Page 17
FIGURE 13
EQUIPMENT IN CONFINED SPACE − ALL AIR FROM INSIDE
OPENINGS
(To Adjacent
Unconfined
Space)
NOTE
− Each opening shall have a free area of at least one square inch
per 1,000 Btu (645 mm
2
per .29 kW) per hour of the total input rating of
all equipment in the enclosure, but not less than 100 square inches
(64516 mm.
2).
ROOF TERMINATED
EXHAUST PIPE
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
ML193UH
Air from Outside
If air from outside is brought in for combustion and ventila-
tion, the confined space shall be provided with two perma-
nent openings. One opening shall be within 12" (305mm)
of the top of the enclosure and one within 12" (305mm) of
the bottom. These openings must communicate directly
or by ducts with the outdoors or spaces (crawl or attic) that
freely communicate with the outdoors or indirectly
through vertical ducts. Each opening shall have a mini-
mum free area of 1 square inch per 4,000 Btu (645mm
2
per 1.17kW) per hour of total input rating of all equipment
in the enclosure. When communicating with the outdoors
through horizontal ducts, each opening shall have a mini-
mum free area of 1 square inch per 2,000 Btu (645mm
2
per .59kW) per total input rating of all equipment in the en-
closure (See figure 14).
FIGURE 14
EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE
(Inlet Air from Crawl Space and Outlet Air to Ventilated Attic)
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)
If air from outside is brought in for combustion and ventila-
tion, the confined 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 indi-
rectly through vertical ducts. Each opening shall have a
minimum free area of 1 square inch (645 mm
2
) per 4,000
Btu (1.17 kW) per hour of total input rating of all equipment
in the enclosure. See figures 14 and 15. When
communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of 1
square inch (645 mm
2
) per 2,000 Btu (.56 kW) per total in-
put rating of all equipment in the enclosure. See
figure 16.
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.
FIGURE 15
EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
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
VENTILATION LOUVERS
(Each end of attic)
INLET AIR
(Ends 12" above
bottom)
ROOF TERMINATED
EXHAUST PIPE
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
FURNACE
