[mrinterweb]

I have a Mitsubishi Hyper Heat, and it operates to -13f, which would be unheard of in Western Oregon (where I live). So long as your house is well insulated, you'd likely be fine with a heat pump. Pay attention to R-Value for insulation, but if you choose the right materials, that goes a long way for heat storage.

I know there exceptions in Minnesota where it can get considerably colder than -13f, but I don't know how long those super low temps are sustained. You would definitely need some sort of emergency heating system. An outdoor propane tank (the larger variety) and a propane heater would likely do the trick as an emergency backup. Not great for air quality in your house, but plenty of people use that as their normal heating.