If you’ve ever purchased an air conditioning system for your home, you’ve probably seen a SEER rating before. It’s one of the numbers listed on the big, yellow Energy Guide stickers you’ll find on the side of each unit. The problem is, however, that those stickers don’t really tell you anything about what the number means. That’s a real problem for buyers since an air conditioner’s SEER rating can and should play a big role in the purchase decision. To help, the experts here at Accurate Home Services thought it would be beneficial to offer a deep dive into SEER ratings. We’ll cover what they are, how they’re calculated, and how to use them to evaluate one air conditioner versus another.

What’s a SEER Rating?

There are two things that an Energy Guide sticker tells you about a SEER rating. One is that the acronym stands for seasonal energy efficiency ratio. The other is that a higher SEER rating means you’re getting a more efficient air conditioner. In the simplest possible terms, a SEER rating is a single number that lets you know how efficient an air conditioner is when you use it throughout an average cooling season.

SEER ratings are the result of a federal law called the Energy Policy and Conservation Act of 1975 (EPCA). Its purpose was to encourage energy savings by empowering the U.S. Department of Energy (DOE) to set minimum efficiency standards for major household appliances. To do this, they developed a series of energy efficiency rating systems, including SEER.

Initially, the authors of the law intended for the DOE to use their new rating systems to set minimum efficiency standards as fast as possible. However, bureaucratic holdups kept those minimums from going into effect until the early 1990s. From that point on, it became illegal to sell a new air conditioning system in the U.S. unless it had a SEER rating of at least 10.

Eventually, the DOE moved to a regional system, which imposed stricter standards in the southern and southwestern states. As of 2015, the minimum in the northern U.S. went up to 13, and it rose to 14 in the southern and southwestern states. In 2023, the standards rose again with the minimum in the northern U.S. rising to 14 and 15 in the southern and southwestern states.

At the same time, the DOE also made some adjustments to the testing conditions used to determine SEER ratings. Specifically, they’ve increased the static pressure applied to each AC by a factor of five during testing. Static pressure is the term that describes the resistance to airflow created by ductwork running throughout a home. The change means that SEER ratings will now reflect operating conditions far closer to what happens in the real world.

As a result of the testing changes, you’re going to start seeing some AC units on the market that bear a rating referred to as SEER2. To buyers, however, SEER and SEER2 remain functionally the same. That is, the higher the number, the more efficient the AC unit.

How a SEER Rating Gets Calculated

To assign a SEER rating to a given air conditioner, the DOE uses a specific mathematical formula. It begins with an older efficiency rating system called energy efficiency ratio (EER). EER is a much simpler efficiency measure that takes a given AC system’s maximum hourly cooling output in BTUs and divides it by the unit’s maximum wattage. The result provides a simple numerical scale to rank air conditioner energy efficiency.

The problem is that nobody uses an AC at maximum output all the time. So, in the real world, an EER rating is all but useless to a homeowner. That’s the exact deficiency that SEER exists to solve. SEER attempts to create a usage model that resembles how people use air conditioning in the real world. Then, it takes the EER rating and applies it to that model. According to the SEER formula, an average cooling season includes:

  • Running your AC at 100% EER for 1% of the season
  • Running your AC at 75% EER for 42% of the season
  • Running your AC at 50% EER for 45% of the season
  • Running your AC at 25% EER for 12% of the season

SEER also assumes that the average summer temperature hovers between 82 and 83 degrees Fahrenheit. By combining an air conditioner’s EER when running at that temperature with the average cooling season model described above, you get a SEER rating.

How Do You Compare SEER Ratings?

It’s important to note, however, that knowing how to calculate a SEER rating doesn’t bring you any closer to knowing how to compare two different AC systems using their ratings. That’s because the difference a single point of SEER makes in terms of efficiency declines a bit as you move up the scale. That means, for example, that the efficiency difference between an air conditioner with a 15 SEER and one with a 16 SEER is approximately 6.67%. However, the difference between an air conditioner with a 22 SEER and one with a 23 SEER is only 4.54%.

The good news is that it’s easy to figure out the efficiency difference between two air conditioners if you know the right formula. All you must do is divide the higher SEER rating by the lower one, subtract 1 from the result, and then multiply that by 100%. So, if you compared an air conditioner with a SEER rating of 20 with another with a SEER rating of 14, the formula above would tell you that there’s a 42.9% efficiency difference between the two.

Once you understand how to compare SEER ratings in that way, it’s far easier to calculate how much the difference in operating costs might be between two air conditioners. That information is far more useful than a raw SEER rating because it can help you decide if a more expensive air conditioner with a high SEER rating is worth purchasing versus a cheaper model. In some cases, you might find that a high-end air conditioner won’t save you nearly as much as you think when you factor in its purchase costs.

Consult the Air Conditioner Efficiency Experts

Hopefully, we’ve given you enough information about SEER ratings to help you become a more informed air conditioning shopper. Of course, there’s quite a bit more to know when the time comes to make a purchase. That’s where the experts here at Accurate Home Services come in. We’re a family-owned and -operated HVAC and electrical company that’s served Crandall, Kaufman, and the surrounding area for over 28 years. We pride ourselves on offering the finest HVAC installation, maintenance, and repair services around. And we complement those services with an array of electrical and air quality services to help you keep your home functional, healthy, and safe.

We even provide 24-hour emergency services, so you can always count on us for help, no matter the time of the day or night. So, if you’re in the market for a new HVAC system for your home, give Accurate Home Services a call today, and we’ll show you why we’ve won the Kaufman Herald Readers’ Choice Award for Best of the Best Air Conditioning and Heating Company every year since 1992!

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