Understanding Furnace Efficiency – The Importance of AFUE

Published on: October 30, 2013

When it comes to dealing with the impending need for a new furnace, there’s a lot that can seem overwhelming. One of the most important factors to understand and consider before making a major HVAC purchase is furnace efficiency, which is reflected by the annual fuel utilization efficiency, or AFUE.

What Is AFUE?

AFUE is a percentage measure of how well a heating system converts fuel to heat over a typical year, based on the ratio of yearly heat output to annual fossil fuel use. An AFUE of 90 refers to a system that converts 90 percent of its fuel into heat, although these numbers don’t include heat loss due to poor ductwork or other energy inefficiencies in your home.

For furnaces, AFUE may vary from 78 upward to as much as 98.5, with condensing and electric units scoring higher. The minimum AFUE is based on the fuel consumed and whether a unit has been weatherized for the outdoors, so northern states will require higher minimums.

To Replace or Retrofit

If you want to increase your current heating system’s efficiency, weigh the costs of retrofitting against buying a new furnace. For older, oversized or otherwise inefficient units, replacing them is generally the better choice. The initial investment may seem high, but high efficiency systems can cut energy bills and pollution by as much as half.

When comparing models, look for the required AFUE on a bright yellow sticker, as well as the Energy Star symbol. You might also consider:

  • An all-electric system if electricity is cheaper than fossil fuels in your region, as they have higher ratings.
  • A condensing furnace, which uses water vapor from combustion to create heat. This type of furnace has a higher AFUE and is well-suited to colder climates.

A reliable contractor can calculate potential running costs for different units based on local energy prices and other variables. For help finding a contractor in your region or for other questions about furnaces, AFUE, and your heating and cooling needs, search AC Southeast® today.