Lennox SIGNATURE SLP99UHV User manual

Page 1
INSTALLATION
INSTRUCTIONS
SLP99UHV
507999-01
10/2021
Supersedes 08/2021
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.
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.
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.
NOTICE
A thermostat is not included and must be ordered
separately.
• A communicating thermostat must be used in
communicating applications.
•In non-communicating applications, the Lennox
ComfortSense® 7500 thermostat may be used, as well
as other non-communicating thermostats.
In all cases, setup is critical to ensure proper system
operation.
Field wiring for both communicating and non-
communicating applications is illustrated in diagrams,
which begin on Page 35
©2021 Lennox Industries Inc.
Dallas, Texas USA
DAVE LENNOX SIGNATURE®
COLLECTION GAS FURNACES
UP/FLOW HORIZONTAL AIR DISCHARGE
Contents
Unit Dimensions .............................................................2
Parts Arrangement..........................................................3
SLP99UHV Gas Furnace ...............................................4
Shipping and Packing List ..............................................4
Safety Information ..........................................................4
Use of Furnace as Construction Heater .........................5
General...........................................................................6
Installation - Setting Equipment......................................6
Filters............................................................................10
Duct System .................................................................10
Pipe Fittings Specications...........................................13
Joint Cementing Procedure..........................................14
Venting Practices..........................................................15
Vent Pipe Guidelines ....................................................15
Gas Piping....................................................................30
Electrical.......................................................................33
Integrated Control.........................................................41
Unit Start-Up.................................................................50
Gas Pressure Measurement ........................................51
Operating Pressure Signal Measurement ....................52
Proper Combustion.......................................................53
High Altitude Information ..............................................53
Other Unit Adjustments.................................................53
Heating Sequence of Operation ...................................54
Service..........................................................................56
Repair Parts List...........................................................58
Integrated Control Diagnostic Codes............................59
Conguring Unit Size Codes ........................................62
Troubleshooting: Heating Sequence of Operation .......63

Page 2
Unit Dimensions - inches (mm)
SLP99UH Model
No..
A B C D
in. mm in mm in mm in mm
070XV36B 17-1/2 446 16-3/8 416 16 406 7-5/8 194
090XV36C
090XV48C
090XV60C
110XV60C
21 533 19-7/8 505 19-1/2 495 9-3/8 238
135XV60D 24-1/2 622 23-3/8 594 23 584 11-1/8 283
AIR FLOW
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)
3-1/4
(83)
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
1-1/2 (38)
Front Panel
COMBUSTION
AIR INTAKE
2 (51)
(Either Side)
1-7/8 (48)
CONDENSATE
TRAP CONNECTION
(Either Side)
2
Optional Side Return Air Filter Kit is not for use
with the Optional Return Air Base.
1
Flue Condensate Trap Assembly
Furnished for external
field installation
on either side of unit.
(See installation instructions
for additional
information.)
7
(178)
NOTE - 60C and 60D 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.

Page 3
Parts Arrangement
BURNER BOX ASSEMBLY
VARIABLE
CAPACITY
GAS VALVE
HEAT EXCHANGER
A
CCESS PANEL
CONTROL BOX
(includes variable capacity integrated control
transformer, circuit breaker and door switch)
VARIABLE SPEED BLOWER MOTOR
BAG ASSEMBLIES
(shipping location)
COLD END HEADER
BOX
PRESSURE SWITCHES
VARIABLE SPEED
COMBUSTION AIR
INDUCER
INNER BLOWER
ACCESS PANEL
SIGHT GLASS
PRIMARY LIMIT
SHIPPING BLOCK
(-135 UNITS ONLY)
FIGURE 1

Page 4
SLP99UHV Gas Furnace
The SLP99UHV category IV gas furnace is equipped with
a variable-capacity, variable-speed integrated control.
This control ensures compatibility with a communicating
thermostat, the iHarmony® zone control system, or a ther-
mostat which provides humidity control. Each SLP99UHV
is shipped ready for installation in the upow, horizontal
left air discharge or horizontal right air discharge position.
The furnace is equipped for natural gas applications only.
A changeover kit may be ordered for LP applications.
The SLP99UHV must be installed only as a Direct Vent
gas furnace.
NOTE - In Direct Vent installations, combustion air is tak-
en from outdoors and ue gases are discharged outdoors.
See FIGURE 2 for applications including roof termination.
DIRECT VENT INSTALLATION
EXHAUST OUTLET
COMBUSTION
AIR INTAKE
OUTSIDE OF
HOUSE
FIGURE 2
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled SLP99UHV 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 cap clamp
1 - 3/4” Threaded street elbow
1 -Flue Coupling
1- Bag containing discharge air sensor
Check equipment for shipping damage. If you nd any
damage, immediately contact the last carrier.
The following items may also be ordered separately:
1 - Thermostat
1 - Natural to LP gas conversion kit
1 - High altitude kit
1 - Horizontal suspension kit
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.
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, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves
and protective clothing.
Use only the type of gas approved for use with this fur-
nace. Refer to unit nameplate.
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
Installed Locations
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.
This furnace is designed for installation clearances to
combustiblematerial as listed on the unit nameplate and
in the tables in FIGURE 10 and FIGURE 11. Accessibility
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.
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

