Abstract: An apparatus and method for providing a hot water supply for a building such as a mobile home, house, or business. A hot water storage tank is positioned within the building. A gas-fueled burner is positioned outside the building adjacent a heat exchanger which is connected in fluid communication with the indoor water storage tank. A pump circulates water from the tank through the heat exchanger and back into the tank responsive to a thermostat in the tank. The heat exchanger includes a thermostat for sensing the temperature of water therein to activate the pump and circulate relatively warm water from the tank through the heat exchanger to prevent freezing of water within the heat exchanger, such as during winter months when the ambient temperature falls below freezing. The gas heater may be used to convert a conventional electric water heater to operate from gas which is combusted outside of the building.

Abstract: A rapid recovery gas water heating system having a water storage tank, a gas water heater separate from the storage tank and having a compact heat exchanger for the flow of water therethrough from the storage tank, a water pump for pumping of water from lower regions of the storage tank into and through the heat exchanger and back into the storage tank, and a thermostat having water temperature sensing means positioned in the storage tank and serving for actuating the water pump and the gas water heater in response to the temperature of the water in the storage tank falling below a predetermined temperature value.