Abstract: A zero-clearance firebox with a much simplified construction enables efficient air exchange directly through one opening in which solid combustible materials are placed. The firebox has a metal inner shell and an outer shell of lighter gage metal incorporating a plurality of insulating materials in proximity with the outer and inner shells, including a ceramic blanket, rigid insulation, dead air space, and refractory brick. The firebox can be configured into a rectangle, a wedge or a semicircle for placement into a corner or along a wall of a room. The firebox can easily be adapted for use with liquid fuels such as natural gas, propane, etc. Finishing materials can be attached to the firebox to give the appearance of masonry or adobe.