NATE Gas Heating Practice Exam

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Furnaces with AFUE ratings greater than what percentage are currently available?

85%
90%
100%
110%

The correct answer is: 90%

Furnaces with an Annual Fuel Utilization Efficiency (AFUE) rating greater than 90% are indeed available on the market. AFUE is a measure of a furnace's efficiency in converting fuel to energy over the course of a year, expressed as a percentage. A furnace with an AFUE rating of 90% means that 90% of the fuel consumed is converted to heat for the home, while 10% is lost as exhaust. Models achieving AFUE ratings above 90% typically employ advanced technology such as condensing heat exchangers, which allow for the capture and use of heat from the exhaust gases. This type of high-efficiency furnace not only provides significant energy savings but also contributes to lower greenhouse gas emissions. While options like 85%, 100%, and 110% may suggest efficiency ratings, furnaces rated at 85% would simply qualify as mid-efficiency models. A rating of 100% theoretically conveys complete efficiency, but in practice, exceeding 100% is not possible since some energy loss is inevitable. Thus, the most accurate current standard for high-efficiency furnaces is indeed those rated over 90%.