Furnace Efficiency Ratings 101

The efficiency rating of your furnace is one of its most important features – but what makes a furnace “high efficiency”?

A good place to start the investigation is with your equipment’s AFUE (Annual Fuel Utilization Efficiency) rating. An AFUE rating is the number you typically find on a yellow sticker on your heating equipment; it tells you how much of the fuel your furnace consumes will actually produce heat in your home. In a furnace with an 85 AFUE rating, for example, 15 percent of the energy consumed will be lost on the way to your living space. Some older heating equipment models may not have an AFUE rating.

Identifying a furnace with no AFUE rating

If you have an older furnace, it may have never received an AFUE rating – or perhaps it received a rating, but the AFUE sticker has fallen off over the years. In these situations, you can still approximate a furnace’s efficiency by its features.

Here are the U.S. Department of Energy’s (DOE) guidelines for identifying a low-, medium-, and high efficiency furnace:

Old, low-efficiency heating systems (56-70 AFUE)

  • Natural draft that creates a flow of combustion gases
  • Continuous pilot light
  • Heavy heat exchanger

Mid-efficiency heating systems (80-83 AFUE)

  • Exhaust fan controls the flow of combustion air and combustion gases more precisely
  • Electronic ignition (no pilot light)
  • Compact size and lighter weight to reduce cycling losses
  • Small-diameter flue pipe

High-efficiency heating systems (90 to 98.5 AFUE)

  • Condensing flue gases in a second heat exchanger for extra efficiency
  • Sealed combustion

Of course if you want to get the most accurate reading of the efficiency rating of your furnace in your home, an AFUE rating can be measured by a professional.

Current minimum efficiency requirements for warm air furnaces

The federal government sets minimum requirements for furnace AFUE to try to encourage home energy efficiency. Here are the current minimum furnace efficiency requirements for warm air furnaces, courtesy of the DOE:

Equipment Type Size Category (Input) Subcategory or Rating Condition Minimum Efficiency
Warm-air furnace, gas fired < 225,000 Btu/h Maximum capacity ≥ 95.0% (U.S. North/Canada)
≥ 90.0% (U.S. South)
≥ 225,000 Btu/h* Maximum capacity 80% Et
Warm-air furnace, oil fired < 225,000 Btu/h Maximum capacity ≥ 85% AFUE
≥ 225,000 Btu/h* Maximum capacity 81% Et
* Furnaces with input equal to or greater than 225,000 Btu/h are not covered by federal purchasing requirements. Minimum efficiency presented is consistent with ASRHAE 90.1-2013.

These minimum efficiency requirements are significantly higher than they were even 10-20 years ago – a big part of the reason why upgrading to a high efficiency furnace is often one of the smartest moves you can make for your Maryland home.

Looking for a high efficiency furnace upgrade? Trust the pros at Carroll. Contact us today for a FREE, no obligation furnace estimate and see how much you can save!

For everything you need in home heating, trust the pros at Carroll Home Services – keeping Maryland homes warm for more than a century! Contact us to get started today!