I have an LG mini split system as my only source of heat. Outdoor temps went down to -18 with wind chill of -39 here and I had no problems at all. This is the second winter with these and last year also went down to -15 at least once and it was fine. These units are rated to -13F. When it gets down below zero they work harder but they still provide full heat. I turned them up to 74 on Friday and by Saturday morning I noticed the bigger unit, that had a much bigger area to heat, only kept it up to around 70, but that’s more than enough. I assume the larger indoor unit shut off occasionally as the outside unit probably couldn’t produce enough heat to keep sending hot air in and the inside unit shut off to avoid pumping in cold air, but I don’t know anything about them really and that’s only a theory. In any case, 70 degrees indoors when the wind chill was -39 outdoors isn’t bad at all I’d say.