Which of the following is true about condensing boilers?

• A. They condense moisture from the flue gases.
• B. They require no fuel input.
• C. They operate by condensing refrigerant in a compressor.
• D. They do not produce any condensate.

Answer: (A)

Condensing boilers maximize efficiency by recovering heat from the moisture in the exhaust. As fuel burns, the flue gases carry water vapor. By cooling these gases in a high‑efficiency heat exchanger, the temperature drops below the dew point and the water vapor condenses into liquid condensate, releasing latent heat that is reused to heat the water in the system. This is why the true statement is that they condense moisture from the flue gases. They still require fuel to operate and they do produce condensate that must be drained, and they are not related to condensing refrigerants used in air conditioning.