Lennox SL280DFNV Series User manual

Page 1
INSTALLATION
INSTRUCTIONS
SL280DFNV
508150-02
08/2021
Supersedes 508150-01
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is a safety alert symbol and should never be
ignored. When you see this symbol on labels or in man-
uals, be alert to the potential for personal injury or death.
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.
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 21.
© 2021 Lennox Industries Inc.
Dallas, Texas USA
DAVE LENNOX SIGNATURE®
GAS FURNACE DOWNFLOW
AIR DISCHARGE
Contents
Unit Dimensions - inches (mm) ......................................2
Parts Arrangement..........................................................3
SL280DFNV Gas Furnace..............................................4
Shipping and Packing List ..............................................4
Safety .............................................................................4
Use of Furnace as a Construction Heaterl .....................5
General...........................................................................5
Combustion, Dilution, Ventilation Air...............................5
Setting Equipment ........................................................10
Filters............................................................................ 11
Duct System .................................................................12
Venting .........................................................................12
Gas Piping....................................................................17
Electrical.......................................................................19
Integrated Control Settings...........................................29
Blower Motor Performance...........................................33
Unit Start-Up.................................................................37
Gas Pressure Measurement.........................................38
Proper Combustion.......................................................38
Other Unit Adjustments.................................................39
Sequence of Operation.................................................39
Service..........................................................................41
Repair Parts List...........................................................43
Integrated Control Diagnostic Codes............................44
Program Unit Capacity Size Mode ...............................50
Troubleshooting............................................................51
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.

Page 2
Unit Dimensions - inches (mm)
1-1/2 (38)
Front Panel
GAS PIPING INLET
(Either Side)
FLUE OUTLET
(Top)
ELECTRICAL INLET
(Either Side)
RETURN AIR
OPENING
FRONT VIEW SIDE VIEW
TOP VIEW
A
B
C
D
3/4
(19)
27-3/4
(705)
19-1/4
(489)
6-5/8 (168) Right
7-1/8 (181) Left
5-3/8 (137) Right
2-3/16 (56) Left
33
(838)
AIR FLOW
3/4
(19)
19-7/16
(494)
9/16
(14)
B
Supply
Air
Supply
Air
9/16
(14)
9/16
(14)
3-1/8
(79)
9/16
(14)
9/16
(14)
19-7/16
(494)
3/4
(19)
Model A B C D
in mm in mm in mm in mm
SL280DF060NV36B 17-1/2 446 16-3/8 416 16 406 6-1/4 159
SL280DF080NV60C 21 533 19-7/8 504 19-1/2 495 8 203

Page 3
Parts Arrangement
Control box
Flue chase
Internal flue pipe assembly
Blower assemblyBlower assembly
Heat exchanger assembly
Air fuel intake assembly
Gas valve
Combustion air inducer
Access panel
FIGURE 1

Page 4
SL280DFNV Gas Furnace
The SL280DFNV gas furnace is equipped with a twostage,
variable speed integrated control. the control is compati-
ble with:
Communicating thermostats.
Non-communicating thermostats - ComfortSense or other
conventional thermostats.
Control systems - Harmony III™ Zone Control System
(non-communicating). Each SL280DFNV unit is shipped
ready for installation in the downow position.
Shipping and Packing List
Package 1 of 1 contains
1 - Assembled SL280DFNV unit
1 - Bag assembly containing the following:
2 - Screws
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 -Vent warning label
1 - Owner’s manual and warranty card
The following items may be ordered separately:
1 - Thermostat
1 - Propane/LP changeover kit
1 - Combustible ooring base
Check equipment for shipping damage. If you nd any
damage, immediately contact the last carrier.
Safety Information
DANGER
Danger of explosion.
There are circumstances in which odorant used with
LP/propane gas can lose its scent. In case of a leak,
LP/propane gas will settle close to the oor and may
be di󰀩cult to smell. An LP/propane leak detector
should be installed in all LP applications.
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.
Certications
SL280DFNV units are CSA International certied.
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI-Z223.1). The National Fuel Gas Code is
available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036
Clearances
Adequate clearance must be made around the air open-
ings into the vestibule area. In order to ensure proper unit
operation, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code.
Vent installations must be consistent with the venting ta-
bles (in this instruction) and applicable provisions of local
building codes.
This furnace is CSA International certied for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in gure 14. Accessibility and
service clearances must take precedence over re protec-
tion clearances.
Installed Locations
For installation in a residential garage, the furnace must
be installed so that the burner(s) and the ignition source
are located no less than 18 inches (457 mm) above the
oor. The furnace must be located or protected to avoid
physical damage by vehicles. When a furnace is installed
in a public garage, hangar, or other building that has a
hazardous atmosphere, the furnace must be installed ac-
cording to recommended good practice requirements and
current National Fuel Gas Code.
NOTE - Furnace must be adjusted to obtain a temperature
rise (high and low re) 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 exchang-
er failure. This SL280DFNV furnace must be installed so
that its electrical components are protected from water.
This SL280DFNV furnace must be installed so that its
electrical components are protected from water.
Installed in Combination with a Cooling Coil
When this furnace is used with cooling 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 (see gure 2). If the
damper is manually operated, it must be equipped to pre-
vent operation of either the heating or the cooling unit,
unless it is in the full HEAT or COOL setting.

