507651-01
Issue 1907
Page 7 of 32
per 4,000 Btu (1.17 kW) per hour of total input rating of all
equipment in the enclosure. See Figure 3 and Figure 4.
When communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of 1
square inch (645 mm2) per 2,000 Btu (.56 kW) per total
input rating of all equipment in the enclosure. See Figure 5.
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 no less than 3 inches (75 mm). In
calculating free area, the blocking effect of louvers, grilles,
or screens must be considered. If the design and free area
of protective covering is not known for calculating the size
opening required, it may be assumed that wood louvers
will have 20 to 25 percent free area and metal louvers and
grilles will have 60 to 75 percent free area. Louvers and
grilles must be fixed in the open position or interlocked
with the equipment so that they are opened automatically
during equipment operation.
Figure 3.
Equipment in Confined Space - All Air from
Outside
NOTE:
The inlet and outlet air openings shall each have a free
area of at least one square inch per 4,000 Btu (645 mm² per
1.17 kW) per hour of the total input rating of all equipment in the
enclosure.
(Inlet Air from
Crawlspace &
Outlet Air to
Ventilated Attic)
Figure 4.
Equipment in Confined Space - All Air from
Outside (Ventilated Attic)
NOTE:
The inlet and outlet air openings shall each have a free
area of at least one square inch per 4,000 Btu (645 mm² per
1.17 kW) per hour of the total input rating of all equipment in the
enclosure.
NOTE:
Each air duct opening shall have a free area of at least one
square inch per 2,000 Btu (645 mm² per .59 kW) per hour of the
total input rating of all equipment in the enclosure. If the equipment
room is located against an outside wall and the air openings
communicate directly with the outdoors, each opening shall have
a free area of at least 1 square inch per 4,000 Btu (645 mm² per
1.17 kW) per hour of the total input rating of all other equipment in
the enclosure.
Figure 5.
Equipment in Confined Space - All Air from
Outside
