An electric resistance high temperature vacuum furnace having radiant heating units evenly spaced around the sides and ends of the furnace hot zone. Pairs of units are automatically regulated both radially and longitudinally according to the temperature required by the workload in the hot zone. The units each comprise parallel aligned elements electrically connected in series at their one ends. Each element has lengthwise surfaces angularly disposed from each other to form a beam structure of high section modulus for stiffness and resistance to sagging. Also, the angles of the element surfaces facing a heat-reflective assembly substantially enable all of the energy radiated toward the assembly to be reflected into the hot zone in addition to the direct radiation from the surfaces facing the hot zone. The furnace includes a re-circulating cooling system for rapid cooling of the furnace and workload. An inert cooling fluid bypasses the hot zone, passing instead around the outside of the heat assembly and through a heat exchanger until the circulated fluid temperature drops below the maximum tolerated by all component parts in the cooling system, after which the fluid passes directly through the hot zone.