Page 5
AIR HANDLER
GAS UNIT
Dampers
(open during cooling
operation only)
Dampers
(open during heating
operation only)
FIGURE 2
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National Elec-
tric Code, ANSI/NFPA No. 70. The National Electric Code
(ANSI/NFPA No. 70) is available from the following ad-
dress:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
NOTE - This furnace is designed for a minimum continu-
ous return air temperature of 60°F (16°C) or an intermittent
operation down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The SL280DFNV furnace may be installed in alcoves,
closets, attics, basements, garages, and utility rooms in
the downow position.
This furnace design has not been CSA International
certied for installation in mobile homes, recreational
vehicles, or outdoors.
Use of Furnace as Construction Heater
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 SL280DFNV furnace:
• Place the furnace as close to the center of the air
distribution system as possible. The furnace should
also be located close to the chimney or vent termi-
nation point.
• Do not install the furnace where drafts might blow
directly into it. This could cause improper combus-
tion and unsafe operation.
• Do not block the furnace combustion air openings
with clothing, boxes, doors, etc. Air is needed for
proper combustion and safe unit operation.
• When the furnace is installed in an attic or other
insulated space, keep insulation away from the fur-
nace.
Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in su󰀩cient
outdoor air for combustion. Inltration provided all the air
that was needed. In today’s homes, tight construction
practices make it necessary to bring in air from outside for
combustion. Take into account that exhaust fans, appli-
ance vents, chimneys, and replaces force additional air
that could be used for combustion out of the house. Un-
less outside air is brought into the house for combustion,
negative pressure (outside pressure is greater than inside
pressure) will build to the point that a downdraft can oc-
cur in the furnace vent pipe or chimney. As a result, com-
bustion gases enter the living space creating a potentially
dangerous situation.
In the absence of local codes concerning air for combus-
tion and ventilation, use the guidelines and procedures in
this section to install SL280DFNV furnaces to ensure ef-
cient and safe operation. You must consider combustion
air needs and requirements for exhaust vents. A portion of
this information has been reprinted with permission from
the National Fuel Gas Code (ANSI‐Z223.1). This reprint-
ed material is not the complete and o󰀩cial position of the
ANSI on the referenced subject, which is represented only
by the standard in its entirety.
CAUTION
Do not install the furnace in a corrosive or
contaminated atmosphere. Meet all combustion
and ventilation air requirements, as well as all local
codes.

