Abstract: A device for heating air includes at least one rotatable disc pressed against at least one stationary disc and rotatably driven by a drive motor having variable speed. The friction between the discs generates heat that is taken up by a circulating fluid. A fan generates a current of air that takes up the heat from the fluid in a heat exchanger. A proportioning temperature regulated speed control senses the difference between a preset temperature and the air temperature and regulates the speed of the drive motor proportionally so that the greater the difference the faster the disc rotates and the more frictional heat is generated. The discs are made of special metal in thin section for enhanced heat transfer and reduced weight. The metal has high tensile strength at high temperature and special abrasion and temperature resistant coating for reduced wear and maintenance.