There is provided a system including: an automatic supplement valve configured to automatically supplementing direct water; an expansion tank configured to be connected to the automatic supplement valve to adjust expansion pressure depending on the temperature change of the direct water; an exhaust heat pump configured to be connected to the expansion tank to circulate heat in an exhaust heat line connecting the exhaust heat source and the hot water tank; and a mixing valve configured to be extendedly formed between a first hot water (1H) line for receiving the exhaust heat of the exhaust heat source and a second hot water (2H) line having passed through the exhaust heat exchanger of the hot water tank to mix the first hot water (1H) with the second hot water (2H).