Page 6
CAUTION
Insu󰀩cient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in
rusting and premature heat exchanger failure.
Excessive exposure to contaminated combustion
air will result in safety and performance related
problems. Avoid exposure to the following
substances in the combustion air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
All gasred appliances require air for the combustion
process. If su󰀩cient combustion air is not available, the
furnace or other appliances will operate ine󰀩ciently and
unsafely. Enough air must be provided to meet the needs
of all fuel-burning appliances and appliances such as ex-
haust fans which force air out of the house. When replac-
es, exhaust fans, or clothes dryers are used at the same
time as the furnace, much more air is necessary to ensure
proper combustion and to prevent a downdraft. Insu󰀩cient
air causes incomplete combustion which can result in car-
bon monoxide.
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace com-
ponents.
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is in-
stalled in an unconned or a conned space.
Unconned Space
An unconned space is an area such as a basement or
large equipment room with a volume greater than 50 cubic
feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the com-
bined input rating of all appliances installed in that space.
This space also includes adjacent rooms which are not
separated by a door. Though an area may appear to be
unconned, it might be necessary to bring in outdoor air
for combustion if the structure does not provide enough air
by inltration. If the furnace is located in a building of tight
construction with weather stripping and caulking around
the windows and doors, follow the procedures in the air
from outside section.
Conned Space
A conned space is an area with a volume less than 50
cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of
the combined input rating of all appliances installed in that
space. This denition includes furnace closets or small
equipment rooms.
When the furnace is installed so that supply ducts carry
air circulated by the furnace to areas outside the space
containing the furnace, the return air must be handled by
ducts which are sealed to the furnace casing and which
terminate outside the space containing the furnace. This
is especially important when the furnace is mounted on
a platform in a conned space such as a closet or small
equipment room. Even a small leak around the base of
the unit at the platform or at the return air duct connection
can cause a potentially dangerous negative pressure con-
dition. Air for combustion and ventilation can be brought
into the conned space either from inside the building or
from outside.
EQUIPMENT IN CONFINED
SP
ACE ALL AIR FROM INSIDE
CHIMNE
Y
OR GAS
VENT
FURNACE
WATER
HEATER
OPENINGS
(To Adjacent
Room)
NOTE - Each opening shall have a free area of at least one square
inch (645 mm2
ing of all equipment in the enclosure, but not less than 100 square
inches (64516 mm2).
AIR FLOW
Figure 3
Air from Inside
If the conned space that houses the furnace adjoins a
space categorized as unconned, air can be brought in by
providing two permanent openings between the two spac-
es. Each opening must have a minimum free area of 1
square inch (645 mm2) per 1,000 Btu (.29 kW) per hour of
total input rating of all gas-red equipment in the conned
space. Each opening must be at least 100 square inches
(64516 mm2). One opening shall be within 12 inches (305
mm) of the top of the enclosure and one opening within 12
inches (305 mm) of the bottom. See gure 3.

Page 7
Air from Outside
If air from outside is brought in for combustion and ventila-
tion, the conned space must have two permanent open-
ings. One opening shall be within 12 inches (305 mm) of
the top of the enclosure and one opening within 12 inches
(305 mm) of the bottom. These openings must communi-
cate directly or by ducts with the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors or in-
directly through vertical ducts. Each opening shall have a
minimum free area of 1 square inch (645 mm2) per 4,000
Btu (1.17 kW) per hour of total input rating of all equipment
in the enclosure. See gures 4 and 5. When communi-
cating with the outdoors through horizontal ducts, each
opening shall have a minimum free area of 1 square inch
(645 mm2) per ,000 Btu (.56 kW) per total input rating of
all equipment in the enclosure. See gure 6.
When ducts are used, they shall be of the same cross-sec-
tional area as the free area of the openings to which they
connect. The minimum dimension of rectangular air ducts
shall be no less than 3 inches (75 mm). In calculating free
area, the blocking e󰀨ect of louvers, grilles, or screens
must be considered. If the design and free area of protec-
tive covering is not known for calculating the size opening
required, it may be assumed that wood louvers will have
20 to 25 percent free area and metal louvers and grilles
will have 60 to 75 percent free area. Louvers and grilles
must be xed in the open position or interlocked with the
equipment so that they are opened automatically during
equipment operation.
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)
NOTE-The inlet and outlet air openings shall each have a free area of at least one square inch (645
mm
2
)per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR WATER
HEATER
INLET
AIR
CHIMNEY OR
GAS VENT
FURNACE
VENTILATION
LOUVERS
(For unheated crawl space)
AIR FLOW
FIGURE 4

