Air preheater are heat exchanger to preheat or air heating of the combustion air by means of flue gas, steam, water or thermal oil. Air preheaters are used when exhaust temperatures of combustion systems are particularly high. This extracts the hot exhaust valuable energy, which discharged otherwise unused into the atmosphere and warming means of this exhaust heat the combustion air of the combustion process.

In the classical use, air preheaters are connected behind high-pressure steam boilers or thermal oil boilers with a flue gas temperature up to 400 ° C. Their exhaust temperatures lend themselves to preheat the combustion air up to 300 ° C. In this way, an air preheater save up to 10% of fuel costs and thus enables payback periods of less than two years. Meanwhile, air preheater also be used in low temperature ranges in order to make the most efficient use of the fuels and counter the rising fuel prices.