b. One Permanent Opening Method: Provide one
permanent opening beginning within 12 inches
(305 mm) of the top of the space. The opening
shall communicate directly with the outdoors,
communicate through a vertical or horizontal duct,
or communicate with a space that freely
communicates with the outdoors. The opening
shall have a minimum free area of 1 in
2
per 3000
Btu/hr. of total rated input for all appliances in the
space and not less than the sum of the cross
sectional areas of all vent connectors in the space.
The gas-fired equipment shall have clearances of
at least 1 inch (25 mm) from the sides and back
and 6 inches (150 mm) from the front of the
appliance. See Figure 1.7 for this arrangement.
6. Combination Indoor and Outdoor Combustion Air: If
the required volume of indoor air exceeds the
available indoor air volume, outdoor air openings or
ducts may be used to supplement the available indoor
air provided:
a. The size and location of the indoor openings
comply with Subsection 3.
b. The outdoor openings are to be located in
accordance with Subsection 4.
c. The size of the outdoor openings are to be sized
as follows:
where:
A
req
= minimum
area of outdoor openings.
A
full
= full size of outdoor openings calculated
in accordance with Subsection 4.
V
avail
= available indoor air volume
V
req
= required indoor air volume
7. Engineered Installations: Engineered combustion air
installations shall provide an adequate supply of
combustion, ventilation, and dilution air and shall be
approved by the authority having jurisdiction.
5
Figure 1.4: Air Openings – All Air Directly from
Outdoors
Figure 1.5: Air Openings – All Air from Outdoors
through Vertical Ducts
Figure 1.6: Air Openings – All Air from Outdoors
through Horizontal Ducts
Figure 1.7: Air Openings – All Air from Outdoors
PREINSTALLATION
A
req
= A
full
x 1 –
V
avail
V
req
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