Abstract: Presented is a wall heater or furnace extension structure for mounting in the space between a conventional wall furnace or heater and the ceiling of the room in which the wall furnace or heater are installed. The wall material normally found in this area of the wall is removed to expose the flue connected to the fire-box of the furnace or heater. The furnace extension structure is mounted on the wall so as to enclose the flue, draw air from the room into the space surrounding the flue, and then discharge the heated air back into the room from which it emanated.