Heating degree days are used to relate how much more or less you might be spending to heat your home. Knowing the heating degree days for a period can help you compare your heating costs from year to year.
To calculate the heating degree days for a particular day, find the day's average temperature by adding the days high and low temperatures and dividing by two. If the number is above 18, there are no heating degree day's that day. If the number is less than 18, subtract it from 18 to get the number of heating degree days.
For example, if the day's high temperature is 10°C and the low is 4°C, the average temperature is 7°C. 18 minus 7 is 11 heating degree days.
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