The No. 939 is a 2,000 degree F gas-heated box furnace from Grieve, currently used for preheating metals prior to forging. Workspace dimensions measure 72" Wx36" Dx48"H. 700,000 BTU, installed in two modulating natural gas burners with a floor-mounted combustion air blower, heat the unit. This Grieve furnace features 7" insulated walls made with 5" of 2,300 degrees F ceramic fiber and 2" of 1,700 degrees F ceramic fiber. The 7" floor comprises 4.5" of 2,300 degrees F firebrick and 2.5" of 1,900 degrees F block insulation. A firebrick plate hearth is supported by firebrick piers. The unit has a manually-operated vertical lift door. No. 939 also includes a digital indicating temperature controller, manual reset excess temperature controller with separate contactors and a fused disconnect switch.