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FRESH AIR FOR COMBUSTION
WARNING I
Be sure to provide enough fresh air for combustion. Enough air ensures proper
combustion and assures that no hazard will develop due to the lack of oxygen.
I NOTE [
If you use a fireplace or a kitchen or a bathroom exhaust fan, you should install an
outside air intake. These devices will rob the boiler and water heater of combustion air.
You must provide enough flesh air to assure proper combustion. The fire in the boiler uses oxygen. It must have a
continuous supply. The air in the house contains only enough oxygen to supply the burner for a short time. Outside
air must enter the house to replace the air used by the burner. Study the following examples 1 and 2 to determine your
fresh air requirements.
EXAMPLE 1: Boiler Located in Unconfined Space
If your boiler is in an open area (unpartitioned basement) in a conventional house, the air that leaks through the cracks
around the doors and windows will usually be adequate to provide air for combustion. The doors should not fit tightly.
Do not caulk the cracks around the windows.
An unconfined space is defined as a space whose volume is not less than 50 cubic feet per 1,000 Btu per hour of the
total input rating of all appliances installed in that space.
EXAMPLE 2: Boiler Located in Confined Space
A. All Air from Inside the Building: The confined space shall be provided with two permanent openings
communicating directly with an additional room(s) of sufficient volume so that the combined volume of all spaces
meets the criteria for an unconfined space. The total input of all combustion equipment installed in the combined
space shall be considered in making this determination. Each opening shall have a minimum free area of one
square inch per 1,000 Btu per hour of the total input rating of all combustion equipment in the confined space, but
not less than 100 square inches. One opening shall be within 12 inches of the top and one within 12 inches of the
bottom of the enclosure.
Example: Your boiler is rated at 100,000 Btu per hour. The water heater is rated at 30,000 Btu per hour. The
total is I30,000 Btu per hour. You need two grilles, each with 130 square inches of FREE opening. Metal grilles
have about 60% FREE opening. To find the louvered area needed, multiply the free opening required by 1.7 (130
x 1.7 = 221.0 sq. in. louvered area). In this example, two grilles each having an 8" x 30" (24-0 sq. in.) louvered
area would he used.
AIR OPENINGS FOR BOILER LOCATED IN CONFINED SPACE (CLOSET OR UTILITY ROOM)
VENTILATING I
GRILLE 1
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COMBUSTION
AIR GRILLE
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