Frequently Asked Questions

Home » Frequently Asked Questions » What are furnace ratings?


What are furnace ratings?

Furnaces are rated by the Annual Fuel Utilization Efficiency ratio (AFUE), which is the percent of heat produced for every dollar of fuel consumed. Like the miles per gallon on you car, the higher the AFUE rating, the lower your fuel costs. All furnaces manufactured must meet at least 78% AFUE. If your furnace is 10 to 15 years old, it probably falls well below the current furnace minimum and wastes energy.

Isolated Combustion System (ICS): A New Rating In 1989, the U.S. Department of Energy (DOE) adopted a new, fair way to rate furnaces for AFUE efficiency. Isolated Combustion System, or ICS, is the industry standard that has been designed to reflect the efficiency of a furnace installed in a home setting.

What does this rating mean? The AFUE rating shows the efficiency of a particular furnace. Your contractor can determine your potential cost savings for your fuel costs, annual usage and efficiency. The AFUE rating provides consumers with one consistent number for comparison. Essentially, the ICS test compares “apples to apples.” That is, all furnaces are tested equally. Manufacturers determine AFUE ratings by testing furnaces under set conditions for various lengths of time. The conditions were determined by the DOE to simulate an average home setting.

Therefore, the ICS rating is the best way to compare furnace efficiencies, since all manufacturers must comply with the same testing procedures. So I can just look for a furnace with the highest AFUE rating, right?

Not exactly. The efficiency rating is just one factor to consider when looking at new furnaces. Furnaces use electricity to run fans and motors. The amount of electricity used varies greatly, depending on the type of furnace. Be sure to check electricity usage before making a purchase decision. Other important factors to consider include:

  • How long you plan to live in your house
  • Special comfort needs
  • Fuel availability
  • Fuel cost
  • Geographic area and climate

All these factors, plus your lifestyle and family needs, add up to show you which system is best for you. Let your Lennox dealer show you the best furnace for your home.

Ready to go 24/7/365

Weiss-Johnson is Edmonton's 1st Choice for all your Heating, Air Conditioning and Plumbing needs.

Our certified technicians are available 24/7 year round to ensure that you can get help whenever that may be. Our team is committed to total customer satisfaction no matter what time of day it is.

What Our Customers Say About Us

"The guys were very friendly. They took lots of care and attention when removing the old furnace and replacing it with the new one to not damage anything along the way. Once finished they took the time to explain the operation and go through any questions we had. I would definitely use them again."

- Kyle J.


"This review is for Noel who came to my home to see why our electric air cleaner was not working. He was punctual and super friendly. Found the problem within 15 minutes. Had the part ordered, and 9 days later it literally only took him 3 minutes to replace it for us!"

- Joy H.


"Booking an appointment for a furnace checkup was a very quick and simple phone call. The technician was on time as promised, very knowledgeable and professional. It gave us piece of mind that our 10 year old furnace was in good working order."

- Nicolas L.