Heating and Cooling Degree Days

Society
Temperature
Trends in the energy demand implied by outdoor temperatures, nationally and by state.

This indicator examines changing temperatures from the perspective of heating and cooling needs for buildings.

Figures

Figure 1. Heating and Cooling Degree Days in the Contiguous 48 States, 1895–2023

Data source: NOAA, 2024
Web update: June 2024

Figure data (CSV) EPA source workbook (XLSX)

Figure 1

This figure shows the average number of heating and cooling degree days per year across the contiguous 48 states.

Show the data behind this figure
year Heating degree days Cooling degree days
1895 5092 1149
1896 4661 1280
1897 4711 1209
1898 4704 1264
1899 4842 1244
1900 4521 1315
1901 4937 1251
1902 4748 1170
1903 4852 1010
1904 5048 1082
1905 4942 1190
1906 4664 1198
1907 4800 1082
1908 4556 1173
1909 4745 1138
1910 4679 1141
1911 4596 1307
1912 5072 1110
1913 4515 1162
1914 4802 1182
1915 4694 1072
1916 4881 1149
1917 5268 1060
1918 4724 1205
1919 4661 1218
1920 4884 1076
1921 4122 1348
1922 4540 1265
1923 4662 1138
1924 5019 1077
1925 4634 1298
1926 4858 1178
1927 4421 1138
1928 4630 1125
1929 4789 1153
1930 4645 1244
1931 4213 1351
1932 4542 1222
1933 4438 1359
1934 4466 1392
1935 4747 1210
1936 4757 1382
1937 4774 1266
1938 4291 1255
1939 4393 1328
1940 4890 1110
1941 4449 1252
1942 4628 1168
1943 4768 1263
1944 4674 1253
1945 4635 1174
1946 4234 1157
1947 4729 1252
1948 4712 1223
1949 4403 1290
1950 4654 1104
1951 4692 1194
1952 4542 1295
1953 4232 1298
1954 4378 1300
1955 4675 1303
1956 4540 1212
1957 4487 1211
1958 4835 1187
1959 4533 1317
1960 4850 1200
1961 4650 1153
1962 4781 1187
1963 4815 1208
1964 4633 1187
1965 4628 1153
1966 4785 1144
1967 4678 1091
1968 4766 1125
1969 4811 1192
1970 4736 1230
1971 4623 1192
1972 4750 1157
1973 4406 1235
1974 4464 1130
1975 4538 1175
1976 4764 1036
1977 4636 1299
1978 4976 1245
1979 4810 1123
1980 4718 1321
1981 4529 1221
1982 4637 1153
1983 4642 1254
1984 4518 1230
1985 4646 1223
1986 4274 1272
1987 4329 1280
1988 4612 1299
1989 4662 1188
1990 4008 1290
1991 4182 1347
1992 4392 1078
1993 4657 1232
1994 4428 1251
1995 4465 1314
1996 4629 1223
1997 4479 1190
1998 3949 1449
1999 4108 1329
2000 4376 1285
2001 4156 1297
2002 4266 1401
2003 4441 1304
2004 4260 1247
2005 4272 1409
2006 3979 1387
2007 4211 1410
2008 4436 1299
2009 4433 1259
2010 4429 1468
2011 4280 1482
2012 3739 1502
2013 4444 1312
2014 4535 1298
2015 4078 1483
2016 3879 1549
2017 3833 1418
2018 4292 1571
2019 4327 1484
2020 3920 1503
2021 3945 1474
2022 4268 1530
2023 3828 1444
Figure 2

Figure 2. Change in Annual Heating Degree Days by State, 1960–2023 Versus 1895–1959

Data source: NOAA, 2024
Web update: June 2024

Figure data (CSV) EPA source workbook (XLSX)

Figure 3

This map shows how the average number of heating degree days per year has changed in each state over time. The map was created by comparing the first 65 years of available data (1895–1959) with the most recent 64 years (1960–2023). “Warmer” colors indicate an increase in temperatures between the two periods, leading to less of a need to turn on the heat—that is, fewer heating degree days. “Cooler” colors indicate a decrease in temperatures, leading to more of a need to turn on the heat—that is, more heating degree days. Click on a state to reveal the trend in a line graph.

