Yes, when you get down to -20 C or so, the efficiency drops below 1. Depending on the model. I think air heat pumps are more common due to their low price. The

Yes, when you get down to -20 C or so, the efficiency drops below 1. Depending on the model. I think air heat pumps are more common due to their low price. They are easy to install and work well as a complement to other heat sources. Geothermal is popular too, but the installation cost is significantly higher.