Page 7
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE
(Inlet Air from Crawl Space and Outlet Air to Outside)
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
2
per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
OUTLET
AIR
INLET
AIR
VENTILATION
LOUVERS
(For unheated
crawl space)
FURNACE
ROOF TERMINATED
EXHAUST PIPE
VENTILATION LOUVERS
(Each end of attic)
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
Figure 5
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Attic and Outlet Air to Outside)
-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645m
m
2
per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
Ventilation Louvers
Inlet Air
(Minimum
12 in.(305mm) Above
attic floor)
Roof Terminated
Exhaust Pipe
Furnace
*Intake Debris
Screen
(Provided)
Figure 6
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
2
per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Crawlspace and Outlet Air to Outside)
Roof Terminated
Exhaust Pipe
Furnace
Ventilation
Louvers
(Crawl space)
*Intake Debris Screen Provided)
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
Coupling or
3 in. to 2 in.
Transition
(Field Provided)
Figure 7
If air from outside is brought in for combustion and ventila-
tion, the conned space must have two permanent open-
ings. One opening shall be within 12 inches (305 mm) of
the top of the enclosure and one opening within 12 inches
(305 mm) of the bottom. These openings must communi-
cate directly or by ducts with the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors or in-
directly through vertical ducts. Each opening shall have a
minimum free area of 1 square inch (645 mm2) per 4,000
Btu (1.17 kW) per hour of total input rating of all equip-
ment in the enclosure. See Figure 5 and Figure 8. When
communicatin with the outdoors through horizontal ducts,
each opening shall have a minimum free area of 1 square
inch (645 mm2) per 2,000 Btu (.56 kW) per total input rat-
ing of all equipment in the enclosure. See Figure 9.
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 eect 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 xed in the open position or interlocked with the
equipment so that they are opened automatically during
equipment operation.
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