Canonical Definition
Degree days are a measure of how much and for how long outdoor temperatures deviated from a base temperature (commonly 65°F), used to quantify heating and cooling needs. Heating degree days (HDD) accumulate when daily average temperatures fall below the base; cooling degree days (CDD) accumulate when they rise above it. Utilities use degree days to explain weather-driven bill variation, forecast load, and perform weather normalization of usage data.
Plain Language
Degree days measure how much heating or cooling the weather likely required. They are based on how far each day's average temperature was from a base level, usually 65°F. Cold days add heating degree days. Hot days add cooling degree days. Utilities use them to explain why your bill changed. A month with many more degree days than last year usually means your heating or cooling ran more.
Simplest Explanation
Degree days are a way to measure how cold or hot the weather was, which helps explain why heating and cooling bills go up and down. More very cold days means more heating degree days.
Do Not Say
- ✕Do not attribute a bill increase solely to degree days without noting other possible factors.
- ✕Do not assume a 65°F base applies everywhere; base temperatures and methods can vary.
Analogies
- ✓general
Degree days are like a pollen count for heating and cooling — a daily score of how hard the weather pushed your systems.
- ✓homeowners
Think of them like difficulty ratings on a hiking trail: a harsher month racks up more points, explaining the extra effort your furnace put in.
- ✓younger-audiences
It's like counting how many days the playground was too hot or too cold — the bigger the count, the more the heater or AC had to run.