What Are Heating and Cooling Degree Days?

Engineers who wanted a way to relate each day's temperatures to the demand for fuel to heat and cool buildings developed the concept of degree days.

Cooling Degree Days are the number of degrees the day's average temperature is above 65°. This relates the day's temperature to the energy demands of air conditioning. For example, if the day's average temperature was 85°, then there would be 20 cooling degree days for that day. To calculate the cooling degree days for a particular day, find the day's average temperature by adding the day's high and low temperatures and dividing by two. (If your answer is less than 65, there were no cooling degrees that day).

Conversely, Heating Degree Days are the number of degrees the day's average temperature was below 65°. This relates the day's temperature to the energy demands for heating. Subtract the average daily temperature from 65.

The greater the value is above or below 65, the more energy it will take to cool or heat a room. Energy bills are often higher in months that have the highest heating/cooling degree days.

Average Temperature (AT) = (Maximum Temperature + Minimum Temperature) / 2
• AT - 65 = Cooling Degree Days
• 65 - AT = Heating Degree Days
• Average Number of Heating and Cooling Degree Days in Grand Junction, CO
Month Heating Degree Days Cooling Degree Days
January 1194 0
February 860 0
March 656 0
April 409 2
May 178 44
June 33 232
July 12 394
August 1 318
September 73 100
October 367 1
November 792 0
December 1125 0