Lennox SIGNATURE SLP99DFV User manual

Page 1
INSTALLATION
INSTRUCTIONS
SLP99DFV
508001-02
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
DOWNFLOW AIR DISCHARGE
Contents
Unit Dimensions - inches (mm) ......................................2
Parts Arrangement..........................................................3
SLP99DFV Gas Furnace................................................4
Shipping and Packing List ..............................................4
Safety Information ..........................................................4
Building Codes ...............................................................4
Use of Furnace as Construction Heater .........................5
General...........................................................................6
Installation - Setting Equipment......................................6
Filters..............................................................................9
Duct System ...................................................................9
Pipe & Fittings Specications ....................................... 11
Venting Options ............................................................13
Joint Cementing Procedure..........................................14
Venting Pracitces..........................................................15
Gas Piping....................................................................30
Electrical.......................................................................33
Integrated Control.........................................................41
Blower Data..................................................................45
Unit Start-Up.................................................................50
Turning O󰀨 Gas to Unit.................................................51
High Altitude Information ..............................................51
Gas Pressure Measurement.........................................51
Proper Combustion.......................................................51
Heating Sequence of Operation ...................................54
Service..........................................................................56
Repair Parts..................................................................57
Integrated Control Diagnostic Codes............................58
Conguring Unit Size Codes ........................................61
Troubleshooting: Heating Sequence of Operation .......62

Page 2
Unit Dimensions - inches (mm)
AIR
EXHAUST AIR
OUTLET
COMBUSTION
AIR INTAKE
FLOW
2-1/16 (52)
GAS PIPING INLET
(Either Side)
ELECTRICAL INLET
(Either Side)
RETURN AIR
OPENING
FRONT VIEW SIDE VIEW
TOP VIEW
A
B
C3/4
(19)
27-3/4
(705)
19-1/4
(489)
9-1/8 (232) Right
6-9/16 (167) Left
2 (51)
Either Side
33
(838)
3/4
(19)
B
Supply
Air
Supply
Air
9/16
(14)
9/16
(14)
9/16
(14)
9/16
(14)
19-7/16
(494)
3/4
(19)
CONDENSATE
TRAP CONNECTION
5
(127)
6-7/16 (163)
Either Side
9 (229)
Either Side
2-1/4
(57)
(Either Side)
1-1/2 (38)
Front Panel
Flue Condensate Trap Assembly
Furnished for external
field installation
on either side of unit.
(See installation instructions
for additional
information.)
7
(178)
Model A
in - mm
B
in - mm
C
in - mm
SLP99DF070V36 17-1/2 - 446 16-3/8 - 416 16 - 406
SLP99DF090V36C
SLP99DF090V48C
SLP99DF090V60C
SLP99DF110V60C
21 - 553 19-7/8 - 505 19-1/2 - 495

Page 3
Parts Arrangement
BURNER BOX ASSEMBLY
GAS VALVE
ACCESS PANEL
COMBUSTION AIR INDUCER
BLOWER
ACCESS
PANEL
BLOWER ASSEMBLY
(Variable Speed Blower
Motor Is Hidden)
BAG ASSEMBLY
CONTROL BOX
(includes variable capacity
integrated control,
transformer, circuit breaker
and door switch)
PRIMARY LIMIT
SIDE VENT
PATCH PLATE
FIGURE 1

