Archived raw data from the NOAA National Climate Data Center has been downloaded, re-processed and loaded into this database.

Degree Days

What are heating degree days and cooling degree days?

Heating degree days are indicators of household energy consumption for space heating. It was found that for an average outdoor temperature of 65 degrees Fahrenheit, most buildings require heat to maintain a 70 degree temperature inside. Similarly, for an average outdoor temperature of 65 degrees or more, most buildings require air-conditioning to maintain a 70 degree temperature inside.

How are heating and cooling degree days computed
Take the high and low temperature for the day, and average them. If this number is greater than 65 F, then we have (Average temperature - 65) cooling degree days. If the average temperature is less than 65 degrees, then we have (65 - Average temperature) heating degree days. Running totals are kept for these units over a time period of a year so fuel distributors and power companies can assess average demands.

For example, if the average outside temperature for a day was 60°F, it records as 5 heating degree days (HDD); if it was 70°F, it records as 5 cooling degree days (CDD).


For any individual day, degree days indicate how far that day's average temperature departed from 65 degrees F.

HDD which measures heating energy demand, indicates how far the average temperature fell below 65 degrees F (since cooler weather means more heating fuel demand).

Similarly, CDD which measures cooling energy demand, indicates how far the temperature averaged above 65 degrees F.

In both cases, smaller values represent less fuel demand, but values below 0 are set equal to 0, because energy demand cannot be negative. Furthermore, since energy demand is cumulative, degree day totals for periods exceeding 1 day are simply the sum of each individual day's degree day total.

For example, if some location had a mean temperature of 60 degrees F on day 1 and 80 degrees F on day 2, there would be 5 HDD's for day 1 (65 minus 60) and 0 for day 2 (65 minus 80, set to 0 since degree days cannot be negative). For the day 1 + day 2 period, the HDD total would be 5 + 0 = 5. In contrast, there would be 0 CDD's for day 1 (60 minus 65, reset to 0), 15 CDD's for day 2 (80 minus 65), resulting in a 2-day CDD total of 0 + 15 = 15.

1 National Climatic Data Center, NOAA