Annual Fuel Utilization Efficiency AFUE
AFUE, or Annual Fuel Utilization Efficiency, is a measure used in the United States to show how efficiently furnaces, boilers, and space heaters convert fuel into usable heat. Set by the U.S. Department of Energy, the rating works on a simple rule: the higher the percentage, the more efficient the appliance. Heating products sold in the U.S. must meet a minimum AFUE of 78%. Each appliance displays its AFUE on a yellow Energy Guide label for customers to compare.
AFUE is calculated by dividing a boiler’s total annual heat output (in BTUs) by its total annual energy input (also in BTUs) and multiplying by 100. In practice, measuring AFUE is quite technical because it requires sensors and equipment to track heat output over time. Once the total yearly heat output is known, it is compared to a standard figure of 100 million BTUs, which represents the typical fuel needed for a heating season.
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