PURPOSE: To save energy consumption when rooms are heated, by exchanging heat of waste gas contained in the exhaust gas, from a heating equipment of combustion type installed in a downstair room, by a heat exchanger, and utilizing the heat exchanger medium to heat an upstair room, by feeding the medium into a floor heating equipment installed under the floor of an upstair room.

CONSTITUTION: A heat exchanger 1 is installed so as to enclose the outer periphery of an exhaust path 4 extended from a heating equipment 3 of combustion type, installed in a downstair room 2. In the case that a heat exchanger 1 is installed in the exhaust path 4 already established, the heat exchanger 1 in the shape of a flat board, consisting of a zigzag tube 6, made of a flexible flat board 5 with which copper, stainless steel, or the like, is internally equipped, having some upward gradient, is used, bent and rolled, and attached to an exhaust path 4. The heat exchanger 1 is interconnected to a floor heating equipment 12 installed under the floor 11 of upstairs 10 by the intermediary of circulating pipes 8 and 9. With such an arrangement, the waste heat contained in exhaust gas coming from a heating equipment 3 of combustion type is heat-exchanged to a heat exchanger medium in a heat exchanger 1, and the heat exchanger medium is fed into a floor heating equipment 12 to utilize it for heating rooms.