Abstract: A combustible element has a defined geometrical configuration and comprises a fragmented non-consolidated content of combustible material and a combustible enclosure for the material. A plurality of such elements define in a combustion chamber a channel having a geometrically defined configuration, which provides the combustion area and access for the air utilized in the combustion of the fragmented content of the element and of combustible gases evolved during combustion of the combustible material, as well as egress means for gaseous combustion products. Apparatus for the combustion of such elements is preferably provided with a heat exchanging surface defined by a smoke chamber laterally surrounding the combustion chamber. High combustion efficiency and other advantages are stated.