louvers will have
20 to 25 percent free area and metal louvers and grilles
will have 60 to 75 percent free area. Louvers and grilles
must be xed in the open position or interlocked with the
equipment so that they are opened automatically during
equipment operation

Page 7
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(Inlet Air from Crawlspace 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 (645
mm
2
)per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR WATER
HEATER
INLET
AIR
CHIMNEY OR
GAS VENT
FURNACE
VENTILATION
LOUVERS
(For unheated crawl space)
AIR FLOW
FIGURE 3
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 (645 mm2) per 4,000
ment in the enclosure.
CHIMNEY
OR GAS
VENT
WATER
HEATER
OUTLET
AIR
VENTILATION LOUVER
S
(Each end of attic)
INLET AIR
(Ends 12 in.
above bottom)
FURNACE
AIR FLOW
FIGURE 4
EQUIPMENT IN
CONFINED SP
ACE
ALL AIR FROM
OUTSIDE
OUTLET AIR
INLET AIR
WATER
HEATER
CHIMNEY
OR GAS
VENT
NOTE - Each air duct opening shall have a free area of at least
one square inch (645 mm2) per 2,000 Btu (.59 kW) per hour of
the total input rating of all equipment in the enclosure. If the
equipment room is located against an outside wall and the air
openings
ing shall have a free area of at least one square inch (645 mm2)
per 4,000 Btu (1.17 kW) per hour of the total input rating of all
other equipment in the enclosure.
FURNACE
AIR FLOW
FIGURE 5

Page 8
Setting Equipment
WARNING
Do not install the furnace on its front or its back. Do
not connect the return air ducts to the back of the
furnace. Doing so will adversely a󰀨ect the operation
of the safety control devices, which could result in
personal injury or death.
The ML180UHV gas furnace can be installed as shipped
in either the upow position or the horizontal position.
Select a location that allows for the required clearances
that are listed on the unit nameplate. Also consider gas
supply connections, electrical supply, vent connection,
and installation and service clearances [24 inches (610
mm) at unit front]. The unit must be level.
NOTE - Units with 1/2 hp blower motors are equipped with
three exible legs and one rigid leg. See gure 6. The rigid
leg is equipped with a shipping bolt and a at white plastic
washer (rather than the rubber mounting grommet used
with a exible mounting leg). The bolt and washer must
be removed before the furnace is placed into opera-
tion. After the bolt and washer have been removed, the
rigid leg will not touch the blower housing.
RIGID LEG
remove shipping bolt and washe
Units with 1/2 or 3/4 HP Blower Motor
FIGURE 6
Upow Applications
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in gure 7.
Upflow Application Installation Clearances
Top
Bottom
Left Side Right Side
Type of Vent
Connector Type CType B1
Top1 in. (25 mm)1 in. (25 mm)
*Front 2-1/4 in. (57 mm)** 2-1/4 in. (57 mm)
Back 0 0
Sides 0†0
Vent 6 in. (152 mm)1 in. (25 mm)
Floor 0‡0‡
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
** 4-1/2 in. if single wall vent pipe is used.
‡For installation on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other
than wood flooring.
†Left side requires 3 inches if a single wall vent is used on 14-1/2
in. cabinets, or 2inches if a single wall vent pipe is used on 17-1/2
in. cabinets.
FIGURE 7

Page 9
Return Air -- Upow Applications
Return air can be brought in through the bottom or either
side of the furnace installed in an upow 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 cab-
inet for installations that require side return air. Cut the
furnace cabinet at the maximum dimensions shown on
page 2.
NOTE - 60C units that require air volumes over 1800 cfm
(850 L/s) must have one of the following:
1 - Single side return air and Optional Return Air Base
with transition that must accommodate required
20 x 25 x 1 inch (508 x 635 x 25 mm) air lter to
maintain proper velocity.
2 - Bottom return air
3 - Return air from both sides.
4 - Bottom and one side return air.
Refer to Engineering Handbook for additional information.
