3DJH
When the furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space con-
tainingthe furnace, thereturnair must be handledby ducts
which are sealed to the furnace casing and which termi-
nate outside the space containing the furnace. This is es-
pecially important when the furnace is mounted on a plat-
form in a confined space such as a closet or small equip-
ment room. Even a small leak around the base of the unit
at the platform or at the return air duct connection can
cause a potentially dangerous negative pressure condi-
tion. Air for combustion and ventilation can be brought into
the confined space either from inside the building or from
outside.
Air from Inside
If the confined space housing the furnace adjoins space
categorizedas unconfined,aircanbebroughtinby provid-
ing two permanent openings between the two spaces.
Each opening must have a minimum free area of 1 square
inch per 1,000 Btu per hour of the total input rating of all
gas-fired equipment in the confined space. Each opening
must be at least 100 square inches. One opening shall be
within 12 inches of the top of the enclosure and one open-
ing within 12 inches of the bottom (See figure 25).
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM INSIDE
FIGURE 25
NOTE-Each opening shall have a free area of at least one square
inch per 1,000 Btu per hour of the total input rating of all equip-
ment in the enclosure, but not less than 100 square inches.
CHIMNEY OR
GAS VENT
WATER
HEATER
OPENINGS
(To Adjacent
Room)
G23(X)
FURNACE
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 inches of
the top of the enclosure and one within 12 inches of the
bottom. These openings must communicate directly or by
ducts with theoutdoorsor spaces(crawlor attic) that freely
communicate with the outdoors or indirectly through verti-
cal ducts.Each opening shallhave a minimum freeareaof
1 square inch per 4,000 Btu per hour of total input rating of
all equipment in the enclosure (See figures 26 and 27).
When communicating with the outdoors through horizon-
tal ducts, each opening shall have a minimum free area of
1 square inch per 2,000 Btu per total input rating of all
equipment in the enclosure (See figure 28).
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 per hour of the
total input rating of all equipment in the enclosure.
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR
WATER
HEATER
INLET
AIR
CHIMNEY
OR GAS
VENT
VENTILATION
LOUVERS
(For unheated
crawl space)
FIGURE 26
G23
FURNACE
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 per hour of the
total input rating of all equipment in the enclosure.
CHIMNEY
OR GAS
VENT
WATER
HEATER
OUTLET
AIR
VENTILATION LOUVERS
(Each end of attic)
INLET AIR
(Ends 12 above
bottom)
FIGURE 27
G23(X)
FURNACE
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