NATE Gas Heating Practice Exam 2025 – All-in-One Guide to Master Your Certification!

A furnace achieves combustion efficiency primarily by minimizing excess air in the combustion process. Combustion efficiency refers to how effectively the furnace uses fuel to produce heat, retaining as much of that energy as possible in the heating process. When there is too much excess air, it not only dilutes the fuel-air mixture, but it also causes a portion of the energy generated during combustion to be used to heat that excess air rather than to heat the space effectively.

When the furnace is optimized to burn fuel completely with the right amount of air, it results in cleaner combustion, higher energy output from the same amount of fuel, and reduced emissions. This means that the fuel is utilized more efficiently, lowering energy costs and contributing to a reduced environmental impact. Therefore, minimizing excess air directly correlates with achieving higher combustion efficiency.

In contrast, using lower gas pressure might create issues with combustion stability, enhancing airflow through exhaust vents is more related to venting efficiency than combustion itself, and increasing the size of the heat exchanger does not directly affect the combustion efficiency but rather the heat transfer efficiency of the system. Thus, focusing on controlling the mixture of air and fuel to minimize excess air is the key to getting the best performance from a furnace.