Show the data behind this figure
State Change in heating degree days
Mississippi 33.14
Alabama 15.85
Louisiana 8.82
Tennessee -17.73
Arkansas -18.68
Oklahoma -49.84
Georgia -62.48
Kentucky -64.54
West Virginia -73.83
Florida -86.42
South Carolina -90.69
North Carolina -93.79
Texas -104.24
Missouri -127.00
Iowa -152.55
Indiana -159.55
Virginia -162.93
Kansas -164.45
Ohio -220.79
Arizona -221.47
Illinois -228.57
Idaho -233.43
Nebraska -241.18
Nevada -248.64
New Mexico -252.50
Washington -264.62
Pennsylvania -267.26
Maryland -275.01
Utah -297.59
South Dakota -299.27
Wisconsin -303.11
Delaware -321.50
Oregon -331.46
Colorado -359.59
Montana -377.67
Michigan -383.28
California -386.79
New York -407.87
Wyoming -413.60
Massachusetts -419.09
Vermont -428.64
Connecticut -433.81
New Hampshire -438.01
Minnesota -440.72
New Jersey -448.68
North Dakota -456.97
Rhode Island -483.14
Maine -508.20
Figure 4

Figure 3. Change in Annual Cooling Degree Days by State, 1960–2023 Versus 1895–1959

Data source: NOAA, 2024
Web update: June 2024

Figure data (CSV) EPA source workbook (XLSX)

Figure 5

This map shows how the average number of cooling degree days per year has changed in each state over time. The map was created by comparing the first 65 years of available data (1895–1959) with the most recent 64 years (1960–2023). “Warmer” colors indicate an increase in temperatures between the two periods, leading to more demand for air conditioning—that is, more cooling degree days. “Cooler” colors indicate a decrease in temperatures, leading to less demand for air conditioning—that is, fewer cooling degree days. Click on a state to reveal the trend in a line graph.

Show the data behind this figure
State Change in cooling degree days
Florida 329.35
Arizona 294.59
California 211.08
Nevada 207.34
New Jersey 149.20
Rhode Island 143.46
Delaware 135.22
Connecticut 114.53
Maryland 113.93
Massachusetts 111.60
New York 105.82
New Mexico 103.02
Utah 89.33
Oregon 67.20
New Hampshire 62.51
Idaho 60.29
Maine 59.99
Colorado 57.33
Pennsylvania 56.39
Wyoming 52.43
Washington 45.50
North Dakota 45.04
Texas 42.40
Minnesota 40.16
Virginia 35.92
Michigan 35.72
Vermont 35.12
Montana 33.79
South Dakota 28.15
Louisiana 15.24
Illinois 12.25
Wisconsin 9.98
Ohio 4.16
Nebraska -0.88
Kansas -9.07
North Carolina -11.79
West Virginia -24.48
South Carolina -25.28
Iowa -28.51
Indiana -32.00
Missouri -43.62
Arkansas -54.51
Tennessee -64.71
Mississippi -66.66
Kentucky -70.45
Oklahoma -79.65
Georgia -93.73
Alabama -100.10
Figure 6

Key Points

  • Heating degree days have declined in the contiguous United States, particularly in recent years, as the climate has warmed (see Figure 1). This change suggests that heating needs have decreased overall.

  • Overall, cooling degree days have increased over the past 100 years. The increase is most noticeable over the past few decades, suggesting that air conditioning energy demand has also been increasing recently (see Figure 1).

  • Heating degree days have generally decreased and cooling degree days have generally increased throughout the North and West. The Southeast, with the exception of Florida, has seen the opposite: little change in heating degree days and fewer cooling degree days (see Figures 2 and 3).

