Abstract: A powered downdraft type combustion unit which substantially completely gasifies the fuel burned therein during the combustion process and produces a maximum amount of usable heat for utilization at a location remote from the combustion unit is provided. The present combustion unit includes a heavily insulated outer shroud enclosing insulated sequential combustion chambers to prevent heat loss from the combustion chambers. A primary combustion chamber is separated from a secondary combustion chamber by a plurality of refractory grates. Fuel is fed to the primary combustion chamber to be combusted therein, and the products of this stage of combustion then pass to the secondary combustion chamber where the combustion process is completed. The heat-containing combustion gases are directed from the secondary combustion chamber to a heat utilizing appliance through a conduit connected therebetween.