How does a condensing boiler achieve higher efficiency than non-condensing models?

How does a condensing boiler achieve higher efficiency than non-condensing models?

• A. By increasing combustion temperature
• B. By using an electric heating element
• C. By reducing airflow through the burner
• D. By condensing water vapor in flue gases to recover latent heat

Answer: (D)

Efficiency is improved by capturing heat that would otherwise escape in the exhaust. In a condensing boiler, the flue gases are cooled enough that the water vapor they contain condenses into liquid water. When this condensation happens, the latent heat of vaporization is released and transferred back into the boiler’s heat exchanger, where it heats the return water again. This means more of the fuel’s energy ends up as usable heat rather than being carried away as hot exhaust. Non-condensing boilers vent hotter gases and miss this extra heat, so their efficiency is lower. Keeping the return water temperature low enough to promote condensation is part of how these boilers achieve their higher efficiency, and the system must be built with materials that resist the acidic condensate.

Efficiency is improved by capturing heat that would otherwise escape in the exhaust. In a condensing boiler, the flue gases are cooled enough that the water vapor they contain condenses into liquid water. When this condensation happens, the latent heat of vaporization is released and transferred back into the boiler’s heat exchanger, where it heats the return water again. This means more of the fuel’s energy ends up as usable heat rather than being carried away as hot exhaust. Non-condensing boilers vent hotter gases and miss this extra heat, so their efficiency is lower. Keeping the return water temperature low enough to promote condensation is part of how these boilers achieve their higher efficiency, and the system must be built with materials that resist the acidic condensate.