Page 12
outside the space containing the furnace. This is especially im
portant when the furnace is mounted on a platform in a con
fined space such as a closet or small equipment 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 condition. Air for combustion and ventilation
can be brought into the confined space either from inside the
building or from outside.
Air from an Adjacent Space
If the confined space housing the furnace adjoins space
categorized as unconfined, air can be brought in by pro
viding two permanent openings between the two
spaces. Each opening must have a minimum free area of
1 square inch
(6.4 square centimeters) per 1,000 Btu
(293 W) per hour of the total input rating of all fuel-fired
equipment in the confined space. Each opening must be
at least 100 square inches (614.5 square centimeters).
One opening shall be within 12" (305 mm) of the top of
the enclosure and one opening within 12" (305 mm) of
the bottom (See figure 11).
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM INSIDE
CHIMNEY OR
OIL VENT
WATER
HEATER
OPENINGS
(To Adjacent Room)
FIGURE 11
NOTE-Each opening shall have a free area of at least 1 square inch
(6.4 square centimeters) per 1,000 Btu (293 W) per hour of the total
input rating of all equipment in the enclosure, but not less than 100
square inches
(614.5 square centimeters).
OIL
FURNACE
Air from Outside
If air from outside is brought in for combustion and ven
tilation, the confined space shall be provided with two
permanent openings. One opening shall be within 12"
(305 mm) of the top of the enclosure and one within 12"
(305 mm) 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 minimum
free area of 1 square inch (6.4 square centimeters) per 4,000
Btu (1172 W) per hour of total input rating of all equipment in
the enclosure (See figures 12 and 13). When communicating
with the outdoors through horizontal ducts, each opening
shall have a minimum free area of 1 square inch (6.4
square centimeters) per 2,000 Btu (586 W) per total input
rating of all equipment in the enclosure (See 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 (6.4 square centimeters) per 4,000 Btu (1172
W) 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 OIL
VENT
VENTILATION
LOUVERS
(For unheated
crawl space)
FIGURE 12
OIL
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 (6.4 square centimeters) per 4,000 Btu (1172 W)
per hour of the total input rating of all equipment in the enclosure.
CHIMNEY
OR OIL
VENT
WATER
HEATER
OUTLET
AIR
VENTILATION LOUVERS
(Each end of attic)
INLET AIR
(Ends 12" above
bottom)
FIGURE 13
OIL
FURNACE