Page 4
SLP99DFV Gas Furnace
The SLP99DFV category IV gas furnace is equipped with
a variable-capacity, variable-speed integrated control.
This control ensures compatibility with the Lennox com-
mincating thermostat and iHarmony® zone control system,
as well as a thermostat which provides humidity control.
The furnace is equipped for installation in natural gas ap-
plications only. A changeover kit may be ordered for LP
applications.
The SLP99DFV must be 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.
See FIGURE 2 for applications including roof termination.
DIRECT VENT INSTALLATION
EXHAUST OUTLET
COMBUSTION
A
IR INTAKE
OUTSIDE OF
HOUSE
FIGURE 2
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled SLP99DFV unit
1 - Bag assembly containing the following:
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 - Condensate trap
1 - 3/4” Threaded street elbow
1 - Flue Coupling
2 - 2” Street elbows
2 - Side vent sealing plates
2 - Side vent sealing gaskets
6 - Sheet metal screws
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
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
Installation Locations and Clearances
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
combustible material as listed on the unit nameplate and
the table in FIGURE 7. Accessibility and service clearanc-
es must take precedence over re protection clearances.
For installation in a residential garage, the furnace must
be installed so that the burner(s) and the ignition source
are located no less than 18 inches (457 mm) above the
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 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 section on page 9 for
installing the optional discharge air sensor used to mea-
sure temperature rise. The sensor is shipped with the unit.
This SLP99DFV furnace must be installed so that its elec-
trical components are protected from water.

Page 5
Installed in Combination with a Cooling Coil
When this furnace is used with cooling units, it shall be
installed in parallel with, or on the upstream side of, cool-
ing units to avoid condensation in the heating compart-
ment. 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 (FIGURE 3).
If the damper is manually operated, it must be equipped to
prevent operation of either the heating or the cooling unit,
unless it is in the full HEAT or COOL setting.
AIR HANDLER
GAS UNIT
Dampers
(open during cooling
operation only)
Dampers
(open during heating
operation only)
FURNACE INSTALLED PARALLEL
WITH COOLING COIL
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 contin-
uous return air temperature of 60°F (16°C) or an inter-
mittent operation down to 55°F (13°C) dry bulb for cases
where a night setback thermostat is used. Return air tem-
perature must not exceed 85°F (29°C) dry bulb. See “Duct
System” on page 9 for installing the optional discharge
air sensor used to measure temperature rise. Sensor is
shipped with the unit.
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 SLP99DFV 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.
• 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.

Page 6
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
SLP99DFV 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
following general recommendations must be considered
when installing a SLP99DFV 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.
Installation - Setting Equipment
WARNING
Do not install the furnace on its front, back or in the
horizontal position. See FIGURE 5. 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.
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 4.
SETTING EQUIPMENT
FRONT VIEW SIDE VIEW
AIR FLOW AIR FLOW
1/2”
max.
AIR FLOW
SIDE VIEW
Unit must be level side-to-side. Unit may be positioned
from level to 1/2” toward the front to aid in draining.
FIGURE 4
Front
NOTE - Do not install the furnace on its front, back or in the horizontal position
Back Horizontal
FIGURE 5

Page 7
NOTE - The 1/2 hp blower motor used in the SLP99D-
F070V36B and SLP99DF090V36C unit is equipped
with three exible legs and one rigid leg. 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
r
UNITS WITH 1/2 HP
BLOWER MOTOR
FIGURE 6
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in FIGURE 7.
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.
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.
IThe unit may be installed three ways in downow applica-
tions: on non-combustible ooring, on combustible oor-
ing using a base, or on a reverse-ow cooling coil cabinet.
Do not drag the unit across the oor in the downow
position. Floor and ange damage will result. Refer
to FIGURE 7 for clearances in downow applications.
Downflow Application Installation Clearances
Top
Bottom
Left Side Right Side
Top 0
*Front 0
Back 0
Sides 0†
Vent 0
Floor NC‡
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
†Allow proper clearances to accommodate condensate trap and
vent pipe installation.
‡
tional base is installed between the furnace and the combustible
floor.
FIGURE 7
Installation on Non-Combustible Flooring (FIGURE 8)
1 - Cut oor opening keeping in mind clearances listed
on unit rating plate. Also keep in mind gas supply
connections, electrical supply, ue and air intake
connections and su󰀩cient installation and servicing
clearances. See TABLE 1 for correct oor opening
size.
2 - Flange warm air plenum and lower the plenum into
the opening.
3 - Set the unit over the plenum and seal the plenum
to the unit.
Ensure that the seal is adequate.

