A heat pump uses existing heat energy to heat the car, therefore reducing the cold weather drop. However, you’re looking at a relatively small gain on losses and those losses are only about 20-40% of your range depending upon car and heating use. So, in reality you’d be saving about 10% of your losses, which means you’d have to drive a very long way to recoup the expense of buying a heat pump. If you do very long drives in very cold conditions, the benefits would be bigger, however if you’re toddling around town twice a week, you’d need to keep the car for a decade.
My Ioniq 5 has a heat pump, I still lose about 40 miles of the 270 I get in summer. Without having one without a pump, it’s impossible to be sure I’m saving lots/some/none.
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I'll try to give my honest opinion but am always open to learning.
Mark