Rapid recovery gas hot water heater

The combination with a building structure of a rapid recovery water heating system therefor comprising a water storage tank positioned within said building structure and having a cold water inlet communicating with lower regions of the tank and a hot water outlet communicating with upper regions of the tank, a gas water heater separate from said storage tank and mounted outside said building structure and being the sole water heating means for said building, said gas water heater comprising a housing, a heat exchanger for the flow of water therethrough positioned in said housing, said heat exchanger having a water capacity of only a small fraction of the capacity of said water storage tank, said heat exchanger having inlet and outlet ends, said outlet end communicatively connected with upper regions of said storage tank and said inlet end communicatively connected with lower regions of said storage tank, gas burner means positioned adjacent said heat exchanger for heating the water therein, a water pump communicating with said heat exchanger and with said storage tank for pumping of water from lower regions of said storage tank into and through said heat exchanger and back into said storage tank, a thermostat having water temperature sensing means positioned in said storage tank adjacent lower portions thereof, and means operatively connecting said thermostat to said water pump and said gas burner means for actuating both the water pump and said gas burner means in response to the sensed temperature of the water in said storage tank falling below a predetermined temperature value as when heated water in upper regions of the tank is drawn off causing cold inlet water to enter said storage tank.