AFUE

AFUE stands for Annual Fuel Utilization Efficiency. It is a standard measure of a furnace’s efficiency in converting fuel to heat over a typical year. Expressed as a percentage, AFUE indicates how much of the fuel becomes heat for the home and how much is lost through exhaust and other components. For example, an AFUE of 90% means 90% of the energy in the fuel becomes heat, while 10% is lost.

AFUE is determined using standardized testing conducted to U.S. Department of Energy (DOE) and AHRI standards. The test simulates a typical heating season and accounts for losses through the chimney, ventilation, and standby operation. It does not directly measure heat delivered to rooms, which depends on the distribution system, thermostat settings, and climate.

AFUE values vary by fuel type and technology. Traditional noncondensing gas furnaces are often in the 80% range, while modern condensing gas furnaces commonly reach 90%–98%. Oil furnaces typically range from about 80% to 85%. AFUE does not reflect installation quality, ductwork, or home insulation and air leakage.

In practice, AFUE is used to compare furnaces and boilers and to meet labeling and incentive requirements. Higher AFUE units usually have higher upfront costs but lower operating costs over time. When selecting a system, it is important to consider whole-house energy performance, climate, and proper installation to realize the stated efficiency.