Return Air
Plenum
Transition
20” X 25” X 1”
(508mm X 635mm X 25mm)
Cleanable Filter
AIR FLOW
Single Side Return Air
(with transition and filter)
FIGURE 8
Optional Return Air Base
(Upflow Applications Only -- For use with A, B, C and D cabinets)
NOTE- Optional Side Return Air Filter Kits are not for use with Optional Return Air Base.
1Both 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 or more of air (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.
2To minimize pressure drop, the largest opening height possible (up to 14 inches 356 mm) is preferred.
FURNACE
FRONT
AIR FLOW
14−1/2 (368) A Width (65W75)
17−1/2 (446) B Width (50W98)
21 (533) C Width (50W99)
24−1/2 (622) D Width (51W00)
1Unit side return air
Opening
SIDE VIEW
3−1/4
(83)
1
23 (584)
Overall
(Maximum)
(584)
23
3/4
(19)
122−7/16
(570)
Overall
(Maximum)
SIDE RETURN
AIR OPENINGS
(Either Side)
5−5/8
(143)
1Minimum
11 (279)
2Maximum
14 (356)
(683)
26−7/8
7−1/4
(184)
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
FIGURE 9

Page 10
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 gure 10.
Removing the Bottom Panel
Screw
Bottom Panel
Bottom Cap
FIGURE 10
Horizontal Application
Installation Clearances
Top
Bottom
Left
End
Right
End
AIR FLOW
Vent Connector
Type Type CType B1
Top 0 0
*Front 2-1/4 in. (57 mm)**2-1/4 in. (57 mm)
Back 0 0
Ends 2 in. (51 mm)2 in. (51 mm)
Vent 6 in. (152 mm) 1 in. (25 mm)
Floor 0‡0‡
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
** 4-1/2 in. if singlewall vent pipe is used.
‡For installations on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other
than wood flooring.
FIGURE 11
Horizontal Applications
The ML180UHV furnace can be installed in horizontal ap-
plications. Order horizontal suspension kit (51W10) from
Lennox, or use equivalent suspension method.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in gure 11.
This furnace may be installed in either an attic or a crawl-
space. Either suspend the furnace from roof rafters or
oor joists, as shown in gure 12, or install the furnace on
a platform, as shown in gure 13.
Typical Horizontal Application
Unit Suspended in Attic or Crawlspace
Bracket
Bottom Cap
Metal Strap
3/16 inch
Air Flow
FIGURE 12
NOTE - Heavy-gauge perforated 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 pip-
ing installation. Cooling coils and supply and return air
plenums must be supported separately.
NOTE - When the furnace is installed on a platform in a
crawlspace, it must be elevated enough to avoid water
damage and to allow the evaporator coil to drain.
Return Air -- Horizontal Applications
Return air must be brought in through the end of a fur-
nace installed in a horizontal application. The furnace is
equipped with a removable bottom panel to facilitate in-
stallation. See gure 10.

Page 11
Horizontal Application
Unit Installed on Platform
clearances.
GAS
ENTRY VENT
PIPE
See the unit nameplate for
Line contact is permissible
SERVICE PLATFORM
FIGURE 13
WARNING
Improper installation of the furnace can result in
personal injury or death. Combustion and ue
products must never be allowed to enter the return
air system or the living space. Use screws and joint
tape to seal the return air system to the furnace.
In platform installations with bottom return air, 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.
The return and supply air duct systems must never
be connected to or from other heating devices
such as a replace or stove, etc. Fire, explosion,
carbon monoxide poisoning, personal injury and/or
property damage could result.
WARNING
The blower access panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal
injury or death.
Filters
This unit is not equipped with a lter or rack. A eld-pro-
vided high-velocity lter is required for the unit to operate
properly. Table 1 lists recommended lter sizes.
A lter must be in place any time the unit is operating.
IMPORTANT
If a highe󰀩ciency lter is being installed as part
of this system to ensure better indoor air quality,
the lter must be properly sized. Highe󰀩ciency
lters have a higher static pressure drop than
standarde󰀩ciency glass/foam lters. If the pressure
drop is too great, system capacity and performance
may be reduced.
The pressure drop may also cause the limit to trip
more frequently during the winter and the indoor
coil to freeze in the summer, resulting in an increase
in the number of service calls.
