What is the primary function of air-preheaters in a boiler system?

• A. To heat air going to burners and improve efficiency
• B. To cool the flue gas and reduce smoke
• C. To filter particulates from the air
• D. To store excess heat for later use

Answer: (A)

Air preheaters recover heat from the hot flue gases leaving the boiler and use it to warm the air that goes to the burners. Heating the incoming air lowers the additional energy needed to reach combustion temperature, which makes combustion more efficient and reduces fuel consumption for the same boiler output. Warmer air also helps with flame stability and smoother operation, especially during cold starts or load changes, by avoiding the shock of cold air entering the burners. The other options describe roles that aren’t performed by an air preheater—cooling flue gas, filtering particulates, or storing heat—so they don’t fit this device’s purpose.