Akoaka, I think we start to get condensation at 35 F. It turns to frost below 30. Interestingly, the amount of frost does not increase as temps drop from there. The amount of frost we had our coldest night last winter (-23F) was about the same as in more moderate sub freezing temps. I agree with what others have said about outside air circulation and leaving shades up. These strategies help with the windows but not the window frames.
Brian, I suspect you are right. Those of us using this equpment in the winter are a small minority of the market.