14
The confined space should be provided with two permanent
horizontal ducts, one commencing within 12 inches (300 mm) of
the top and one commencing within 12 inches (300 mm) of the
bottom of the enclosure. The horizontal ducts should communicate
directly with the outdoors. See Figure 9C.
Each duct opening should have a minimum free area of 1 square
inch per 2,000 Btu/hr (1100 mm
2
per kW) of the aggregate input
rating of all appliances installed in the enclosure.
When ducts are used, they should 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 should be not less
than 3 inches.
OUTDOOR AIR THROUGH TWO VERTICAL DUCTS
The illustrations shown in this section of the manual are
a reference for the openings that provide fresh air into
confined spaces only.
Do not refer to these illustrations for the purpose of vent
installation. See Venting Installation on page 19 for complete
venting installation instructions.
FIGURE 9D.
The confined space should be provided with two permanent
vertical ducts, one commencing within 12 inches (300 mm) of
the top and one commencing within 12 inches (300 mm) of the
bottom of the enclosure. The vertical ducts should communicate
directly with the outdoors. See Figure 9D.
Each duct opening should have a minimum free area of 1 square
inch per 4,000 Btu/hr (550 mm
2
per kW) of the aggregate input
rating of all appliances installed in the enclosure.
When ducts are used, they should be of same cross sectional area
as free area of openings to which they connect. The minimum
dimension of rectangular air ducts should be not less than 3 inches.
AIR FROM OTHER INDOOR SPACES
FIGURE 9E.
The confined space should be provided with two permanent
openings, one commencing within 12 inches (300 mm) of the top
and one commencing within 12 inches (300 mm) of the bottom of
the enclosure. See Figure 9E.
Each opening should communicate directly with an additional
room(s) of sufficient volume so that the combined volume of all
spaces meets the criteria for an Unconfined Space.
Each opening should have a minimum free area of 1 square inch
per 1,000 Btu/hr (1100 mm
2
per kW) of the aggregate input rating
of all appliances installed in the enclosure. Each opening should
not be less than 100 square inches (645 cm
2
).