Page 5
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 or CSA B149 standard.
NOTE - Furnace must be adjusted to obtain a temperature
rise (100% percent capacity) within the range(s) specied
on the unit nameplate. Failure to do so may cause erratic
limit operation and may also result in premature heat ex-
changer failure. See ““Duct System” on page 10 for in-
stalling the optional discharge air sensor used to measure
temperature rise. Sensor is shipped with the unit.
This SLP99UHV 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.
With a parallel ow arrangement, a damper (or other
means to control the ow of air) must adequately prevent
chilled air from entering the furnace. If the damper is man-
ually 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. See FIGURE 3.
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 3
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.
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.
CAUTION
Do not set thermostat below 60F (16C) in heating mode.
Setting below 60F (16C) reduces the number of heating
cycles. Damage to the unit may occur that is not covered
by the warranty.
The SLP99UHV furnace may be installed in alcoves, clos-
ets, attics, basements, garages, and utility rooms.
This furnace is not designed for installation in mobile
homes, recreational vehicles, or outdoors.
Never use an open ame to test for gas leaks. Check all
connections using a commercially available soap solution
made specically for leak detection.
Use of Furnace as Construction Heater
Units may be used for heating of buildings or structures
under construction, if the following conditions are met to
ensure proper operation:
DO NOT USE THE UNIT FOR CONSTRUCTION HEAT
UNLESS ALL OF THE FOLLOWING CRITERIA ARE
MET:
• Furnace must be in its nal location. The vent system
must be permanently installed per these installation in-
structions.
• Furnace must be installed as a two pipe system and
one hundred percent (100%) outdoor air must be pro-
vided for combustion air requirements during construc-
tion.
• A room thermostat must control the furnace. The use
of xed jumpers that will provide continuous heating is
prohibited.
• The input rate and temperature rise must be set per the
furnace rating plate.
• Supply and Return air ducts must be provided and
sealed to the furnace. Return air must be terminated
outside of the space where furnace is installed.
• Return air temperature range between 60°F (16°C) and
80°F (27°C) must be maintained.
• MERV 11 or greater air lters must be installed in the
system and must be regularly inspected and maintained
(e.g., regular static checks and replaced at end of life)
during construction.
• Blower and vestibule access panels must be in place on
the furnace at all times.
• The furnace heat exchanger, components, duct system,
and evaporator coils must be thoroughly cleaned follow-
ing nal construction clean−up.

Page 6
• Air lters must be replaced upon construction comple-
tion.
• All furnace operating conditions (including ignition, in-
put rate, temperature rise and venting) must be veried
in accordance with these installation instructions.
EQUIPMENT MAY EXPERIENCE PREMATURE COM-
PONENT FAILURE AS A RESULT OF FAILURE TO FOL-
LOW THE ABOVE INSTALLATION INSTRUCTIONS.
FAILURE TO FOLLOW THE ABOVE INSTALLATION IN-
STRUCTIONS VOIDS THE MANUFACTURER’S EQUIP-
MENT LIMITED WARRANTY. LENNOX DISCLAIMS
ALL LIABILITY IN CONNECTION WITH INSTALLER’S
FAILURE TO FOLLOW THE ABOVE INSTALLATION IN-
STRUCTIONS.
NOTWITHSTANDING THE FOREGOING, INSTALLER
IS RESPONSIBLE FOR CONFIRMING THAT THE USE
OF CONSTRUCTION HEAT IS CONSISTENT WITH THE
POLICIES AND CODES OF ALL REGULATING ENTI-
TIES. ALL SUCH POLICIES AND CODES MUST BE AD-
HERED TO.
General
CAUTION
SLP99UHV unit should not be installed in areas normally
subject to freezing temperatures..
These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the fol-
lowing general recommendations must be considered
when installing a SLP99UHV furnace:
• Place the furnace as close to the center of the air distri-
bution system as possible. The furnace should also be
located close to the chimney or vent termination point
• When the furnace is installed in an attic or other insulat-
ed 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.
• Please consult the manufacturer of your evaporator
coil for their recommendations on distance required
between the heat exchanger and their drain pan. Ad-
equate space must be provided between the drain pan
and the furnace heat exchanger.
Installation - Setting Equipment
WARNING
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.
WARNING
Do not install the furnace on its front or back.
See FIGURE 4.
See figure 4.
Front Back
FIGURE 4
Upow Applications
The SLP99UHV gas furnace can be installed as shipped
in the upow position. Refer to gure 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 5.