Before using any lter with this system, check the
specications provided by the lter manufacturer
against the data given in the appropriate Lennox
Product Specications bulletin. Additional
information is provided in Service and Application
Note ACC002 (August 2000).
TABLE 1
Furnace Cabinet
Width
Filter Size
Side Return Bottom Return
A - 14-1/2” 16 X 25 X 1 (1) 14 X 25 X 1 (1)
B - 17-1/2” 16 X 25 X 1 (1) 16 X 25 X 1 (1)
C - 21” 16 X 25 X 1 (1) 20 x 25 x 1 (1)

Page 12
Duct System
Use industry-approved standards (such as those pub-
lished by Air Conditioning Contractors of America or Amer-
ican Society of Heating, Refrigerating and Air Condition-
ing Engineers) to size and install the supply and return
air duct system. This will result in a quiet and low-static
system that has uniform air distribution. See gure 14 for
proper duct installatiion.
NOTE - Do not operate the furnace in the heating mode
with an external static pressure that exceeds 0.5 inches
w.c. Higher external static pressures may cause erratic
limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a remov-
able access panel must be installed in the supply air duct.
The access panel should be large enough to permit in-
spection (either by smoke or reected light) of the heat
exchanger for leaks after the furnace is installed. 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. Install self tapping screws in the
three evaporator coil screw holes made for horizontal ap-
plications to seal the top cap to the vestibule panel.
Return Air Plenum
NOTE - Return air must not be drawn from a roomwhere
this furnace, or any other gas-fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
replace) 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 ue products can be
pulled back down the vent pipe and into the room. This
reverse ow of the ue gas may result in incomplete com-
bustion and the formation of carbon monoxide gas. This
toxic gas might then be distributed throughout the house
by the furnace duct system.
In upow applications, the return air can be brought in
through the bottom or either side of the furnace. If a fur-
nace 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 berglass sealing strips, caulking, or equiva-
lent sealing method between the plenum and the furnace
cabinet to ensure a tight seal. If a lter is installed, size the
return air duct to t the lter frame.
HORIZONTAL UNIT
SUPPLY
AIR
SUPPLY
AIR Install self tapping screws
to seal any potential air
leaks
UPFLOW UNIT
FIGURE 14

Page 13
Venting
A 4-inch diameter ue transition is factory-installed on
the combustion air inducer outlet of all models. Figure 16
shows the combustion air inducer as shipped from the fac-
tory.
Mounting Screws Location
Mounting Screws
Flue Transition
FIGURE 15
UPFLOW POSITION
Top Vent Discharge
FLOW
AIR
Collector Box
Vent Pipe
Flue
Transition
Pressure
Switch
Make-Up
Box
FIGURE 16
IMPORTANT
The unit will not vent properly with the ue transition
pointed down in the 6 o’clock position. The
combustion air inducer may be rotated clockwise
or counterclockwise by 90° to allow for top or side
vent discharge in all applications. When the unit is
installed, the ue transition must be in the 9 o’clock,
12 o’clock or 3 o’clock position.
If necessary, reposition the combustion air inducer, pres-
sure switch and/or make-up box as needed per the follow-
ing steps. See gures 17 through 21.
1 - Remove the four mounting screws (gure 15) which
secure the combustion air inducer / pressure switch
assembly to the orice plate. Lift the assembly and
rotate it 90 degrees clockwise or counterclockwise
to either the 3 o’clock position or to 9 o’clock
position. Resecure with four screws. Gasket should
be left in place.
2 - Use tin snips to cut preferred opening on the cabinet
for repositioning the ue outlet. Use the cut-out piece
as a cover plate to patch unused opening on cabinet.
UPFLOW POSITION
Left Side Vent Discharge
Gas supply piping must be brought into the unit from the right
side in order to accommodate the flue pipe.
ference with inducer motor
Remove make-up box assembly (2 screws) and cut wire tie to
free make-up box wires. Re-install make-up box on other side
of cabinet.
Re-secure make-up box wires: Either pull excess wires
through the blower compartment and secure using supplied
wire tie, or coil excess wire and secure to the gas manifold.