Page 8
TABLE 1
NON-COMBUSTIBLE FLOOR OPENINGSIZE
Cabinet Width Front to Rear Side to Side
in mm in mm
B Cabinet 17 - 1/2” 19 - 3/4 502 16 - 5/8 422
C Cabinet 21” 19 - 3/4 502 20 - 1/8 511
NOTE - Floor opening dimensions listed are 1/4 inch (6 mm) larger than
the unit opening. See dimension drawing on page 2.
SUPPLY AIR
PLENUM
PROPERLY
SIZED FLOOR
OPENING
FURNACE
FIGURE 8
Installation on Combustible Flooring (FIGURE 9)
1 - When unit is installed on a combustible oor,
a downow combustible ooring base must be
installed between the furnace and the oor. The
base must be ordered separately. See TABLE 2 for
opening size to cut in oor.
CAUTION
The furnace and combustible ooring base shall not be
installed directly on carpeting, tile, or other combustible
material other than wood ooring.
TABLE 2
COMBUSTIBLE FLOORING BASE OPENING SIZE
Cabinet
Width
Catalog
Number
Front to Rear Side to Side
in mm in mm
B Cabinet
17 - 1/2”
11M60 22 559 18 - 3/4 476
C Cabinet
21”
11M61 22 559 22 - 3/4 578
FURNACE
SUPPLY AIR
PLENUM
COMBUSTIBLE
FLOORING BASE
PROPERLY
SIZED FLOOR
OPENING
FIGURE 9
2 - After opening is cut, set combustible ooring base
into opening.
3 - Check berglass strips on combustible ooring
base to make sure they are properly glued and
positioned.
4 - Lower supply air plenum into combustible ooring
base until plenum anges seal against berglass
strips.
NOTE - Be careful not to damage berglass strips.
Check for a tight seal.
5 - Set the furnace over the plenum.
6 - Ensure that the seal between the furnace and
plenum is adequate.
Installation on Cooling Coil Cabinet (FIGURE 10)
NOTE - Downow combustible ooring base is not used.
1 - Refer to reverse-ow coil installation instructions for
correctly sized opening in oor and installation of
cabinet.
2 - When cooling cabinet is in place, set and secure
the furnace according to the instructions that are
provided with the cooling coil. Secure the furnace
to the cabinet.
3 - Seal the cabinet and check for air leaks.
COOLING COIL
PLENUM
PROPERLY
SIZED FLOOR
OPENING
FURNACE
FIGURE 10

Page 9
Return Air Opening -- Downow Units
Return air may be brought in only through the top opening
of a furnace installed in the downow position. The follow-
ing steps should be taken when installing plenum:
1 - Bottom edge of plenum should be anged with a
hemmed edge (See FIGURE 11 or FIGURE 12).
2 - Sealing strips should be used to ensure an airtight
seal between the cabinet and the plenum.
3 - In all cases, plenum should be secured to top of
furnace using sheet metal screws.
4 - Make certain that an adequate seal is made.
SECURE FROM
OUTSIDE CABINET
PLENUM
(Field Provided)
SEALING STRIP
(Field Provided)
Side View
CABINET
SIDE PANEL
FIGURE 11
SECURE FROM
INSIDE CABINET
PLENUM
(Field Provided)
SEALING STRIP
(Field Provided)
Side View
CABINET
SIDE PANEL
FIGURE 12
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
3 lists recommended lter size.
A lter must be in place whenever 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 3
Furnace Cabinet Width Fillter Size
B Cabinet 17-1/2” 16 X 25 X 1 (1)
C Cabinet 21-1/2”
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 FIGURE 13 below for proper duct installation.
Duct Installation
Down-Flow Unit
SUPPLY
AIR
FIGURE 13
Discharge Air Temperature Sensor
This furnace is shipped with a discharge air temperature
sensor that can be installed in the furnace plenum. The
sensor is used to measure temperature rise in the heat-
ing mode and temperature drop in the cooling mode. See
TABLE 4 and FIGURE 14. Drill a 3/8 inch diameter hole
in the plenum 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. Field
supplied wiring must be used to connect the sensor to the
discharge air temperature sensor terminals on the inte-
grated control board. See FIGURE 14.
NOTE - If unable to mount at specied location, sensor
can be mounted in the coil cabinet 1” from the bottom and
5” from the right side. Care must be exercised to avoid
hitting the coil/drainpan while drilling through the cabinet.
A communicating thermostat can be used to run tempera-
ture rise and temperature drop tests and viewed in the
installation reports. See FIGURE 48 on page 36 for
thermostat wiring. If a communicating thermostat is not
being used, then the discharge air temperature can be
viewed on the seven segment LED on the integrated con-
trol shown in FIGURE 14.
For zoning applications the discharge air sensor must be
installed and wired to the zoning control board. Wiring to
the furnace control board is not required.

