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What does a furnace’s AFUE mean?

Today’s furnaces operate with about 50% greater efficiency than the old models produced decades ago. Whereas a 1970s furnace might have had 60% efficiency, today’s are often 90% or higher. These ratios are calculated as Annual Fuel Utilization Efficiency (AFUE) ratings, which tells you how well the furnace converts fuel to heated air.

The exact calculations of AFUE are fairly complex, but the rating tells you a simple percentage. For example, 95% AFUE means the furnace converts 95% of the energy it draws into heated air for the home. The rating is on an annual basis so you get a good idea of the efficiency over time. A furnace might operate more or less efficiently in mild and severe weather, for instance, but AFUE tells you the efficiency over the course of an entire year.

AFUE is also designed to provide an idea of real-world efficiency. The equipment gets put through the ringer, so to speak, so the data reflects all seasons and a variety of conditions. Ultimately, you get an apples-to-apples comparison of how furnaces stack up in terms of efficiency.

There are two minimum AFUE ratings: a minimum for the furnace to be on the market, and a minimum to earn Energy Star approval from the EPA.

All gas and oil furnaces must have an AFUE of 78% or higher. In the southern half of the United States, gas furnaces need 90% AFUE to be considered an Energy Star product (colder climates need to be even higher at 95%). Oil-fueled furnaces, on the other hand, need 85% AFUE to be considered highly efficient.

Do you always want to buy a furnace with the highest AFUE you can find? All things being equal, the higher AFUE is better. However, in the Los Angeles area where winters are not exactly tundra conditions, you may not want to invest thousands of extra dollars for the highest-efficiency models. No harm in getting the greenest model you can afford, though!

The other main energy efficiency consideration is the heating power, measured in BTUs. The BTU rating should be appropriate for the square footage and insulation quality of your home. Too little power, and the furnace will have to run more often, increasing the energy consumption. Too much power, and you’ll be needlessly burning fossil fuels.

Other factors are mostly external — your home’s insulation, drafty windows, cathedral ceilings — so keep in mind that a difficult home to heat needs a high-AFUE furnace to enjoy the efficiency you’ve been promised by the manufacturer. And of course, better installation by qualified experts helps ensure you get the performance you expect.

Choosing a new furnace for your home or business? We can give a few AFUE pointers to select the best efficiency and performance for your property. Contact us at Dynamic Air Services for furnace installation and service in the Orange County area.