In this installment, we will explain what are SEER and SEER2 AC ratings and provide a simple formula for determining your annual operating costs for air conditioning.
SEER stands for Seasonal Energy Efficiency Ratio. To calculate SEER, you simply divide Cooling output (in BTUs) by the total energy used in Watts. Let’s look at an example:
Let’s say you have a 3 ton AC system. Each ton is 12,000 BTUs. So, that is 36,000 BTUs per HOUR output
If your system used 3,000 watts in an hour of operation, you would have a 36,000/3000 = 12 SEER system.
This sort of math is really more useful to look at when you already know the SEER of your unit and you are looking to calculate the operating cost. You can find the SEER on the big yellow sticker on your outside unit, or you can look up the model number which is found on the data plate (again on the outside model). For example, I have a Trane XL16i at my home. A quick search on the internet shows that it has a rating of “up to 16.5” SEER. As a 5.0 ton system, it is probably a bit lower than that. Let’s use 16.0 in our example.
5.0 ton is 60,000 BTU. 60,000 / 16 = 3750 Watts per hour or 3.75 KWh. Where I live in Eastern TN, our electric rate is really low at about $0.12/KWh. So 3.75 x 0.12 = $0.45 cost per hour of operation.
Next, let’s look up annual cooling hours. This is an estimation for how many hours your AC system will run in an average year. Unusually hot summers mean more hours. And the inverse is true too: Cool summers, fewer hours.
Cooling Hours Examples:
- Buffalo, NY: 571
- New York, NY: 1,089
- Charlotte, NC: 1,325
- Indianapolis, IN: 948
- Tulsa, OK: 1,486
- Bristol, TN: 1,066
- Tampa, FL: 3,068
- Houston, TX: 2,209
- Palm Springs CA: 2,092
So, my 5.0 ton, 16 SEER system, using 1150 cooling hours (an average of Bristol, TN and Knoxville, TN) should use about 1150 x 3.75 KHw or 4,312 KWh in a year. At $0.12/KWh, that is $517. Not Bad!
Let’s look at one more example. You may have an older unit that only gets 10 SEER and you live in Houston TX. So, for a 4.0 Ton system: 48,000 / 10 / 1000 = 4.8 KWh. X 2209 cooling hrs = 10,603 KWh. X $0.179/KWh (average for Houston) = $1,898/year. Over a 5-month summer, you will spend almost $400/month on just your cooling.
In 2023, the industry moved to SEER2 ratings. The difference is slight. SEER2 tried to account for regional climate data, ductwork leakage, humidity, and other factors to arrive at a more accurate calculation of efficiency. Overall, SEER2 numbers are about 4.5% lower than SEER numbers.
You may also encounter EER numbers. Energy Efficiency Ratio. This measurement gets used on window AC systems. EER is raw efficiency at an instantaneous point in time, rather than over a season.
To help visualize the difference that higher SEER ratings make, I made a chart. This chart gives you an idea for your annual cooling costs. Note the assumptions of 1150 cooling hours and $0.18/KWh are about average across the country. Your mileage may vary! The bigger your AC System, and the hotter the climate in your area, the more difference it makes when you upgrade to higher efficiency equipment. A 3.0 ton system at a lower efficiency of 6 SEER (probably 20+ years old and not well maintained) will cost more than $1200 per year to operate while an 18 SEER 5.0 ton unit will have a cost to operate of less than $700. I included up to 10 tons in case you have multiple units in your home. And don’t even think about 30 SEER2 unless you have a geothermal unit.
It should be said, there are more reasons to choose higher efficiency equipment than just the absolute cost to operate the AC. For example, at about 16 SEER, you encounter 2-stage units. These models do a better job removing humidity and will often run at the first stage, resulting in quieter operation.
At 17 SEER and above, you will find variable output units. These models have many stages and can vary their output to match the conditions in the house. They do an even better job removing humidity and are very quiet.
And of course, if your system is a heat pump, you have both cooling AND heating efficiency to think about, making system efficiency a bigger deal.
Lastly, there are tax credits and other incentives that may encourage you to select higher efficiencies. When considering installation costs, I find a sweet spot at 15 SEER for heat pumps, 16 SEER for AC and again at 18 SEER for both. 20 SEER and above is nice, but returns only a modest savings in all but the hottest of climates. A significant 30% tax credit on geothermal systems, which return efficiencies of 25-30 SEER2 makes them a good choice too.
So there you have it, SEER, SEER2, operating costs for AC and what matters! If you have any questions about SEER, or really anything HVAC, just let us know!
