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FIGURE 6.1: ALL AIR FROM OUTDOORS, VENTILATED CRAWL SPACE AND ATTIC
2)
Unconfined Space - Natural infiltration into the boiler room will normally provide adequate air for combustion and venti
-
lation 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 4).
• Each opening must have a free area of 1 square inch per 1000 BTU/hr input of all fuel 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.
For Buildings of Unusually Tight Construction:
1) Openings must be installed between the boiler room and the outdoors or a ventilated space, such as an attic or crawl
space, which communicates directly with the outdoors.
2) Two openings are required. The top edge of the upper opening must be within 12 inches of the ceiling. The bottom edge
of the lower opening must be within 12 inches of the floor.
3) Size openings and ducts as follows:
• Vertical ducts or openings directly outdoors (Figure 6.1, Figure 6.2, and Figure 6.3) - Each opening must have a free
cross sectional area of 1 square inch per 4000 BTU/hr of the total input of all fuel fired appliances in the boiler room
but not less than 100 square inches. Minimum opening size is 3 inches.
• Openings to outdoors via horizontal ducts (Figure 6.4) - Each opening must have a free cross sectional area of 1 square
inch per 2000 BTU/hr of the total input of all fuel fired appliances in the boiler room but not less than 100 square
inches. Minimum opening size is 3 inches.
• 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.
