The idea of wood as energy resource is an ancient idea. Mankind always warmed at wood fire. Our current data explain why this did not happen by accident. Out of the biomass based renewable energy resources thermal energy can be generated from wood in the most efficient way.Traditional wood heating used to be a true science. All the activities that it assumed wood transport, kindling, guarding the fire can hardly be learnt again. However, it always had a few disadvantages. Thats why it has become unfashionable for a while.