How Boston's 2025–26 heating season compared to normal
A first look at Data Digs: this winter's heating-degree-day accumulation at Boston Logan, charted against a 12-year normal.
This is the first post in what we’re calling Data Digs — short, chart-first pieces built directly from the datasets we maintain for our own analysis. We’re starting with heating degree days (HDD), the standard measure of how much heating demand a cold day generates, at Boston Logan Airport.
The chart below shows cumulative HDD across the Oct 1–May 31 heating season: each day’s HDD gets added to the running total, so the steepness of the line at any point tells you how cold that stretch of the season was, and the total height at the end tells you how much heating demand the whole season generated.
The gold line is the season that just ended, 2025–26. The dashed green line is the 12-year normal — the average of the twelve prior seasons. The faint tan lines in the background are those same twelve seasons individually, so you can see the normal isn’t just an abstraction — it’s sitting in the middle of a real spread of winters.
The 2025–26 season finished at about 5,544 HDD, roughly 7% above the 12-year normal of 5,163 HDD — a meaningfully colder-than-average winter, though not the coldest of the last dozen years. Hover over the chart to see the running total on any given day.
This is exactly the kind of underlying data — degree days, weather-normalized demand, avoided-cost calculations — that goes into the gas-system planning work we do. Reading a single season’s curve against its normal is a small example of the broader analysis: understanding how much heating demand a given piece of infrastructure actually needs to serve, and how that demand is shifting.
We’ll be adding more of these as we build out the Data Digs series — other stations, other metrics, and eventually some of the utility and rate data that underlies our regulatory testimony.