Page 10
TABLE 4
Discharge Air Temperature Sensor
Location Downow
SLP99DF Model “a” “b” 1Mounting Surface
070XV36B
6” Center Plenum Duct
090XV36C
090XV48C
090XV60C
110XV60C
Discharge Air Sensor Location and Wiring
Downflow
AIR FLOW
+
DISCHARGE AIR
SENSOR
TERMINALS
W915
W951
W914
EAC
HUM
Coil
ab
Plenum
FIGURE 14

Page 11
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.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas-fueled appliance (i.e., water
heater), or carbon monoxide-producing device (i.e.,
wood 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 pres-
sure, 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 combustion and the formation of
carbon monoxide gas. This toxic gas might then be dis-
tributed throughout the house by the furnace duct system.
Use berglass sealing strips, caulking, or equivalent seal-
ing 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.
IMPORTANT
SLP99DFV 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.
Use PVC primer and solvent cement or ABS solvent ce-
ment meeting ASTM specications, refer to TABLE 5.
As an alternate, 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 recommended. Metal
or plastic strapping may be used for vent pipe hangers.
Uniformly apply a liberal coat of PVC primer for PVC.
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
Canadian Applications Only - Pipe, ttings, primer and
solvent cement used to vent (exhaust) this appliance must
be certied to ULC S636 and supplied by a single manu-
facturer as part of an approved vent (exhaust) system. In
addition, the rst three feet of vent pipe from the furnace
ue collar must be accessible for inspection.
TABLE 6 lists the available exhaust termination kits.

Page 12
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
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 8 for vent accelerator requirements.
6 2 in. to 1-1/2 in. eld provided reducer required.

Page 13
Venting Options
The SLP99DF is shipped with vent exhaust / air intake
connection at the top cap. See FIGURE 15. Using parts
provided, the furnace may be eld modied to have these
connections on the right side of the furnace cabinet. See
FIGURE 17 and follow the steps below. For left side vent-
ing order kit 87W73.
1 - Remove inner blower door.
2 - Loosen hose clamps which attach rubber ttings to
the white PVC pipes inside the vestibule area. See
FIGURE 15.
3 - Loosen the clamp which secures the pipes at the
blower deck. See FIGURE 15.
4 - Remove white PVC pipes, slide up and out thru the
top cap.
5 - Remove the remaining parts of the pipe clamp at
the blower deck.
6 - Remove the black plastic tting in top cap which
previously aligned the PVC pipes.
7 - Remove the sheet metal patch plate on the side
of the cabinet which covers the openings for side
venting option. Save screws for reuse.
8 - Re-use the patch plate to cover the hole in the top
cap. See FIGURE 16. Remove the 2 screws which
secure the top cap to the furnace on the right side
and re-install securing the right edge of the patch
plate and the right side of the top cap to the furnace.
Use 2 self-drilling sheet metal screws (provided) to
nish securing the left edge of the patch plate on
the left side.
9 - Use a utility knife to cut out the cabinet insulation for
the right side vent / air intake.
10 - Install the two 90° street elbows (provided) through
the side of the cabinet. The male side of each
elbow should extend down through the blower deck
and connect to the rubber ttings below. Once the
elbows are properly positioned, tighten each clamp.
11 - Peel protective backing from side vent sealing
gaskets (2) and apply to side vent sealing plates (2)
as shown in FIGURE 17.
12 - Install the side vent sealing plates and gaskets
on the exterior of the cabinet as shown in gure
15. Secure with six mounting screws (four reused
and two provided from bag assembly). Holes are
pre-punched in the parts and cabinet, no drilling is
required.
13 - Install sheet metal screws (provided) to seal extra
two holes in cabinet not used with side vent clamps.
IMPORTANT
Side vent sealing plates and side vent sealing gaskets
must be used when converting to right side venting.
Failure to use gaskets and plates may lead to improper
operation of unit.
Top Vent Configuration
Exhaust/Air
Intake Connections
Pipe Clamp
Hose Clamp
FIGURE 15
Sheet Metal
Patch Plate
Patch Plate Top Cap
FIGURE 16

