A hvac technician working on a air conditioning unit with the words, AFUE vs. thermal efficiency.

When you are investing in a brand new heater, you may hear the terms AFUE and Thermal Efficiency Rating being thrown around quite a bit. What does AFUE stand for? What is Thermal Efficiency Rating? Is one more important than the other? Why do they even matter?  Not to worry, when you have questions, the experts at Cote’s Mechanical have the answers. Here is what you need to know about AFUE and thermal efficiency.


AFUE stands for annual fuel utilization efficiency. This fancy term just refers to a heater’s ability to maximize fuel efficiency. For example, a unit with a 90% AFUE rating means that 90% of the fuel being burned is turning into heat, while the other 10% is wasted.

Why Is AFUE Important?

AFUE determines how effective your unit is going to be at using the fuel you are paying for. If you are using a gas-powered furnace instead of an electric one, you will want to pay close attention to this number. While a heater with a higher AFUE percentage may be initially a higher cost than a lower percentage unit, it will save you more money in the long run. This is because your unit is making more use of its fuel. In other words, think of AFUE as gas mileage. While an older car may be cheaper than buying a new car, the gas mileage in the new car is higher. This means you will be spending less money on fuel and more time enjoying the road. It may cost more upfront but in the long run, you will make back your investment.

If your heater is an electric heater, AFUE doesn’t make much of a difference for you, because electricity is the only energy source in which all heaters will have an AFUE of 100%. The only downside is that electricity is more expensive than gas, meaning that you will still be spending a considerable amount of money to heat your home.

Thermal Efficiency Rating

Thermal efficiency rating means the amount of work your unit’s putting in to get the results that you want. Fortunately for most homeowners, thermal efficiency rating is used mostly for commercial boilers. Basically, it tells a company how much heat their unit is able to put out with a minimal amount of work.

So Why Is it Combined with AFUE?

It can be confusing because even though they are different, AFUE and the Thermal Efficiency Rating are often used interchangeably, even within the industry. The thermal efficiency rating is not judging a unit’s energy efficiency but how powerful it is at creating heat, while AFUE is determining energy efficiency. It is important for commercial companies to pay attention to both, as they will want to get a unit that can correctly heat their building. For homeowners, the more important number is the AFUE rating.

Still Have Questions?

Cote’s Mechanical Heating & Air Conditioning loves to help our clients find the perfect heater for their home or business. If you are confused about AFUE or thermal efficiency ratings, we understand. That’s why we take the time to talk through our client’s needs and help them find the perfect solution for their home. We also offer expert installation services and maintenance to help keep your unit running strong. Contact our HVAC technicians today for more information and feel free to bring any questions you may have; we love helping our clients find their perfect temperature.