NATE Gas Heating Practice Exam

How do condensing furnaces enhance efficiency?

1. By condensing water vapor out of the air at the burner

2. By adding condensed oxygen to the fuel

3. By removing the latent heat of condensation from flue gases

4. None of the above is correct

The correct answer is: By removing the latent heat of condensation from flue gases

Condensing furnaces enhance efficiency primarily by removing the latent heat of condensation from flue gases. In these systems, the design allows for the flue gases to cool down significantly, which leads to the condensation of water vapor present in the exhaust. This process not only extracts heat that would otherwise be wasted but also utilizes it to preheat incoming air or water, contributing to the overall efficiency of the furnace. The fundamental principle here is that traditional furnaces typically vent hot flue gases that still contain substantial heat content. In contrast, condensing furnaces take advantage of that remaining heat by condensing the flue gases, recovering energy in the form of heat which can then be harnessed to improve heating efficiency. This advanced technology results in higher Annual Fuel Utilization Efficiency (AFUE) ratings compared to non-condensing models, making condensing furnaces a more energy-efficient choice for heating.