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having a total free area of not less than 1 square inch per 5,000 BTU per hour of total input
rating of all appliances shall be provided. Ducts may be used to convey make-up air from
the outdoors and shall have the same cross-sectional area of the openings to which they
are connected.
4. When air for combustion and room ventilation is from inside buildings, the confined
space shall be provided with two permanent openings, one starting 12 inches from the top
and one 12 inches from the bottom of the enclosed space. Each opening shall have a
minimum free area of 1 square inch per one thousand (1,000) BTU per hour of the total input
rating of all appliances in the enclosed space, but must not be less than one hundred (100)
square inches. These openings must freely communicate with the interior areas having
adequate infiltration from the outside. See figure 1 below.
5. When the boiler is installed in a confined space and all air is provided from the outdoors,
the confined space shall be provided with two permanent openings, one commencing within
12 inches from the top and one commencing 12 inches from the bottom of the enclosure. The
openings shall communicate directly, or by ducts, with the outdoors or spaces (crawl or attic)
that freely communicate with the outdoors. One of the following methods must be used to
provide adequate air for ventilation and combustion.
A. When directly communicating with the outdoors, each opening shall have a minimum
free area of 1 square inch per 4,000 BTU per hour of total input rating of all equipment in
the enclosure. See figure 2, above.
B. When communicating with the outdoors by means of vertical ducts, each opening
shall have a minimum free area 1 square inch per 4,000 BTU per hour of total input rating
of all appliances in the enclosed space. See figure 3 on page 5.
C. If horizontal ducts are used, each opening shall have a minimum free area 1 square
inch per 2,000 BTU per hour total input rating of all appliances in the enclosed space. See
figure 4 on page 5.
D. When ducts are used, they shall be of the same cross sectional area as the free area
of the area of the openings to which they connect. The minimum dimension of rectangular
FIGURE 1
FIGURE 2
