Understanding Furnace Energy Efficiency (AFUE)

The link between your wallet & your comfort

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Understanding Furnace Energy Efficiency (AFUE)

The link between your wallet & your comfort

Written by

  • Energy Efficiency
  • furnace
  • Photo of the ENERGYGUIDE Label for the Lennox SLP98 gas furnace showing a 98 AFUE rating
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    Annual Fuel Utilization Efficiency (AFUE)

    Heating costs make up a good chunk of the budget for the average homeowner in the Sioux City area. If you’re in the market for a new furnace or other heating system, it makes sense to consider your options, and energy efficiency ratings should be included in your decision. Annual Fuel Utilization Efficiency (AFUE) ratings help determine how well your electric or gas furnace uses energy. Like the miles per gallon rating on your car, the higher the AFUE rating, the lower your fuel costs.

    How Furnace Efficiency is Measured

    According to the United States Department of Energy, AFUE is the ratio of annual heat output of the furnace compared to the total annual fossil fuel energy consumed by a furnace. For example, an AFUE of 80% means that 80% of the energy in the fuel becomes heat for the home while the other 20% is lost. Note: AFUE doesn’t account for heat losses through your ducts which can be significant. Take a look at the EnergyGuide labels below:

     

    Older Units Without Ratings

    AFUE ratings are required on all new furnaces. Older models may not have a rating, or it’s possible that the rating was removed.
    If you don’t see en EnergyGuide label on your furnace like the ones above, don’t panic.

    There are a few ways to get a rough estimate of your furnace efficiency rating. Furnaces that use a continuous pilot light are considered low efficiency furnaces. They require you to relight the pilot light every time it goes out. Systems like these are between 56-70% efficient. Systems that fall in the 80-83% range have a fan that controls the air flow. There’s no pilot light to relight, and they use electric ignition. With high efficiency furnaces, two heat exchangers are used, and you can expect 90-98.5% efficiency.

    Minimum Furnace Efficiency Requirements

    The Department of Energy has proposed higher minimum standards for furnace efficiency, but those higher standards would not go into effect until 2021. Under the new plan, gas furnaces would require a minimum AFUE of 92% which would effectively eliminate noncondensing furnaces. The following are current standards for non-weatherized (indoor) units.
    Gas furnaces must be 80% efficient.
    Mobile home furnaces must be 80% efficient.
    Oil furnaces must be 83% efficient.
    All gas furnaces in the northern states, (including Iowa, Nebraska, and South Dakota) must be 90% efficient.

    Should You Replace Your Furnace?

    Are your energy bills on the rise? Are repairs costing you an arm and a leg? If you are questioning whether or not your furnace needs to be replaced, you might want to check out our article, Is It Time to Replace Your Furnace?, but generally, if your unit is old, inefficient, worn out, or oversized, replacing is with a high-efficiency unit is the best option. Replacing your inefficient furnace with a high efficiency furnace can often cut your pollution output in half. It can also save you some major cash. If you replace an old system with an AFUE of 60% with a new system of 90% AFUE, you will save $33.33 for every $100. The perfect candidates for replacement are coal burning furnaces that were once switched over to gas or oil or, as we mentioned above, furnaces with pilot lights instead of electronic ignition.

    Before you decide to replace your furnace, you may want to work at improving the energy efficiency of your home. Heat losses through your ducts or pipes can account for as much as 35% of total heating energy. If you have questions about improving the energy efficiency of your home, call us. If you need to replace your furnace, you can rely on our trusted HVAC professionals to guide you through the buying process, and most importantly, properly install a correctly sized unit.

    US Department of Energy Energy Saver 101 Infographic: Home Heating
    Energy Saver 101 Infographic: Home Heating

    Written by

  • Energy Efficiency
  • furnace