[meindnoch]

>Air conditioners could do it too, right?

Some heat pumps do this. E.g. Panasonic Aquarea EcoFleX. When cooling the house, the domestic hot water tank is used to dump heat into (up to a certain temperature).

[SoftTalker]

Years ago I worked at a fast-food restaurant and they used all the heat from their ice makers to pre-heat water for washing up.