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b. Find the volume of the room in cubic feet. The volume of the room in cubic feet is:
Length (ft) x width (ft) x ceiling height (ft)
In calculating the volume of the boiler room, consider the volume of adjoining spaces only if no doors are installed
between them. If doors are installed between the boiler room and an adjoining space, do not consider the volume
of the adjoining space, even if the door is normally left open.
c. Divide the volume of the boiler room by the input in thousands of BTU/hr. If the result is less than 50, the boiler
room is a
confined space.
Example:
An AWI162EN and a water heater are to be installed in a room measuring 6 ft - 3 in x 7 ft with an 8 ft ceiling.
The water heater has an input of 30000 BTU/hr:
Total input in thousands of BTU/hr = (162000 BTU/hr + 30000 BTU/hr)/1000 = 192
Volume of room = 6.25 ft x 7 ft x 8 ft = 350 ft
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350/192 = 1.82. Since 1.82 is less than 50, the boiler room is a confined space.
2) Unconfined Space - Natural infiltration into the boiler room will normally provide adequate air for combustion and
ventilation without additional louvers or openings into boiler room.
3) Confined Space - Provide two openings into the boiler room, one near the floor and one near the ceiling. The top edge of
the upper opening must be within 12” of the ceiling and the bottom edge of the lower opening must be within 12” of the floor
(Figure 3).
• Each opening must have a free area of 1 square inch per 1000 BTU/hr input of all gas burning appliances in the
boiler room. The minimum opening dimension is 3 inches. Minimum opening free area is 100 square inches per
opening.
• If the total volume of both the boiler room and the room to which the openings connect is less than 50 cubic feet
per 1000 BTU/hr of total appliance input, install a pair of identical openings into a third room. Connect additional
rooms with openings until the total volume of all rooms is at least 50 cubic feet per 1000 BTU/hr of input.
• The “free area” of an opening takes into account the blocking effect of mesh, grills, and louvers. Where screens
are used, they must be no finer than ¼” (4 x 4) mesh.
• If providing openings into adjacent rooms is undesirable, combustion and ventilation air can be brought into the
boiler room from outdoors. See the instructions under “For Buildings of Unusually Tight Construction”.
FIGURE 3: BOILER INSTALLED IN CONFINED SPACE,
ALL AIR FROM INSIDE
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