507715-01
Page 26 of 61
Issue 1716
Figure 29.
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 exhausted air as well as the maximum volume of
combustion air required for all gas appliances serviced
by this space.
CAUTION
Follow the next two steps when installing the unit in Non–
Direct Vent applications where combustion air is taken
from indoors and flue gases are discharged outdoors.
1. Use field-provided materials and the factory-provided
air intake screen to route the intake piping as shown in
Figure 29 or Figure 30. Maintain a minimum clearance
of 3” (76 mm) around the air intake opening. The air
intake opening (with the protective screen) should
always be directed forward or to either side in the
upflow position, and either straight out or downward in
the horizontal position.
Figure 30.
The air intake piping must not terminate too close to the
flooring or a platform. Ensure that the intake air inlet will
not be obstructed by loose insulation or other items that
may clog the debris screen.
2. If intake air is drawn from a ventilated attic (Figure
31) or ventilated crawlspace (Figure 32) the exhaust
vent length must not exceed those listed in Table 5B
or Table 6C. If 3” diameter pipe is used, reduce to 2”
diameter pipe at the termination point to accommodate
the debris screen.
3. Use a sheet metal screw to secure the intake pipe to
the connector, if desired.
Figure 31.
Equipment in Confined Space
(Inlet Air from Ventilated Attic & Outlet Air to Outside)
Ventilation Louvers
Inlet Air
(Minimum 12 in.
(305mm) above
Attic Floor)
Roof Terminated
Exhaust Pipe
Furnace
*Intake Debris
Screen
(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 (645 mm
2
per
1.17 kW) per hour of the total input rating of all equipment in the
enclosure.
