AC ENGS -- Furnace Efficiency Ratings -- 03-17-16

What Are The Ratings For Furnace Efficiency?

When it’s time to buy a new furnace, being aware of energy efficiency ratings can help you make a wise choice. The ratings will impact how much of the system’s energy directly heats your home versus how much is wasted.

The Rating Used for Furnace Efficiency

The energy efficiency of a furnace is measured by the Annual Fuel Utilization Efficiency rating (AFUE). This rating reflects the furnace’s production of heat compared with the energy used to produce the heat. For example, a furnace rated at 90 percent AFUE has a 10 percent energy loss, while the remaining 90 percent becomes heat. Heat can often become lost through ductwork as well, and this loss isn’t calculated into the rating, because the ductwork is highly variable depending on the specific home. However, ducts that run through attic spaces can lose as much as 35 percent of the generated energy.

Energy Efficiency for Older Units

All new furnaces have AFUE ratings, as required by the Federal Trade Commission. Some older systems, however, don’t have ratings readily available. The guidelines below can give you a rough idea of the efficiency rating of your older furnace:

  • Low-Efficiency Furnaces—These furnaces have octopus-style ductwork and use a continuous pilot light that must be relit if it goes out. The furnaces rely on drafts and naturally rising heat for distribution. Low-efficiency furnaces are usually about 56 to 70 percent efficient, though some have aftermarket blowers installed which can raise the efficiency a bit.
  • Mid-Range Furnaces—These models have a fan that controls airflow, and they use an electronic ignition instead of a pilot light. Mid-range models have an energy efficiency of between 80 and 83 percent.
  • High-Efficiency Furnaces—These furnaces have two heat exchangers. The condensing units send gas to the second heat exchanger after removing water, which increases the energy efficiency, and the combustion units on these models are sealed. High-efficiency furnaces have about 90 to 98.5 percent energy efficiency.

Air Conditioning Engineers can work with you to find the ideal furnace for your home. Our NATE certified technicians install, replace and repair furnaces in order to provide our customers optimal efficiency. Contact us to schedule a service call or consultation.