Regenerative air heaters transfer heat from the flue gases to combustion air using a:

• A. Large Metal Wheel
• B. Coiled Tubes
• C. Ceramic Bricks
• D. Fan

Answer: (A)

Regenerative air heaters rely on a large metal wheel that acts as a rotating heat exchanger. Flue gases give up heat to the wheel as they pass by, and the wheel then rotates so the heated surfaces come into contact with the incoming combustion air, preheating it before it enters the burner. This design recovers energy from exhaust to boost boiler efficiency without adding extra fuel. Coiled tubes would be a fixed heat exchanger, not a rotating regenerative wheel. Ceramic bricks are static insulation/material for different setups, not a rotating heat-transfer element. A fan simply moves air and does not transfer heat.