A heat pump water heater never made sense to me: Because it pulls the heat from the surrounding air it makes the air in that room cooler. Which the main heat system has to re-warm up. So it's just making your main house heating system work harder, you might as well just power your heater with gas or electricity anyway.

A house heat pump pulls the heat in from outside, so is more efficient than a straight electric heater (there is almost always heat outside even when cold). Geothermal makes optimal sense as it pulls the heat from the ground around your home which is warm-ish even when it's truly cold.

But I don't see the logic in a heat pump water heater. Even if you exhaust the cold air outside it still pulls inside air through it which creates a vacuum in the house which just pulls air in from the outside (which is um... cold). So wut....