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SUPPLY
AIR
INTERIOR
HEATED
SPACE
RETURN AIR
* Minimum opening size is 100 square in. with
minimum dimensions of 3-In.
†
Minimum of 3-In. when type-B1 vent is used.
Fig. 3—Confined Space: Air for Combustion and Ventilation
from an Unconfined Space
b. If building is constructed unusually tight, a permanent
opening directly communicating with the outdoors shall
be provided. See item 2 below.
c. If furnace is installed on a raised platform to provide a
return-air plenum, and return air is taken directly from
hallway or space adjacent to furnace, all air for combus-
tion must come from outdoors.
2. Air from outside the structure requires 1 of the following
methods:
a. If combustion air is taken from outdoors through 2
vertical ducts, the openings and ducts MUST have at
least 1 sq in. of free area per 4000 Btuh of total input for
all equipment within the confined space. (See Fig. 4 and
Table 2.)
b. If combustion air is taken from outdoors through 2
horizontal ducts, the openings and ducts MUST have at
least 1 sq in. of free area per 2000 Btuh of total input for
all equipment within the confined space. (See Fig. 4 and
Table 2.)
c. If combustion air is taken from outdoors through a single
opening or duct (horizontal or vertical) commencing
within 12 in. of the top of the confined space, opening
and duct MUST have at least 1 sq in. of free area per
3000 Btuh of the total input for all equipment within the
confined space and not less than the sum of the areas of
all vent connectors in the confined space. (See Fig. 4 and
Table 2.) Equipment clearances to the structure shall be
at least 1 in. from the sides and back and 6 in. from the
front of the appliances.
VENT THROUGH ROOF
12" MAX
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
UNCONFINED
SPACE
6" MIN
(FRONT)
†
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
12" MAX
A89012
12" MAX
1 SQ IN.
PER 2000
BTUH*
DUCTS
TO
OUTDOORS
1 SQ IN.
PER 2000
BTUH*
12" MAX
RETURN AIR
*Minimum dimensions of 3-In.
NOTE:
Use any of the following
combinations of openings:
A & B
Fig. 4—Confined Space: Air for Combustion and Ventilation
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 ducts must not be less than 3 in. (See Fig.
4.)
WARNING: Do not install the furnace on its back or
sides. 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 filter and move filter retaining
hardware, if necessary, before attaching return-air duct. After
return-air duct has been connected to furnace, install filter(s) inside
furnace blower compartment. See Fig. 5 for side return application
and Fig. 6 for bottom return application.
A bottom closure panel is factory installed in bottom of furnace.
When bottom return inlet is desired, remove and discard enclosure
panel.
Filter retaining brackets, supports, and retainers are factory as-
sembled and shipped installed for side return application, with 1
set of all required hardware on each furnace. (See Fig. 5.)
For bottom return applications, remove front and back brackets
and supports from each side. The back bracket(s) are installed in
the rear of the furnace casing. Dimples are provided to mark
mounting screw locations.
The front bracket(s) are installed on bottom front plate, as shown
in Fig. 6, once bottom enclosure has been removed. Rotate filter
supports 180° so filter will rest on support and reinstall. Do not
—5—
DUCTS
TO
OUTDOORS
D
VENT
A
THROUGH
SUPPLY
ROOF
AIR
E
B
C
12" MAX
DUCT
TO
OUTDOORS
C & D
D & E
F & G
from Outdoors
1 SQ IN.
PER 4000
BTUH*
12"
MAX
F
1 SQ IN.
PER
4000
BTUH*
1 SQ IN.
PER
4000
BTUH*
G
12"
MAX
1 SQ IN.
PER 4000
BTUH*
A89013
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