GrieveNo. 908 is a natural-gas-heated, heavy-duty box furnace from Grieve. Maximum operating temperature is 2000°F, and the workspace dimension is a 48-inch cube. One million BTU/hour is installed in four modulating natural gas burners with a floor-mounted combustion air blower onboard. This furnace features 7-inch-thick walls comprised of 5 inches of 2300°F firebrick and 2 inches of 1700°F ceramic fiber insulation, plus a 7-inch-thick floor made from 4.5 inches of 2300°F firebrick and 2.5 inches of 1900°F block insulation.