SEER vs EER - How to Use SEER and EER to Compare AC Units

SEER vs EER - How to Use SEER and EER to Compare AC Units

We often get asked questions about SEER ratings, but those that have done a little research know that EER is also a useful means of measuring an air conditioner’s efficiency, which leads one to ask the question, when looking at SEER vs EER, which do you choose? Those of you who read our articles regularly, know that we are a small, U.S. Veteran-Owned HVAC company in Southern California, and pride ourselves in giving people honest, straight answers to their questions.  In short, we are unbiased.  But when it comes to SEER vs EER, there are some very specific instances in which to use each.  Both SEER and EER are measurements of an air conditioner’s energy efficiency and are given as a value ranging from around 8 (such as SEER-8) and 30 (such as EER-16).  The higher an air conditioner’s SEER or EER rating is then the more energy efficient the unit.  In this article, we will explain what SEER is, what EER is, and finally when to use SEER vs EER.

SEER vs EER - What is SEER, and What is EER?

What is SEER?

Before tackling the SEER vs EER debate, let’s take a look at each individually, starting with SEER.  SEER stands for Seasonal Energy Efficiency Ratio and is the most common way to evaluate an air conditioner’s efficiency.  Now it is important to understand that this is only a measure of cooling power, and applies to air conditioning.  An air conditioner’s SEER rating is the
ratio of the cooling output of an HVAC unit over a typical cooling season (measured in British Thermal Units, or BTUs), divided by the energy consumed in Watt-Hours.  It is the average over a cooling season, and is calculated using a constant indoor temperature and varying outdoor temperatures ranging from the 60’s to over 100 degrees.  SEER also uses average US household energy expenditures in its calculation.  A unit’s SEER value is displayed on its Energy Guide Tag (left) as a number ranging from around 8 to 30, although right now there are few air conditioning units more efficient than about SEER-23.  So for instance, an air conditioner with a value of SEER-23 will be far more efficient than a unit with a rating of SEER-14.

If you are trying to find out what a good SEER rating is, or if it is worth it to upgrade your SEER value, also see:

For more about SEER, check out Wiki: Seasonal Energy Efficiency Ratio.

  • Do You Live in Santa Clarita, California or Seattle, Washington?  The Problem With SEER.

SEER can be misleading.  What people often don’t realize is that SEER is a ratio that only applies to a very specific set of test parameters which cover a pre-set temperature range.  The problem with this is that when SEER is calculated it is calculated across the same universal range, regardless of where the person who is purchasing the air conditioner lives.

Ask yourself, when was the last time that it was 65 degrees in the summer if you live in Santa Clarita, California?  Probably a lot less likely than if you live in Lake Arrowhead or worse yet, Seattle, Washington.  So although SEER is a universal measure of efficiency, it can be misleading in the sense that the average temperature range in Santa Clarita is far different from the average summer temperatures in Bozeman, Montana, but yet the same SEER rating would be on the tag in each.

How to Calculate Your Equivalent SEER Rating for Your Climate Zone.

SEER vs EER - Using SEER and EER to Compare AC Units

As a guideline, SEER is calculated across a wide temperature range but the average of that range is about 83 degrees.  If 83 degrees is the average summer temperature for your area, then an AC unit’s SEER value is spot on for your home (and I envy you).  If your area is hotter, however, then subtract 2 points from a unit’s SEER rating for every ten degrees above 83 that is the average temperature for your area.  For instance, in Santa Clarita where average summer high temperatures might be 93 degrees.  This would mean that an HVAC unit with a SEER rating of SEER-14 would have an equivalent rating of SEER-12 in Santa Clarita.

  • 93 – 83 = 10
  • +10 = 2 SEER points
  • SEER-14 rating – 2 SEER points = SEER-12 rating, or the equivalent SEER rating calculated for your climate area.


How Important is SEER Rating?

SEER vs EER operating costs

After calculating the equivalent SEER rating for your area, you can take a look at how much energy a high SEER rating can save you:

As you can see, paying for an air conditioner with a SEER value of SEER-23 over the lifetime of the unit will save you about $8,500 in electricity costs over the lifetime of your unit as compared to an older unit that has a rating of SEER-8.  Since 2006, the Federal Government requires a minimum SEER rating of SEER-13 for all new air conditioners, but an older AC might be lower.

Lennox has a useful calculator that will tell you how much money you can save by upgrading to a newer air conditioner from an older SEER-10 unit.  This calculator is only an estimate, of course, and one thing I don’t like about it is that you can’t enter in a starting SEER value – it instead assumes that your start value is SEER-10.  Just enter in the new SEER value and it will calculate your 5, 10 and 15-year energy-expense savings:

For more information on how to lower your air conditioning costs, try:

What is EER?

Again, before tackling the question of when you should use SEER or EER, you need to know what each of them is.  EER stands for Energy Efficiency Ratio, and is actually an older means of calculating energy efficiency than SEER, having been used since 1975.  Like SEER, an air conditioner’s EER rating is a means of measuring an air conditioner’s efficiency, but where SEER is a means of measuring seasonal efficiency ratings, an HVAC system’s EER is more of a constant.

Simply put, EER is more of an engineering number, than a marketing number, and will probably be used by an HVAC technician.  EER values are also often encountered when looking at smaller window AC units for which calculating a SEER value would be impractical.  EER is calculated using a constant outside temperature of 95 degrees, a constant inside temperature of 80 degrees and a humidity level of 50%.  No seasonal temperature changes are factored into a unit’s EER rating.

