Operating instructions

o
All Air from Outdoors: The confined space shall communicate with the outdoors in accordance with Methods A or B below. The
minimum dimension of air openings shall not be less than 3 in. Where ducts are used, they shall be of the same cross-sectional area as
the free area of the openings to which they connect.
Method A: Two permanent openings, one commencing within 12 inches of the top, and one commencing within 12inches of the bot-
tom, of the enclosure shall be provided. The openings shall communicate directly, or by the ducts, with the outdoors or spaces (crawl or
attic) that freely communicate with the outdoors.
1. Where directly communicating with the outdoors (see Figure 3B) or where communicating to the outdoors through vertical ducts
(see Figure 3C), each opening shall have a minimum free area of 1 sq. in. per 4000 Btu per hour of total input rating of all equip-
ment in the enclosure.
Figure 3B - Directly Communicating to the Outdoors Figure 3C - Vertical Ducts Communicating to the Outdoors
Air
Pipe
3"x 12" 144,000 108,000 36,000
8"x 8" 256,000 192,000 64,000
8"x 12" 384,000 288,000 96,000
8 ½"x16" 512,000 384,000 128,000
Louver Allowance
The free areas of openings means the area after reduction for any installed louvers or grilles. Be
sure to consider this reduction when sizing the air openings.