[nightski]

They aren't readily available in the U.S. and even if you could buy it online or something no local place tends to service them. This is a generalization, so I am sure there are exceptions but it seems to be the case in most places I've seen.

As far as ground sourced those are significantly more expensive. The cost/benefit is not there unless the only factor in your purchase is climate change.

[midoridensha]

Yeah, this is what I was referring to. The heat pumps available in the US only seem to work down to freezing (0C). After that, they just turn on resistive heating, which is very inefficient.