PURPOSE: To automatically prevent radiation rate from becoming excessive without using any motive power such as a pump, etc., by providing on the entry side of a radiator a heatexchanger which is designed to cool the incoming heating media by outgoing heating media from the radiator.
CONSTITUTION: Hot water being supplied from a hot water supply pipe 14 to a floor-heating panel 13, which is provided with a hot water coil 12 in its inside, is made to pass through a heatexchanger 16, in which low-temperature warm water returning from the floor-heating panel 13 cools incoming hot water to lower the temperature and return to a return pipe 15 after being circulated. In this case, the heatexchanger 16 is provided with a bypass 17 for moderating temperature of hot water to be supplied to the floor-heating panel 13, and this is also provided with a bypass flow control valve 18. Separately from this control valve 18, a main flow passage side is also provided with a main passage flow control valve 20 to control flow of the hot water being supplied. It is also possible to conduct automatic temperature control by linking this control valve 20 to a room thermostat 21.