FLOW
AIR
Make-Up
Box
Pressure
Switch
Flue
Transition
Vent Pipe
Cover PlateCollector Box
FIGURE 17
UPFLOW POSITION
Right Side Vent Discharge
FLOW
AIR
Cover PlateFlue Transition
Vent Pipe
Pressure
Switch
Make-Up
Box
Collector Box
Cut combustion air inducer tubing from 9” to 5” to avoid
interference with inducer motor
FIGURE 18

Page 14
HORIZONTAL LEFT POSITION
Top Vent Discharge
Disconnect pressure switch hose from barbed fitting on the
pressure switch assembly. Remove pressure switch assembly
(1 screw) and cut wire tie to free pressure switch wires. Re-
install pressure switch on the other side of orifice plate and re-
connect pressure switch hose.
Re-secure pressure switch wires: Either pull excess wires
through the blower compartment and secure using supplied
wire tie, or coil excess wire and secure to the gas manifold.
Pressure
Switch
Vent Pipe
Flue
Transition
Cover Plate
Make-Up BoxCollector Bo
x
FLOW
AIR
FIGURE 19
Make-Up Box Collector Box
Vent Pipe
Pressure Switch
HORIZONTAL LEFT POSITION
Side Vent Discharge
Disconnect pressure switch hose from barbed fitting on the
pressure switch assembly. Remove pressure switch assembly
(1 screw) and cut wire tie to free pressure switch wires. Re-
install pressure switch on the other side of orifice plate and re-
connect pressure switch hose.
Re-secure pressure switch wires: Either pull excess wires
through the blower compartment and secure using supplied
wire tie, or coil excess wire and secure to the gas manifold.
FLOW
AIR
ference with inducer motor
FIGURE 20
HORIZONTAL RIGHT POSITION
Top Vent Discharge
Remove make-up box assembly (2 screws) and cut wire tie to
free make-up box wires. Re-install make-up box on other side
of cabinet.
Re-secure make-up box wires: Either pull excess wires through
the blower compartment and secure using supplied wire tie, or
coil excess wire and secure to the gas manifold.
FLOW
AIR
Flue
Transition
Vent Pipe
Pressure Switch
Cover Plate
Make-Up Box
Collector Box
tom in order to accommodate the flue pipe.
ference with inducer motor
FIGURE 21
HORIZONTAL RIGHT POSITION
Side Vent Discharge - no modifications necessary
FLOW
AIR
Pressure Switch
Flue Transition
Collector Bo
x
Make-Up Box
Vent Pipe
FIGURE 22

Page 15
The ML180UHV series units are classied as fan-assisted
Category I furnaces when vertically vented according to
the latest edition of National Fuel Gas Code (NFPA 54 /
ANSI Z223.1) in the USA. A fan-assisted Category I fur-
nace is an appliance equipped with an integral mechan-
ical means to either draw or force combustion products
through the combustion chamber and/or heat exchanger.
The ML180UHV is not approved for use with horizontal
venting.
NOTE - Use these instructions as a guide. They do not
supersede local codes. This furnace must be vented ac-
cording to all local codes these installation instructions,
and the provided venting tables in these instructions
The venting tables in this manual were extracted from the
National Fuel Gas Code (NFPA 54 / ANSI Z223.1) and are
provided as a guide for proper vent installation. Proper
application, termination, construction and location of vents
must conform to local codes having jurisdiction. In the ab-
sence of local codes, the NFGC serves as the dening
document.
Use self-drilling sheet metal screws or a mechanical fas-
tener to rmly secure the vent pipe to the round collar of
the ue transition. If self-drilling screws are used to attach
the vent pipe, it is recommended that three be used. Drive
one self-drilling screw through the front and one through
each side of the vent pipe and collar. See gure 23.
Install the rst vent connector elbow at a minimum of six
inches (152 mm) from the furnace vent outlet. See gure
23.
IMPORTANT
Once the venting system is installed, attach the
“Disconnected Vent” warning sticker to a visible
area of the plenum near the vent pipe. See gure 23.
The warning sticker is provided in the bag assembly.
Order kit 66W04 for additional stickers.
