How do you calculate Degree Days?

Degree Days are the product of a day and the difference between a base temperature and the outside air temperature.

The base temperature (also called the balance point) is a threshold value of the outside air temperature below which heating or cooling is required to maintain the desired room temperature.

The unit is Kelvin days (K • d). Degree Days are only determining days on which the outside air temperature drops below (for Heating Degree Days) or exceeds (for Cooling Degree Days) the balance point. Otherwise, the day counts as zero Degree Days.