Patent ID: 8302566

Claim:
A double pipe heat exchanger for an instantaneous boiler for supplying heating water and hot water, the heat exchanger comprising: an outer pipe used for a hot water pathway, to which combustion heat is directly transferred from a burner in a combustion chamber; an inner pipe used to a heating water pathway and extending through the outer pipe; a heating water supply pipe connected to the inner pipe of the heat exchanger; a heating water line connected to the heating water supply pipe; and a heating water returning pipe connected to the inner pipe, wherein the inner pipe of the heat exchanger, the heating water supply pipe, the heating water line, and the heating water returning pipe are connected to one another in series, and a circulation pump that is coupled to the inner pipe and is configured to operate (1) when only heating water is supplied and (2) if a quantity of heat to be required in the hot water is less than a maximum quantity of heat that can be supplied during use of the hot water, when both hot water and heating water are supplied.