Abstract: A solid fuel burning hot water heater is described having a primary combustion chamber with a refractory material base portion which forms the locus of combustion. A water jacket defines an upright portion over the refractory base portion for receiving a charge of fuel in a generally vertical stack. The water jacket is coupled to a source of water for at least convection circulation and assists in confining the locus of solid fuel combustion to the base of the chamber. Heat exchange channels or pathways are defined around the outer periphery of the water jacket in heat exchange relationship with the water jacket for transfer of heat from the end products of combustion to the circulating water. A flue gas delay channel arrangement extends from the draft outlet at the base of the combustion chamber to the heat exchange pathways.