unless they got some garbage not classed for cold climate the only problem when it gets really cold for the heat air pumps is the loss of efficiency. down to 5c or so theyre 3* the cost efficiency of direct electric heating, and they reach 1:1 at about -15 or so iirc. obviously they cant go lower than that. theyre actually good tech, my grandma had one in her house in a region where its -35 during daytime for at a full month per year, usualy two.
Sweden