Specifications

42
440 01 1024 04
Specifications are subject to change without notice
The Subbase for Combustible Floors MUST be used when a
downflow 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 13. The hole
in the floor must be cut to the dimensions listed in Table 13
since the base is equipped with locating tabs that center the
base over the opening.
The opening in the base is 1
1
/
4
″ (31.8mm) shorter and 1
1
/
8
″
(28.6mm) 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 13.
Note that the dimensions given are outside dimensions.
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 41, Figure 42 and Figure 43.
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.
This subbase for combustible floors has been designed so that the
height of the subbase raises the downflow coil off the floor to allow
easy installation of the condensate drain. See Figure 44.
Figure 41
Plenum
S
T
A
Hole in
Floor
M
N
25-20-46
Combustible
Floor Base
L
R
H
K
2″ (50.8mm)
1″ (25.4mm)
J
P
A = 4 1/4” (108mm) Minimum clearance from back of hole to wall or other
obstruction.
Exploded View of Sub−Base for
Furnace ONLY
2″
(50.8mm)
Figure 42
Exploded View of Base for
Downflow Cased Coil
2
1
/
2
″ (63.5mm)
1
1
/
2
″(38.1mm)
25−20−46a
Furnace/Coil Box
Wood Screw
Plenum
Wood Floor
Figure 43
Setting the Subbase
Installation of
Combustible
Floor Base
Condensate Line Raised by Base
Figure 44
25−20−52
Checks and Adjustments
NOTE: Verify the input rate of the furnace.
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in
personal injury, death and/or property damage.
Turn OFF gas at shut off before connecting
manometer.
!
WARNING
Startup
NOTE: Refer to the start−up procedures in the “User’s Information
Manual” or to the “Operating Instructions Label” on the furnace.
Gas Supply Pressure
Gas supply pressure should be within minimum and maximum
values listed on rating plate. Pressures are usually set by gas
suppliers.