Abstract: A furnace has a top from which very hot gases are exhausted. An exhaust system has a vent stack connected to the top of the furnace. The stack is cooled with a heat-transfer medium to a predetermined temperature. A plurality of support elements hold the stack off a floor, and the support elements are heated with a heat-transfer medium generally to the predetermined temperature.

Abstract: In combination with a furnace having a top from which very hot gases are exhausted, a cooling system has an outwardly open collar fixed to the top of the furnace and open inward into the furnace, a tubular exhaust stack adjacent the furnace, a connecting duct extending from the stack and fitted concentrically to the collar, a network of heat-exchange tubes lining the top of the furnace. The collar, and the connecting duct, and means for circulating through all of the tubes a coolant at generally the same temperature.