No. 939 is a 2000°F gas-heated box furnace used for preheating metals prior to forging. Workspace dimensions are 72 inches wide x 36 inches deep x 48 inches high. The unit is heated by two modulating natural gas burners of 700,000 BTU capacity with a floor-mounted combustion air blower. The furnace features 7-inch insulated walls made with 5 inches of 2300°F ceramic fiber and 2 inches of 1700°F ceramic fiber. The 7-inch floor comprises 4.5 inches of 2300°F firebrick and 2.5 inches of 1900°F block insulation. The firebrick plate hearth is supported by firebrick piers. The unit has a manually operated vertical-lift door and includes a digital indicating temperature controller, manual reset excess temperature controller with separate contactors and a fused disconnect switch.