degree day

Unit for estimating the demand for energy required for heating or cooling. In the US, the typical standard indoor temperature is 65ºF (18.3ºC). For each 1ºF decrease or increase from this standard in the average outside temperature one heating or cooling degree day is recorded. For example, if the average outside temperature for a day was 60ºF, it records as 5 heating degree days (HDD); if it was 70ºF, it records as 5 cooling degree days (CDD).