Oxford study proves heat pumps triumph over fossil fuels in the cold::Published Monday in the scientific journal Joule, the research found that heat pumps are two to three times more efficient than their oil and gas counterparts, specifically in temperatures ranging from 10 C to -20 C.
Would depend on how well insulated it is, but yeah since homes aren’t exactly built to be air tight there’s realistically an upper limit to the temperature delta you’re going to be able to achieve. Ultimately the question isn’t how hot/cold is the inside/outside of the house, but how big a difference are you looking at between those two.