Flue gas cooler Hot, dirty flue gas streams from hot engines , boiler and other heating machines were cooled before entering in to atmosphere. Air or water is typically the cooling medium; however, fluids can be used as well. Automatic cleaning systems can also be provided for keeping the heat transfer surfaces clean. Effective method to cool the hot flue gas is Fin tube heat exchanger and shell and tube heat exchanger. Material that used to construct this type of heat exchanger is stainless steel. Because stainless steel is one of the best material that withstand for hot corrosion gases and environment.