What is SEER? A guide to the seasonal energy efficiency ratio

SEER stands for seasonal energy efficiency ratio, and SEER and SEER2 numbers indicate your air conditioner’s energy efficiency. The number represents the total cooling output of an air conditioner divided by the electricity it takes to run it. 

Purchasing the best air conditioner with a high SEER rating will usually save you money on heating and cooling bills over the lifetime of your equipment.

“While the initial cost for a SEER2-rated system is higher, the investment can pay off over time through reduced energy bills,” said Tim David, an HVAC technician with 30 years of experience and owner of Airlucent, a resource for all things heating and cooling. He also noted that regions where electricity is costly and air conditioner usage is continuous, such as the Southwest, will likely see the most financial benefits.

Understanding SEER is crucial if you’re shopping for a new air conditioner, but it’s also helpful for identifying your current AC unit’s performance. We’ll cover what a SEER number is, how to calculate it, and why you should care.

What does SEER indicate about an air conditioner’s efficiency?

An air conditioner’s SEER rating is a measure of its efficiency. In general, higher-efficiency air conditioners have higher SEER values and use less electricity to produce the same amount of cooling as lower-efficiency, low-SEER ACs. That means lower electricity bills for you as well as a lower carbon footprint.

You can’t measure your air conditioner’s SEER directly, but most modern air conditioning systems come with both a power rating and a SEER value. How much energy your AC uses depends on its power rating, SEER rating and the amount of time it runs.

Here’s an example. Let’s say you have an air conditioner with an energy consumption of 1,465 watts (W). That’s approximately 5,000 British thermal units (Btus) per hour (h), which indicates the amount of heat it can remove from a room in one hour. For simplicity, assume that summer lasts for 125 days in your area. If your AC unit runs for eight hours per day, the total amount of cooling energy produced would be the following:

5,000 Btu/h x 8 h/day x 125 days/year = 5,000,000 Btu/year

If your air conditioner has a SEER of 18 Btu/(Wh), then the amount of energy it consumes would be the following:

5,000,000 Btu/year / 18 Btu/(Wh) = 278 W

That means that your air conditioner consumes an average of 278 W, or approximately 0.3 kW, per hour.

Now imagine that your air conditioner is less efficient and has a SEER value of 10. The above calculation becomes the following:

5,000,000 Btu/year / 10 Btu/(Wh) = 500 W

That means that your air conditioner consumes an average of 500 W, or approximately 0.5 kW, per hour.

The take-home points from the example above are as follows:

• SEER measures the ratio of input electrical energy used to produce output cooling energy.
• The higher the SEER value, the more efficient your air conditioner is and the less electricity you will need to cool your home.

How does SEER affect your energy bills?

We can extend the calculations above to see how SEER actually affects your utility bills. 

Let’s say you have a less efficient air conditioner with a SEER of 10. That means that it takes 0.5 kW to cool your home for one hour. The average price for electricity in the United States in November 2023 was around 16 cents/kWh, according to recent reports from the U.S. Energy Information Administration. 

Multiplying your energy usage of 0.5 kW by 16 cents/kWh gives you an operating cost of 8 cents per hour. If your AC runs for eight hours per day, cooling your home costs you 64 cents per day or approximately $19.20 per month.

With the more efficient 18-SEER air conditioner, you only consume 0.28 kW per hour to cool your home. At the same electricity rate of 16 cents/kWh, it only costs you about 4 cents per hour, 32 cents per day, or $9.60 per month — roughly half the costs of a lower-SEER unit.

All you really need to know is that higher SEER ratings will save you money on utility bills over time. If you run the AC during the warm season lasting 125 days, an AC with a SEER rating of 18 would save you $40 annually compared to one with a SEER rating of 10. With an average AC life span of 15 years, that’s a potential lifetime savings of $600 on your electric bills.

In more extreme climates or in areas with above-average electric bills, those savings could increase. For example, in New England, where the average price of electricity is 27 cents, opting for an AC with a SEER of 18 as opposed to 10 would yield a lifetime savings of approximately $840.

What is a good SEER rating?

Generally speaking, SEER ratings of 14 or higher are considered good, and SEER ratings of 16 or higher are considered very efficient. A SEER rating of 16 is the minimum to qualify for the Energy Star rating.

