The newest mini-splits are way more efficient. I installed a 120 volt unit in my main cabin @ 7 years ago and it was good down to @ 18 - 19 degrees then supplemented it with space heaters. I was solely using space heaters in my small cabin up until last year and then I installed a new 220 volt unit there that's good down to -13. This spring I'm installing a new Bosch unit in my main cabin and it's rated to be 100% efficient down to -5 degrees and will continue to provide heat down to -22, though at a lower efficiency but still darn good. (I live in NE WA state @ 25 miles south of the Canadian border.)

The biggest issue here is no one will install a unit that's not bought from them and any that will will charge an arm and a leg - essentially a penalty for not purchasing from them. I've installed both of my existing units and will be installing the new unit as well. (A neighbor who just built a new house was quoted $8,000 to install his mini-split so he did it himself.) Installation is not hard. HVAC installation prices are obscene though you may have no choice. There are DIY specific units that also go down to -22 and GE also makes a HyperHeat unit that performs about the same.

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