FIGURE 4
PAGE 4
FIGURE 3
FIGURE 2
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 one or two permanent openings according to
methods A or B. 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 air ducts shall be not less than 3 x 3 inches or 9 square inches.
A. When installing two openings, one must commence within 12 inches from the top and
the other within 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.
1. 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.
2. 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 above.
3. If horizontal ducts are used, each opening and duct shall have a minimum free
area 1 square inch per 2,000 BTU per hour of total input rating of all appliances in the enclosed
space. See figure 4 at right.
B. One permanent opening, commencing within 12 inches of the top of the enclosure,
shall be permitted where the equipment has clearances of at least 1 inch from the sides, 1
inch from the back, and 6 inches from the front of the boiler. The opening shall directly
communicate with the outdoors or shall communicate through a vertical or horizontal duct to
the outdoors or spaces (crawl or attic) that freely communicate with the outdoors. The
openings must have a minimum free area of 1 square inch per 3000 Btu per hour of the total
