How does excess air affect boiler efficiency and fuel usage?

How does excess air affect boiler efficiency and fuel usage?

• A. Excess air slows heat transfer, cools the combustion zone, and increases fuel consumption and stack losses.
• B. Excess air increases flame temperature and reduces fuel consumption.
• C. Excess air has no effect on boiler efficiency.
• D. Excess air reduces stack losses.

Answer: (A)