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Furnace efficiency rating: What is AFUE and why is it important?

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Winter is around the corner, and that means it’s time to check in on the old heating system. And if it’s time to think about replacing an aging furnace or boiler, you should know about AFUE. 

What is AFUE?

AFUE is an acronym for Annual Fuel Utilization Efficiency. It’s a standardized measure of the fuel efficiency for furnaces and boilers, used much the same way you would use miles-per-gallon (MPG) for cars. According to Energy.gov

• AFUE is the ratio of annual heat output of the furnace or boiler compared to the total annual fossil fuel energy consumed by a furnace or boiler.

• It is expressed in terms of percentage. For example, if you have a 90% AFUE furnace, 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere.

• AFUE does not account for heat loss resulting from ducting or piping in an unconditioned space, such as an attic or garage.

Why is AFUE Important?

The Federal Trade Commission requires new furnaces and boilers to display their AFUE so consumers can compare the efficiency of different models. As you research your new heating system, keep in mind that the Department of Energy puts efficiency levels into three categories:

Low efficiency – older models with AFUE in the 56 – 70% range (new units must meet current AFUE minimums, which are higher)

Mid efficiency – 80% - 83% AFUE (these models meet current minimum standards for new equipment)

High efficiency – 90% - 98.5% AFUE (many of these models also offer comfort-enhancing technology in addition to high energy efficiency)

When making a purchase decision using AFUE ratings, it is important to note that models with higher AFUEs are often deluxe units with extra features such as: 

• Two heat exchangers

• Multi-stage heating

• Variable-speed fans

• Communicating “intelligent” controls

The added components and technology can lead to higher price tags for the higher AFUE models. 

Making the right decision for your home’s furnace efficiency

Actual performance and efficiency of any furnace or boiler in your home will depend on additional variables including:

• Age, size and condition of home

• Condition and quality of windows, insulation and ductwork

• Personal temperature settings and usage habits

Your local Carrier HVAC contractor can be an excellent source for navigating the many AFUE options available for your new heating system. They have the tools and expertise to assess your home, your personal preferences and your budget considerations to help you make the right decision for your family.