Page 14
Right Side Vent Configuration
Side Vent
Sealing Plate
Side Vent
Sealing Gaskets
Street Elbows (2)
Intake
Exhaust
FIGURE 17
Joint Cementing Procedure
All cementing of joints should be done according to these
peci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
DANGER OF EXPLOSION! Fumes from PVC glue may
ignite during system check. Allow fumes to dissipate for
at least 5 minutes before placing unit into operation.
1 - Measure and cut vent pipe to desired length.
2 - Debur and chamfer end of pipe, removing any
ridges or rough edges. If end is not chamfered,
edge of pipe may remove cement from tting socket
and result in a leaking joint.
3 - Clean and dry surfaces to be joined.
NOTE - Check the inside of vent pipe thoroughly for
any obstruction that may alter furnace operation.
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
primer to dry before applying cement.
7 - Immediately after applying last coat of cement to
pipe, and while both inside socket surface and end
of pipe are wet with cement, forcefully insert end of
pipe into socket until it bottoms out. Turn PVC pipe
1/4 turn during assembly (but not after pipe is fully
inserted) to distribute cement evenly. DO NOT turn
ABS or cellular core pipe.
NOTE - Assembly should be completed within 20
seconds after last application of cement. Hammer
blows should not be used when inserting pipe.
8 - After assembly, wipe excess cement from pipe at
end of 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.

Page 15
Venting Pracitces
* See Piping and Fittings Specifications table
Piping Suspension Guidelines
NOTE - Isolate piping at the point where it exits the outside wall o
r
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 18
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 19
1 - n 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 21, FIGURE 22 and FIGURE
23)
Route piping to outside of structure. Continue with instal-
lation following instructions given in piping termination
section.
WARNING
Carbon Monoxide Poisoning Hazard
Cutting or altering exhaust or air intake pipes, which
are located in the blower compartment, could result
in Carbon Monoxide Poisoning or Death.
CAUTION
Do not discharge exhaust into an existing stack
or stack that also serves another gas appliance. If
vertical discharge through an existing unused stack
is required, insert PVC pipe inside the stack until the
end is even with the top or outlet end of the metal
stack.
CAUTION
The exhaust vent pipe operates under positive
pressure and must be completely sealed to prevent
leakage of combustion products into the living
space.
Vent piping Guidliens
NOTE - Lennox has approved the use of DuraVent® and
Centrotherm manufactured vent pipe and terminations
as an option to PVC. When using the PolyPro® by Du-
raVent or InnoFlue® by Centrotherm venting system the
vent pipe requirements stated in the unit installation in-
struction – minimum & maximum vent lengths, termination
clearances, etc. – apply and must be followed. Follow the
instructions provided with PoyPro by DuraVent and Inno-
Flue® by Centrotherm venting system for assembly or if
requirements are more restrictive. The PolyPro by Du-
ravent and InnoFlue by Centrotherm venting system must
also follow the uninsulated and unconditioned space crite-
ria listed in TABLE 10.
The SLP99DFV is installed only as a Direct Vent gas
central furnace.
NOTE - In Direct Vent installations, combustion air is taken
from outdoors and ue gases are discharged outdoors. In-
take and exhaust pipe sizing -- Size pipe according to TA-
BLE 7 and TABLE 8. Count all elbows inside and outside
the home. TABLE 7 lists the minimum vent pipe lengths
permitted. TABLE 8 lists the maximum pipe lengths per-
mitted.