The Advantages of an Air Conditioner’s EER Rating.

If you read the section on a unit’s SEER value, then you know that SEER is a good approximation of a unit’s efficiency if the average summer temperature in your area is around 83 degrees, but can be misleading if you live in Southern California or the South.  Conversely, an EER value is an objective, set standard that can be used to directly compare two air conditioning units without worrying about the seasonal changes in your area.

For instance, how a SEER-21 rated air conditioner operates during the summer in Bozeman, Montana is far different from how it will perform in a Santa Clarita summer.  A unit’s EER rating can also be used to directly compare a Carrier Infinity Series air conditioner to a Lennox Signature Series, for instance, but in short, EER is a more technical, objective means of rating an air conditioner’s efficiency, but doesn’t take into account seasonal changes.

EER is best used if you live in an arid climate that has high average temperatures.  If used in more moderate climates, the numbers won’t accurately reflect your energy bills over a year as they won’t account for seasonal changes.

Now that you know about energy ratings, you can start shopping for more energy efficient air conditioners.  For more information on the energy efficient Carrier Infinity-21 Series or the Amana-18, check out:

SEER vs EER energy ratingWhen to Use SEER vs EER

So now that we know the differences between SEER vs EER, we can take a look at when to use each.  Like we discussed, SEER is a great way to get an idea of how a unit operates throughout a cooling season, and a unit’s EER is an objective way to measure an air conditioner’s efficiency, but here’s when to use each:

When to Use SEER

SEER is the most common.  SEER can be used to compare one AC unit to another directly and is most commonly encountered when looking at large, central air conditioning units.  However, it should not be used to measure how efficiently your new air conditioner will operate or how much money you can expect to save without making a calculation.

This is because, as discussed above, a SEER rating is only a rating based on a standard test across a specific seasonal temperature range.  As such, use the calculation in the SEER section above to first figure out what your equivalent SEER rating would be for your climate zone, then make the best decision for your area.  Once you’ve found the equivalent SEER rating for your area, then you can easily calculate your expected energy used and money saved.  Simply put, SEER is a means of estimating how much energy your new unit will use in a year, accounting for seasonal changes.

When to Use EER

EER ratings are more commonly encountered with smaller window mounted air conditioners, but are being listed more frequently on energy tags.  An air conditioner’s EER rating is best used to objectively compare air conditioners or to do any type of load or engineering calculation.  Because it is not diluted by additional inputs, the EER value, in my opinion, is the most accurate way to compare two different HVAC units.  But remember, I’m a contractor, not a homeowner.

You have to realize that the EER value will not give you an accurate representation of your energy bills over a typical cooling season.  As such, EER is more effective if you live in an arid climate that is always hot, or if you are making some kind of calculation.

Don’t Overpay for Your New AC.

For those of you who are really concerned about choosing the right SEER value and AC unit for the job, this online site can save you money, and help you avoid the tricks and traps of predatory contractors:



Which is Better for a Homeowner, SEER or EER?

To be perfectly honest, it can be hard to even find a central air conditioner’s EER value without digging into some manuals.  Most of the time, EER is used on smaller, window air conditioners where using SEER would be impractical.  Some manufacturers will note it, but it is used far less frequently than a SEER value.

However, they are being listed more frequently, so you might be able to find them!  In the end, the most important part is to compare apples to apples, and oranges to oranges.  So, when shopping for a new air conditioner, compare EER to EER, or SEER to SEER.  Never compare the EER of one unit to the SEER value of another; they don’t correlate!

In general, if you are a homeowner then I would use the SEER value as a means of comparing units to one another if you live in a more moderate climate, and I’d use a unit’s EER value if you are looking at a window AC unit or if you live in an arid climate like the Mojave Desert.

Final SEER vs EER Tips:

At the end of the day, SEER and EER can be very useful for comparing different air conditioning units to one another, but are not the end of the road to increasing efficiency and decreasing energy costs.  More important than SEER or EER would be an HVAC unit’s size, and whether it is the proper size for your house.  If you pay the money for a SEER-21 unit and that unit is too big for your house, then it will not run as efficiently as it should, so I’d check out:

Additionally, a SEER-21 air conditioner will only run efficiency if it is installed properly.  I can’t emphasize this enough: research your local HVAC contractors.  What good is spending the money for an awesome HVAC unit if it is installed improperly?  Here are some tips on how to pick a licensed HVAC contractor in your area:

I hope this article has helped you understand the pros and cons of using SEER vs EER, as well as what each of them stands for.  For more questions on SEER vs EER and other related topics, visit ASM’s Air Conditioning Blog or if you live in Southern California or the Santa Clarita area, give us a call.  You’ll be happy you did.




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Timothy Kautz
About the author
Tim K.

The University of Virginia - 2005 / The Wharton School of Finance - 2016 / U.S. Naval Aviator 2005-2015. At All Systems Mechanical air conditioning and heating, we believe that the experience our clients have is every bit as important as the products they receive. Simply put, our results speak for themselves, and we'd be happy to help. If you're in the market for a new AC or furnace, make sure that you get a fair price! Try our online calculator; click the tab on the top of this page for more information.

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