Page 7
SETTING EQUIPMENT
UPFLOW APPLICATION
HORIZONTAL APPLICAT ION
SIDE VIEW
FRONT VIEW END VIEW
UNIT
FRONT
AIR FLOW
UNIT
FRONT
1/2”
max.
1/2”
max.
AIR FLOW
Unit must be level side-to-side. Unit may be positioned from level to 1/2” toward the front to aid in draining.
Place level on the front blower
deck to check side to side
Place level on blower
deck screws to check
forward tilt
FIGURE 5
Side Return Air
(with transition and filter)
Return
Air
Plenum
Transition
20” X 25” X 1”
(508mmX635mmX
25mm)
Air Filter
FIGURE 6
SLP99UHV 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
feet) require either a return air base or eld-fabricated
transition to accommodate an optional IAQ accessory
taller than 14.5”. See FIGURE 6.
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 7.
Removing the Bottom Panel
Screw
Bottom Panel
Bottom Cap
FIGURE 7

Page 8
Optional Return Air Base
(Upflow Applications Only)
NOTE- Optional side return air filter kits are not for use with 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.
2
To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.
FRONT VIEW
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)
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)
FIGURE 8
NOTE - Units with 1/2 hp blower motor are equipped
with three exible legs and one rigid leg. The rigid leg is
equipped with a shipping bolt and a at white plastic wash-
er (rather than the rubber mounting grommet used with
a exible mounting leg). See FIGURE 9. The bolt and
washer must be removed before the furnace is placed
into operation. After the bolt and washer have been re-
moved, the rigid leg will not touch the blower housing.
RIGID LEG
remove shipping bolt and washer
UNITS WITH 1/2 HP
BLOWER MOTOR
FIGURE 9
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in FIGURE 10 and FIGURE
11.
WARNING
The blower door must be securely in place when the
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into the
living space resulting in personal injury or death.
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 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 replace or stove, etc.
Fire, explosion, carbon monoxide poisoning, personal
injury and/or property damage could result..

Page 9
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 -- Upow Units
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 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.
Setting an Upow Unit
When the side return air inlets are used in an upow appli-
cation, it may be necessary to install shims on the bottom
of the furnace.
Horizontal Applications
The SLP99UHV furnace can be installed in horizontal ap-
plications with either right- or left-hand air discharge. Re-
fer to FIGURE 11 for clearances in horizontal applications
Horizontal Application
Installation Clearances
dnEthgiRdnEtfeL
Right-Hand Discharge
Left-Hand Discharge
Top
Bottom (Floor)**
Bottom (Floor)**
dnEthgiRdnEtfeL
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 11
Suspended Installation of Horizontal Unit
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 FIGURE 12, or install the furnace
on a platform, as shown in FIGURE 13. A horizontal sus-
pension 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.

Page 10
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.
HORIZONTAL SUSPENSION KIT
Bracket
(typical)
Metal Strap
(typical)
Air
Flow
Internal Brace
(provided with kit)
FIGURE 12
Platform Installation of Horizontal Unit
1 - Select location for unit keeping in mind service and
other necessary clearances. See FIGURE 11.
2 - Construct a raised wooden frame and cover frame
with a plywood sheet. If unit is installed above
nished space, fabricate an auxiliary drain pan
to be installed under unit. Set unit in drain pan as
shown in FIGURE 13. Leave 8 inches for service
clearance below unit for condensate trap.
3 - Provide a service platform in front of unit. When
installing 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.
5 - If necessary, run the condensate line into a
condensate 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.
*Gas connector may be
used for Canadian
able by local authority
having jurisdiction.
*GAS CONNECTION
RAISED
PLATFORM
SERVICE PLATFORM
INTAKE PIPE
EXHAUST PIPE
FIGURE 13
Return Air -- Horizontal Applications
Return air must be brought in through the end of a fur-
nace installed in the horizontal position. The furnace is
equipped with a removable bottom panel to facilitate in-
stallation. See FIGURE 7.
Filters
This unit is not equipped with a lter or rack. A eld-provid-
ed lter is required for the unit to operate properly. TABLE
1 lists recommended lter sizes.
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 standard e󰀩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).
A lter must be in place when the unit is operating.
NOTE - In upow applications where side return air lter is
installed on same side as the condensate trap, make sure
that clearance is maintained to ensure future access to
the lter access panel.
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. This will result in a qui-
et and low-static system that has uniform air distribution.
See below for proper duct installation.
FIGURE 14
HORIZONTAL UNIT
SUPPLY
AIR
SUPPLY
AIR Install self tapping screws
to seal any potential air
leaks
UPFLOW UNIT

