39
440 01 2021 01
Figure 44
Standoff Filter Rack
25--21--45a
Using Optional
Standoff Filter
Rack
Downflow Furnace Installation
Non-Combustible F loor Installation
Fabricate a plenum to the dimensions given in Figure 4, for the fur-
nace outlet. Plenum should be flanged, approximately
3
/
4
² for sup -
port.
Note: The three(3) screws in the top panel of the furnace next to
the duct flange MUST be removed to provide serviceability of the
primary heat exchangers i n the downflow installation
1. Position plenum through the floor and set the furnace over
the opening in the floor. If necessary, grout around the base
to seal air leaks between the base and the floor.
Combustible Floor Installation
FIRE HAZARD.
Failure to install unit on noncombustible subbase
could result in death, personal injury and/or
property damage.
Place furnace on noncombustible subbase on
downflow applications, unless installing on non--
combustible flooring.
!
W
RNING
Subbase for Combustible Floor
NOTE: The three(3) screws in the top panel of the furnace next to
the duct flange MUST be removed to provide serviceability of the
primary heat exchangers i n the downflow installation
Note: When using the subbase for combustible floors, the dis-
charge air duct flanges on the furnace MUST be broken down to
provide proper fit up to the subbase. Use duct pliers to bend the
duct flanges flat onto the furnace casing. DO NOT bend the duct
flanges inward (toward the heat exchangers) as air flow restric-
tions may occur.
The Subbase for Combustible Floors MUST be used when a
downflow furnace is set on a combustible floor, even when the fur-
nace is installed on a coil box.
1. Cut the opening in the floor according to Table 8. The hole in
the floor must be cut to the dimensions listed in Table 8
since the base is equipped with locating tabs that center the
base over the opening.
The opening in the base is 1
1
/
4
² shorter and 1
1
/
8
² narrower than
the recommended size of the opening in the floor. This is done to
maintain clearance between the floor and the plenum.
2. Fabricate the plenum to the dimensions given in Table 8.
Note that the dimensions given are outside dimensions.
Table 8 Subbases for Combustible Floors Dimensions
Subbase for Combustible
Subbase for Combustible
Floor Dimensions
OpeningInFloor
Opening In Base
For Plenum
Typical Plenum
Dimensions
oors
art
um
er
H* J* K** L M N P R S T
Furnace Subbase
NAHH001SB
15
11
/
16
28
3
/
4
14
9
/
16
16 16
1
/
4
14
5
/
8
15 13
1
/
2
15 13
1
/
2
NAHH002SB
19
5
/
16
28
3
/
4
18
3
/
16
16 16
1
/
4
18
1
/
4
15 17
1
/
8
15 17
1
/
8
NAHH003SB
22
5
/
16
28
3
/
4
21
13
/
16
16 16
1
/
4
21
7
/
8
15 19
3
/
4
15 19
3
/
4
NAHH010SB
24
11
/
16
28
3
/
4
23
9
/
16
16 16
1
/
4
23
5
/
8
15 22
1
/
2
15 22
1
/
2
Subbase for Coil Cabinets
NAHH004SB
15
11
/
16
20
9
/
16
14
9
/
16
16
1
/
4
16
1
/
4
14
5
/
8
15 13
1
/
2
15 13
1
/
2
NAHH005SB
19
5
/
16
20
9
/
16
18
3
/
16
16
1
/
4
16
1
/
4
18
1
/
4
15 17
1
/
8
15 17
1
/
8
NAHH006SB
23 20
9
/
16
21
13
/
16
16
1
/
4
16
1
/
4
21
7
/
8
15 19
3
/
4
15 19
3
/
4
NAHH009SB
24
3
/
4
20
9
/
16
23
9
/
16
16
1
/
16
16
1
/
4
23
5
/
8
15 22
1
/
2
15 22
1
/
2
*
Outside Dimension
**
Base Spacer Side To Side
3. Set the base over the opening in the floor, centering it over
the opening. Fasten the base to the floor with screws or
nails. See Figure 45, Figure 46 and Figure 47.
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