Background

Outdoor temperatures can affect daily life in many ways. In particular, temperature affects our health, comfort level, and demand for heating and air conditioning. Collectively, heating and cooling the spaces in which we live accounts for 52 percent of the energy that American households use every year.1 As climate change contributes to an increase in average temperatures, an increase in unusually hot days, and a decrease in unusually cold days (see the U.S. and Global Temperature and High and Low Temperatures indicators), the overall demand for heating is expected to decline and the demand for cooling is expected to increase.

One way to measure the influence of temperature change on energy demand is using heating and cooling degree days, which measure the difference between outdoor temperatures and a temperature that people generally find comfortable indoors. These measurements suggest how much energy people might need to use to heat and cool their homes and workplaces, thus providing a sense of how climate change could affect people’s daily lives and finances.

About the Indicator

This indicator uses daily temperature data from thousands of weather stations across the United States to calculate heating and cooling degree days. A “degree day” is determined by comparing the daily average outdoor temperature with a defined baseline temperature for indoor comfort (in this case, 65°F). For example, if the average temperature on a particular day is 78°F, then that day counts as 13 cooling degree days, as a building’s interior would need to be cooled by 13°F to reach 65°F. Conversely, if the average outdoor temperature is 34°F, then that day counts as 31 heating degree days, as a building’s interior would need to be warmed by 31°F to reach 65°F. This does not mean that all people will actually heat or cool buildings to 65°F; it is just a number to allow for consistent comparisons over time and across the country. For reference, New York City experiences far more heating degree days than cooling degree days per year—a reflection of the relatively cool climate in the Northeast—while Houston, Texas, has far more cooling degree days than heating degree days—a reflection of the much warmer climate in the South.2

Figure 1 shows each year’s average heating and cooling degree days across the contiguous 48 states. Figures 2 and 3 show how heating and cooling degree days have changed by state, based on a comparison of the first 65 years of available data (1895–1959) with the most recent 64 years (1960–2023). State and national averages were calculated by finding the total number of heating and cooling degree days per year at each weather station, averaging the results from all stations within regions called climate divisions (each state within the contiguous 48 has up to 10 climate divisions), then calculating state and national averages weighted by the population of each climate division. With this population-weighting approach, average state and national heating and cooling degree days more closely reflect the conditions that the average resident would experience.

About the Data

Indicator Notes

Heating and cooling degree days suggest how temperature changes affect energy demand, but they do not necessarily reflect actual energy use. Many other factors have influenced energy demand over time, such as more energy-efficient heating systems, the introduction and increasingly widespread use of cooling technologies, larger but better-insulated homes, behavior change, and population shifts (such as more people moving to warmer regions). All of the population-weighting in this indicator is based on the population distribution according to the 2020 U.S. Census, so any changes in heating and cooling degree days over time in this indicator reflect actual changes in the climate, not the influence of shifting populations. A nationally applied baseline—in this case, 65°F—has certain limitations considering the various climate zones across the United States.

Data Sources

The data for this indicator were provided by the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information, which maintains climate data online at: www1.ncdc.noaa.gov/pub/data/cirs/climdiv.

Technical Documentation

References

  1. EIA (U.S. Energy Information Administration). (2023). Residential Energy Consumption Survey (RECS). www.eia.gov/consumption/residential/index.cfm
  2. NOAA (National Oceanic and Atmospheric Administration). (2024). U.S. climate normals 2020: U.S. annual/seasonal climate normals (1991–2020). www.ncei.noaa.gov/access/search/data-search/normals-annualseasonal-1991-2020
  3. NOAA (National Oceanic and Atmospheric Administration). (2024). NOAA Monthly U.S. Climate Divisional Database (nClimDiv). www1.ncdc.noaa.gov/pub/data/cirs/climdiv

Text on this page is EPA’s own published wording (a U.S. Government work, not subject to domestic copyright), extracted from EPA’s source document and verified paragraph by paragraph against the published page. Data, chart code, and the full extraction pipeline are maintained in the heating-and-cooling-degree-days repository, which this page reads its data from directly.

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