The term, AFUE (annual fuel utilization efficiency), describes how efficiently a combustion heating system converts fuel into usable heat in the home. It’s measured by calculating the amount of fuel the system uses and comparing it to its total heat output. The efficiency rating for any furnace does not include thermal or air losses from ductwork.
AFUE is expressed as a percentage, and the current federal minimum for new residential combustion furnaces stands at 78 percent. This means that the appliance converts 78 percent of its fuel to heat and wastes 22 percent up the chimney or elsewhere. Furnaces are currently available that achieve 98 percent efficiency, wasting just 2 percent of the fuel they burn.
What Should Your Furnace’s AFUE Be?
The U.S. Department of Energy recently changed its annual AFUE ratings for furnaces and boilers for the Energy Star program. The minimum rating for Southern states is 90 percent. In the Northern states, the minimum is 95 percent. In the Mid-Atlantic region, it places West Virginia and Pennsylvania in the Northern states, and Delaware, Virginia and the District of Columbia in the Southern states.
The only heating systems that achieve these Energy Star ratings are condensing furnaces that use two heat exchangers to extract maximum heat from fuel. They capture residual heat from the combustion exhaust before it gets sent outside via the chimney or sidewall vent.
AFUE and Utility Bills
It’s important to know the AFUE rating system because furnace efficiency greatly affects your heating bills, and when it’s time to replace a system, the size and capacity of the new equipment. A furnace with a higher AFUE rating delivers more heat, and the furnace doesn’t need to be as large to heat the same amount of space. A 98 percent efficient furnace will deliver 20 percent more heat with the same amount of fuel compared to one with a 78 rating.
The heating efficiency rating is a key consideration when buying a new furnace, since a higher AFUE translates into lower energy bills over the long haul but also costs more to install. You and your reliable HVAC technician will want to calculate the return on investment with a new high-efficiency furnace to make sure it’s the right choice for your home.
To learn more about AFUE and furnace efficiency, please contact us at Griffith Energy Services, Inc., serving the Mid-Atlantic region for more than 100 years.
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Written by Kevin Spain