Abstract: A passive type of space heater having a vertical air heating duct located at the rear of the combustion chamber and a flue duct extending through the air heating duct with its inlet located so as to draw the flue gases from the combustion chamber around the surfaces of the air heating duct. Air for combustion is supplied to the top of the combustion chamber by an air supply duct which extends inside of the flue duct and has orifices to provide air in the flue duct for secondary combustion of the flue gases passing through the flue duct. The air supply duct also has an ejector to draw a portion of the flue gases into the air supply duct for recirculation to the combustion chamber for tertiary combustion. A separate air supply duct is provided for supplying air for combustion during start-up.