You can get heat pumps that work in colder weather, those are very common here in Canada. Certainly plenty sufficient for NYC. You can also mix and match a var

You can get heat pumps that work in colder weather, those are very common here in Canada. Certainly plenty sufficient for NYC. You can also mix and match a variety of backup/supplemental heat sources (only some of which make sense in an urban context), and of course a ground source heat pump is another (expensive) option for very cold climates.