Depends upon your groundwater temps I suppose, they’re going strong in residential here. Going strong in RV’s too, much less power draw plus the space for the tank is freed up for storage or other use, both of which are big pluses in an RV, especially one set up for dry camping without utility hookups.
On of the biggest selling points for the tankless heaters is the “instant” hot water claim. But that’s if you have the unit in close proximity to the tap. That’s not always doable, and there are numerous taps in most houses.
We put in a ground source heat pump system when we built new in 2002. Incoming water temp in the Missouri Ozarks is around 59 F.
Sytem has four 200 foot wells under the driveway. House has heated main floor via a storage tank in the furnace room, heated via the geo-thermal...