A heat exchanger of a non-condensing storage type boiler for preventing condensation is provided. The heat exchanger include a heating water outflow port installed on an upper portion of the boiler, a heating water inflow port installed lower than the heating water outflow port, and an internal pipe extending spirally from the heating water inflow port and being installed in a water tube of the boiler. The internal pipe is connected to an extension pipe that extends through a re-entry outlet passing through a wall of the boiler to be connected with a re-entry inlet.