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Roof Terminated
Exhaust Pipe
Ventilation
Furnace
Louvers
(Crawl space)
Coupling or
3 in. to 2 in.
Transition
(Field Provided)
* See Maximum Vent Lengths table
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
hour of the total input rating of all equipment in the enclosure.
Figure 9. Equipment in Confined Space
(Inlet Air from Ventilated Crawlspace & Outlet Air to
When communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of 1
square inch (645 mm²) per 2,000 Btu (.56 kW) per hour of
the total input rating of all equipment in the enclosure. See
Figure 10.
Figure 10. Equipment in Confined Space - all Air from
When ducts are used, they shall be of the same cross-
sectional area as the free area of the openings to which
they connect. The minimum dimension of rectangular
air ducts shall be no less than 3 inches (75 mm). In
calculating free area, the blocking effect of louvers, grilles,
or screens must be considered. If the design and free area
of protective covering is not known for calculating the size
508391-01
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
*Intake Debris Screen Provided)
2
per 1.17kW) per
Outside)
Outside
opening required, it may be assumed that wood louvers
will have 20 to 25 percent free area and metal louvers and
grilles will have 60 to 75 percent free area. Louvers and
grilles must be fixed in the open position or interlocked
with the equipment so that they are opened automatically
during equipment operation.
If this unit is being installed in an application with
combustion air coming in from a space serviced by an
exhaust fan, power exhaust fan, or other device which
may create a negative pressure in the space, take care
when sizing the inlet air opening. The inlet air opening
must be sized to accommodate the maximum volume
of exhaust air as well as the maximum volume of
combustion air required for all gas appliances serviced
by this space.
Installation
Setting Equipment
Do not install the furnace on its front, back or in the
horizontal position. See Figure 13. Do no connect the
return air ducts to the back of the furnace. Doing so
will adversely affect the operation of the safety control
devices, which could result in personal injury or death.
Select a location that allows for the required clearances
that are listed on the unit nameplate. Also consider gas
supply connections, electrical supply, vent connection,
condensate trap and drain connections, and installation
and service clearances [24 inches (610 mm) at unit front].
The unit must be level from side to side. Tilt the unit slightly
(maximum 1/2 in. from level) from back to front to aid in the
draining of the heat exchanger. See Figure 12.
Shipping Bolt Removal
NOTE: Units with a 1/2 hp blower motors are equipped
with three flexible legs and one rigid leg. The rigid leg
is equipped with a shipping bolt and a flat white plastic
washer (rather than the rubber mounting grommet used
with a flexible mounting leg). See Figure 11. The bolt and
washer must be removed before the furnace is placed into
operation. After the bolt and washer have been removed,
the rigid leg will not touch the blower housing.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in Figure 15.
Issue 2327
WARNING
WARNING
Page 9 of 52
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