Conveniently, the USDA publishes a map specifically suited to this question: https://en.wikipedia.org/wiki/Hardiness_zone#/media/File:2012_USDA_Plant_Hardiness

Conveniently, the USDA publishes a map specifically suited to this question: https://en.wikipedia.org/wiki/Hardiness_zone#/media/File:2012_USDA_Plant_Hardiness_Zone_Map_(USA).jpg https://en.wikipedia.org/wiki/Hardiness_zone#/media/File:201... Anywhere in yellow (8a) or warmer can use a heat pump, no problem -- the best heat pumps go down to about 0 F (-20 C) intake temperature. That's about half the country. With good construction it should work down to 7a (light green), and this transition zone includes DC/Philly/NYC. The darker green and blue regions need more advancements in the tech to rely on them. But it's mostly the US that has this problem. By contrast, practically everyone in Latin America / Africa / Southern Asia should have no trouble switching to heat pumps (if they need heating at all, i.e. Zone <10): https://upload.wikimedia.org/wikipedia/commons/a/a7/World_Hardiness_Zones.png https://upload.wikimedia.org/wikipedia/commons/a/a7/World_Ha... Since many of these countries are industrializing during the efforts to mitigate global warming, hopefully they will get heating right sooner rather than later.