Venting Using a Masonry Chimney
The following additional requirements apply when a lined
masonry chimney is used to vent this furnace.
Masonry chimneys used to vent Category I central furnac-
es must be either tile-lined or lined with a listed metal lining
system or dedicated gas vent. Unlined masonry chimneys
are prohibited. See gures 24 and 25 for common venting.
A chimney with one or more sides exposed to the outside
of the structure is considered to be an exterior chimney.
An exterior masonry chimney that is not tile-lined must be
lined with B1 vent or a listed insulated exible metal vent.
An exterior tile-lined chimney that is sealed and capped
may be lined with a listed uninsulated exible metal vent.
If the existing chimney will not accommodate a listed met-
al liner, either the chimney must be rebuilt to accommo-
date one of these liners or an alternate approved venting
method must be found.
Insulation for the exible vent pipe must be an encapsu-
lated berglass sleeve recommended by the exible vent
pipe manufacturer. See gure 24. Refer to the tables and
the venting information contained in these instructions to
properly size and install the venting system.
IMPORTANT
Once the venting system is installed, attach the
“Disconnected Vent” warning sticker to a visible
area of the plenum near the vent pipe. See gure 23.
The warning sticker is provided in the bag assembly.
Order kit 66W04 for additional stickers.
FLUE TRANSITION
COLLAR
VENT PIPE
(min. 6” length)
“DISCONNECTED VENT”
WARNING
STICKER
FLUE
TRANSITION
COLLAR
VENT CONNECTION UPFLOW AND HORIZONTAL POSITION
VENT PIPE
(min. 6” length)
“DISCONNECTED VENT”
WARNING
STICKER
FIGURE 23

Page 16
Common Venting Using Metal-Lined Masonry Chimney
4 in. (102 mm)
minimum
MIN. LENGTH -- AS
SHORT AS PRACTICAL
MAX. LENGTH
-- SEE NOTE 1
BELOW.
SEALED
PERMANENTLY
SEALED FIREPLACE
OPENING
EXTERIOR
CHIMNEY WITH
METAL
LINER
VENT CONNECTOR
NOTE 1 - Refer to the provided venting tables for installations. Refer
to the capacity requirements shown in the provided venting tables.
OTHER
APPLIANCE
FURNACE
5 ft. (1.5 m)
minimum
AIR FLOW
FIGURE 24
DO NOT insulate the space between the liner and
the chimney wall with pu󰀨ed mica or any other loose
granular insulating material.
IMPORTANT
SINGLE appliance venting of a fan-assisted furnace
into a tile-lined masonry chimney (interior or outside
wall) is PROHIBITED. The chimney must rst be
lined with either type B1 vent or an insulated single
wall exible vent lining system which has been
sized according to the provided venting tables and
the vent pipe manufacturer’s instructions.
A fan-assisted furnace may be commonly vented into an
existing lined masonry chimney if the following conditions
are met:
• The chimney is currently serving at least one draft-
hoodequipped appliance;
• The vent connectors and chimney are sized accord-
ing to the provided venting tables.
If type B1 double‐wall vent is used inside a chimney, no
other appliance can be vented into the chimney. The outer
wall of type B1 vent pipe must not be exposed to ue prod-
ucts. A type B1 vent or masonry chimney liner shall termi-
nate above the roof surface with a listed cap or a listed
roof assembly according to the terms of their respective
listings and the vent manufacturer’s instructions.
When inspection reveals that an existing chimney is not
safe for the intended purpose, it shall be rebuilt to conform
to nationally recognized standards, lined or relined with
suitable materials, or replaced with a gas vent or chimney
suitable for venting ML180UHV series units. The chimney
passageway must be checked periodically to ensure that
it is clear and free of obstructions.
Do not install a manual damper, barometric draft regulator,
or ue restrictor between the furnace and the chimney.
Never connect a Category I appliance to a chimney that is
servicing a solid-fuel appliance. If a replace chimney ue
is used to vent this appliance, the replace opening must
be permanently sealed.
A type B or listed chimney lining system that passes
through an unused masonry chimney ue is not consid-
ered to be exposed to the outdoors.