Page 11
Discharge Air Temperature Sensor
This furnace is shipped with a discharge air temperature sensor that can be installed in the supply air plenum. The sen-
sor is used to measure temperature rise in the heating mode and temperature drop in the cooling mode. See TABLE 2
and FIGURE 15 (upow) or TABLE 3 and FIGURE 16 (horizontal left) or TABLE 4 and FIGURE 17 (horizontal right) for
correct location. Drill a 3/8 inch diameter hole in the supply duct based on the specied location. Center the discharge
air temperature sensor in the middle of the hole and use two eld provided screws to secure in place. The orientation of
the sensor mounting ange is not critical and can be oriented to whatever position is needed to prevent interference with
the evaporator coil, air duct etc. Field supplied wiring must be used to connect the discharge air temperature sensor to
the discharge air temperature sensor terminals on the integrated control board. Either wire can be connected to either
terminal. See FIGURE 18.
A communicating thermostat can be used to run temperature rise and temperature drop tests and viewed in the installa-
tion reports. See “FIGURE 53” on page 36 for communicating thermostat wiring. If a communicating thermostat is not
being used, then the discharge temperature can be viewed on the seven segment LED on the integrated control shown in
FIGURE 18. For zoning applications the discharge air sensor must be installed and wired to the zoning control board and
should not be wired to the furnace control board.
NOTE - The discharge air temperature sensor must be located per TABLE 2, TABLE 3 or TABLE 4 to provide an accurate
temperature measurement.
NOTE - If the system does not include an evaporation coil, the sensor should be installed according to the following:
1 - Place the sensor as far away from the direct heat source in the main plenum as possible. A minimum of 19” is recom
mended but up to 36” is preferred.
NOTE - If the system does not include an evaporation coil, the sensor should be installed according to the following:
1 - Place the sensor as far away from the direct heat source in the main plenum as possible. A minimum of 19” is recom
mended but up to 36” is preferred.
2 - Oset the sensor 1/4 of the width of the plenum from the left edge of the plenum in upow, top edge of the plenum in
horizontal right and bottom of the plenum in horizontal left. For example, if the plenum is 16” wide then oset the sensor 4”
from the edge. The sensor should report a temperature within the rise range of the furnace. If the readings from the sensor
appear to be below the rise range of the furnace, move the sensor in 1” increments towards the center of the plenum until
the sensed temperature is within the rise range of the furnace. If the sensor reading appears to be too high, move the sen-
sor in 1” increments towards the edge of the plenum until the sensed temperature is within the rise range of the furnace.
TABLE 2
Discharge Air Temperature Sensor Location Upow
SLP99UH Model “a” “b” Mounting Surface
070XV36B 2” Center
Plenum
Duct
090XV36C 3” Center
090XV48C 2” 7” from right
090XV60C 3” 4” from left
110XV60C 2” 8” from right
135XV60D 2” 7” from left
Coil
Plenum
a
b
Upflow
AIR FLOWAIR FLOW
Discharge Air Temperature Sensor Location
FIGURE 15

Page 12
TABLE 3
Discharge Air Temperature Sensor
Location Horizontal Left
SLP99UH
Model “a” “b” Mounting Surface
070XV36B 5” Center
Plenum Duct
090XV36C 3” 4” from bottom
090XV48C 2” 7” from bottom
090XV60C 4” 3” from bottom
110XV60C 3” 8” from bottom
135XV60D 2” 7” from bottom
a
bCoil
Plenum
Discharge Air Temperature Sensor Location
Horizontal Left
AIR FLOW
Horizontal Left
FIGURE 16
TABLE 4
Discharge Air Temperature Sensor
Location Horizontal Right
SLP99UH
Model “a” “b” Mounting Surface
070XV36B 5” Center
Plenum Duct
090XV36C 2” 8” from bottom
090XV48C 3” Center
090XV60C 3” 7” from top
110XV60C 3” Center
135XV60D 2” 7” from top
Coil Plenum
b
a
Horizontal Right
AIR FLOW
Discharge Air Temperature Sensor Location
FIGURE 17
Discharge Air Temperature Sensor Field Wiring
+
DISCHARGE AIR
TEMPERATURE
SENSOR
TERMINALS
W915
W951
W914
EAC
HUM
7 SEGEMENT LED
FIGURE 18

