What defines a heating degree day (HDD)?

A heating degree day (HDD) is defined as each degree below a specific base temperature, typically set at 65 degrees Fahrenheit in many contexts. The concept of heating degree days is used to estimate the energy demand required for heating buildings. When daily average temperatures fall below the base temperature, those differences indicate the need for heating. For instance, if the average temperature for a day is 60 degrees, that represents 5 heating degree days, since it is 5 degrees below the base temperature.

In this context, understanding this definition helps gauge heating requirements and manage energy use effectively during colder periods.