1. A heater of the character described comprising a sheet metal housing having closed front and side walls, a rear wall having a forwardly and upwardly inclined upper section, top closure means for said housing in the form of a box-like member, the lower edge of which is outwardly flanged, flanges on the upper edges of said housing on which the flanges of said box-like member rest and are secured, a combustion chamber for a gas-fired log of similar shape and arranged within and spaced from the side, rear and a portion of the front wall of said housing, a common opening in the front of said housing and combustion chamber, a transparent window panel covering said common opening, a hot water pipe entering from the lower portion of said combustion chamber and arranged in a to and fro manner along the inclined upper section thereof to expose a substantial area to heat generated therein, an imperforate plate closing the upper end of said combustion chamber, the upper end of said pipe projecting through said imperforate plate, and exhaust flue means for the products of combustion from said combustion chamber extending laterally through openings in the upper end portions of said housing and combustion chamber in the region directly below said imperforate plate, said exhaust flue means comprising a pair of exhaust pipes arranged respectively adjacent opposite ends of said combustion chamber.