Page 13
TABLE 5
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 D3188
CANADA PIPE & FITTING & SOLVENT
CEMENT MARKING
PVC & CPVC Pipe and Fittings
ULCS636
PVC & CPVC Solvent Cement
ABS to PVC or CPVC Transition
Cement
POLYPROPYLENE VENTING SYSTEM
PolyPro® by Duravent
InnoFlue® by Centrotherm
UL 1738 CERTIFIED GAS VENTING SYSTEM
IPEX System1738 Schedule 40 PVC
Pipes and Fittings UL1738
IPEX System1738 PVC FGV Cement &
Primer
IMPORTANT
SLP99UHV 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 ttings in the unit.
NOTE - Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an ex-
ternal static pressure which exceeds 0.8 inches w.c. may
result in erratic limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a remov-
able access panel should be installed in the supply air
duct. The access panel should be large enough to permit
inspection (by reected light) of the heat exchanger for
leaks after the furnace is installed. If present, this access
panel must always be in place when the furnace is oper-
ating and it must not allow leaks into the supply air duct
system. In horizontal units, install self tapping screws in
the three evaporator coil screw holes made for upow ap-
plications to seal the top cap to the vestibule panel.
Return Air Plenum
Return air must not be drawn from a room where this fur-
nace, or any other gas-fueled appliance (i.e., water heat-
er), or carbon monoxide-producing device (i.e., wood re-
place) is installed. When return air is drawn from a room,
a negative pressure is created in the room. If a gas appli-
ance 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 re-
sult in incomplete combustion and the formation of carbon
monoxide gas. This toxic gas 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 (return air brought in through either
side of the furnace allowed in upow applications only). 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 proper-
ly and safely. Use berglass sealing strips, caulking, or
equivalent 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.
Pipe Fittings Specications
All pipe, ttings, primer and solvent cement must conform
with American National Standard Institute and the Ameri-
can Society for Testing and Materials (ANSI/ASTM) stan-
dards. The solvent shall be free-owing and contain no
lumps, undissolved particles or any foreign matter that
adversely a󰀨ects the joint strength or chemical resistance
of the cement. The cement shall show no gelation, strati-
cation, or separation that cannot be removed by stirring.
Refer to TABLE 5 for approved piping and tting materials.
CAUTION
Solvent cements for plastic pipe are ammable 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 re hazard and to minimize breathing of solvent
vapors. Avoid contact of cement with skin and eyes.

Page 14
Use PVC primer and solvent cement or ABS solvent cement meeting ASTM specications, refer to TABLE 5. As an alter-
nate, use all purpose cement, to bond ABS, PVC, or CPVC pipe when using ttings and pipe made of the same materials.
Use transition solvent cement when bonding ABS to either PVC or CPVC. Low temperature solvent cement is recom-
mended. Metal or plastic strapping may be used for vent pipe hangers. Uniformly apply a liberal coat of PVC primer for
PVC.
TABLE 6
OUTDOOR TERMINATION USAGE*
Input Size Vent Pipe
Dia. in.
STANDARD CONCENTRIC
Flush Mount
Kit
Wall Kit
Field
Fabricated
1-1.2 inch 2 inch 3 inch
2 inch 3 inch 71M80 (US)
444W92
(CA)
69M29 (US)
444W92
(CA)
60L46 (US)
444W93
(CA)
51W11 (US)
51W12
(CA)
22G44 (US)
430G28 (CA)
44J40 (US)
481J20 (CA)
070
61-1/2 3YES YES 1YES 5YES 2YES
23YES YES 1YES 5YES 2YES
2-1/2 3YES YES 1YES 5YES 2YES
33YES YES 1YES 5YES 2YES
090
23YES YES 5YES YES YES
2-1/2 3YES YES 5YES YES YES
33YES YES 5YES YES YES
110
2 YES YES 5YES YES YES
2-1/2 YES YES 5YES YES YES
3 YES YES 5YES YES YES
135 3 YES YES 5YES YES
NOTE - Standard Terminations do not include any vent pipe or elbows external to the structure. Any vent pipe or elbows external to the structure must be included in total
vent length calculations. See vent length tables.
* Kits must be properly installed according to kit instructions.
1Requires eld-provided outdoor 1-1/2” exhaust accelerator.
2Concentric kits 71M80 and 44W92 include 1-1/2 in. outdoor accelerator, when used with 070 input models. When 1-1/2 in. pipe is used it must transition to 2 in. pipe with
the concentric kit.
3 Flush mount kits 51W11 and 51W12 includes 1-1/2 in. outdoor exhaust accelerator, required when used with 070 and 090 input models. When 1-1/2 in. pipe is used it
must transition to 2 in. pipe with the ush mount kit.
4 Termination kits 30G28, 44W92, 4493 and 81J20 are certied to ULC S636 for use in Canada only.
5 See table 7 for vent accelerator requirements.
6 2 in. to 1-1/2 in. eld provided reducer required.
Joint Cementing Procedure
All cementing of joints should be done according to the specications outlined in ASTM D 2855.
NOTE - A sheet metal screw may be used to secure the
intake pipe to the connector, if desired. Use a drill or self
tapping screw to make a pilot hole.
DANGER
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 tting 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 t joint and mark depth of tting 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 tting and male end of pipe to
depth of tting socket.
6 - Promptly apply solvent cement to end of pipe and
inside socket surface of tting. Cement should be
applied lightly but uniformly to inside of socket. Take
care to keep excess cement out of socket. Apply
second coat to end of pipe.
NOTE - Time is critical at this stage. Do not allow prim-
er to dry before applying cement.

