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Buying a High Efficiency Furnace: What’s the AFUE Rating and How Does It Work?


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All furnaces are certainly not created the same and, if you are a homeowner, you are probably aware that efficiency makes a big difference to your heating bill every month. 

If you have a furnace in your home that is more than twenty years old, it’s likely that it isn’t meeting current standards for efficiency and you are paying too much.

What is the AFUE rating?

The AFUE (Annual Fuel Utilization Efficiency) rating is how a furnace’s cost-to-heat ratio is analyzed. 

AFUE is measured by percentage. So if a furnace uses 80% of its fuel to actually heat the home, it has an 80% AFUE rating. Simply put, the furnace will give you 80% of the fuel you pay for in heat return. The remaining 20% floats up a chimney or out a PVC pipe in the form of exhaust, or is lost in condensation or other factors.

Older furnaces generally have a lower AFUE rating of about 78-80%. Today, the minimum AFUE rating permissible in any home in Canada is 90%, with different required ratings for different types of furnaces. 

There are many different types to consider when installing a high-efficiency furnace. The AFUE rating is used to measure efficiency on all types of heating systems, including:

  • propane
  • natural gas
  • electric 
  • heating oil
  • even wood-burning stoves are evaluated with the AFUE rating.

Which high-efficiency furnace is best for your home?

While AFUE is a good measure of cost efficiency of furnaces, it is important to know which type of furnace is most suitable for your location and needs before you compare AFUE ratings. For example, a propane furnace with a 90% AFUE rating might seem less efficient than an electric furnace with 98% AFUE, but not if you live in a rural area where propane is the more readily available and economical type of fuel. In this case, you would limit your search to AFUE ratings of propane furnaces only.

Within the different types of furnaces, there are different efficiencies to consider. 

Single-stage furnace – Minimum 80% AFUE

Single-stage furnaces are the oldest type of furnace and use a continuous pilot light and single heat exchange. There is simply an “on” and an “off” setting. When the house gets cold, the furnace releases a single draft of hot air at full blast and switches off again when it warms up. This type of furnace tends to let the house get too cold before it turns on, and too warm before it kicks off again. It can also leave pockets of the house cold where the blast was not able to reach, and too hot where heat gathers, providing rather uneven heating of the house.

Two-stage or dual-stage furnace – Minimum 96% AFUE

This type of furnace has three settings, as opposed to two: “on/high”, “on/low” and “off”. It is able to use two levels of heating blasts to heat the space in a more efficient way than a single stage. It is usually more expensive than a single-stage furnace.

Variable or modulating high-efficiency furnace – Minimum 98.2% AFUE

This is the most efficient type of furnace, as well as the most expensive to purchase. But what you spend on the initial purchase and installation will pay off with lower heating bills over the long run and more comfortable home. 

These types of furnaces use sealed combustion, two heat exchangers, and nuanced sensors to keep an even level of warmth in your home. 

Every high-efficiency furnace has its pros and cons and can be affected by factors like your location, your long term requirements, and how correctly your unit was installed.Ashton Service Group can help you determine which high-efficiency furnace is best for your needs and your budget. We can also help you retrofit your existing furnace for improved efficiency. Click here to explore our furnace and boiler services and get started today.

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