A degree day is a simple number that measures how cold (or hot) a day was, compared with a comfortable baseline. The colder the day, the more heating degree days it counts, and the more heating fuel people burn.
The idea is built around a baseline temperature, usually 65 degrees, the point where buildings need little heating or cooling. To find a day’s heating degree days, you take that baseline and subtract the day’s average temperature. A day that averages 45 degrees counts 20 heating degree days. A warm day near the baseline counts almost none.
The number matters because fuel use for heat tracks it closely. A house or building burns heating oil or propane in rough proportion to how cold it is, so a cold week piles up degree days and empties tanks faster. Add up the degree days since a customer’s last fill and you have a solid estimate of how much fuel they have used.
This is the engine behind automatic delivery in the heating fuel and propane business. By watching degree days for each customer, a marketer can predict when a tank is getting low and schedule the truck before the customer runs out, which keeps routes full and prevents the emergency call on the coldest night.
In useAfter a stretch of hard degree days, the dispatcher’s system flags two dozen home tanks as due, and the bobtails are routed to fill them before the weekend cold sets in.
See also Keep-full, Heating oil