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Burners draw their combustion air from the boiler room.
Therefore it is necessary to replace this air through Fresh Air and Combustion Air Vents to avoid strong negative pressure in the boiler room. Such negative pressure could affect the operation of the burner. Considerations At least Two Air Vents should be provided, one for Ventilation Air and one for Combustion Air. The Fresh Air Vent should be supplied with a total free cross-sectional area of at least 10 percent of the area required for the Combustion Air Vent but not less than 10 sq. inches. The Combustion Air Vent should have a total free cross-sectional area of not less than 1 sq.