Page 15
7 - Immediately after applying last coat of cement to
pipe, and while both inside socket surface and end
of pipe are wet with cement, forcefully insert end of
pipe into socket until it bottoms out. Turn PVC pipe
1/4 turn during assembly (but not after pipe is fully
inserted) to distribute cement evenly. DO NOT turn
ABS or cellular core pipe.
NOTE - Assembly should be completed within 20 sec-
onds 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 tting socket. A properly made joint will show
a bead around its entire perimeter. Any gaps may
indicate a defective assembly due to insu󰀩cient
solvent.
9 - Handle joints carefully until completely set.
Venting Practices
* See Piping and Fittings Specifications table
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 edistuoedisni
24” maximum
3/4” minimum
Wall Thickness Guidelines
FIGURE 19
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.
Exhaust Piping FIGURE 23, FIGURE 24 and FIGURE
26 (vent adapter)
3 - Route piping to outside of structure. Continue with
installation following instructions given in piping
termination section..
Intake Piping FIGURE 23 and FIGURE 24
The SLP99UHV furnace may be installed only in direct
vent applications.
The SLP99UHV is designed for combustion air intake
through an inlet in the unit’s top cap. Intake air piping is
independent of exhaust piping.
If replacing 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.
REPLACING FURNACE THAT WAS PART OF A
COMMON VENT SYSTEM
CHIMNEY
OR GAS
VENT
(Check sizing
for water
heater only)
FURNACE
(Replaced)
WATER
HEATER
OPENINGS
(To Adjacent
Room)
FIGURE 20
CAUTION
Do not discharge exhaust into an existing stack or
stack that also serves another gas appliance. If vertical
discharge through an existing unused stack is required,
insert PVC pipe inside the stack until the end is even
with the top or outlet end of the metal stack.
CAUTION
The exhaust vent pipe operates under positive pressure
and must be completely sealed to prevent leakage of
combustion products into the living space.
Vent Pipe Guidelines
NOTE - Lennox has approved the use of DuraVent® and
Centrotherm vent pipe and terminations as an option to
PVC. When using the PolyPro® by DuraVent or Inno-
Flue® by Centrotherm venting system the vent pipe re-
quirements stated in the unit installation instruction – min-
imum & maximum vent lengths, termination clearances,
etc. – apply and must be followed. Follow the instructions
provided with PoyPro by DuraVent and InnoFlue® by
Centrotherm venting system for assembly or if require-
ments are more restrictive. The PolyPro by Duravent and
In noFlue by Centrotherm venting system must also follow
the uninsulated and unconditioned space criteria listed in
TABLE 9.

