Abstract: Normally wasted heat from the pilot burner and flue of a fuel fired hot water heater is used to preheat the water supplied to the main tank. An auxilliary storage tank receives incoming cold water. Water from the storage tank circulates through a conduit loop which extends in a spiral pattern through the flue and also through a special heat exchanger which concentrates heat generated by the pilot burner. The water that is preheated in the conduit loop is returned to the storage tank for storage until required by the main tank, at which time the preheated water is delivered to the main tank through a transfer conduit. Alternative embodiments are arranged to effect automatic flushing of the conduit loop when hot water is withdrawn from the main tank.

Abstract: Normally wasted heat from the pilot burner and flue of a fuel fired hot water heater is used to preheat the water supplied to the main tank. An auxilliary storage tank receives incoming cold water. Water from the storage tank circulates through a conduit loop which extends in a spiral pattern through the flue and also through a special heat exchanger which concentrates heat generated by the pilot burner. The water that is preheated in the conduit loop is returned to the storage tank for storage until required by the main tank, at which time the preheated water is delivered to the main tank through a transfer conduit. Alternative embodiments are arranged to effect automatic flushing of the conduit loop when hot water is withdrawn from the main tank.