Abstract: A wood or coal burning heater or stove employing a catalytic combustor in its combustion chamber having a primary air supply which feeds air to the fuel, and a secondary air supply which feeds air directly to the catalytic combustor by means of an air diffuser which sprays air evenly over the undersurface of the catalytic combustor. Combustion gases from the burning fuel in the combustion chamber pass through the catalytic combustor to a heat exchanger and then to an exhaust flue. The primary and secondary air supplies are simultaneously controlled so that maximum primary air and reduced secondary air are supplied when maximum heat is demanded, and reduced primary air and maximum secondary air are supplied when minimum heat is demanded. The ratio of primary to secondary air is precisely controlled to maximize overall heating efficiency consonant with high BTU output.