How Furnace Efficiency Is Measured

Furnace energy efficiency is measured by the AFUE standard. AFUE stands for Annual Fuel Utilization Efficiency and is a measurement that calculates the percentage of the energy input that is converted to heat (BTUs). The higher the percentage, the more efficient the furnace.

In the last couple of years the minimum AFUE required for most furnaces is 80 percent AFUE. When shopping for a new furnace, the ENERGY STAR® rating label will help you know how efficient the unit will be and how much you can expect to pay to operate it during a typical year.

High-efficiency furnaces operate at 90 to 98.5 percent efficiency by utilizing two heat exchangers in a sealed combustion chamber. A condensing unit removes moisture from exhaust gases before sending the gas through the second exchanger for increased efficiency.

If you have an older furnace, it may not be rated. The government only requires manufacturers of newer furnaces to show efficiency ratings. If your furnace has a continuous pilot light that requires you to light it when it goes out, it's a safe bet that it's a low-efficiency furnace that may not even have a fan. This type of furnace will typically operate in the 56 to 70 percent efficiency range.

Have questions about furnace efficiency? Give ABC plumbing a call; we're here to help.