We’ll discuss the U.S. Department of Energy’s mandates for SEER ratings later, but for now, it’s helpful to know the minimum SEER ratings allowed for new air conditioners by region:

• North: 14
• Southeast: 15
• Southwest: 15

Any SEER rating greater than these minimum values is considered good for the region. A SEER of 20 is 33% more efficient than a SEER of 14, which is the minimum value allowed in any region and is a reasonable place to draw the line between good and excellent air conditioners.

“While a higher SEER rating indicates greater energy efficiency, it doesn’t always mean that purchasing the highest SEER unit available is the most cost-effective decision for every situation,” David said. “The effectiveness of a high SEER unit is most pronounced in areas with long, hot summers, where the air conditioner is in constant use,” he continued. “In these scenarios, the higher upfront cost of a high SEER unit can be offset by substantial energy savings over time.”

Additionally, SEER value isn’t the only factor that determines what is efficient in terms of heating and cooling equipment. “You might also consider other performance indicators such as EER2 (energy efficiency ratio 2), which measures efficiency at a specific temperature and is often used for rating window units, and HSPF2 (heating seasonal performance factor 2) for the heating efficiency of heat pumps,” David said.

SEER vs. SEER2

As of 2023, SEER2 replaced SEER as the energy efficiency benchmark for air conditioners. SEER2 values are calculated slightly differently than SEER values, but otherwise, they play the same role in determining minimum energy efficiencies for new ACs.

The only difference is in how the cooling value for the units is determined. Because the AC’s efficiency can vary significantly under different pressures, SEER2 ratings involve testing air conditioners under different pressure conditions. “By evaluating performance across the different conditions, SEER2 provides a more accurate reflection of how an AC will perform in a typical home setting,” David said.

SEER2 also recognizes the efficiency of the unit when running for a long time and cycling on and off. “What separates SEER2 from traditional energy testing is quantification in several very short runs, unlike one long running time,” David added. “These differences in efficiency through the unit’s operating cycle were not reflected proportionally in the original SEER rating.”

Like SEER ratings, SEER2 ratings are for air conditioners, heat pumps, packaged air conditioners, evaporator coils and gas furnaces.

Minimum SEER requirements

Minimum SEER values for new ACs depend on where you live and differ from minimum SEER2 numbers.

Region	Minimum SEER	Minimum SEER2
North	14	13.4
Southeast	15	14.3
Southwest	15	14.3

The values in the table above are the minimum SEER and SEER2 values allowable by law for new air conditioners, but there are different requirements for tax credit eligibility. The federal government offers tax incentives for energy-efficient home improvements, including rebates for installing a “high-efficiency system,” defined by Energy Star as a SEER2 of greater than 16.

The current tax credits allow you to claim 30% of a project’s cost, up to a maximum credit of $600. There is also an aggregate limit of $3,200 per year for all clean energy upgrades you make to your home.

How is SEER calculated?

SEER is the ratio of the output cooling energy of an air conditioner divided by the input energy it consumes when it runs. If you have those two numbers, calculating SEER is easy, but how do you measure cooling output to calculate SEER?

SEER efficiency ratings measure the thermal output of air conditioners in controlled lab conditions. The tests measure how much cooling a unit provides, assuming an external static pressure equal to 0.1 inches of water. This pressure is meant to mimic the level of pressure a typical air conditioner has to fight against to circulate cool air.

SEER2 ratings update the external static pressure value to 0.5 inches of water. Research has found that this value is a better match to the real-world conditions in the ductwork where most air conditioners operate.

You can get more detailed information on this from the U.S. Department of Energy’s Test Procedures for Central Air Conditioners and Heat Pumps document.

What’s next? 

Investing in an air conditioner with a higher SEER rating is probably worth it for most homeowners. Going from a SEER 16 to a SEER 20 air conditioner gives you a 25% efficiency boost and can decrease your cooling bills by up to 25%, as well. However, savings will be more drastic in areas where AC usage is higher, such as in the Southwest U.S.

Check whether your new AC’s SEER rating is greater than or equal to 16, as that means you are eligible for the federal government’s Energy Star tax credit program. You can claim up to 30% of the cost of the air conditioner as a federal income tax credit, up to $600.

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