To prevent piping and heat equipment from being rusted while saving the energy of the source of heat, and to prevent an impurity from adhering for improving the durability of a device itself by providing a tourmaline granular aggregate to the water-supply line of a heat exchanger so that heated water can be circulated.

When a cutoff valve 21 is closed, cutoff valves 17 and 18 are opened, and condensate is circulated in a body 11 of a heat-up device 9 being provided in a water supply line 5, blow water being stored in a blow water container 15 preheats the condensate to approximately 60-90°C. A plurality of cartridges are provided in the body 11, and each cartridge accommodates a number of tourmaline granular objects. The tourmaline generates potential difference due to the heat energy of the condensate, thus ionizing one part of the condensate (hydrogen ion and hydroxidce ion) and preventing an impurity such as scale from adhering on the piping of the water supply line 5, heat exchange piping in a boiler 1, and the piping of a discharge line 7. Also, the heat energy is generated due to the electrolysis of the condensate, and the temperature of the condensate is raised by approximately 2-10°C.