Abstract: A furnace, for example of the home-heating type, has heat storage elements located in a combustion gas chamber of the furnace, the heat storage elements being placed in a path of flow of combustion gases to increase flow resistance to the combustion gases. The heat storage elements are of such size that they can be inserted into the combustion gas chamber and removed therefrom through door openings normally available in the furnace, for example to change over the furnace from liquid to solid fuels, for cleaning or the like. The storage elements preferably are metal-jacketed bodies of refractory material, for example of clay. If the furnace has a water jacket for heating of water, the clay bodies are placed against the water jacket surface, with the metal jacket of the clay bodies perforated at the side facing the water jacket. A group of such heat storage elements may be commonly supported on a carrier for removal as an assembly.