Lennox COWB2

8
B. All Air from Outdoors: The conned space
shall be provided with two permanent
openings, one commencing within 12 inches
of the top and commencing within 12 inches
of 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.
1. When directly communicating with the
outdoors, each opening shall have a
minimum free area of one square inch
per 4,000 Btu per hour of total input rating
of all equipment in the enclosure.
2. When communicating with the outdoors
through vertical ducts, each opening
shall have a minimum free area of one
FresH air dUCT CapaCiTies FOr dUCTs sUpplYiNg FresH air TO
BOiler iN TigHTlY CONsTrUCTed HOUses
square inch per 4,000 Btu per hour of
total input rating of all equipment in the
enclosure.
3. When communicating with the outdoors
through horizontal ducts, each opening
shall have a minimum free area of one
square inch per 2,000 Btu per hour of
total input rating of all equipment in the
enclosure.
4. 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 three inches.
FresH air FOr COMBUsTiON
FRESH AIR DUCT CAPACITIES
THROUGH LOUVERS
Fresh Air
Duct Size
¼” Mesh
Screen
Wood
Louvers
Metal
Louvers
(Btuh)* (Btuh)* (Btuh)*
3 ½” x 12” 144,000 36,000 108,000
8” x 8” 256,000 64,000 192,000
8” x 12” 384,000 96,000 288,000
8” x 16” 512,000 128,000 384,000
*Btuh = British Thermal Units per hour based on
opening covered by ¼” mesh screen , wood louvers,
or metal louvers.