Abstract: A fireplace heating unit provided with a firebox. A vertically elongated hollow member defining in horizontal cross section a square and formed primarily of transparent material, is open at both ends and is secured at its lower end to the firebox. A hollow top section having a relatively small open upper end which defines a chimney and a lower open and conforming to and engaging the upper end of said member has a narrow horizontal peripheral border having the same shape and essentially the perimeter as said square. Shaped openings partially blocked by louvers are formed in the border of the top and bottom section and hinged flaps are mounted outside of the louvers so as to control the amount of air passing into the heating unit through the louvers.