Cooling Degree Days History

Hot days, which may require the use of energy for cooling, are measured in cooling degree-days. On a day with a mean temperature of 75 degrees F, for example, 10 cooling degree-days would be recorded (75 65 base = 10 CDD).

Heating Degree Days History

A heating degree-day is calculated when there is a 1-degree Fahrenheit difference between 65 degrees F and a mean outdoor air temperature of 64 degrees F, on any given day.

A degree-day compares the outdoor temperature to a standard of 65 degrees Fahrenheit (F); the more extreme the temperature, the higher the degree-day number. Thus, degree-day measurements can be used to describe the effect of outdoor temperature on the amount of energy needed for space heating or cooling.

Cold days are measured in heating degree-days. For a day with a mean temperature of 35 degrees F, 30 heating degree-days would be recorded (65 base 35 = 30 HDD). Two such cold days would result in a total of 60 heating degree-days for the 2-day period.