A masonry heater is heated with a single fire per day. After a 2 hr fire the heat will warm the house for 24 hours. The upper chamber can, after the fire is out, be used, as a bake oven for bread, meals etc. 87% of the burningvalue of the wood (5,226kwh/kg dry wood minus 0,695kwh/kg water) became heat in the house, and approximately 10% went to the chimney as absolutely nessesary draft. In others words - very close to 100% efficiency, and of course,- very clean burning.