Abstract: A fuel-fired heating apparatus, representatively a forced draft or natural draft gas-fired water heater having a combustion chamber, is provided with a flammable vapor control system that functions, during firing of the apparatus, to substantially prevent entry into and combustion within the combustion chamber of extraneous flammable vapors externally adjacent the bottom of the apparatus, without detecting the extraneous flammable vapors or terminating firing of the apparatus. The flammable vapor control system includes a dilution air flow passage connected to a discharge portion of the apparatus vent structure and having an inlet externally adjacent a bottom portion of the apparatus and operative to draw dilution air and extraneous flammable vapors into the vent structure discharge portion, and a combustion air flow passage having an inlet disposed adjacent the upper end of the apparatus, and an outlet communicated with the interior of the combustion chamber.

Abstract: A gas-fired water heater has a combustion chamber with a bottom wall defined by a perforated flame arrestor plate forming a portion of a flow path through which combustion air may be supplied to a burner structure within the combustion chamber. During firing of the water heater a combustion air shutoff system having a heat-frangible temperature sensing structure disposed within the combustion chamber senses an undesirable temperature increase in the combustion chamber, caused by for example a partial blockage of the flow path, and responsively terminates further air flow into the combustion chamber, thereby shutting down the burner, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide.

Abstract: Fuel fired power vented and natural draft type water heaters are provided with flammable vapor sensors operative to detect flammable vapors exteriorly adjacent the water heater and responsively preclude fuel flow to the burner portion of the water heater. In each water heater a flow tube is extended between the flammable vapor sensor and the draft structure of the water heater and forms a flow path isolated from the combustion chamber of the water heater. In the event that flammable vapors are present exteriorly adjacent the water heater, the forced or natural draft of the water heater creates a biased flow of flammable vapors which is sequentially drawn across the vapor sensor and through the isolated flow path to the draft structure of the water heater.