Abstract: A generally rectangular shaped heater having an open front and a pyramid shaped roof is designed with a double wall at its rear section. Air is blown into the cavity between the two walls where it absorbs heat and is thereafter expelled through ducts which project through the front of the heater. A grate is recessed in a horizontal opening below the open front of the heater and damper means are provided to admit air below the grate and thereby facilitate the combustion of the material deposited on the grate. Air passes into the heater below the grate, up through the grate, upward against the inner surface of the rear wall which is sloped forwardly, up around the ducts to the roof section of the heater and rearwardly to exit at a flue.