A device built into an appliance, or made a part of the flue or vent connector from an appliance, which is designed to (a) assure the ready escape of the products of combustion from the combustion chamber in the event of no draft, back draft, or stoppage beyond the draft hood; (b) prevent a back draft from entering the combustion chamber of the appliance; and (c) neutralize the effect of stack action of the chimney or gas vent upon the operation of the appliance.