The efficiency rating of a gas furnace is typically expressed as what?

The efficiency rating of a gas furnace is typically expressed as AFUE, which stands for Annual Fuel Utilization Efficiency. This metric measures how effectively a furnace converts fuel into heat over the course of a year. Specifically, AFUE is expressed as a percentage, indicating the proportion of the fuel's energy that is actually turned into usable heat. For example, an AFUE of 90% means that 90% of the fuel consumed is converted into heat, while 10% is lost through exhaust or other inefficiencies.

Other terms listed have specific roles but do not relate to gas furnace efficiency in the same way. BTU refers to British Thermal Units, a unit of measurement for heat energy, but it does not provide a measure of efficiency. EER, or Energy Efficiency Ratio, is typically used for cooling systems, particularly air conditioning, and compares the cooling output to energy consumption at a specific temperature. SEER, or Seasonal Energy Efficiency Ratio, also pertains specifically to cooling systems and evaluates efficiency over a season rather than an annual basis for heating. Hence, AFUE is the most pertinent measure for evaluating gas furnace efficiency.