When is the middle of winter according to heating degree days? January 20.

Updated January 15, 2024

I mostly heat by burning firewood and my wood pile has shrunken quite seriously already this year so I was wondering when the middle of the winter is from an HVAC perspective. Surprisingly, I couldn’t find the answer, so I downloaded data from DegreeDays.net for the Findlay, Ohio airport weather station for 2017-2023 and calculated that January 20 has been the middle of the winter for heating degree days in recent years.

When the first part of a year has been warmer than average, the second half is likely to require more heating due to regression to the mean, but if you are wondering how much more firewood you will need for the rest of the year and you know how much firewood you have burnt before January 20, it should be about half of the total amount you will burn for the entire heating season if the rest of the year continues on the same trend. 

The beginning of the official seasons are set according to the length of day which has always been a crucial concept for pagans and astrologists. Winter officially begins on the shortest day of the year–the winter solstice on December 21 or 22. Fall and spring officially begin on the equinox when the day and night are equal in length and the summer officially begins on the longest day of the year–the summer solstice on June 20 or 21.

But these astrological dates have very little to do with seasonal climatic changes and their affects on biological needs. The real onset of winter and summer weather always begins earlier in most of the world than the start dates on the official astrological calendar. The real mid-winter is January 20 according to our climate in NW Ohio (and probably most places) even though the middle of winter is February 3 according to the official seasons that we have inherited from astrology. The seasons are one of the last vestiges where astrology still rules modern life rather than more practical measurements of how the weather changes with the seasons.

In the western United States, the middle of winter is probably much earlier given that the coldest day of the year usually occurs in December, often before the official start of winter, but here in northwest Ohio, the coldest day of the year usually comes around January 24 due to cold arctic air sloshing down into my neighborhood later in the year. 

Given that we cannot even abolish our barbaric tradition of daylight wasting time, it seems there is zero hope for a sensible reform of the calendar to reflect when the seasons actually change rather than based upon symmetries in the daylight/night ratio.