PURPOSE: To make economical space heating at a low fuel cost by supplying a number of raw logs aligned in parallel, igniting the butt end by an assistant fuel, and preheating supply water and scraping out of the charcoal layer on the surface of logs so as to continuously carry out complete combustion.

CONSTITUTION: A log 1 is introduced into a furnace 3 by means of a chain conveyor 5, and the butt end is ignited by an assistant fuel material. Combustion air is sent into the furnace 3 from a blower 3 via an air blow-in pipe 7. A steel-made scraping bar 11 is intermittently rotated by means of a motor 12, thus obtaining early combustion of the log core or scraped-off carbide. An air shielding screen 13 made of an asbestos cloth or the like for preventing surplus air invasion is placed on the log supply port. Air from the blower 15 is heated on a combustion gas by a heat exchanger 14 and heats a house or the like.