What is a Furnace’s AFUE Rating?

South End Plumbing, Heating, & Air Expert Tips

What is a Furnace’s AFUE Rating?

AFUE stands for Annual Fuel Utilization Efficiency. Gas furnaces, boilers, and water heaters have an AFUE rating or score. It measures a unit’s energy usage and efficiency. What is a furnace’s AFUE rating telling you?

What’s AFUE Telling You?

Annual Fuel Utilization Efficiency is a standard, uniform way to know energy effectiveness. Heat pumps don’t use AFUE, but use a measurement called HSPF, Heating Season Performance Factor. The AFUE number on a gas furnace, water heater or boiler is a percentage. The closer the AFUE is to 100, the more energy efficient the machine is. This can still depend on other factors, such as the maintenance of the whole system, but on average this number is a way to compare different units or machines.

AFUE was first developed by the American Society of Heating, Refrigeration, and Air Conditioning Engineers, ASHRAE. It’s a nationwide standard for measuring and is required by the U.S. Department of Energy.

Boiled down, pun maybe intended, AFUE is calculating the heat output of a machine in ratio to the total fuel consumed by it. So, it’s the quantity of energy used to create and put out the desired heat. The higher the AFUE rating, the lower your gas and energy costs should be.

AFUE By the Numbers

If you have a unit with an AFUE of 90%, 90% of the fuel is being used for heating. The other 10% is going to a variety of outputs. Some are necessary, some is waste. The AFUE percentage, though, doesn’t calculate issues specific to your own HVAC system, house or other factors. AFUE ratings, for example, do not count heat loss in ductwork or piping, which could be a loss of as much as 35% of the power of heating systems if the ducts are damaged, dirty or are in unconditioned spaces, such as attics or garages.

The U.S. government – the Department of Energy – requires new gas furnaces to have a minimum AFUE rating of 90% for most of the country or 80% for the south and southwest regions of the U.S. Nearly every new furnace now has an AFUE of 90% or higher.

A home’s heating unit and system are usually the home’s largest energy users. It makes up an estimated 45% of a home’s energy expenses according to the U.S. Department of Energy.

AFUE and Money

An easier way to think about an AFUE rating is to cut to the chase and think about money.

Say, for instance, you have an 80% AFUE furnace. For each dollar you spend on gas, only 80 cents is going toward heating the house. Other functions by the machine or system, or waste, make up the other 20%.

On the other hand, a 95% AFUE furnace makes use of 95 cents of every dollar to warm your house, which tells you on average the energy usage is better and you spend less for your heating system to run as it should. Modern furnaces have AFUE ratings at about 98%.

It’s a major cost to repair or replace a furnace or water heater. You want to make smart decisions that will also be efficient and make financial sense in the long run. According to Customer Reports, a gas furnace generally lasts about 18 years.

If you are concerned about the costs and efficiency of your gas furnace, you’ve possibly heard the term AFUE before. The AFUE of your furnace tells you a lot about the money it’ll take to heat your home.

The EnergyGuide label has a unit’s AFUE rating.
The EnergyGuide label has a unit’s AFUE rating.

Finding the AFUE

The government, the Federal Trade Commission, requires furnaces, water heaters and boilers with AFUE scores to easily display the AFUE so consumers know it before buying it and it’s easy to find should you need it again. If a machine or appliance has an AFUE rating, it will be on the yellow EnergyGuide label. If you can’t find the label or it’s been removed, you can find the AFUE in an owner’s manual or on the company, manufacturer, or some retail stores’ websites.

It’s likely, especially with an older unit, or an older system, or in older homes, the AFUE rating is not actually how efficiently it’s producing. You can get a true, up-to-the-minute AFUE rating with a measurement done by an HVAC technician. They are able to take the heat output in BTUs and the fuel being used in BTUs and give you an exact number.

How to Compare AFUE Scores

You can get a good estimate of the money you’ll save with an upgraded, energy-efficient furnace or water heater. Follow these two steps.

  1. Locate your current furnace’s AFUE ranking. The rating must also be on your furnace’s faceplate. If it’s not, get the model or serial number, which should be on the machine or on the compressor outside. Enter the serial number in on the company’s website to find the AFUE rating.
  2. Compare the AFUE rating with other, likely newer, AFUE ratings on Energy.gov. On Energy.gov, you can find a graph named “Annual Estimated Savings for Every $100 of Fuel Costs by Increasing Your Heating Equipment Efficiency.” You’ll be able to tell how much you should save with appliances according to their AFUE scores.

Here’s an example of following these two steps and coming up with an answer.

  1. You see your old furnace has an AFUE of 70%.
  2. On the Energy.gov graph, you see if you update to a furnace with a 95% AFUE, you can save $26.32 for each $100 you spend on gas – a savings of 26%.

At South End Heating and Air, we specialize in HVAC and furnace repair, call us for a free consult. We’ll evaluate your system and help make recommendations for optimum value. After all, we want to keep you cool all summer long and warm in the winter. Just schedule a visit with one of our technicians to talk about how we can help with your heating needs. Would you like to learn more options our techs can help you with? Give us a call 704-684-5339.

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