I have a geothermal heat pump. I am not in the US (3 phase 400V electricity is common here). I'd suppose nowadays they should be pretty standard. Some heat pumps also work both ways, e.g. they can heat and cool.
As an extra benefit the heat pumps have lower maintenance, risk.
(responding here, but applies to all currently at this level)
Ahh, now I see where there might be confusion. Heat pumps that operate on electricity are increasingly common in the US. Most of them are air-to-air, but some are ground-source. What I'm claiming are rare-to-non-existent are residential heat pumps that operate directly off of natural gas, using an ammonia absorption process, with no electricity involved.
Arguably 'freemint' was saying that it's more efficient to generate electricity centrally using natural gas and then distribute this electricity to power heat pumps than to burn natural gas for heat at each site. Yes, likely. My surprise was that I thought he was claiming that non-electric natural gas powered heat pumps were currently available to residential consumers. I knew this style exists (see the link I gave above) but I've never seen one in operation.
As an extra benefit the heat pumps have lower maintenance, risk.