PURPOSE: To reduce the cost thereof and facilitate the maintenance and control of the system by a method wherein fluid of air heated in a heat collector by solar heat is introduced into a heat accumulating tank to obtain hot water by effecting heat exchange in the heat accumulating tank.

CONSTITUTION: The heat collector 1 is connected to the heat accumulating tank 5 through ducts 2, 3 equipped with fans 7, 8 and the fluid of air heated by solar heat is introduced into the heat accumulating tank 5 to obtain hot water by effecting heat exchange in the heat accumulating tank 5. According to this method, air may be used as a medium, therefore, cost down due to the simplification of the system may be planned and the maintenance as well as the control of the system may be facilitated.