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What is a SEER Rating?

By Adam Hill
Updated: May 17, 2024

A common way to measure the energy-efficiency of an air conditioning unit is through the seasonal energy efficiency ratio (SEER). The more energy-efficient an air conditioner is, the higher its SEER rating will be. Defined mathematically, this rating is the amount of cooling output, measured in British Thermal Units (BTUs) during a typical cooling season, divided by its energy usage, measured in watt-hours, during the same cooling season. As energy prices have increased, the importance of energy efficiency in air conditioning, and therefore that of the SEER rating, has increased significantly.

The SEER rating of an air conditioner measures efficiency over a whole season, and the energy efficiency ratio (EER) rating measures it for one given point in time. For example, an air conditioner's efficiency for the summer of 1998 would be measured by this rating, but its efficiency at 3:07 in the afternoon on 4 August would be reflected in an EER rating. The SEER rating of a unit is usually a number between about six and 25. Newer units usually have a higher rating, reflecting more efficient energy usage.

If an air conditioner operates for a total of 800 hours during a cooling season, and has an output of 5,000 BTUs per hour, then the total energy output for the season will be four million BTUs. If the unit has a SEER rating of 20, then the total energy usage will calculated as 4 million divided by 20, to find the watt-hours used. The result is 200,000 watt-hours for the whole season. The number that the rating represents, therefore, is the number of BTUs that are produced for every watt-hour of energy consumption.

Some governments have instituted laws, mandating a specific minimum level of energy efficiency, as measured by a SEER ratio. For example, in the United States, all air conditioners sold on or after 1 January 2006 are required to have a SEER rating of at least 13. Air-conditioners that are mounted in windows are not affected by this law, and it is common for these to have a rating of about nine or ten. For a unit to have the special Energy Star certification, its rating must be at least 14.

It is possible to see significant savings in cooling costs by upgrading to a more efficient air conditioner, in many cases. For example, an upgrade from a SEER rating of nine to 12 would translate into almost a third less energy used per season. This can potentially result in hundreds of dollars of savings per year, to the point that a new unit could even pay for itself in savings.

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Discussion Comments
By anon135600 — On Dec 19, 2010

A question from one of my customers.

If he pays $4000 for a mini-split 18000btu inverter heat-pump with a seer rating of 24 as opposed to $2700 for a comparable system rated at 18 seer. Is it worth the difference in price and how long will it take to get the 'pay back'. How can we make the calculation?

By anon131043 — On Nov 30, 2010

highly recommend replacing it. you may also be eligible for tax benefits.

By anon114702 — On Sep 29, 2010

For those who have replaced a central system recently, there should be a pretty good increase in efficiency, leading to lower energy bills just from the increase in the SEER rating. Large savings differences will show up in the heating season, when heat pumps will save a lot of money over resistance electric heating.

The cooling season alone will not give a good indication of the savings that can be achieved. A bit on the negative side, heat pumps should be serviced each year in the heating and cooling seasons to ensure that they are delivering the best performance. If you do not check their performance, you have no idea if you are saving any money or not.

Some of the energy savings goes toward the servicing, but it ensures that you are getting the savings you should achieve. Failure to check performance will eventually lead to creeping operational costs.

By babyksay — On Jul 29, 2010

@gameaddicted - Great, thanks for the information. When I had compared central air conditioner prices with my contractor, he told me that the best central air conditioners cost a little bit more. I have had this unit in for only one summer so I will see what happens. I guess this really beats having a window air conditioner. I had a window unit for the past five years. Thank you again.

By gameaddicted — On Jul 29, 2010

@leiliahrune - The SEER rating measures the effective use of power over a whole season, not just in one month; the (EER) in SEER means “energy efficiency ratio.” The SEER of a unit is a number between 6 and 25 and the newer the unit is, it will generally have a higher rating which prevents the unit from constantly running.

By leiliahrune — On Jul 29, 2010

@GeminiMama - So how does the SEER rating save me money? I just spent almost $10,000.00 on a new unit but my contractor didn’t really explain how central air conditioner ratings saves. Well at least I didn’t understand him. Can you explain this to me?

By GeminiMama — On Jul 27, 2010

I had no idea what a ‘SEER rating’ was until I needed our heat pump replaced this summer. We live in Phoenix, Arizona where air conditioning is a necessity. So unfortunately, this summer’s vacation fund went to buy a new high efficiency heat pump. We are saving so much money each month on air conditioning expenses that I’ve put some aside for a fall vacation to Disneyland!

Although the higher SEER rating units cost more, the money you save on energy conservation and helping our environment is seriously worth it.

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