By installing a heat pump in his house in the hills of Oslo, Oyvind Solstad killed three birds with one stone, improving his comfort, finances and climate footprint.
I have a heat pump and a gas furnace. The furnace is only used if the heat pump isn't able to heat and that's typically around -25c. This keeps me off gas most of the winter.
I live in NC where a very cold day is +20F and I have to say I do not feel my heat pump keeps my house very warm. Maybe l just have a very high expectation of what a warm house feels like, but based purely on comfort I would not pick a heat pump. My house is only about 7 years old, so maybe the technology has improved since then?
it’s just physics, and at sub-zero temperatures the air heat pump simply switches to electricity
it’s another matter if your pump uses the ground or a well, then of course it will work at any outside temperature