The well pit definitely got cold during those nights when the air temperature dropped well below zero:
Match that against the attic air temperature:
The well pit has two vent holes made from old-school fluted steel downspout pipe embedded vertically in a half-foot concrete slab. They’re maybe five feet apart and the southwest hole seems to be the air inlet:
The northeast hole must be the outlet for all that ground-warmed air:
The logger hangs from the string entering from the center left, with a ring hung over an abandoned hose bib rising straight out of the concrete.
Surely it’s been that cold before without freezing the pipes, so I won’t worry too much…