This firebox features a radiant design with heat circulating air ducts and has a 36" fireplace opening. The firebox can be installed with non-combustible material up to the opening of the fireplace for a true masonry look. The tavern brown firebrick liner creates a beautiful finished look. Black louvers are included with this CSA design certified firebox. The required framing dimensions are 41-1/4" W x 35" H x 17-1/2" D. Hearth dimensions are 34" W x 21-7/8" H x 15-3/4" D x 27-3/8" RW.