As I wrote above, the only time I've seen mine falter was at 6F (last year's mega freeze in Austin). It occasionally gets to 13F-15F in the winter, and the heat

As I wrote above, the only time I've seen mine falter was at 6F (last year's mega freeze in Austin). It occasionally gets to 13F-15F in the winter, and the heat pump works in this environment without having to resort to "aux heat". I'm sure it's become rather inefficient, but it does work.