Furnace frame is constructed of heavy steel angle with 18 gauge sheet metal panels to form exterior case. Case is finished in a pleasing gray hammertone. The vertical rising door is mounted on heavy levers and is opened by lifting up on a wide handle. The counterweight holds the door up in the raised position and the weight of the door gives a good brick to brick seal in the lowered position. A Kaowool® rope seal is installed on the door where it meets the chamber. This door protects the operator from burns because the hot surface always faces away from him. Door opens manually very smoothly and easily. All walls and door are constructed of 4 1/2” of the finest quality insulating brick backed up by 1 1/2″ of block insulation. The roof is arched giving added strength and providing space for fan. This combination of insulation and wall thickness helps to give fast heat up and excellent retention for economical operation.