How much your furnace will cost you in your bills hugely depends on the efficiency of the furnace. The AFUE rating is the measurement of the efficiency of the furnace. In this article, I’m going to explain the AFUE rating, its importance, and how to use it to make an informed decision.
What is AFUE?
AFUE’s full form is Annual Fuel Utilization Efficiency. It is the measurement of efficiency for a furnace, boiler, or heating equipment in HVAC. AFUE reflects the percentage of fuel used for heating. A better rating indicates more energy per fuel unit. The higher the AFUE rating the more usable heat a unit produces for the same fuel.
With greater efficiency, a higher AFUE rating also results in lower bills. Since the fuel waste is low, higher-rated models are environmentally friendly too. These factors are key when choosing a furnace.
How Annual Fuel Utilization Efficiency (AFUE) Ratings Work
Annual Fuel Utilization Efficiency (AFUE) is measured in percentages. 80% AFUE means 80% fuel is converted to heating energy. The rest 20% is lost.
There are different test procedures that measure this rating. Manufacturers simulate the operating conditions to access the ratio of the output and input. During testing, the heat exchanger—a key component that transfers heat from the combustion process to the air—is evaluated for its ability to minimize heat loss. The results are then used in the formula:
AFUE = (Heat Output / Energy Input) X 100
Note: The “annual” aspect of AFUE accounts for the varying frequency of use and energy loss over the whole heating season which is the total annual heat output. This is done to accurately measure the efficiency over a period instead of instantaneous efficiency.
What is a Good AFUE Rating for Energy Efficiency?
Modern furnaces have minimum efficiency standards. So, anything above that is technically “good”. Some older systems might have AFUE of 56-70% and might not qualify for the standards.
However, going for more ratings always yields more energy savings.
Especially in colder climates, going for a high-efficiency, above 90% rating is recommended for saving energy. To qualify as an Energy Star-rated system, a furnace also has to be above 90%.
In summary, you should consider:
- Your Climate: The colder the area you live in, the higher efficiency you need.
- Your Budget: Higher-efficiency models are costlier.
- Fuel Cost: A low AFUE furnace will consume more fuel. If the fuel cost doesn’t affect you much, the AFUE rating won’t either. Although, it is not recommended considering the environmental impact.
Minimum AFUE Rating Requirements
The U.S. Department of Energy (DOE) sets the minimum standards for AFUE ratings. It has been working to increase the rating requirement over the years.
In 2023, the required minimum AFUE rating has been set to 81. From 2015 to 2022, it has been 80 for the South and Southwest regions. The North’s required minimum is still 90.
Keep in mind that these numbers change over the years. The intent is to support energy conservation and tackle the greenhouse effect as much as possible.
Benefits of High-Efficiency Furnace
Even though a high AFUE-rated furnace has more initial cost, it offers many benefits:
- Since higher AFUE ratings mean more output from less fuel, you can save more energy with higher AFUE units.
- Using less energy means your carbon footprint will be lower and your contribution to greenhouse gas emissions will get lower.
- Higher AFUE units are usually more advanced. So, you can enjoy improved heating consistency and reliability.
Types of Furnaces and Their AFUE Ratings
The AFUE rating is primarily applied to fuel-burning furnaces. If the types are same, the older models are always less efficient than modern ones.
Here is a breakdown of AFUE for different types of furnaces:
Natural Gas and Propane Furnaces
Propane and other gas furnaces often share a similar efficiency range which is:
| Furnace Type | AFUE Rating |
| Low-efficiency (Conventional) | Below 80% |
| Mid-efficiency | 80% to 89% |
| High-efficiency | 90% and above |
Oil Furnaces
- Older Oil Furnaces have an AFUE rating that falls in the 60s range.
- Modern Oild Furnaces have mid-80s AFUE values.
Electric Furnaces
Electric furnaces have the maximum efficiency out of all the types. The heating process also produces heat by depending less on fossil fuels.
In these furnaces, Electricity directly heats at the point of use. So, the efficiency is almost a perfect 100%.
However, the efficiency of electricity generation is also an important factor because it determines how much fuel the furnace will get. That is often below 100%. It affects the efficiency rating of electric furnaces.
How to Find and Interpret AFUE Ratings
Finding the AFUE rating of your furnace helps you compare different furnaces better. You can also compare the efficiency of the models you want to buy with your existing furnace. In that case, it helps you decide wisely too.
To find the AFUE of your furnace, follow these steps:
- Look in the yellow EnergyGuide label in the furnace. This label is mandated by the US Department of Energy and Federal Trade Commission.
- If the label is missing or you can’t find it, check the owner’s manual.
- Retailers also have model specifications on their websites. Check out the manufacturer’s or retailer’s website to get the AFUE rating as well as other information about your system as well.
A qualified technician can help you find the AFUE rating of a furnace. If you are unsure of all the steps, consult a professional.
FAQ
Q. What is the difference between AFUE and SEER ratings?
A: Both AFUE and SEER ratings compare energy input and output and indicate the performance of the HVAC units. While the AFUE rating focuses on heating systems (e.g. furnaces, broilers), the SEER rating focuses on cooling systems (e.g. AC, heat pumps). Another key difference is AFUE ratings are expressed in percentages while SEER ratings are expressed in numbers.
Can I improve the AFUE rating of my existing furnace?
A: You can’t change the AFUE rating of an existing furnace because a unit is already built on a design to generate a fixed cooling or heating output. You can consider steps like regular maintenance, upgrading sealing and insulation, and adding zoning systems to improve the overall efficiency instead. If your furnace is old, it’s better to replace it with a higher-rated furnace.
How often should I replace my furnace to maintain high efficiency?
A: Most furnaces have a service life ranging from 15 to 20 years. If your furnace is already 15 years old, it’s best to replace it. Additional considerations are energy bill spikes, frequent repairs, inconsistent heating, etc. New heating systems always have more heating efficiency and thus more energy efficient.
Are high AFUE furnaces worth the upfront cost?
A: Yes, high AFUE furnaces are worth the upfront cost. Besides making up for lower energy bills, it will give you more comfort, rebates, and incentives along with lower environmental impact.
Conclusion
The AFUE rating indicates how efficient a furnace going to be in its lifetime. Although there are different rated furnaces available in the market, the lower-than-standard rated ones eventually get phased out.
Despite that, try to go for a high AFUE rating if your budget allows for it. Prioritizing energy efficiency is always beneficial for cost savings and environmental concerns. Suggest consulting a professional to evaluate your current furnace or explore high-efficiency options.
See the infographic summary here – Comparing AFUE Gas Furnace HVAC Energy Efficiency Ratings [Infographic]
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