Page 16
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.
TABLE 7
MINIMUM VENT PIPE LENGTHS
SLP99DF
Model
Min. Equiv.
Vent Lenght Example
070
15 ft.*
5 ft. plus 2 elbows of 1-1/2”,
2”, 2-1/2” or 3” diameter pipe
090,110 5 ft. plus 2 elbows of 2”,
2-1/2” or 3” diameter pipe
*Any approved termination may be added to the minimum equiv-
alent length listed. Two 45 degree elbows are the equivalent to
one 90 degree elbow.
NOTE - It is acceptable to use any pipe size which ts
within the guidelines allowed in TABLE 8.
NOTE - The exhaust collar on all models is sized to ac-
commodate 2” Schedule 40 vent pipe. Contact the Appli-
cation Department for more information concerning sizing
of vent systems which include multiple pipe sizes.
NOTE - If right side venting option is used, you must in-
clude the elbow at the furnace in the elbow count. If tran-
sitioning to 3” dia pipe, this elbow equates to 20’ of equiv-
alent vent length for all models.
NOTE - All horizontal runs of exhaust pipe must slope
back toward unit. A minimum of 1/4” (6mm) drop for each
12” (305mm) of horizontal run is mandatory for drainage.
NOTE - Exhaust pipe MUST be glued to furnace exhaust
ttings.
NOTE - Exhaust piping should be checked carefully to
make sure there are no sags or low spots.
Use the following steps to correctly size vent pipe diam-
eter.
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 20
NOTE - Lennox oers a glueless vent adapter kit 17H92
as an option for exhaust exiting at the furnace top cap
coupling.

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 - 4500’
Number
Of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 070 090 110 070 090 110 070 090 110
1 15
N/A N/A
91 69 14 140 93 43 162 143 118
2 10 86 64 9 135 88 38 157 138 113
3
N/A
81 59
N/A
130 83 33 152 133 108
4 76 54 125 78 28 147 128 103
5 71 49 120 73 23 142 123 98
6 66 44 115 68 18 137 118 93
7 61 39 110 63 13 132 113 88
8 56 34 105 58
N/A
127 108 83
9 51 29 100 53 122 103 78
10 46 24 95 48 117 98 73
Standard Termination at Elevation 4501’ - 7500’
Number
of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 070 090 110 070 090 110 070 090 110
1 13
N/A N/A
66 69 14 115 93 43 137 143 118
2 8 61 64 110 88 132 138 113
9 38
3
N/A
56 59 105 83 127 133 108
N/A
33
4 51 54 100 78 122 128 103
28
5 46 49 95 73 23 117 123 98
6 41 44 90 68 18 112 118 93
7 36 39 85 63 107 113 88
13
8 31 34 80 58 102 108 83
29
9 26 75 53 97 103 78
24
10 21 70 48 92 98 73
Standard 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
070 090 110 070 090 110 070 090 110 070 090 110
1
N/A N/A N/A
41 44
N/A
90 68
N/A
112 118 93
2 36 39 85 63 107 113 88
3 31 34 80 58 102 108 83
4 26 29 75 53 97 103 78
5 21 24 70 48 92 98 73
6 16 19 65 43 87 93 68
711 14 60 38 82 88 63
8
N/A N/A
55 33 77 83 58
9 50 28 72 78 53
10 45 23 67 73 48
NOTE - Table 8 continued on next page with concentric terminations.

