Lennox DAVE LENNOX SIGNATURE SL297UHNV User manual

Page 1
INSTALLATION
INSTRUCTIONS
SL297UHNV
507760-04
09/2019
Supersedes 507760-03
NOTICE
A thermostat is not included and must be ordered
separately.
A communicating thermostat must be used in
communicating applications.
In non-communicating applications, any Lennox
conventional 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 34.
IMPORTANT
DO NOT use the heat exchanger tubes to lift, drag or
pull the furnace to its installation location.
Doing so will damage the tubes causing noise and or
unsafe operation.
© 2019 Lennox Industries Inc.
Dallas, Texas USA
DAVE LENNOX SIGNATURE®
GAS FURNACE UPFLOW / HORIZONTAL
AIR DISCHARGE
Contents
Unit Dimensions - inches (mm) ......................................2
Parts Arrangement..........................................................3
SLP297UHNV Gas Furnace...........................................4
Shipping and Packing List ..............................................4
Safety .............................................................................4
Use of Furnace as a Construction Heaterl .....................5
General...........................................................................6
Combustion, Dilution, Ventilation Air...............................6
Setting Equipment ..........................................................6
Filters............................................................................ 11
Duct System ................................................................. 11
Pipe Fittings Specications...........................................12
Joint Cementing Procedure..........................................13
Venting Practices..........................................................14
Gas Piping....................................................................29
Electrical.......................................................................32
Integrated Control.........................................................41
Blower Motor Performance...........................................44
Unit Start-Up.................................................................48
Gas Pressure Measurement.........................................49
Proper Combustion.......................................................50
High Altitude .................................................................50
Repair Parts Lsit...........................................................50
Sequence of Operation.................................................51
Service..........................................................................53
Program Unit Capacity Size Mode ...............................61
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.
Heatexchanger Tubes

Page 2
SL297UHNV Unit Dimensions - inches (mm)
AIR FLOW
23
(584)
(19)
3/4
(19)
1Bottom Return
Air Opening
GAS PIPING INLET
(Right Side Only)
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
B9/16 (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)
2OPTIONAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
16
(406)
14-3/4
(375)
2OPTIONAL
SIDE RETURN
AIR FILTER KIT
(Either Side)
5/8
(16)
1
3-1/4
(83)
23-3/4
(603)
25
(635)
1-1/2 (38)
Front Panel
COMBUSTION
AIR INTAKE
1-7/8 (48)
CONDENSATE
TRAP CONNECTION
(Either Side)
INTAKE AIR
2-1/4
(57)
2-7/8
(73)
6-5/8
(168)
Not Used
2
Optional Side Return Air Filter Kit is not for use
with the Optional Return Air Base.
1
NOTE - 60C size units that require air volumes over
1800 cfm must have one of the following:
1. Single side return air and Optional Return Air Base
with transition that must accommodate required
20 x 25 x 1 inch (508 x 635 x 25 mm) air filter to
maintain proper velocity.
2. Bottom return air.
3. Return air from both sides.
4. Bottom and one side return air.
See Blower Performance Tables for additional information.
Model No. A
in - mm
B
in - mm
C
in - mm
SL297UH040NV36B
SL297UH060NV36B 17-1/2 - 446 16-3/8 - 416 16 - 406
SL297UH080NV48C
SL297UH080NV60C 21 - 533 19-7/8 - 505 19-1/2 - 495

Page 3
Parts Arrangement
FIGURE 1
Heat Exchanger
Gas Valve
Combustion
Air Inducer
Indoor Blower
Two-Stage Control
Cabinet
Panel
Inner Panel
Gas Pipe Inlet
(right side only)
Inlet Vent Pipe
Exhaust Vent Pipe
Exhaust Coupling
Intake Air Assembly
Rollout Switch
Burner Assembly

