PURPOSE: To improve a thermal conducting efficiency from a heating member to a thermal conducting medium and make a compact heating system by a method wherein the thermal conducting medium is infiltrated under its pressurized condition to the heater member having an electrode fixed to an electrical conductive block including several fine through holes.

CONSTITUTION: Hot water acting as thermal transmitting medium pressurized by a pressurizing means flows from a left inlet port into a main body 1 of a boiler. Porous carbon blocks 2 acting as electrical conductive blocks having several fine through holes are fixed within the main body 1 of the boiler. The porous carbon blocks 2 are energized by electrodes 3 and 3 so as to heat water. The hot water entered the main body 1 of the boiler infiltrate into the carbon blocks 2 and is heated while passing through it. The hot water flows out of an outlet port of the right main body of the boiler 1 and is supplied as the heated hot water. In particular, this is a means suitable for a heat supplying power generation plant. That is, since the generated electricity is directly supplied to the heating member within the boiler 1, this heating system becomes an auxiliary boiler system having a high efficiency.