FWIW there is a whole lot of science involved in heat pumps and it comes down to how much you are able to spend and how much physical space you have. A particular heat pump may work down to 0F for example because of it's physical design like compressor size and the number of square feet of coil. Same deal with air conditioning, the hotter the climate the bigger you make the system. Heat pumps don't have a certain temp where they stop working....well they would at absolute zero but that is another story. Lots of trials have been run with heat pumps in Canada's far north and they work extremely well if properly sized. The problem is they are hugely expensive and physically massive so it just doesn't make sense. Most heat pumps in cold climates (like mine) are actually water to air using pipe loops buried in the ground and not the usual air to air that more temperate zones can support (can't do that with a Bolt though) With regard to the Bolt...they only have so much room for condenser coil and can only spend so much money before it becomes unworkable. You can't design the car to work flawlessly in Nunavut and price it as such if the majority of your sales are in California where the heating needs are far less so they go with the option that covers the majority of use cases.