Part of the decision-making process for selecting a new furnace is comparing models by furnace efficiency ratings. The standard measurement for furnace efficiency is the AFUE percentage. Checking furnace efficiency ratings will tell you how efficient the new system will operate, and how much you should see in savings over the life of the furnace.

What Is AFUE?

AFUE stands for Annual Fuel Utilization Efficiency. This is a percentage of how much fuel the furnace will convert into usable heat for your home. The closer the AFUE rating is to 100 percent, the higher its efficiency. As an example, if a furnace has an 85 percent AFUE, that means for every 100 BTUs of fuel consumed by the furnace, it yields 85 BTUs of heat.

Older systems may not have an AFUE rating because they were installed before it became an industry standard. Most older systems run anywhere from 55 to 70 percent AFUE. Older wood-burning units can have an efficiency as low as 45 percent AFUE. Currently, the U.S. Department of Energy has set standards for the minimum AFUE new residential furnaces must meet. As of November 2013, the minimum for a non-weatherized (inside) furnace was 78 percent AFUE. To achieve federal Energy Star certification, the furnace must have an AFUE of at least 90 percent, which is also the point at which high-efficiency condensing furnaces start.

What Is an Energy-Efficient AFUE Rating?

Minimum furnace efficiency ratings do not make a system energy efficient by modern standards, and in fact the federal minimum was going to be boosted to AFUE 90 percent for residential furnaces in Northern states earlier this year, until a court case delayed that change. The case is still pending.

Today the highest AFUE rating is found in condensing furnaces. These units run between 90 and 98 percent AFUE. They capture waste heat from the flue to further heat the air. They also have sealed combustion chambers and an electronic ignition instead of a pilot light. These furnaces typically cost more than standard-efficiency furnaces, though when operating in a cold-winter climate such as Northeast Ohio, they will deliver ample savings in utility bills over the life of the system.

For more help in selecting the furnace that’s right for your home or to answer questions on home comfort, please contact us here at Stack Heating & Cooling. We have been proudly serving the Greater Cleveland area since 1976.

Our goal is to help educate our customers in Cleveland, Ohio about energy and home comfort issues (specific to HVAC systems).  For more information about furnaces and other HVAC topics, download our free Home Comfort Resource guide.

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