An auxiliary heating device for supplementing the performance of a standard hot water type home heating system with the heat produced by combusting a low cost, readily available fuel is disclosed. The device comprises a cylindrical fire chamber substantially closed at both ends and an elongated annular water chamber closed at both ends surrounding at least a portion of the fire chamber in a noncoaxial relationship thereto. Means are provided for plumbing the water chamber into the main heating system, whereby cool water enters the water chamber and heated water is pumped by the main system's pump to radiators disposed around the home. A combustion air passageway is provided for passing air to the combustion chamber. Means for varying the size of the passageway in response to the temperature of water in the water chamber are also provided so as to control the combustion rate of the fuel. Means for supplying fuel to the combustion chamber are further provided.