John Wood Commercial - 300-400K BTU - Manual (Page 19)

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air from other indoor spaces
figure 14
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 14.
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 (1100 mm2 per kW) of the aggregate input
rating of all appliances installed in the enclosure. Each opening
shall not be less than 100 square inches (645 cm2).
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 20 for complete
venting installation instructions.
figure 13
The confined space shall 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 shall communicate directly with the
outdoors. See Figure 13.
Each duct opening shall have a minimum free area of 1 square
inch per 4,000 btu/hr (550 mm2 per kW) of the aggregate input
rating 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.