The 2200 F Buzzer Fiber-Box(tm) oven furnace operates on natural gas or propane and is available in four standard sizes ranging from 12 in. wide x 18 in. long to 12 in. wide x 48 in. long. It incorporates both fiber and firebrick insulation, and, for ruggedness, insulating firebrick is used throughout the furnace in the combustion chamber, vestibule, and door seal. The addition of fiber insulation on side and rear walls takes full advantage of the material's thermal shock resistance and low heat storage. Standard packaging includes spark ignition, silicon carbide hearth plates, semi-muffle design and digital temperature controls. It can be used for hardening low, medium and high carbon steel and tool steel, as well as annealing, pack carburizing and stress relieving.