Page 16
The SLP99UHV is installed only as a Direct Vent gas
central furnace.
NOTE - In Direct Vent installations, combustion air is tak-
en from outdoors and ue gases are discharged outdoors.
Intake and exhaust pipe sizing -- Size pipe according to
TABLE 7 and TABLE 8. Count all elbows inside and out-
side the home.
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 10.
In some applications which permit the use of several dif-
ferent sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox’ Application Department for assis-
tance in sizing vent pipe in these applications.
Use the steps in FIGURE 22 to correctly size vent pipe
diameter.
NOTE - It is acceptable to use any pipe size which ts
within the guidelines allowed in TABLE 8.
Horizontal Installation Offset Requirements
NOTE - Exhaust pipe MUST be glued to furnace exhaust fitting,
unless the optional glueless vent adapter kit 17H92 is used..
NOTE -
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.
Exhaust Pipe
Horizontal
Gas Furnace
12” Min.
12” Max.
FIGURE 21
NOTE - The exhaust collar on all models is sized to ac-
commodate 2” Schedule 40 vent pipe. In horizontal ap-
plications, any transition to exhaust pipe larger than 2”
must be made in vertical runs of the pipe. Therefore a 2”
elbow must be added before the pipe is transitioned to
any size larger than 2”. This elbow must be added to the
elbow count used to determine acceptable vent lengths.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.
NOTE - Lennox oers a glueless vent adapter kit 17H92
as an option for exhaust exiting at the furnace top cap
coupling. If the kit is not used then the exhaust pipe MUST
be glued to the furnace exhaust tting.
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations..
Piping Size Process
1
2
3
4
5
6
Which style termination
being used?
Standard or
concentric?.
Which needs
most elbows?
Intake or
exhaust?
How many elbows?
Count all elbows inside
and outside house.
Desired pipe size?
Find max intake or
exhaust pipe length.
Includes all vent pipe and
elbows inside and outside
the house.
What is the altitude of
the furnace installation?
7
What is the
furnace capacity?
FIGURE 22
TABLE 7
MINIMUM VENT PIPE LENGTHS
SLP99UHV
MODEL
MIN.EQUIV. VENT
LENGTH EXAMPLE
070
15 ft*
5 ft. plus 2 elbows of
1-/12”, 2”, 2-1/2” or
3” diameter pipe
090, 110
5 ft. plus 2 elbows
of 2”, 2-1/2” or 3”
diameter pipe
135 5 ft. plus 2 elbows of
3” diameter pipe
*Any approved termination may be added to the minimum equivalent
length listed. Two 45 degree elbows are the equivalent to one 90 de-
gree elbow.

Page 17
TABLE 8
Maximum Allowable Intake or Exhaust Vent Length in Feet
*Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be same pipe size.
NOTE - Additional vent pipe and elbows used to terminate the vent pipe outside the structure must be included in the total vent length calculation.
Standard Termination at Elevation 0 - 7500’
Number
Of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 135 070 090 110 135 070 090 110 135 070 090 110 135
120
N/A N/A N/A
91 69 14
N/A
140 93 43
N/A
162 143 118 114
215 86 64 9 135 88 38 157 138 113 109
310 81 59
N/A
130 83 33 152 133 108 104
4
N/A
76 54 125 78 28 147 128 103 99
571 49 120 73 23 142 123 98 94
666 44 115 68 18 137 118 93 89
761 39 110 63 13 132 113 88 84
856 34 105 58
N/A
127 108 83 79
951 29 100 53 122 103 78 74
10 46 24 95 48 117 98 73 69
Standard Termination at Elevation 7501’ - 10,000’
Number
of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 135 070 090 110 135 070 090 110 135 070 090 110 135
112
N/A N/A N/A
66 44
N/A N/A
115 68
N/A N/A
137 118 93 89
27 61 39 110 63 132 113 88 84
3
N/A
56 34 105 58 127 108 83 79
451 29 100 53 122 103 78 74
546 24 95 48 117 96 73 69
641 19 90 43 112 93 68 64
736 14 85 38 107 88 63 59
831
N/A
80 33 102 83 58 54
926 75 28 97 78 53 49
10 21 70 23 92 73 48 44

Page 18
TABLE 8 Cont.
Maximum Allowable Intake or Exhaust Vent Length in Feet
*Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be same pipe size.
NOTE - Additional vent pipe and elbows used to terminate the vent pipe outside the structure must be included in the total vent length calculation
Concentric Termination 0 - 7501”
Number
of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 135 070 090 110 135 070 090 110 135 070 090 110 135
115
N/A N/A N/A
83 67 12
N/A
130 89 39
N/A
146 139 114 105
210 78 62 7 125 84 34 141 134 109 100
3
N/A
73 57
N/A
120 79 29 136 129 104 95
468 52 115 74 24 131 124 99 90
563 47 110 69 19 126 119 94 85
658 42 105 64 14 121 114 89 80
753 37 100 59
N/A
116 109 84 75
848 32 95 54 111 104 79 70
943 27 90 49 106 99 74 65
10 38 22 85 44 101 94 69 60
Concentric Termination 7501” - 10,000”
Number
of 90
Elbows
Used
1-1/2” Pipe 2” pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 135 070 090 110 135 070 090 110 135 070 090 110 135
110
N/A N/A N/A
58 42
N/A N/A
105 64
N/A N/A
121 114 89 80
2
N/A
53 37 100 59 116 109 84 75
348 32 95 54 111 104 79 70
443 27 90 49 106 99 74 65
538 22 85 44 101 94 69 60
633 17 80 39 96 89 64 55
728 12 75 34 91 84 59 50
823
N/A
70 29 86 79 54 45
918 65 24 81 74 49 40
10 13 60 19 76 69 44 35

