A draft hood is a device used to insure the maintenance of constant low draft conditions in the combustion chamber. By this action, it contributes to the stability of the air supply for the combustion process. A draft hood will also prevent excessive chimney draft and downdrafts that tend to extinguish the gas burner flame. Because of this last function, a draft hood is often referred to as a draft diverter. A gas-fired furnace should be equipped with a draft hood attached to the flue outlet of the appliance. The draft hood used on the appliance should be certified by the American Gas Association.

Only gas conversion furnaces equipped with power-type burners and conversion burner installations in large steel boilers with inputs in excess of 400,000 Btu/hr are not required to have draft hoods. Draft hoods may be either internally or externally mounted depending upon the design of the furnace. Never use an external type draft hood with a furnace already equipped with an internal draft hood. Either vertical or horizontal discharge from the draft hood is possible.

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