How Is Furnace Efficiency Measured?

Shopping for home comfort equipment these days can be confusing, especially with all those acronyms to sift through – SEER, EER, and HSPF, to name a few. But when it comes to shopping for a new furnace, one acronym is particularly important: AFUE.

AFUE – or Annual Fuel Utilization Efficiency – tells you what percentage of the fuel your furnace burns is converted to hot air. For example, in a 90 AFUE unit, 90 percent of the fuel consumed by the machine is used to generate heat – the remaining 10 percent is lost in the system along the way. One way to think about AFUE is to consider it in terms of the dollars you spend on fuel: In a 90 AFUE furnace, 90 cents of every dollar you spend on fuel goes to heating your home.

What is a typical AFUE rating for a furnace?

The AFUE ratings of modern propane furnaces are quite high, with some reaching into the upper 90s; most oil-fired furnaces have a slightly lower AFUE rating. But older furnaces weren’t nearly as efficient – and poorly maintained older furnaces fare even worse.

Here are some typical furnace AFUE ranges, per the U.S. Department of Energy:

• Low-efficiency (older systems): 56-70 percent AFUE
• Mid-efficiency (older or newer systems): 80-85 percent AFUE
• High-efficiency (mostly newer systems): 90-98.5 percent AFUE

As of 2015, the minimum standard AFUE for new furnaces Is 80 percent; most are higher, some considerably so (especially gas furnaces).

As you can see, the efficiency of an older furnace can be quite low – sometimes 30 or more percent lower than a new furnace. That kind of difference in performance can often tip the scales toward a heating system upgrade in the repair vs. replace discussion.

Energy efficiency is about more than AFUE

Of course, AFUE doesn’t tell the whole energy efficiency story for your furnace – proper heating system installation and regular heating system maintenance by an expert are also extremely important pieces of the equation, as are several other factors. But knowing the AFUE rating remains an important piece of the furnace replacement puzzle.

Looking for an energy efficient furnace or heating system? W.H. Riley & Son has them. Contact us today for a FREE, no obligation estimate on a heating solution for your southeastern MA or northern RI home.