Page 4
SL297UHNV Gas Furnace
The SL297UHNV Category IV gas furnace is shipped
ready for installation in the upow or horizontal position.
The furnace is shipped with the bottom panel in place. The
bottom panel must be removed if the unit is to be installed
in horizontal or upow applications with bottom return air.
The SL297UHNV is to be installed as Direct Vent gas
central furnace only. The furnace is equipped for in-
stallation in natural gas applications only.
NOTE - In Direct Vent installations, combustion air is tak-
en from outdoors and ue gases are discharged outdoors.
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 SL297UHNV unit
1 - Bag assembly containing the following:
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 - Condensate trap
1 - Condensate trap cap
1 - Condensate trap clamp
1 - 2” diameter debris screen
1 - 3/4” Threaded street elbow
Check equipment for shipping damage. If you nd any
damage, immediately contact the last carrier. The follow-
ing items may also be ordered separately:
1 - Thermostat
1 - Return air base kit
1 - Horizontal suspension kit
Safety Information
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.
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.
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.
Use only the type of gas approved for use with this fur-
nace. Refer to unit nameplate.
SL297UHNV units are CSA International certied to ANSI
Z21.47 and CSA 2.3 standards.
Building Codes
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI-Z223.1/NFPA 54). The National Fuel
Gas Code is available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036
In Canada, installation must conform with current National
Standard of Canada CSA-B149 Natural Gas and Propane
Installation Codes, local plumbing or waste water codes
and other applicable local codes.
Installation Locations
This furnace is CSA International certied for installation
clearances to combustible material as listed on the unit
nameplate and in the table in gure 6. Accessibility and
service clearances must take precedence over re protec-
tion 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
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 standards.
NOTE - Furnace must be adjusted to obtain a temperature
rise within the range specied on the unit nameplate. Fail-
ure to do so may cause erratic limit operation and prema-
ture heat exchanger failure.
This SL297UHNV furnace must be installed so that its
electrical components are protected from water.

Page 5
Installed in Combination with a Cooling Coil
When this furnace is used with cooling coils (gure 3), it
shall be installed in parallel with, or on the upstream side
of, cooling coils to avoid condensation in the heating com-
partment. 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 manually operated, it must be equipped to prevent op-
eration of either the heating or the cooling unit, unless it is
in the full HEAT or COOL setting.
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
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.
Gas Unit
Heating Unit Installed Upstream of Cooling Coil
Gas Unit
Dampers
(open during heating operation only)
Dampers
(open during cooling operation only)
Heating Unit Installed Parallel to Air Handler Unit
Air Handler Unit
Cooling Coil
AIR FLOWAIR FLOW
AIR FLOW AIR FLOW
FIGURE 3
NOTE - This furnace is designed for a minimum continu-
ous return air temperature of 60°F (16°C) or an intermittent
operation down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The SL297UHNV furnace may be installed in alcoves,
closets, attics, basements, garages, crawl spaces and
utility rooms in the upow or horizontal position.
This furnace design has not been CSA certied for instal-
lation in mobile homes, recreational vehicles, or outdoors.
Use of Furnace as Construction Heater
Construction heat is not allowed with this furnace.
General
These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the
following general recommendations must be considered
when installing a SL297UHNV furnace:
• Place the furnace as close to the center of the air
distribution system as possible. The furnace should
also be located close to the vent termination point.
• When the furnace is installed in an attic or other
insulated space, keep insulation away from the fur-
nace.
• 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.
Adequate space must be provided between the
drain pan and the furnace heat exchanger.
CAUTION
SL297UHNV unit should not be installed in areas
normally subject to freezing temperatures.
Shipping Bolt Removal
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 washer (rather
than the rubber mounting grommet used with a exible
mounting leg). See gure 4. 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 4

Page 6
Installation - Setting Equipment
WARNING
Do not connect the return air duct 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
Blower access panel must be securely in place when
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into living
space resulting in personal injury or death.
Upow Applications
The SL297UHNV gas furnace can be installed as shipped
in the upow position. Refer to gure 6 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. The unit may be
positioned from level to ½” toward the front. See gure 5.
Allow for clearances to combustible materials as indicated
on the unit nameplate.
SETTING EQUIPMENT
HORIZONTAL APPLICAT ION
FRONT VIEW
AIR FLOW
END VIEW
UNIT
FRONT
1/2”
max.
Unit must be level side-to-side. Unit may be positioned from level to 1/2” toward the front to aid in draining.
FRONT VIEW SIDE VIEW
1/2” max.
AIR FLOW
UNIT
FRONT
SIDE VIEW
UNIT
FRONT
UPFLOW APPLICATION
Figure 5

