what is a degree day?
A degree day is a unit of measure for recording how hot or how cold it has been over a 24-hour period. If the mean temperature for the day is, say, 5 degrees higher than 65, then there have been 5 cooling degree days. On the other hand, if the weather has been cool, and the mean temperature is, say, 55 degrees, then there have 10 heating degree days (65 minus 55 equals 10).