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Figure 8. Equipment in Confined Space - All Air from
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.
Roof Terminated
Exhaust Pipe
* 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 Attic and Outlet Air to
508390-01
Outside
WARNING
Ventilation Louvers
Inlet Air
(Minimum
12 in.(305mm) Above
attic floor)
*Intake Debris
Screen
(Provided)
Furnace
2
per 1.17kW) per
Outside)
Roof Terminated
Exhaust Pipe
Ventilation
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 10. Equipment in Confined Space
(Inlet Air from Ventilated Crawlspace and Outlet Air to
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
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.
Issue 2327
Inlet Air
(Minimum
12 in.(305mm)
Furnace
Above crawl
space floor)
*Intake Debris Screen Provided)
2
per 1.17kW) per
Outside)
Page 9 of 60
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