PRODUCT DESIGN
34
A duct system should be installed in accordance with Stan-
dards of the National Board of Fire Underwriters for the In-
stallation of Air Conditioning, Warm Air Heating and Venti-
lating Systems, Pamphlets No. 90A and 90B.
A return air filter is not supplied with the furnace. The in-
staller must supply a means of filtering all of the return air.
Filter(s) shall comply with UL900 or CAN/ULC-S111 Stan-
dards. If the furnace is installed without filters, the warranty
will be voided.
FURNACE INPUT
FILTER SIZE
40M
320 in
2
60M
483 in
2
80M
640 in
2
100M
800 in
2
120M
738 in
2
140M
738 in
2
DISPOSABLE NOMINAL 300 F.M. FACE VELOCITY
MINIMUM FILTER SIZES for DISPOSABLE FILTERS
Cabinet
Width
(In.)
Nominal
Filter
Size (In.)
Approx.
Flow Area
(In.)
Cabinet
Width
(In.)
Nominal
Filter
Size (In.)
Approx.
Flow Area
(In.)
All
16x25x1
400
14"
14X25X1
350
17-1/2
14X25X1
350
21
16x25x1
400
24-1/2
20X25X1
500
SIDE RETURN
BOTTOM RETURN
Refer to Minimum Filter Area tables to determine filter area
requirement.
NOTE:
Filters can also be installed elsewhere
in the duct system such as a central return.
One inch throwaway filters should be sized for a face veloc-
ity of 300 feet per minute or less (14x25x1 throwaway = 730
CFM maximum, 16x25x1 throwaway = 830 CFM maximum,
18x25x1 throwaway = 940 CFM maximum, 20x25x1 throw-
away = 1040 CFM maximum) All other filters should be sized
according to their manufacturer's instructions.
To find the miminum filter requirement (in
2
) for either perma-
nent or disposable filters divide the required airflow (CFM)
by the rated velocity of the filter, either 300ft/min for dis-
posable filter or 600ft/min for permanent filter. Multiply the
number by 144 in.
2
to obtain the minimum filter require-
ment (in
2
).
EXAMPLE:
Filter Size (in
2
) =
1400 CFM x 144 in
2
600 ft./min. (Permanent)
Filter Size (in
2
) =
1400 CFM x 144 in
2
300 (Disposable) ft./min.
Filter Size = 672in
2
Disposable
Filter Size = 336in
2
Permanent
Upflow furnaces with air delivery of less than 1800 CFM:
Use one side return or one bottom return ductwork connec-
tion.
Upflow furnaces with air delivery of 1800 CFM or higher:
Use two side returns or one side return and one bottom
return connection.
Guide dimples locate the side and bottom return cutout lo-
cations. Use a straight edge to scribe lines connecting the
dimples. Cut out the opening on these lines. An undersized
opening will cause reduced airflow. For bottom return con-
nection, remove the bottom of the cabinet before setting
the furnace on the raised platform or return air duct.
A closed return duct system must be used, with the return
duct connected to the furnace.
NOTE:
Ductwork must never
be attached to the back of the furnace.
Supply and return
connections to the furnace may be made with flexible joints
to reduce noise transmission, if desired. If a central return
is used, a connecting duct must be installed between the
unit and the utility room wall so the blower will not interfere
with combustion air or draft. The room, closet, or alcove
must not be used as a return air chamber.
When the furnace is used in connection with a cooling unit,
the furnace should be installed in parallel with or on the
upstream side of the cooling unit to avoid condensation in
the heating element. With a parallel flow arrangement, the
dampers or other means used to control the flow of air must
be adequate to prevent chilled air from entering the fur-
nace and, if manually operated, must be equipped with means
to prevent operation of either unit unless the damper is in
the full heat or cool position.
When the furnace is heating, the temperature of the return
air entering the furnace must be between
55°F
and
100°F
.
UPRIGHT FILTER INSTALLATIONS
Depending on the installation and/or customer preference,
differing filter arrangements can be applied. Filters can be
installed in the central return register and a side panel ex-
ternal filter rack kit (upflow filter kit # EFR01). As an alter-
native a media air filter or electronic air cleaner can be
used as the requested filter. Refer to the following minimum
