a furnace provided with a lining of ceramic or other refractory material, which prevents direct contact between the charge and the fuel or heat source. Muffle furnaces with electrical heating elements are used extensively in laboratory work., resistance chamber furnace with a thin wall part inside the heating chamber of a resistance furnace, designed to separate it from the heating elements and wall lining, leek- või elektriahi, kus kuumutatavad tooted asetsevad muhvlis