An electric heating furnace which includes a conductive electric resistance heating element strip mounted within a chamber defined by walls of porous refractory insulating material. Terminal or mounting pins extend through the wall of insulating material and the heating strip are secured thereby. A sleeve of non-porous refractory material surrounds the portion of the pin within the wall of insulating material for electrically insulating the pin from the porous refractory wall material which may have a conductive layer of carbon build up therein under certain heat treating conditions.