Lennox COWB3 Installation Instructions Manual page 8

B. All Air from Outdoors: Confined space shall be pro-
vided with two permanent openings, one commencing
within 12 inches of top and commencing within 12
inches of bottom of enclosure. Openings shall com-
municate directly, or by ducts, with outdoors or spaces
(crawl or attic) that freely communicate with outdoors.
1. When directly communicating with outdoors, each
opening shall have 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 outdoors through verti-
cal ducts, each opening shall have minimum free
area of one square inch per 4,000 Btu per hour of
total input rating of all equipment in the enclosure.
3. When communicating with outdoors through hori-
zontal ducts, each opening shall have minimum
Figure 5 - Fresh Air Duct Capacities For Ducts Supplying Fresh Air To Boiler In
Tightly Constructed Houses
FRESH AIR DUCT CAPACITIES
THROUGH LOUVERS
¼" Mesh
Fresh Air
Screen
Duct Size
(Btuh)*
3 ½" x 12" 144,000
8" x 8" 256,000
8" x 12" 384,000
8" x 16" 512,000
*Btuh = British Thermal Units per hour based on
opening covered by ¼" mesh screen , wood louvers,
or metal louvers.
FRESH AIR FOR COMBUSTION
Wood Metal
Louvers Louvers
(Btuh)* (Btuh)*
36,000 108,000
64,000 192,000
96,000 288,000
128,000 384,000
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 same cross
sectional area as free area of openings to which
they connect. Minimum dimension of rectangular
air ducts shall be not less than three inches.
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