Abstract: A prefabricated open-ended fireplace box for use in fireplace assemblies is molded from a slurry of refractory ceramic fibers and a non-organic binder. The prefabricated fireplace box is preferably formed in or over a mold which provides an accurate shape to the green or semi-rigid open end box which must be dried or partially fired while on the mold to avoid warping or distortion while being removed from the mold. A rigid surround trim in the form of a C-shape is placed in or on the mold at the open ends of the fireplace box. At least one attachment flange of the surround trim is integrally molded into walls of the fireplace box so that at least the open end of the semi-rigid fireplace box is made rigid when removed from the mold.