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6
If the boiler is in a 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 (Fig 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 to the boiler
room from outdoors. See the instructions under “For Buildings of Unusually Tight Construction”
For Buildings of Unusually Tight Construction
a) 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.
b) 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.
c) Size openings and ducts as follows:
• Vertical ducts or openings directly outdoors (Fig 4, Fig 5, Fig 6) – Each opening must have a free cross sectional area
of 1 square inch per 4000 BTU/hr of the total input of all gas-fired appliances in the boiler room. Minimum opening
size is 3 inches. Ducts must have the same cross sectional area as the openings to which they connect.
• Openings to outdoors via horizontal ducts (Fig 7) - Each opening must have a free cross sectional area of 1 square
inch per 2000 BTU/hr of the total input of all gas-fired appliances in the boiler room. Minimum opening size is 3
inches. Ducts must have the same cross sectional area as the openings to which they connect.
• 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.