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AFUE Words on Efficiency

Many of today’s boilers and furnaces are touted as being “high-efficiency” units. In this post we’ll explore what that means. The efficiency of your home heating equipment is measured by a term called “annual fuel utilization efficiency,” or AFUE. Simply put, AFUE (pronounced “a-few”) is a measure of how efficient an appliance is in converting the energy in its fuel to heat over the course of a typical year. Specifically, AFUE is the ratio of annual heat output of the equipment compared to the total fossil fuel energy it consumes annually. An AFUE of 90%, for example, means that 90% of the energy in the fuel becomes heat for your home, and the other 10% escapes up the chimney and elsewhere. If the AFUE was 70%, then 70% of the energy in the fuel would be converted to heat, and 30% would be lost. The higher the AFUE, the more efficient the unit is.

To give you some historical perspective on how home heating equipment has advanced over the decades, the cast iron furnaces and boilers manufactured before 1980 typically had efficiencies ranging from 56% to 70%. The flame retention burners that followed featured AFUEs of 70-78%. As of September 1, 2012, all new oil-fired hot water boilers are required to have a minimum AFUE rating of 84%, and oil-fired steam boilers, 82%. The minimum required AFUE rating for new non-condensing, non-weatherized oil furnaces is 83% if it’s a retrofit, and 85% if it’s new construction. However, some modern heating systems can achieve efficiencies as high as 98.5%, converting nearly all their fuel to useful heat for your home.

Upgrading to a new high-efficiency heating system can cut both your fuel bills and your furnace’s emissions. According to the U.S. Department of Energy, upgrading an older furnace or boiler with an AFUE of 56% to a modern unit with an AFUE of 90% in an average cold-climate house will save 2.5 tons of carbon dioxide emissions each year if you heat with oil. The Federal Trade Commission also requires new furnaces and boilers to display their AFUE so consumers can easily compare heating efficiencies of similar models. However, keep in mind that AFUE alone does not paint a full picture of energy efficiency – especially for boilers. Sizing, airflow and other factors also play a role in determining efficiency and costs (see our November blog post for more information), which is why homeowners should consult an expert when considering a heating system upgrade.