September 2025 EnergyWise SM Tip: Degree Days
September 2025 EnergyWiseSM Tip: Degree Days
By: Energy Efficiency Program Manager Cory Fuehrer
Have you ever reminisced about how hot a summer or how cold a particular winter was? It seems to be human nature to compare current outdoor temperatures to weather we experienced in the past. One of the late Johnny Carson’s favorite ways to set up a weather joke was to start by
saying, “It was so hot today…” Having seen the routine many times, his audience would boisterously reply in unison, “How hot was it?!” Obviously, his reply was the punchline to which everybody laughed. But what if there was a way to quantify how hot or cold it truly was in order to compare it to other days, months or years in the past? Actually, there is and it’s called a “degree day”.
Degree days are a measurement of how cold or warm a particular location was. A degree day compares the daily mean temperature (average of the day’s high and low outdoor temperature) to a standard temperature. In the U.S., that’s usually 65° Fahrenheit (F). The more extreme the outside temperature, the higher the number of degree days. A higher amount of degree days generally results in higher energy use for space heating or cooling.
More specifically, heating degree days (HDDs) are a measure of how cold the temperature was on a given day or during a period of days. For example, a winter day with a mean temperature of 30°F has 35 HDDs. Two such cold days in a row have 70 HDDs for the two-day period. If the daily mean temperature is greater than 65°F, no HDDs are associated with that particular day.
On the other hand, cooling degree days (CDDs) are a measure of how hot the temperature was on a given day. If a summer day had a mean temperature of 80°F, 15 CDDs would be recorded. If the next day had a mean temperature of 85°F, 20 CDDs would be assigned to it. The total CDDs for the two days is 35 CDDs. By totaling HDDs and CDDs for entire months or years, comparisons to previous months or years can be made.
Say you’d like to evaluate an average of how much energy it might take to heat and cool your home. Degree days, along with your heating and cooling system’s efficiencies and other factors can be included in this equation to provide a fairly accurate estimate. Degree days also provide possible insight as to why energy bills were higher or lower than anticipated.
The Nebraska Department of Water, Energy, and Environment (NDWEE) provides historical degree day and degree day normals on a monthly basis for 12 cities around the state in addition to the state's overall average degree days. Degree day normals are 30–year averages over a baseline comparison period. Currently, NDWEE uses 1991–2020 for the baseline.
Nebraska's overall HDD normal for a year is 6281. The CDD normal for a year is 996. (Note that commas are not used degree day data.) In comparison, Hawaii's HDD normal is 1 and its CDD normal is 4766. Hawaiians use almost no energy for heating but need to use huge amounts if they wish to keep indoor spaces below 80°F. In contrast, Colorado's HDD and CDD normals are 7053 and 329 respectively. While our neighbors to the west use a little more energy than us for heating, they require only about one-third of the energy to keep cool.
In the 2024/2025 season, Nebraska's HDD totaled 5956, which was 325 HDD less than normal. This indicates last winter in Nebraska was about 5% warmer than normal.
For the upcoming winter, the “Old Farmer's Almanac” forecasts above-normal temperatures in the Cornhusker state. By the end of next June, we should know if the prediction was right. In the meantime, when a friend claims the winter of 2018/2019 was the coldest they remember, you can prove the winter of 1978/1979 was actually the coldest in more than 50 years.
Regardless of what the upcoming winter is like, your local public power provider, in partnership with Nebraska Public Power District, may have an EnergyWiseSM incentive available when you upgrade your heating, ventilation and air conditioning system’s efficiency. Contact your local utility or visit www.energywisenebraska.com for more details.