General Venting Requirements
Vent all ML180UHV furnaces according to these instruc-
tions:
1 - Vent diameter recommendations and maximum
allowable piping runs are found in the provided
venting tables.
2 - In no case should the vent or vent connector diameter
be less than the diameter specied in the provided
venting tables.
3 - The minimum vent capacity determined by the sizing
tables must be less than the low re input rating and
the maximum vent capacity must be greater than the
high re input rating.
4 - Single appliance vents - If the vertical vent or tile-
lined chimney has a larger diameter or ow area than
the vent connector, use the vertical vent diameter to
determine the minimum vent capacity and the vent
connector diameter to determine the maximum vent
capacity. The ow area of the vertical vent, however,
shall not exceed 7 times the ow area of the listed
appliance categorized vent area, drafthood outlet
area or ue collar area unless designed according to
approved engineering methods.
5 - Multiple appliance vents - The ow area of the largest
section of vertical vent or chimney shall not exceed 7
times the smallest listed appliance categorized vent
area, drafthood outlet area or ue collar area unless
designed
6 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.

Page 17
Common Venting Using Tile-Lined Interior Masonry Chimney and Combined Vent Connector
MINIMUM LENGTH = AS SHORT AS PRACTICAL.
FOR MAXIMUM LENGTH SEE NOTE TO LEFT
INTERIOR TILE-LINED
MASONRY CHIMNEY
NOTE - the chimney must be properly
sized per provided venting tables or
lined with listed metal lining system.
PERMANENTLY
SEALED FIREPLACE
OPENING
VENT
CONNECTOR
NOTE- Refer to provided venting tables
for installations.
FURNACE
OTHER
APPLIANCE
AIR FLOW
FIGURE 25
6 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
7 - Single appliance venting congurations with zero
lateral lengths (tables 3 ) are assumed to have
no elbows in the vent system. For all other vent
congurations, the vent system is assumed to have
two 90° elbows. For each additional 90° elbow or
equivalent (for example two 45° elbows equal one
90° elbow) beyond two, the maximum capacity listed
in the venting table should be reduced by 10% (0.90
x maximum listed capacity).
8 - The common venting tables (4 and 5) were generated
using a maximum horizontal vent connector length of
1-1/2 feet (.46 m) for each inch (25 mm) of connector
diameter as follows:
TABLE 2
Connector Diameter
inches (mm)
Maximum Horizontal
Connector Length feet (m)
3 (76) 4-1/2 (1.37)
4 (102) 6 (1.83)
5 (127) 7-1/2 (2.29)
6 (152) 9 (2.74)
7 (178) 10-1/2 (3.20)
9 - If the common vertical vent is o󰀨set, the maximum
common vent capacity listed in the common venting
tables should be reduced by 20%, the equivalent
of two 90° elbows (0.80 x maximum common vent
capacity). The horizontal length of the o󰀨set shall not
exceed 1-1/2 feet (.46 m) for each inch (25 mm) of
common vent diameter.
10 - The vent pipe should be as short as possible with
the least number of elbows and angles required to
complete the job. Route the vent connector to the
vent using the shortest possible route.
11 - A vent connector shall be supported without any
dips or sags and shall slope a minimum of 1/4 inch
(6.4 mm) per linear foot (305 mm) of connector,
back toward the appliance.
12 - Vent connectors shall be rmly attached to the
furnace ue collar by self-drilling screws or other
approved means, except vent connectors of listed
type B vent material which shall be assembled
according to the manufacturer’s instructions. Joints
between sections of single wall connector piping
shall be fastened by screws or other approved
means.
13 - When the vent connector used for Category I
appliances must be located in or pass through
a crawlspace, attic or other areas which may
be cold, that portion of the vent connector shall
be constructed of listed double-wall type B vent
material or material having equivalent insulation
qualities.
14 - All venting pipe passing through oors, walls, and
ceilings must be installed with the listed clearance
to combustible materials and be re stopped
according to local codes. In absence of local codes,
refer to NFGC (Z223.1).
15 - No portion of the venting system can extend into,
or pass through any circulation air duct or plenum.
16 - Vent connectors serving Category I appliances shall
not be connected to any portion of mechanical draft
systems operating under positive pressure such as
Category III or IV venting systems.

