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Combustion Air and Ventilation for
Appliances Located in Confined Spaces
CONFINED SPACE is a space whose volume is less than
50 cubic feet per 1,000 Btu per hour (4.8 m3 per kW) of the
aggregate input rating of all appliances installed in that space.
A. ALL AIR FROM INSIDE BUILDINGS:
(See Figure 9 on page 9 and Figure 10 below)
The confined space shah be provided with two permanent
openings communicating directly with an additional room(s)
of sufficient volume so that the combined volume of all spaces
meets the criteria for an unconfined space. The total input of
all gas utilization equipment installed in the combined space
shall be considered in making this determination. Each
opening shall have a minimum free area of one square inch
per 1,000 Btu per hour (22 cm_/kW) of the total input rating of all
gas utilization equipment in the confined space, but not less
than 100 square inches (645 cm2). One opening shall
commence within 12 inches (30 cm) of the top and one
commencing within 12 inches (30 cm) of the bottom of the
enclosures.
NT
FUR__ NG
FIGURE10.
B. ALL AIR FROM OUTDOORS: (See Figures 9, 11,12 and 13)
The confined space shall be provided with two permanent
openings, one commencing within 12 inches (30 cm) of the
top and one commencing within 12 inches (30 cm) from the
bottom of the enclosure. The openings shall communicate
directly, or by ducts, with the outdoors or spaces (crawl or attic)
that freely communicate with the outdoors.
CHIMNEY OR
GAS VENT
VENTILATION LOUVERS
IEACH END OF ATTIC)
When directly communicating with the oL_doors, each opening
shall have a minimum free area of 1 square inch per 4,000 Btu
per hour (5.5 cm2/kW) of total input rating of all equipment in the
enclosure. See Figure 12.
When communicating with the outdoors through vertical
ducts, each opening shall have a minimum free area of
1 square inch per 4,000 BTU per hour (5.5 cm2/kW) of total
input rating of all equipment in the enclosure. See
Figure 12.
VENTILATION LOUVERS
FURNACE
INLET AIR DUCT
(ENDS 1' OR 30 cm
ABOVE FLOOR)
FIGURE12.
When communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of 1
square inch per 2,000 BTU per hour (11 cm2/kW) of total
input rating of all equipment in the enclosure. See
Figure 13.
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 short side dimension of
rectangular air ducts shall not be less than 3 inches
(76.2 mm). See Figure 13.
____ CHIMNEY OR GAS VENT
OUTLET AIR DUCT
iNLET AIR DUCT
FIGURE 13.
OUTLET AIR
WATER HEATER
FURNACE
INLET AIR DUCT
ALT. INLET AIR VENTII ATION LOUVERS
FIGUREll.
11
Louvers and Grilles: in calculating free area, considerafion
shall be given to the blocking effect of louvers, grilles or
screens protecting openings. Screens used shall not be
smaller than 1/4 inch (6.4 mm) mesh. Ifthe free area through
a design of louver or grille is known, it should be used in
calculating the size opening required to provide the free
area specified. If the design and free area is not known, it
may be assumed that wood louvers will be 20-25 percent
free area and metal louvers and grilles will have 60-75
percent free area. Louvers and grilles shall be fixed in the
open position or interlocked with the equipment so that they
are opened automatically during equipment operation.