Which Furnaces Are The Most Efficient?

Which Furnaces Are The Most Efficient?

Have you ever wondered how much energy your furnace is using? Furnace efficiency is also known as AFUE, which stands for Annual Fuel Utilization Efficiency and refers to the amount of fuel the furnace consumes to provide heat for your home. Think of it as being comparable to gas mileage for cars—the higher the AFUE, the higher the "gas mileage." In this post, Kennon Heating & Air Conditioning discusses the different types of furnaces and how energy efficient they are.

What You Need to Know About Furnace Efficiency

There are many variables that can contribute to furnace efficiency, such as leaking ductwork, gas pressure and elevation. This is why proper installation by a licensed contractor is so important—installing a furnace incorrectly can cause loss of efficiency.

Since electrical consumption among furnaces is low—comparable to a ceiling fan, it is not a factor for gas furnaces since most furnaces use about the same amount. Instead, the most common way efficiency is referenced in the HVAC industry is by percentage—the percentage of gas that is converted into heat and delivered to the living space. So, if you have an 80% furnace, then 80% of the gas is converted to heat; the rest is sent out the flue as waste.

Main Efficiency Categories

Typical home furnaces can be put into three main efficiency categories: 60%, 80% and 90%. Federal regulations dictate the minimum efficiencies that can be installed in your area. Heating and air conditioning companies in Georgia are allowed to install a minimum efficiency of 80%, but your local heating and air conditioning company can tell you what is available for your region.

  • 60% AFUE Furnaces - The 60% (the least efficient) group is known as natural draft furnaces, which are generally over 20 years old. Luckily, they are no longer manufactured. The 60% furnace is a dinosaur, and they’re quickly being replaced with higher-efficiency furnaces. These furnaces have a standing pilot light that constantly burns, using up gas every day of the year. This is a problem with the 60% furnace—not only do you have gas burning all of the time, you also worry about the pilot light going out. If you currently own one of these furnaces, you could greatly benefit from upgrading to a high-efficiency furnace. You could save as much as 37% on your gas consumption by replacing a 60% furnace!
  • 80% AFUE Furnaces - The most common furnace in homes is the 80% furnace, a mid-efficiency furnace. This furnace can often be identified by the type of flue pipe and by the presence of an induced draft motor, which expels the exhaust fumes from the furnace. The 80% furnace has a metal flue pipe instead of a PVC flue pipe because the heat loss through the exhaust is about 20%, so the flue gets very hot to the touch.
  • 90% AFUE Furnaces - The 90% plus is the last furnace group, and can include furnaces with 90%, 92%, 95%, and 98% efficiencies. They’re also called condensing furnaces because they expel water. They shouldn’t be confused with geothermal units or water source heat pumps, which are entirely different units. The water comes from the condensation of the gas fumes in the secondary heat exchanger. Unlike other furnaces, condensing furnaces have two heat exchangers. The first heat exchanger absorbs heat from the gas exhaust, and the exhaust goes through a second heat exchanger where it is cooled again. The hot gas exhaust cools down so much that condensate is released. The water is generally diverted to a pump or drain outside the home. These furnaces are the most efficient, and some only waste a few percentage points of heat. A correctly installed 95% furnace will turn 95% of the gas put into the furnace into heat and will waste only 5%, maximizing your heating energy savings.

The Importance of Professional Installation

With all of the variables and options today, the most important part of selecting a furnace is the care and attention that is put into the installation of the unit. To ensure you get the most out of a furnace, be sure to use a licensed and insured heating and air conditioning contractor. Consumers can check with the licensing board to verify a contractor’s license status. The heating and air contractor can show you a current certificate of liability to prove they are insured.

Use the Lennox Savings Calculator to see how much you could save!

Call Kennon Heating & Air Conditioning at (678) 820-5230 today or contact us online to schedule a furnace installation service in Gainesville!


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