Abstract: The present invention includes a universal combustion chamber preferably shipped from a factory as a separate unit for field installation into a plurality of different fireplace units and includes a top panel and a floor panel connected to sidewall panel to form a complete ready to use gas tight structure. The combustion chamber is fabricated from flat and/or curved panels which are preferably molded from a thick paste slurry of mixed vitreous alumina silicate fibers combined with an aqueous solution of silica binder and fired to form non-porous gas tight panels which are interconnected to form a gas tight combustion chamber. The connecting joints are preferably reinforced by the addition of a high temperature adhesive added to the mating joints. The joints may be further reinforced and/or sealed by mechanical reinforcing at or in the joints. The joints may be eliminated by forming a one piece combustion chamber on forming molds that are designed to be separated from a formed but uncured combustion chamber.