This entire thread is full of myths about heatpumps. The reason Tesla does not have one is because of laziness.
Modern mass-production heat pumps have design temperatures down to -13F (with performance tapering off below that, but not stopping), with reversing valves so the same unit is the AC in the summer. Even with performance down to -13F, you can keep the resistance heater for backup heat, it's a tiny tiny unit, like 12"x12"x3"
edit - and the conversation about volume is also bunk. Entire homes are heated/cooled via air-source heatpump in very cold climates.
Modern mass-production heat pumps have design temperatures down to -13F (with performance tapering off below that, but not stopping), with reversing valves so the same unit is the AC in the summer. Even with performance down to -13F, you can keep the resistance heater for backup heat, it's a tiny tiny unit, like 12"x12"x3"
edit - and the conversation about volume is also bunk. Entire homes are heated/cooled via air-source heatpump in very cold climates.