What is AFUE for Furnaces? - Cagle Service Heating & Air | Jackson TN
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What is AFUE for Furnaces?

When it comes to understanding the numbers and traits of a furnace, there is probably nothing more important than AFUE or the AFUE rating. In short, this term determines the efficiency of the furnace. The AFUE rating is similar to the SEER or EER rating for an air conditioner. “AFUE” stands for Annual Fuel Utilization Efficiency. It corresponds to how efficiently the furnace utilizes and uses it’s fuel – whether it is propane, natural gas, electric or oil. The most efficient furnaces use the smallest ratio of usable fuel to wasted fuel that is needed to heat up the targeted space.

But how exactly is it calculated? And what is a good AFUE?

Let’s get into those questions below!

How is AFUE Calculated?

Annual fuel utilization efficiency is calculated by determining the percentage of fuel that is actually used in producing the heat that is applied to the targeted area in your home or business. In other words, it states how much of the fuel is actually applied towards heating the indoor environment. It states how much of the fuel is being utilized.

Wait, what? Not all of the fuel is utilized?

What many people don’t know is that the fuel that a furnace uses to produce heat usually isn’t entirely applied to heating the inside of your home or business. In most cases, a portion of it is wasted. For example, a standard furnace uses about 80% of the heat produced to heat the indoors. The remaining 20% of that fuel that is used is lost during the process. Most of it exits through the exhaust. Higher efficiency furnaces can have an efficiency of up to 98.5%. This would mean that only around 1.5% of fuel is wasted.

There is one type of furnace that is 100% efficient and has a AFUE rating of 100%, and that is an electric furnace. We will get more into electric furnaces a little later.

Now that we’ve gone over what annual fuel utilization efficiency is and how it’s calculated, let’s get into what a good, preferred rating would be.

Related: Should I Buy an 80% or 95% Efficiency Furnace?

What is a Good AFUE Rating?

As it is with most subjective topics, determining a good annual fuel utilization efficiency rating is going to come down to opinion. And we are happy to share ours!

We believe the standard mid-range rating of 80% – 85% is a “good” rating. Is it the best? No, but it is good and it should be sufficient for most applications. The best ratings are going to be high efficiency furnaces which range from 90% – 98.5%. These furnaces will cost more upfront, but they will typically end up making up the difference through energy savings in the long run. Then, of course, we have electric furnaces which are the most efficient of all. Their rating of 100% is tops, but there are some other things to consider, especially if savings is your goal.

man with beard pondering what afue is

Some Factors to Consider

The AFUE rating is a great tool to use when shopping for a new furnace. But, if it is savings you are after, don’t consider this rating only. It’s important to consider the type of furnace you are wanting or needing – to be specific, the type of fuel it uses. For example, if you want an electric furnace because of it’s spectacular annual fuel utilization efficiency rating of 100%, don’t let that be your only factor to consider. In most places, electricity costs more than gas. So, even though an electric furnace has the best efficiency rating, it still might cost you more to run the unit over the course of a year because it’s fuel source costs more than the alternatives.

In short, annual fuel utilization efficiency ratings are best used when comparing the same types of furnaces. For example, comparing propane furnaces with propane furnaces. When it comes to savings, comparing different types of furnace’s AFUE ratings can be misleading. As stated above, the fuel source is also going to affect the cost of operation. Both factors need to be considered.

You will also want to consider the current fuel type of the application. Is your specific application all electric? Or does it already have natural gas lines that are accessible? Sometimes, switching to a cheaper fuel source isn’t worth the initial upfront costs of making the switch.

I Hope This Has Helped!

Remember, AFUE simply refers to the efficiency rate that the furnace uses it’s fuel source. The higher the rating, the more fuel is actually utilized and less is wasted. When comparing annual fuel utilization efficiency ratings, make sure you are comparing furnaces with the same fuel source. And lastly, also consider the cost of the fuel source and the initial upfront costs of switching to a new fuel source.

Related: 4 Tips for Buying a New Furnace

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