Recent conversations with net-zero builders indicate that ground-source pumps are being pushed away for most single-family residential projects in favor of the

Recent conversations with net-zero builders indicate that ground-source pumps are being pushed away for most single-family residential projects in favor of the new-generation, highly-effective, cold-climate air-source heat pumps. Mitsubishi and Fujitsu seem to have a large lead in cold-climate air-source heat pumps that are rated effective to -13F (anecdotal reports greenbuildingadvisor.com indicating effectiveness down to -20F). Yet, talking to builders, contractors, friends, and family, you will often still hear old tales about how "heat pumps aren't effective below 40F". Heat pumps come in a wide range of flavors. It's clearly possible to heat your house exclusively using an air-source heat pump in most USA climates.