Yes it is. I don't have a large dataset of exact temp conditions and charging curves (Elon certainly does though, someone go ask him!) I can tell you if the outdoor temps are below 15F a standard outlet has negative net energy input.
A heat pump solution would certainly be more efficient, knowing Tesla I can only assume it's peltier junctions.
All the hype about the efficiency of an EV goes out the window when it's blowing 16kwh+ a day just keeping the battery above freezing.
A heat pump should be able to do a lot better.
Also you're probably only going to get 16 amps of actual draw on a 20 amp circuit.
Not necessarily. In Minnesota, people often put sandbags in trunks/truck beds to get better traction in Winter. Also, one has to be careful when following semi tractor-trailers, as in some Winter conditions, they actually have a shorter stopping distance than your car.
Putting a pair of sandbags in the back-end of an unloaded rear wheel
drive pickup is not the same thing as driving a 9000 lb sedan.
The weight of the battery pack is great for traction in warm / dry conditions, but when driving on ice that weight is just momentum sending you sliding into snow banks.
After a bumper or body panel gets ripped off during the inevitable extraction from above mentioned snow bank, expect to wait 6-9 months for the most basic of body work.
The self driving is an absolute clown show in anything but perfect conditions (mounting evidence it sucks in perfect conditions too~)
Nothing in the world excites me more than expensive nerd toys with electric power trains, but as a Minnesota native I'll take a $900 rolling trash can beater car over a top of the line Tesla six months out of the year. There is a very valuable lesson in observing the legacy auto industry existing in Michigan where the winters get very cold and cars need to perform with snow or ice on the roads. Meanwhile Tesla mostly engineers their cars to be good at driving from LA to SF and back.