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You can them however you want pretty much. They can heat the water plenty enough, and if you choose the right one you won’t notice any difference other than a lower powerbill.
How hot can this get my water, or are they only meant for forced air?
You can get heat pump water heaters, they can get sufficienrlt hot, but are kind of slow though.
Not necessarily, you can get air/water heatpumps that outputs way more than a normal hot water tank can handle. They are expensive though.
You can them however you want pretty much. They can heat the water plenty enough, and if you choose the right one you won’t notice any difference other than a lower powerbill.
And you can use the cold air to cool down your place.