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Page 10
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM INSIDE
OPENINGS
(To Adjacent
Room)
G24−200
FURNACE
CHIMNEY
OR GAS
VENT
NOTE−Each opening shall have a free area of at least one square
inch (645 mm
2
) per 1,000 Btu (.29 kW) per hour of the total input rat-
ing of all equipment in the enclosure, but not less than 100 square
inches (64516 mm
2
).
FIGURE 1
When ducts are used, they shall be of the same cross−sec-
tional 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 protec-
tive 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.
EQUIPMENT IN CONFINED SPACE ALL AIR FROM OUTSIDE
(Inlet Air from Crawl Space and Outlet Air to Ventilated Attic)
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR
INLET
AIR
CHIMNEY OR
GAS VENT
G24−200
FURNACE
VENTILATION
LOUVERS
(For unheated crawl space)
NOTE−The inlet and outlet air openings shall each have a free area of at least one square inch (645 mm
2
)
per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
FIGURE 2