Vacuum furnace hot zones are offered in round and rectangular configurations for operation in range of 1200 to 2600 F (650 to 1430 C) at 10(-5) to 10(-6) torr. Heat input is automatically tuned in multiple trim zones to match thermal characteristics of the workload, in both the vertical and horizontal directions. Heat delivered is variable at the bottom, corners, sides, top and ends as sensed by zone thermocouples while the furnace cycle progresses. The bar heating element is shaped into several planes to distribute radiant heat evenly. The element is stiff, resists sagging and is free of the kinds of distortion found in other heat element designs.