I wish I had known about heat pump water heaters before I replaced mine about 6 years ago. Heat pumps for home heating and water heating should be mandated by building code here in mild California. It’s the perfect environment for them. Unfortunately, I use heating so infrequently during our “winter” that replacing my perfectly functional furnace is not really worth it. So, instead I started using the heat pump mode on my portable air conditioner (yes, I know, but also used infrequently) to provide just those couple of degrees of heat that I need. It’s not bad, with a COP of 2.7.