Mini-Split, Cold Climate Heat Pumps (CCHPs) are single room heaters, not a whole-house, central heating system. They are well suited to smaller homes with an open floor plan.
Why is it so difficult to get a clear answer about the exact cold temperature limitation of CCHPs?
Because the answer will depend on: 1) Your geographic location, which determines your design day . 2) Your home’s heat loss as determined by the integrity of your building envelope (see How Cold is Too Cold for a Cold Climate Heat Pump?) and 3) The performance characteristics of your particular CCHP (see At What Temperature Will a Heat Pump Become Ineffective?)
During coldest winter temperatures auxiliary heat will be necessary to maintain indoor comfort.
The basic principle is that CCHPs become less efficient (and less effective at heating your home) as outdoor temperatures drop. Put simply this is because there is less heat in the outdoor air to convert to indoor heat. If your electric bill is too high, or you have cold areas around your home, here are your options for single-room auxiliary heaters: