Heating Degree Days definitions

Heating Degree Days

A value representing the amount of fuel required for building heating, calculated by summing the difference of each day's average temperature below 65 degrees Fahrenheit.
Found on http://needtoknow.nas.edu/energy/glossary/

---

Heating Degree Days

A form of degree-day used to estimate energy requirements for heating.
Found on https://www.encyclo.co.uk/local/21182

---