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Furnace Efficiency Ratings: What These Numbers Mean for Your Home Comfort

Purchasing a new heating system is a major decision for most homeowners. Whether you install it into a brand-new home or retrofit it into an older home, this new heating system requires a significant financial investment. It has to work as expected while keeping energy costs as low as possible, especially when dealing with a typical Chicago winter. Furnace efficiency ratings help homeowners determine how the new system compares to others in terms of efficiency. For this reason, understanding these ratings is important.

Annual Fuel Utilization Efficiency Rating

The annual fuel utilization efficiency rating, known as AFUE, is the standard rating used on furnaces and condensing boilers in the United States. By FTC regulation, all new units must display the unit’s AFUE rating so that consumers can see it.

This rating system is based on how much heat the system produces compared to how much energy the system consumes. If 70 percent of the fuel’s energy goes toward producing heat, the AFUE rating is 70. The rest of the fuel’s energy (30 percent) is lost via the flue or elsewhere.

AFUE Ratings of Older Systems

Determining the AFUE rating of an older system is difficult. Many don’t show this information. However, you can estimate the AFUE based on some system characteristics:

  • Many older systems use a continuous pilot light. When the pilot light goes out, you have to relight it. These systems feed hot air at floor level without the help of blowers. Most of these systems have AFUE ratings between 56 and 70 percent.
  • If the system has an electronic ignition and uses a blower to move air through the ducts, the likely AFUE rating is between 80 and 83 percent.
  • If the system has two heat exchangers, the likely AFUE rating is over 90 percent.

Minimum AFUE Ratings on New Systems

The federal government has set minimum furnace efficiency ratings bases on the AFUE scale to keep energy use down and to make homes more efficient.

As of January 2014, the following standards are in place for homes in Illinois, Michigan and Indiana:

  • Non-condensing, fossil-fueled furnace (except those manufactured for mobile homes), — minimum AFUE of 78. 
  • Non-condensing, fossil-fueled furnaces manufactured for mobile homes — minimum AFUE of 75.
  • Electric furnaces — minimum AFUE of 78.
  • Gas-fired hot water boilers — minimum AFUE of 82.
  • Oil-fired hot water boilers — minimum AFUE of 84.
  • Oil-fired steam boilers — minimum AFUE of 82.

Some AFUE furnace efficiency ratings were scheduled to go up in May 2013 and in January 2015. As of January 2014, both of these scheduled raises were on hold by court order. If those rating increases eventually go into place, the AFUE ratings for the following heating systems would go up:

  • Non-weatherized gas furnaces in the south will have a minimum AFUE of 80.
  • Non-weatherized mobile home furnaces would have a minimum AFUE of 80.
  • Non-weatherized oil furnaces would have a minimum AFUE of 83.
  • Gas furnaces installed in the northern states (including Illinois, Indiana, and Michigan) would have a minimum AFUE of 90.
  • For weatherized gas furnaces, the minimum AFUE would be 81.
  • For weatherized oil furnaces, the minimum AFUE would be 78.

All other ratings are scheduled to stay the same.

What AFUE Rating Is Right for Your Home?

Determining the AFUE rating for your home is a matter of balancing upfront costs with long-term energy and cost savings.

The more efficient the system you choose, the higher the upfront cost will be. A furnace with an AFUE rating of 90 will cost much more than that with an AFUE rating of 80. However, energy costs over the life of the furnace will be lower. In a climate like Chicago’s, a higher efficiency furnace makes sense due to the harsher winters. Many contractors recommend the higher 90 AFUE rated systems for most Midwest homes.

The best way to determine the AFUE furnace efficiency ratings for your home is to speak with a qualified HVAC contractor. If you need to find such a contractor, contact us at Comfort24-7.com. We recommend qualified contractors in and around Chicago, northwest Indiana and southwest Michigan.