Page 18
17 - If vent connectors are combined prior to entering
the common vent, the maximum common vent
capacity listed in the common venting tables must
be reduced by 10%, the equivalent of one 90° elbow
(0.90 x maximum common vent capacity).
18 - The common vent diameter must always be at least
as large as the largest vent connector diameter.
20 - Do not install a manual damper, barometric draft
regulator or ue restrictor between the furnace and
the chimney.
21 - When connecting this appliance to an existing
dedicated or common venting system, you must
inspect the venting system’s general condition
and look for signs of corrosion. The existing vent
pipe size must conform to these instructions and
the provided venting tables. If the existing venting
system does
TABLE 3
Capacity of Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving a Single Category I Appliance
Height
H
(feet)
Lateral
L
(feet)
Vent and Connector Diameter - D (inches)
3 inch 4 inch 5 inch 6 inch
Appliance Input Rating in Thousands of Btu Per Hour
Min Max Min Max Min Max Min Max
6
0 0 78 0 152 0 251 0 375
2 13 51 18 97 27 157 32 232
4 21 49 30 94 39 153 50 227
6 25 46 36 91 47 149 59 223
8
0 0 84 0 165 0 276 0 415
2 12 57 16 109 25 178 28 263
5 23 53 32 103 42 171 53 255
8 28 49 39 98 51 164 64 247
10
0 0 88 0 175 0 295 0 447
2 12 61 17 118 23 194 26 289
5 23 57 32 113 41 187 52 280
10 30 51 41 104 54 176 67 267
15
0 0 94 0 191 0 327 0 502
211 69 15 136 20 226 22 339
5 22 65 30 130 39 219 49 330
10 29 59 40 121 51 206 64 315
15 35 53 48 112 61 195 76 301
20
0 0 97 0 202 0 349 0 540
2 10 75 14 149 18 250 20 377
5 21 71 29 143 38 242 47 367
10 28 64 38 133 50 229 62 351
15 34 58 46 124 59 217 73 337
20 48 52 55 116 69 206 84 322
30
0 0 100 0 213 0 374 0 587
2 9 81 13 166 14 283 18 432
5 21 77 28 160 36 275 45 421
10 27 70 37 150 48 262 59 405
15 33 64 44 141 57 249 70 389
20 56 58 53 132 66 237 80 374
30 NA NA 73 113 88 214 104 346
NOTE - Single appliance venting congurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other vent congurations, the vent
system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45° elbows equal one 90° elbow) beyond two, the maximum
capacity listed in the venting table should be reduced by 10 percent (0.90 x maximum listed capacity).

Page 19
TABLE 4
Vent Connector Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Height
H
(feet)
Lateral
L
(feet)
Vent and Connector Diameter - D (inches)
3 inch 4 inch 5 inch 6 inch
Appliance Input Rating in Thousands of Btu Per Hour
Min Max Min Max Min Max Min Max
6
1 22 37 35 66 46 106 58 164
2 23 41 37 75 48 121 60 183
3 24 44 38 81 49 132 62 199
8
1 22 40 35 72 49 114 64 176
2 23 44 36 80 51 128 66 195
3 24 47 37 87 53 139 67 210
10
1 22 43 34 78 49 123 65 189
2 23 47 36 86 51 136 67 206
3 24 50 37 92 52 146 69 220
15
1 21 50 33 89 47 142 64 220
2 22 53 35 96 49 153 66 235
3 24 55 36 102 51 163 68 248
20
1 21 54 33 99 46 157 62 246
2 2 57 34 105 48 167 64 259
3 23 60 35 110 50 176 66 271
30
1 20 62 31 113 45 181 60 288
2 21 64 33 118 47 190 62 299
3 22 66 34 123 48 198 64 309
TABLE 5
Common Vent Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)
Vent and Connector Diameter - D (inches)
4 inch 5 inch 7 inch 7 inch
Appliance Input Rating in Thousands of Btu Per Hour
FAN + FAN FAN + NAT FAN + FAN FAN + NAT FAN + FAN FAN + NAT FAN + FAN FAN + NAT
6 92 81 140 116 204 161 309 248
8 101 90 155 129 224 178 339 275
10 110 97 169 141 243 194 367 299
15 125 112 195 164 283 228 427 352
20 136 123 215 183 314 255 475 394
30 152 138 244 210 361 297 547 459

Page 20
Removal of the Furnace from Common Vent
In the event that an existing furnace is removed from a
venting system commonly run with separate gas applianc-
es, the venting system is likely to be too large to properly
vent the remaining attached appliances.
