To dry the web in the Thru-Air Dryer, clean air at ambient temperature is heated up to 180°C by burning natural gas. The heated air is then expelled as flue gas at the exhaust after the recirculation in the machine. If the temperature of clean air at the inlet of the machine can be increased then the natural gas energy consumed will decrease.

The flue gas can be mixed with clean air before the inlet at the heat exchanger. The clean air can be heated up to 60-70°C before entering the dryer. This way a significant amount of heat energy is recovered.