c. When ducts are used, they must be of the same cross-
sectional area as the free area of the openings to which
they connect. The minimum dimension of rectangular
ducts must not be less than 3 in. (See Fig. 3.)
WARNING: Do not install the furnace on its back;
safety control operation will be adversely affected. Never
connect return-air ducts to the back of the furnace. A
failure to follow this warning can cause a fire, personal
injury, or death.
III. FILTER ARRANGEMENT
The factory-supplied filter(s) is shipped in the blower compart-
ment. Determine location for the filter and relocate filter retaining
wire if necessary. See Fig. 4 for side return application and Fig. 5
for bottom return application. See Table 3 to determine correct
filter size for desired filter location. Table 3 indicates filter size,
location, and quantity shipped with the furnace.
For bottom air-return applications, filter may need to be cut to fit
some furnace casing widths. A bottom closure panel is factory
installed in the bottom of the furnace. When bottom return inlet is
desired, remove and discard the bottom closure panel. Remove
side clip(s) and install in hole. Two sets of hardware are needed for
furnaces in 24-1/2-in. wide casings using 2 filters for bottom
return. All hardware is provided for filter installation.
NOTE: Furnaces with a 17-1/2-in. wide casing require an addi-
tional procedure when locating the filter for bottom return-air
application. Field fabricate a sheet metal filler strip1X3X24-1/2
in. and install it along side of the filter as shown in Fig. 5. Drive
2 screws through the casing side and into the filler strip to secure
it in place. Filter should rest on the top of the filler strip when
installed.
WARNING: Never operate unit without a filter or with
filter access door removed. Failure to follow this warning
can cause fire, personal injury, or death.
IV. LEVELING LEGS (IF REQUIRED)
When the furnace is used with side inlet(s) and leveling legs are
required, refer to Fig. 6, and install field-supplied, corrosion-
resistant 5/16-in. machine bolts and nuts.
NOTE: The maximum length of the bolt should not exceed 1-1/2
in.
1. Lay furnace on its back. Locate and drill 5/16-in. diameter
hole in each bottom corner of furnace as shown in Fig. 6.
2. Install nut on bolt and install bolt and nut in hole. (Install
flat washer if desired.)
3. Install another nut on other side of furnace base. (Install flat
washer if desired.)
For Example:
395CAV FURNACE
INPUT BTUH FREE AREA PER OPENING
(SQ IN.) ROUND PIPE
(IN. DIA)
44,000 11.0 4
66,000 16.5 5
88,000 22.0 6
110,000 27.5 6
132,000 33.0 7
154,000 38.5 7
For Example:
395CAV FURNACE
INPUT BTUH FREE AREA PER OPENING
(SQ IN.) ROUND PIPE
(IN. DIA)
44,000 22.0 6
66,000 33.0 7
88,000 44.0 8
110,000 55.0 9
132,000 66.0 10
154,000 77.0 10
Fig. 3—Air For Combustion and Ventilation
(Outside Air)
A89013
1 SQ IN.
PER
4000
BTUH*
DUCTS
TO
OUTDOORS
1 SQ IN.
PER 4000
BTUH*
SUPPLY
AIR
VENT
THROUGH
ROOF
D
B
A
C
E
1 SQ IN.
PER 4000
BTUH*
DUCT
TO
OUTDOORS
RETURN AIR
1 SQ IN.
PER 2000
BTUH*
1 SQ IN.
PER 2000
BTUH*
DUCTS
TO
OUTDOORS
12″ MAX
12″ MAX
12″ MAX
Use any of the following
combinations of openings:
A & B C & D D & E F & G
NOTE:
*Minimum dimensions of 3-In.
CONFINED
SPACE
12″
MAX
12″
MAX
OUTDOORS
1 SQ IN.
PER
4000
BTUH*
F
G
Fig. 4—Side Filter Arrangement
(Control Removed for Clarity)
A93045
FILTER
RETAINER
WASHABLE
FILTER
—5—