Undersized hippopotamus formulated on Sunday :
But what if the kitchen goes down to 10C at night? Who heats their kitchen
in winter at night?

Very unlikely here, we are too well sealed up and insulated. According
to my log for yesterday and last night. Maximum temperature in the
kitchen 20.2C, dropping to 17.7C at 7am. Outside fell to -1.9C at 7am.
The heating system was shut down at 22:30, we retired early due to the
25 hour day.