A.O. Smith 300 Series Instruction Manual page 16

1 square inch per 3000 Btu/hr (733 mm
1.
rating of all appliances located in the enclosure, and
Not less than the sum of the areas of all vent connectors in the
2.
space.
Outdoor Air Through Two Horizontal Ducts
Figure 11. Figure 7
The confined space shall 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 shall communicate directly with the
outdoors. See Figure 7.
Each duct opening shall have a minimum free area of 1 square inch
per 2,000 Btu/hr (1100 mm
2
of all appliances installed in the enclosure.
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 3 inches.
per kW) of the total input
2
per kW) of the aggregate input rating
Air From Other Indoor Spaces
The confined space shall 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 8.
Each opening shall 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 shall have a minimum free area of 1 square inch per
1,000 Btu/hr (2200 mm
all appliances installed in the enclosure. Each opening shall not be
less than 100 square inches (645 cm
16
Figure 12. Figure 8
per kW) of the aggregate input rating of
2
).
2