> Contrary to popular belief, modern cold-climate heat pumps can heat a home efficiently even when the temperature drops below -10 degrees. At this temperature the best cold climate heat pumps are still more energy efficient than furnaces and boilers

This is maybe true if your house is insulated to Scandinavian standards. Our heat pumps here in Maryland get iffy around 20 degrees in our circa 2005 house. We have a nice oil burner heating a hydronic system that does a great job at that point.