It’s all a matter of degree

3 years ago

Here in northern Maine, we’re used to spending plenty of our hard-earned cash to heat our homes, and this year, cooling them has been pretty expensive as well. 

We track energy usage in summer with an index similar to that which we use in winter: degree-days. In winter, we use heating degree-days, and in summer, we use cooling degree-days. Weird terms, I know, but useful numbers to keep track of to compare, for example, your energy usage from one season to the next.

For each of the two degree-day types, an average temperature of 65 is used. The average is computed by adding the high and low for the day and then dividing by two. If the average daily temperature is warmer than 65, it is assumed cooling would be needed, and if it’s cooler than 65, it is assumed heating would be needed.

The next question is, how are they computed? It’s actually pretty simple. In the winter you take your average daily temperature and subtract it from 65, while in the summer, you take your average daily temperature and subtract 65 from it.

Let’s go through an example for both summer and winter. 

Summer. A hot day and a warm night. The high was 88 and the low was 66. Let’s get our average this way: 88 + 66 = 154. Divide that by 2 and it gives you an average daily temperature for that day of 77. Subtracting 65 from 77 leaves you with 12. So in this example of a summer day, we would be said to have had 12 cooling degree-days. These are then summed for the month, and the season. The higher the number, the more energy you’ve used to cool, assuming you cool. 

This season, we have nearly tripled the average cooling degree-days through late July. That means that for every 50 bucks you’d spend to cool in an average year (based on 30-year climatological norms, 1981-2020), through late July, you’ve spent 150 this year. 

Now, let’s move to winter. A cold day and a cold night, with a high of only 14 and a low of 12 below zero. Our average is done this way: 14 + (-12) = 2. Then subtract 2 from 65, and that leaves 63. So in this example of a winter day, that day would have had 63 heating degree-days.

Cities have climatological degree-day annual averages, and Boston’s heating degree-day annual average is only about half of Caribou’s. This means that if you had the same dwelling you are in now, you’d spend about half as much to heat it in Boston as compared to Caribou.

One day, you might consider living in a different part of the country. (I hope you don’t because we’d hate to lose you!) But sometimes duty calls, work or otherwise, and you have to hit the road. Well, if you do ever find yourself considering a major move, I can point you toward tons of info about the climate there, wherever “there” is going to be for you. Just shoot me an email to the address at the bottom of this column.

Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at