How Do EER and SEER Work? A Question From Brookhaven

If you’ve looked for a new air conditioner in Brookhaven recently, you probably noticed each unit comes with an EER or SEER rating. The former is for room air conditioners and the latter for central air conditioning units. In both cases, the number is a measure of how efficiently the system uses electricity. Effectively, if you buy a system with a high rating, you spend less on electricity. Of course, there are tradeoffs. The higher rated machines tend to cost much more, so as a homeowner, you’ll have to evaluate how much you can spend now and how long it will take to save money from that investment.

How EER and SEER Are Measured

These numbers are required by the government to tell you, the consumer, how many BTUs per hour the device can use for every watt of electricity drawn. The more BTUs a system can use, the better for your bill.

Let’s say you want to buy a 10,000 BTU system to cool your living room and dining room. A pretty standard number for a single room unit is 11, meaning the 10,000 BTU system would use about 900 watts per hour to run at full capacity. We figure this out by dividing the BTUs (10,000) by the watts (900).

There is a lot of math to do here, so many people simply look for a higher number within their price range. But, at what point is the upgrade really worth your extra money?

Choosing the Right Energy Efficiency Rating

The easiest way to describe this is to compare two similar devices with different EERs:

Air Conditioner 1 Air Conditioner 2
BTUs 12,000 12,000
EER 9 11
Watts 1333 1091
Price $300 $450

In this particular case, we can spend more for a device that is the same size but uses less electricity. The question then is whether that increased expenditure will pay off in the short term. Let’s assume each device would be operated for 10 hours per day for 30 days in a typical summer month. That’s 300 hours of operation. If the average cost per kWh in you are is $0.09, it will take 4 hours for the first air conditioner to consume 1 extra kilowatt of electricity equal to an additional $0.09. If your air conditioner runs for four months out of the year, we know that it will operate for a total of 1200 hours. That means:

[(1200 hrs x 242 watts) / (1000 watts/kw) ] x $0.09/kWh = $26

So, you save roughly $26 per year from that high efficiency unit. With a $150 price difference, you will break even after 6 years (though probably sooner if the price of electricity goes up).

Don’t forget, however, that central systems are a much more efficient option with SEERs of up to 16.5 and much larger BTU areas to cover. The savings there can add up very quickly. If you need more information to decide which air conditioner is right for you, talk to your air conditioning professional.