Heating Season: When the Heat Goes On, and How Long It Runs

There is no single national date, which is why these pages are built state by state. On the northern plains and in interior Alaska the first sustained week of heating weather arrives in the first half of September; on the Gulf Coast it waits until the middle of November; in Anchorage and Juneau it never leaves at all, because all 30 seasons in this snapshot carried heating weather on every day of the year. Each state page gives the median opening and closing date for two to four NOAA reference stations.

Because they are the number the people who actually plan around heating use, and because NOAA publishes them for every reference station on these pages. The Energy Information Administration defines them this way: "The base temperature we use is 65°F. If the mean temperature is above 65°F, we subtract the base temperature (65°F) from the mean, and the result is Cooling Degree Days (CDD). If the mean temperature is below 65°F, we subtract the base temperature from the mean, and the result is Heating Degree Days (HDD)." And on what they are for: "Degree days are calculated for each day of the year, and we use the daily degree days to compare months and seasons. We often count CDDs and HDDs by census regions and divisions. Generally, people study degree-day patterns to assess the climate and the heating and cooling needs for different regions of the country. For example, the West North Central Census Division generally has the most HDDs, and the West South Central Census Division generally has the most CDDs each year."

Because a date only carries information in the middle of the range. Where NOAA's published normal is 6,000 heating degree days a year or more, the heat is on for two thirds of the year and knowing that it went on in the third week of September tells you very little, so those pages lead with season length and how far the nights fall. Where the normal is under 2,000, heating is a short call rather than a season and leading with dates would oversell it. In between, the two dates are the most useful thing on the page and they lead.

NOAA's published 1991-2020 annual heating degree day normal is 0.0 at Honolulu, 0.0 at Kahului and 0.1 at Hilo. Across the 30 seasons in this snapshot none of the three ran a single run of seven consecutive days needing any heating at all, and the coldest reading in Honolulu's entire record is 52 F. There is no heating season in Hawaii to describe. Every other state has a page.

Part of it does and part of it does not. NOAA's published normal at Miami is 103.6 heating degree days a year and only 5 of the 30 seasons in this snapshot carried a sustained week of heating weather, so the Florida page prints that share for Miami rather than an opening date. Tallahassee needs 1,472.6 degree days and runs a real 132 day season from early November to the middle of March, every year.

No. These pages show climatology from NOAA, show any active National Weather Service cold product verbatim with the issuing office named, and quote the EPA directly on carbon monoxide while linking the EPA and the Consumer Product Safety Commission for the actual guidance. Equipment, fuel and contractor questions are outside their scope.

They are the two halves of the same year and they use the same 150 NOAA reference stations. The heat season pages answer when the hot season opens, how long it stays open and how many nights never fall below 75 F, using cooling degree days. These answer when the heating season opens, how long it runs and how far the nights fall, using heating degree days. Every state page on each side links to its opposite number.