Cooling degree days explained

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As temperatures have, finally, gone up this year, air conditioners have been running more and more. And if you look at your electric bill, it has probably gone up as well. But you might notice something else on the bill called cooling degree days also piling up.

What exactly is it?

The first thing about a "cooling degree day" you need to know is that there can be several of them in any one calendar day.

Cooling degree days are not units of time. They're more measures of temperature.

It's the difference between a day's average temperature and a baseline temperature of 65 degrees. If we have an average temperature of 75 degrees, there will have been 10 cooling degree days accumulated that day.

Can it help you save money, though?

Kerry Spees, spokesperson with WPS, says they're not as useful as their cold-weather counterpart, heating degree days.

"If it's 20% colder, chances are your heating bill is going to be about 20% higher. For cooling degree days, it's a little bit of a different ballgame because so many people use air conditioning, if they have it, differently," says Spees.

Under ideal circumstances - not changing the thermostat, keeping other consumption constant - they can be used to see if your habits have changed with the weather.

That is, using less electricity when the weather is less hot.

But since ideal circumstances are hardly common, the best way to keep summer electricity costs down will always be to simply use less of it.