Page 7
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 injuryand/or property
damage could result.
Installation Clearances
Top
Bottom (Floor)
Left Side Right Side
Top/Plenum 1 in. (25 mm)
*Front 1
Back 1
Sides 1†
Vent 1
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 6
Return Air Guidelines
Return air can be brought in through the bottom or either
side of the furnace installed in an upow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.
Markings are provided on both sides of the furnace cab-
inet for installations that require side return air. Cut the
furnace cabinet at the maximum dimensions shown on
page 2.
Refer to Engineering Handbook for additional information.
SL297UHNV applications which include side return air
and a condensate trap installed on the same side of the
cabinet (trap can be installed remotely within 5 ft.) require
either a return air base or eld-fabricated transition to ac-
commodate an optional IAQ accessory taller than 14.5”.
See gure 7.
Side Return Air
(with transition and filter)
Return
Air
Plenum
Transition
20” X 25” X 1”
(508mmX635mmX 25mm)
Air Filter
FIGURE 7

Page 8
Figure 8
Removing the Bottom Panel
Screw
Bottom Panel
Bottom Cap
FIGURE 9
Removing the Bottom Panel
Remove the two screws that secure the bottom cap to the
furnace. Pivot the bottom cap down to release the bottom
panel. Once the bottom panel has been removed, reinstall
the bottom cap. See gure 9.
Horizontal Applications
WARNING
Do not install the furnace on its front or back. See gure
10.
See figure 4.
Front Back
FIGURE 10
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.
2To 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)

Page 9
The SL297UHNV furnace can be installed in horizontal
applications with either right- or left-hand air discharge.
Refer to gure 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 1
Front* 1
Back 1
Ends 1
Vent 1
Floor 1‡
*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 gure 12, or install the furnace on
a platform, as shown in gure 13. A horizontal suspension
kit (51W10) may be ordered from Lennox or use equiva-
lent.
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.
HORIZONTAL SUSPENSION KIT
Bracket
(typical)
Metal Strap
(typical)
Air
Flow
Internal Brace
(provided with kit)
FIGURE 12
NOTE - When the furnace is installed on a platform or with
the horizontal suspension kit in a crawlspace, it must be
elevated enough to avoid water damage, accommodate
drain trap and to allow the evaporator coil to drain.
Platform Installation of Horizontal Unit
1 - Select location for unit keeping in mind service and
other necessary clearances. See gure 11.
2 - Construct a raised wooden frame and cover frame
with a plywood sheet. If unit is installed above
nished space, install an an auxiliary drain pan
under unit. Set unit in drain pan as shown in gure
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 - Ifnecessary, runthe condensatelineinto acondensate
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

Page 10
Return Air -- Horizontal Applications
Return air may be brought in only through the end of a
furnace installed in the horizontal position. The furnace is
equipped with a removable bottom panel to facilitate in-
stallation. See gure 9.
Filters
This unit is not equipped with a lter or rack. A eld-pro-
vided high velocity rated lter is required for the unit to
operate properly. Table 1 lists recommended lter sizes. 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 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)
Duct System
Use industry-approved standards to size and install the
supply and return air duct system. Figure 14 shows the
correct supply and return duct installation. Refer to ACCA
Manual D. This will result in a quiet and low-static system
that has uniform air distribution.
NOTE - This furnace is not certied for operation in heat-
ing mode (indoor blower operating at selected heating
speed) with an external static pressure which exceeds 0.8
inches w.c. Operation at these conditions may result in
improper limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a remov-
able access panel should be installed in the supply air
duct. The access panel should be large enough to per-
mit inspection of the heat exchanger. The furnace access
panel must always be in place when the furnace is oper-
ating and it must not allow leaks. For horizontal units, in-
stall self tapping screws in the three evaporator coil screw
holes made for horizontal applications to seal the top cap
to the vestibule panel.
Return Air Plenum
NOTE - Return air must not be drawn from a room
where this furnace, or any other gas-fueled appliance
(i.e., water heater), or carbon monoxide-producing de-
vice (i.e., wood replace) is installed.
When return air is drawn from a room, a negative pressure
is created in the room. If a gas appliance is operating in
a room with negative pressure, the ue products can be
pulled back down the vent pipe and into the room. This
reverse ow of the ue gas may result in incomplete com-
bustion and the formation of carbon monoxide gas. This
raw gas or toxic fumes might then be distributed through-
out 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 into either side of
furnace allowed only in upow applications). If a furnace
with bottom return air is installed on a platform, make an
airtight seal between the bottom of the furnace and the
platform to ensure that the unit operates properly and
safely. Use berglass sealing strips, caulking, or equiva-
lent sealing method between the plenum and the furnace
cabinet to ensure a tight seal. If a lter is installed, size the
return air duct to t the lter frame.
HORIZONTAL UNIT
SUPPLY
AIR
SUPPLY
AIR Install self tapping screws
to seal any potential air
leaks
UPFLOW UNIT
Figure 14