What is the function of an air heater in a boiler system?

• A. Filters air
• B. Preheats combustion air to improve efficiency and reduce fuel use
• C. Cools combustion air
• D. Increases boiler pressure

Answer: (B)

Air heaters are used to preheat the combustion air. By taking heat from the boiler’s exhaust or flue gases and transferring it to the incoming air, the air entering the burner is warmer. Warmer combustion air helps the fuel–air mixture ignite more readily and reach the flame temperature with less fuel, improving overall boiler efficiency and reducing fuel consumption. It also supports more complete combustion, which can lower emissions.

Filters are separate components that clean air, so filtering is not the function here. Cooling the combustion air would defeat the purpose of preheating. Increasing boiler pressure is achieved by the boiler’s pressure system, not by heating the air.