State GPG 81 370NEA - Manual (Page 17)

17
fresh air openings for confined spaces
The following instructions shall be used to calculate the size,
number and placement of openings providing fresh air for
combustion, ventilation and dilution in confined spaces. The
illustrations shown in this section of the manual are a reference
for the openings that provide fresh air into confined spaces
only. DO NOT refer to these illustrations for the purpose of vent
installation. See Venting Installation on page 16 for complete
venting installation instructions.
outdoor air through two openings
figure 12.
The confined space shall be provided with two permanent
openings, one commencing within 12 inches (300 mm) of the top
and one commencing within 12 inches (300 mm) of the bottom of
the enclosure. The openings shall communicate directly with the
outdoors. See Figure 12.
each opening shall have a minimum free area of 1 square inch
per 4,000 Btu/hr (550 mm 2 per kW) of the aggregate input rating
of all appliances installed in the enclosure. each opening shall
not be less than 100 square inches (645 cm 2 ).
outdoor air through one opening
figure 13.
Alternatively a single permanent opening, commencing
within 12 inches (300 mm) of the top of the enclosure,
shall be provided. See Figure 12. The water heater shall
have clearances of at least 1 inch (25 mm) from the sides
and back and 6 inches (l50 mm) from the front of the
water heater. The opening shall directly communicate
with the outdoors or shall communicate through a vertical
or horizontal duct to the outdoors or spaces that freely
communicate with the outdoors and shall have a minimum
free area of the following:
1. 1 square inch per 3000 Btu/hr (733 mm 2 per kW) of
the total input rating of all appliances located in the
enclosure, and
2. Not less than the sum of the areas of all vent connectors
in the space.
outdoor air through two horiZontal ducts
figure 14.
The confined space shall be provided with two permanent
horizontal ducts, one commencing within 12 inches (300
mm) of the top and one commencing within 12 inches
(300 mm) of the bottom of the enclosure. The horizontal
ducts shall communicate directly with the outdoors. See
Figure 14.
each duct opening shall have a minimum free area of
1 square inch per 2,000 Btu/hr (1100 mm2 per kW) of
the aggregate input rating of all appliances installed in
the enclosure.
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 not less than 3 inches.