What efficiency metric must furnaces meet according to federal law?

Furnaces are required by federal law to meet a specific efficiency standard known as Annual Fuel Utilization Efficiency (AFUE). AFUE is a measure that indicates how efficiently a furnace converts the energy it uses into heat over the course of a typical year. It is expressed as a percentage, with higher percentages indicating more efficient units. For example, a furnace with an AFUE rating of 90% converts 90% of the fuel used into usable heat, while 10% is lost through the exhaust and other processes.

This standard has been set to ensure that consumers are using heating products that are energy-efficient and to promote energy conservation on a broader scale. While EER, SEER, and COP are all efficiency metrics relevant to other types of HVAC equipment (such as air conditioners and heat pumps), they are not applicable to furnaces when it comes to federal requirements. AFUE is specifically designed for measuring the efficiency of heating equipment, making it the correct metric in this context.