Fireplace liner incorporating thermal expansion stress relief spacers

Claim 1

A prefabricated metallic firebox for a fireplace structure comprising: an inner metallic liner fabricated from relatively heavy gauge metal, said inner liner having front, rear and side walls and including an opening in said front wall defining the fireplace opening and an opening at the top of said front, rear and side walls constituting a flue opening for passage of products of combustion from said firebox; an outer metallic liner having front, rear and side walls corresponding to the front, rear and side walls of said inner metallic liner, the corresponding walls of said inner and outer metallic liners being spaced apart to define a passageway therebetween for the passage of air therethrough, said outer metallic liner being fabricated from sheet metal which is relatively light gauge with respect to the thickness of said inner liner and which has a thermal expansion strength insufficient to damage surrounding masonry structures when heated; and a plurality of Z-shaped spacer baffles interposed between said corresponding walls of said inner and outer liners, each said baffle including a web portion and a flange on each opposite end of said web, said web portions extending transversely between said walls and being angularly disposed with respect to said walls, each said baffle being fixed by means of a corresponding flange to said outer liner and impinging loosely against said inner liner and being flexible whereby when said inner liner is heated outward thermal expansion of said inner liner is accommodated by transverse displacement of said spacer baffles and accompanying lateral displacement of the flanges impinging against said inner liner, without causing an outward displacement of said outer liner, said inner liner being free to flex inwardly when heated to prevent damage to surrounding masonry structure.