Heat pumps are great and are the current go-to for most home energy discussions, but they require a narrow delta between two close areas, basically a ready area

Heat pumps are great and are the current go-to for most home energy discussions, but they require a narrow delta between two close areas, basically a ready area to dump/acquire heat energy in order to warm/cool another area. They are useless in most small and all ad-hoc heating situations. For instance, there could never be a "desktop" heat pump that you can just plug in and blow hot air in room. There will never be a heatpump-heated kettle. The closest thing to a portable heatpump are portable/in-window air conditioners. They can be literally reversed in order to suck heat from outside and dump it into a room, but at that scale they are not very efficient. A heatpump oven might be theoretically possibly, but would be wildly impractical and probably very dangerous to be around.