Install Instructions
32
Installation (Combustion Air Supply) continued-
All Air From Inside the Building
The confined space must be provided with two permanent openings
communicating directly with an additional room(s) of sufficient volume so that
the combined volume of all spaces meets the criteria for an unconfined space.
The total input of all gas utilization equipment installed in the combined space
must be considered in making this determination. Each opening must have a
minimum free area of 1 in.²/1000 BTU (6.5 cm
2
/0.29 kw) per hour of the total
input rating of all gas utilization equipment in the confined space, but not less
than 100 in.² (645 cm
2
). One opening must be within 12 in. (31 cm) of the top
and one within 12 in. (31 cm) of the bottom of the enclosure.
All Air From Outdoors
The confined space must be provided with two permanent openings, one
commencing within 12 in. (31 cm) of the top and one commencing within 12 in.
(31 cm) from the bottom of the enclosure. The openings must communicate
directly, or by ducts, with the outdoors or spaces (crawl or attic) that freely
communicate with the outdoors.
1. When directly communicating with the outdoors, each opening must have a
minimum free area of 1 in.²/4000 BTU (6.5 cm
2
/1.2 kw) per hour of total
input rating of all equipment in the enclosure.
2. When communicating with the outdoors through vertical ducts, each
opening must have a minimum free area of 1 in.² (6.5 cm
2
) per 4000 BTU
(1.2 kw) per hour of total input rating of all equipment in the enclosure.
3. When communicating with the outdoors through horizontal ducts, each
opening must have a minimum free area of 1 in.²/2000 BTU (6.5 cm
2
/0.6
kw) per hour of total input rating of all equipment in the enclosure.
4. When ducts are used, they must 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 must be not less than 3 in. (7.5 cm).
Specially Engineered Installations
The requirements noted in the Confined Spaces section addressed previously
does not necessarily govern when special engineering, approved by the
authority having jurisdiction, provides an adequate supply of air for combustion,
ventilation, and dilution of flue gases.