Page 18
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.
Concentric Termination at Elevation 0 - 4500’
Number
Of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 070 090 110 070 090 110 070 090 110
1 10
N/A N/A
83 67 12 130 89 39 146 139 114
2
N/A
78 62 7 125 84 34 141 134 109
3 73 57
N/A
120 79 29 136 129 104
4 68 52 115 74 24 131 124 99
5 63 47 110 69 19 126 119 94
6 58 42 105 64 14 121 114 89
7 53 37 100 59
N/A
116 109 84
8 48 32 95 54 111 104 79
9 43 27 90 49 106 99 74
10 38 22 85 44 101 94 69
Concentric Termination at Elevation 4501’ - 7500’
Number
of 90
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model Model
070 090 110 070 090 110 070 090 110 070 090 110
1
N/A N/A N/A
58 67 12 105 89 39 121 114 114
2 53 62 100 84 116 109 109
7 34
3 48 57 95 79 111 104 104
N/A
29
4 43 52 90 74 106 99 99
24
5 38 47 85 69 19 101 94 94
6 33 42 80 64 14 96 89 89
7 28 37 75 59 91 84 84
N/A
8 23 32 70 54 86 79 79
27
9 18 65 49 81 74 74
22
10 13 60 44 76 69 69
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
070 090 110 070 090 110 070 090 110 070 090 110
1
N/A N/A N/A
33 42
N/A
80 64
N/A
96 114 89
2 28 37 75 59 91 109 84
3 23 32 70 54 86 104 79
4 18 27 65 49 81 99 74
5 13 22 60 44 76 94 69
6
N/A
17 55 39 71 89 64
7 12 50 34 66 84 59
8
N/A
45 29 61 79 54
9 40 24 56 74 49
10 35 19 51 69 44

Page 19
TYPICAL PIPE CONNECTIONS
TRANSITION
2” 2”
2”
3”
2”
2”
or
DO NOT transition from smaller
to larger pipe size in horizontal
runs of exhaust pipe. TOP VIEW
EXHAUST
INTAKE
* 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.
*2”
TRANSITION
2”
1−1/2”
070 Only
DO NOT transition
from larger to smaller
pipe in horizontal runs
of exhaust pipe.
Exhaust
Exhaust
FIGURE 21
Flue Coupling
The provided ue coupling must be attached to the exhaust
coupling on the furnace top panel. Use provided bands. See
steps below and FIGURE 22.
1 - Remove the caution tag from the ue coupling.
2 - Fully insert ue coupling with both bands loosely
attached on the furnace exhaust coupling.
3 - Insert PVC exhaust pipe through ue coupling. Ensure
vent pipe is fully seated into exhaust coupling.
4 - Tighten both top and bottom bands (do not use glue
or silicone to attach) to 40in-lbs.
Furnace
Top Band
(torque to 40in-lbs)
PVC
Exhaust Pipe
Top Panel
Flue Coupling To Exhaust Coupling
Bottom Band
(torque to 40in-lbs)
Flue Couplig
Furnace
Exhaust Coupling
FIGURE 22

Page 20
TYPICAL EXHAUST CONNECTIONS WITH RIGHT SIDE VENT OPTION
TRANSITION
2” 3”
TOP VIEW
*2”
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE Intake pipe and exhaust pipe must be the same diameter.
Pipe Length
4” Maximum
(Not Furnished)
2”
2”
Plate
(Furnished)
Street Ell
(Not Furnished)
FIGURE 23
TRANSITION
2” 3”
TOP VIEW
*2”
* When transitioning up in pipe size, use the shortest length of 2” PVC pipe possible.
NOTE Intake pipe and exhaust pipe must be the same diameter.
2”
Plate
(Furnished)
TYPICAL AIR INTAKE PIPE CONNECTIONS WITH RIGHT SIDE VENT OPTION
*2”
Street Ell
(Not Furnished)
FIGURE 24