Pure n=1 anecdata. Last winter I was on vacation and saw via Nest app that my boiler died. We have a heat pump that 99% of the time is used for AC, and sometimes for supplemental heat. We only have them in the main rooms, so things like bathrooms and such receive no benefit from them. The unit outside is a Mitsubishi Hyperheat. I logged in and turned the units on just to keep the house from freezing.
BUT during that trip a giant blizzard struck the area. I forget the air temps and they definitely weren't double digit negative but it was quite cold with high winds and a lot of snow to boot. They held the house together well enough in our absence.
BUT during that trip a giant blizzard struck the area. I forget the air temps and they definitely weren't double digit negative but it was quite cold with high winds and a lot of snow to boot. They held the house together well enough in our absence.