Jan 18, 2016 -21°F Coldest day of that winter
Dec 19, 2016 -21°F Early-season Arctic outbreak
Dec 27, 2017 -19°F Part of a prolonged late-December cold wave
Jan 2, 2018 -23°F Deep freeze to start the year
Jan 30, 2019 -30°F Coldest Chicago temp since 1985; “Polar Vortex” event
Feb 14, 2020 -18°F Valentine’s Day Arctic blast
Feb 7, 2021 -21°F Mid-winter cold snap
Dec 23, 2022 -23°F Pre-Christmas Arctic front
Feb 3, 2023 -17°F Last occurrence to date
What's relevant is not how cold it got on the coldest day of the year, but how warm it got on the coldest day, and how long it stayed cold. If the daytime high is mild enough that an undersized heat pump can keep the house at 72, it will take time for that house to cool from 72 to eg. 63 when the temperature drops overnight. And since the heat pump is still trying to keep the house warm, it'll take a lot longer for the house to cool off than if the heat were turned off entirely.
It makes sense but I just wasn’t willing to trust that with my checkbook, you know? There’s how it’s supposed to work on paper and then a reality where I’m stuck with it.
The regular AC and gas furnace combo works and is cheaper so I stuck with that.
edit: downvoted for noticing that it is cold.