AFUE: How Furnace Efficiency is Measured
Many factors go into choosing the heating system that is best for your home. One important factor to understand is the Annual Fuel Utilization Efficiency (AFUE) rating. Because home heating accounts for nearly half of a home’s energy use, knowing how to use this information when purchasing new heating equipment can help you make the best choice, save money and improve your comfort.
What is AFUE?
AFUE is an efficiency rating for combustion heating appliances, which includes furnaces and boilers. It is the ratio of the furnace’s annual heat output compared to the annual fuel energy the furnace consumes. In other words, it measures how much energy consumption actually goes into producing heat for the home. A furnace that has 95% AFUE rating uses 95% of the energy it consumes to heat the home. With a furnace that has a lower AFUE, more of the money you spend on energy costs is lost to inefficiency.
The minimum required AFUE for most furnaces is 80. An AFUE of 90 or higher is considered high efficiency.
How is AFUE calculated?
AFUE is calculated by dividing into the amount of fuel supplied to the furnace or boiler by the amount of heat produced, usually measured in BTUs.
How to find the AFUE rating
The AFUE rating of your current furnace should be on the faceplate. If not, locate the model and serial numbers and use that information to find the AFUE rating on the manufacturer’s website. Look for the AFUE on new furnaces to compare.
How AFUE translates to saving money
Compare AFUE ratings. For every dollar spent on fuel for a furnace with a 95 AFUE, $0.95 cents goes to heating your home and $0.05 is lost in the combustion process. Similarly, for every dollar spent on fuel for a furnace with an 80 AFUE, $0.20 is lost. So while a furnace with a higher AFUE will cost more up front, it will save a lot more in energy costs over its lifetime.
Energy Star is a program of the Department of Energy to help consumers identify the most energy-efficient appliances. Look for the Energy Star logo for furnaces that are up to 15% more efficient than baseline models.
Once you have purchased your furnace, there are many ways to ensure your furnace is operating at peak efficiency, beginning with proper professional installation. In addition, install a programmable thermostat, change the air filter regularly, and schedule annual maintenance to keep your furnace in good condition.