Page 19
TYPICAL EXHAUST AND INTAKE PIPE CONNECTIONS IN UPFLOW
2” 2”
2” 3”
2”
2”
or
DO NOT transition
from smaller to larger
pipe in horizontal runs
of exhaust pipe.
EXHAUST
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE − Exhaust pipe and intake pipe must be the same diameter.
TRANSITION
2”
1−1/2”
070 Only
2”
INTAKE
3”
INTAKE EXHAUST
Exhaust
Exhaust
DO NOT transition
from larger to smaller
pipe in horizontal runs
of exhaust pipe.
Exhaust
6” Min
FIGURE 23
SIDE VIEW
2”
2”
2”
or
TYPICAL EXHAUST AND INTAKE PIPE CONNECTIONS IN HORIZONTAL
(RIGHT HAND DISCHARGE SHOWN)
3”
2”
45°
MAX
45°
MAX
DO NOT transition
from smaller to larger
pipe in horizontal runs
of exhaust pipe.
EXHAUST
12” max.
*2”
*2”
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE − Exhaust pipe and intake pipe must be the same diameter.
TRANSITION
1−1/2”
2”
3”
*2”
*2”
*2”
*2”
INTAKE
2”
2”
or
2”
2”
EXHAUST
INTAKE
/070 Only
Exhaust
DO NOT transition
from larger to smaller
pipe in horizontal runs
of exhaust pipe.
Exhaust
Exhaust
2”
FIGURE 24

Page 20
VENT TERMINATION CLEARANCES
FOR DIRECT VENT INSTALLATIONS IN THE USA AND CANADA
K
D
E
L
B
C
F
G
A
B
J
A
M
I
H
INSIDE CORNER
DETAIL
VENT TERMINAL AIR SUPPLY INLETAREA WHERE TERMINAL
IS NOT PERMITTED
Fixed
Closed
Operable
B
Fixed
Closed
Operable
B
B
A =
B =
C =
D =
E =
F =
G =
H =
I =
J =
K =
L =
M =
US Installations1Canadian Installations2
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
Clearance above grade, veranda,
porch, deck or balcony
Clearance to window or
door that may be opened
6 inches (152mm) for appliances <10,000
pliances > 10,000 Btuh (3kw) and <50,000
pliances > 50,000 Btuh (15kw)
6 inches (152mm) for appliances <10,000
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
Clearance to permanently
closed window
Vertical clearance to ventilated soffit
located above the terminal within a
horizontal distance of 2 feet (610mm)
from the center line of the terminal
Clearance to unventilated soffit
Clearance to outside corner
Clearance to inside corner
tended above meter / regulator assembly
Clearance to service regulator
vent outlet
Clearance to non-mechanical air
pliance
ply inlet
Clearance above paved sidewalk or
paved driveway located on public property
Clearance under veranda, porch, deck or balcony
* 12”
*
*
* 7 feet (2.1m)
3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
3 feet (.9m)
6 inches (152mm) for appliances <10,000
pliances > 10,000 Btuh (3kw) and <50,000
pliances > 50,000 Btuh (15kw)
6 inches (152mm) for appliances <10,000
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
3 feet (.9m) above if within 10 feet
(3m) horizontally
6 feet (1.8m)
7 feet (2.1m)†
12 inches (305mm)‡
1In accordance with the current ANSI Z223.1/NFPA 54 Natural Fuel Gas Code
2In accordance with the current CSA B149.1, Natural Gas and Propane Installation Code
*For clearances not specified in ANSI Z223.1/NFPA 54 or CSA
B149.1, clearance will be in accordance with local installation
codes and the requirements of the gas supplier and these
installation instructions.”
† A vent shall not terminate directly above a sidewalk or paved driveway that is located
between two single family dwellings and serves both dwellings.
‡ Permitted only if veranda, porch, deck or balcony is fully open on a minimum of
two sides beneath the floor. Lennox recommends avoiding this location if possible.
* 12”
* Equal to or greater than soffit depth* Equal to or greater than soffit depth* Equal to or greater than soffit depth
* Equal to or greater than soffit depth*Equal to or greater than soffit depth
* No minimum to outside corner * No minimum to outside corner
3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
3 feet (.9m)
*
*12 inches (305mm)‡
FIGURE 25