AFUE

SEER

Furnace efficiency is measured by its Annual Fuel Utilization Efficiency (AFUE). AFUE is a measure of how efficient the appliance is in converting the energy in its fuel to heat over the course of a typical year. Energy.com explains that an AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere.

Air conditioners are rated according to their Seasonal Energy Efficiency Ratio (SEER) to measure its energy efficiency. SEER is the relative amount of energy needed to provide a specific cooling output. It is the average calculated over an entire season and based on a constant indoor and various outdoor temperatures.