Page 8
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
NOTE-The inlet and outlet air openings shall each have a
free area of at least one square inch (645 mm2) per 4,000
ment in the enclosure.
CHIMNEY
OR GAS
VENT
WATER
HEATER
OUTLET
AIR
VENTILATION LOUVERS
(Each end of attic)
INLET AIR
(Ends 12 in.
above bottom)
FURNACE
AIR FLOW
FIGURE 5
EQUIPMENT IN
CONFINED SPACE
ALL AIR FROM
OUTSIDE
OUTLET AIR
INLET AIR
WATER
HEATER
CHIMNEY
OR GAS
VENT
NOTE - Each air duct opening shall have a free area of at least
one square inch (645 mm2) per 2,000 Btu (.59 kW) per hour of
the total input rating of all equipment in the enclosure. If the
equipment room is located against an outside wall and the air
openings
ing shall have a free area of at least one square inch (645 mm2)
per 4,000 Btu (1.17 kW) per hour of the total input rating of all
other equipment in the enclosure.
FURNACE
AIR FLOW
FIGURE 6
Downow Installation
Downow unit installs in three ways: on non-combustible
ooring, on combustible ooring using a downow com-
bustible ooring base, or on a reverse-ow cooling cabi-
net. Do not drag the unit across the oor.
Installation on Non-Combustible Flooring (Figure 7)
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.
4 - Ensure that the seal is adequate.
UNIT
SUPPLY AIR
PLENUM
OPENING
FIGURE 7
TABLE 1
NON-COMBUSTIBLE FLOOR OPENING SIZE
Cabinet
Width
Front to Rear Side to Side
in mm in mm
B (17.5”) 19-3/4 502 16-1/4 413
C (21”) 19-3/4 502 19-3/4 502
NOTE - Door opening dimensions listed are 1/4 inch (6 mm) larger than
the unit opening. See unit dimensions on page 2.
Installation on Combustible Flooring (Figure 8)
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 downow combustible ooring
base shall not be installed directly on carpeting,
tile, or other combustible material other than wood
ooring.

Page 9
UNIT
SUPPLY AIR PLENUM
DOWNFLOW
COMBUSTIBLE
FLOORING BASE
PROPERLY
SIZED FLOOR
OPENING
FIGURE 8
TABLE 2
COMBUSTIBLE FLOOR OPENING SIZE
Cabinet
Width
Front to Rear Side to Side
in mm in mm
B (17.5”) 22 559 18-3/4 476
C (21”) 22 559 22-3/4 578
2 - After opening is cut, set combustible ooring base
into opening.
3 - Check sealing strips on combustible ooring base to
make sure they are properly glued and positioned.
4 - Lower supply air plenum into downow combustible
ooring base until plenum anges seal against the
strips.
NOTE - Be careful not to damage sealing 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 Cabinet (Figure 9)
1 - Refer to reverse-ow coil installation instructions for
correctly sized opening in oor and installation of
cabinet.
NOTE - Downow combustible ooring kit is not used.
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.
UNIT
COOLING COIL
PLENUM
PROPERLY
SIZED FLOOR
OPENING
FIGURE 9
Return Air Opening -- Downow Units
The following steps should be taken when installing ple-
num:
1 - Bottom edge of plenum should be anged with a
hemmed edge (See gure 10).
SECURE FROM
OUTSIDE CABINET
HEMMED EDGE
PLENUM
SEALING STRIP
(Field Provided)
CABINET SIDE PANEL
Side View
FIGURE 10
2 - Sealing strip should be used.
3 - In all cases, plenum should be secured to top anges
of furnace with sheet metal screws.
4 - In closet installations, it may be impossible to install
sheet metal screws from the outside. In this case,
make plenum with a removable front and install
screws from the inside (See gure 11).
5 - Make certain that an adequate seal is made.
SIDE CABINET
HEMMED EDGE
FIBERGLASS
SEALING STRI
P
(Field Provided)
CABINET SIDE
PANEL
PLENUM
Side View
FIGURE 11

Page 10
Setting Equipment
WARNING
Do not install the furnace on its front, back or in the
horizontal position. See gure 13 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.
Install the SL280DFNV gas furnace as shipped in the
downow position only. Do not install the furnace horizon-
tally.
Select a location that allows for the required clearances
that are listed on the unit nameplate. Also consider gas
supply connections, electrical supply, vent connection,
and installation and service clearances [24 inches (610
mm) at unit front]. The unit must be level.
NOTE - Units with 1/2 hp blower motors are equipped with
three exible legs and one rigid leg. See gure 12. 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 wash-
er must be removed before the furnace is placed into
operation. After the bolt and washer have been removed,
the rigid leg will not touch the blower housing.
RIGID LEG
remove shipping bolt and washe
r
MODELS WITH 1/2 HP
BLOWER MOTOR
FIGURE 12
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.
Front Back Horizontal
FIGURE 13