Conduct the following test while each appliance is oper-
ating and the other appliances (which are not operating)
remain connected to the common venting system. If the
venting system has been installed improperly, you must
correct the system as indicated in the general venting re-
quirements section.
IMPORTANT
CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for
each appliance connected to the venting system
being placed into operation could result in carbon
monoxide poisoning or death. The following steps
shall be followed for each appliance connected to
the venting system being placed into operation,
while all other appliances connected to the venting
system are not in operation:
1 - Seal any unused openings in the common venting
system.
2 - Inspect the venting system for proper size and
horizontal pitch. Determine that there is no blockage,
restriction, leakage, corrosion, or other deciencies
which could cause an unsafe condition.
3 - Close all building doors and windows and all doors
between the space in which the appliances remaining
connected to the common venting system are located
and other spaces of the building. Turn on clothes
dryers and any appliances not connected to the
common venting system. Turn on any exhaust fans,
such as range hoods and bathroom exhausts, so they
will operate at maximum speed. Do not operate a
summer exhaust fan. Close replace dampers.
4 - Follow the lighting instructions. Turn on the appliance
that is being inspected. Adjust the thermostat so that
the appliance operates continuously.
5 - After the burner have operated for 5 minutes, test
for leaks of ue gases at the draft hood relief opening.
Use the ame of a match or candle.
6 - After determining that each appliance connected to
the common venting system is venting properly, (step
3) return all doors, widows, exhaust fans, replace
dampers, and any other gas-burning appliances to
their previous mode of operation.
7 - If a venting problem is found during any of the
preceding tests, the common venting system must
be modied to correct the problem. Resize the
common venting system to the minimum vent pipe
size determined by using the appropriate tables in
Appendix G. (These are in the current standards of
the National Fuel Gas Code ANSI Z223.1.
Gas Piping
Gas supply piping should not allow more than 0.5”W.C.
drop in pressure between gas meter and unit. Supply gas
pipe must not be smaller than unit gas connection.
CAUTION
If a exible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet. The exible connector can then
be added between the black iron pipe and the gas
supply line.
WARNING
Do not over torque (800 in-lbs) or under torque (350 in-
lbs) when attaching the gas piping to the gas valve.
Gas Supply
1 - This unit is shipped standard for left or right side
installation of gas piping (or top entry in horizontal
applications) Connect the gas supply piping into the
gas valve. The maximum torque is 800 in lbs and
minimum torque is 350 in lbs
2 - When connecting the gas supply piping, consider
factors such as length of run, number of ttings, and
furnace rating to avoid excessive pressure drop.
Table 6 lists recommended pipe sizes for typical
applications.
3 - The gas piping must not run in or through air ducts,
clothes chutes, gas vents or chimneys, dumb waiters,
or elevator shafts.
4 - The piping should be sloped 1/4 inch (6.4 mm) per
15 feet (4.57 m) upward toward the meter from the
furnace. The piping must be supported at proper
intervals [every 8 to 10 feet (2.44 to 3.01 m)] with
suitable hangers or straps. Install a drip leg in vertical
pipe runs to the unit.
5 - A 1/8” N.P.T. plugged tap or pressure post is located
on the gas valve to facilitate test gauge connection.
See gure 36.
6 - In some localities, codes may require the installation
of a manual main shut-o󰀨 valve and union (furnished
by the installer) external to the unit. The union must
be of the ground joint type.
IMPORTANT
Compounds used on threaded joints of gas piping
must be resistant to the actions of liquied petroleum
gases.
NOTE - If emergency shuto is necessary, shut o the
main manual gas valve and disconnect main power to the
furnace. The installer should properly label these devices.