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440 01 2020 01
Downflow Furnace Installation
Non- Combustible Floor Installation
Fabricate a plenum to the dimensions given in
Figure 3
, 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 pri-
mary heat exchangers in 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 can
result in death, personal injury and/or property damage.
Place furnace on noncombustible subbase on downflow
applications, unless installing on non--combustible
flooring.
!
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 in 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 restrictions
may occur.
The Subbase for Combustible Floors
MUST
be used when a down-
flow furnace is set on a combustible floor, even when the furnace is
installed on a coil box.
1. Cut the opening in the floor according to
Table 7
. The hole in
the floor must be cut to the dimensions listed in
Table 7
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 main-
tain clearance between the floor and the plenum.
2. Fabricate the plenum to the dimensions given in
Table 7
.
Note that the dimensions given are outside dimensions.
Table 7
Subbases for Combustible Floors Dimensions
Subbase for Combustible
Floors Part Number
Subbase for Combustible
Floor Dimensions
Opening In Floor
Opening In Base
For Plenum
Typical Plenum
Dimensions
Floors Part Number
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 37, Figure 38
and
Figure 39
.
4. Drop the plenum through the opening in the base. The
flange of the plenum should rest on top of the subbase.
5. Position furnace or coil cabinet and furnace on subbase so it
aligns between the locating tabs.
T
S
H
J
1”
2”
N
M
R
P
L
2”
25--20--46
Plenum
Combustible
Floor Base
Furnace Subbase
Figure 37
A
A = 4
1
/
4
” Minimum
clearance from back of
hole to wall or other
obstruction.
Hole in
Floor
K
Summary of Contents for 9MPT050F12A
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