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VI Air for Ventilation
Air for combustion must always be obtained directly from outdoors, however sufficient air for ventilation must
still be provided in the boiler room. Air for ventilation is required to keep various boiler components from over-
heating and is always obtained from indoors. To ensure an adequate ventilation air supply, perform the following
steps:
Step 1: Determine whether the boiler is to be installed in a confined space - A confined space is defined by the
National Fuel Gas Code as having a volume less than 50 cubic feet per 1000 BTU/hr input of all appliances
installed in that space. To determine whether the boiler room is a confined space:
1) Total the input of all appliances in the boiler room in thousands of BTU/hr. Round the result to the next
highest 1000 BTU/hr.
2) 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.
3) 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:
A BWC120 and a water heater are to be installed in a room measuring 6ft – 3 in x 7ft with an 8 ft ceiling. The
water heater has an input of 30000 BTU/hr:
Total input in thousands of BTU/hr = (120000 BTU/hr + 30000 BTU/hr) / 1000 = 150 MBTU/hr
Volume of room = 6.25 ft x 7 ft x 8 ft = 350 ft3
350/150 = 2.33. Since 2.33 is less than 50, the boiler room is a confined space.
Step 2a: If the boiler is to be placed 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 6.1). The minimum opening dimension is 3 inches.
• If the BWC boiler is the only gas-burning appliance in the boiler room, these openings must each have a
minimum free area of 100 square inches.
• If other gas-burning appliances are in the boiler room, size the openings in accordance with the appliance
manufacturer’s instructions or the National Fuel Gas Code. Minimum opening free area is 100 square
inches even if opening requirements for other appliances are less.
WARNING
OUTDOOR COMBUSTION AIR MUST BE PIPED TO THE AIR INTAKE. NEVER PIPE COMBUSTION
AIR FROM AREAS CONTAINING CONTAMINATES SUCH AS SWIMMING POOLS AND LAUNDRY
ROOM EXHAUST VENTS. CONTAMINATED COMBUSTION AIR WILL DAMAGE THE BOILER
AND MAY CAUSE PROPERTY DAMAGE, PERSONAL INJURY OR LOSS OF LIFE.
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