Mine is air to water, so all you really need is someone who can plonk it there and then plumbers to do their stuff.

Vast majority of the work for mine was replacing the entire central heating system, but that would have been a good idea even if I wanted a gas boiler because of how old and shit it was.

Now my cat can sleep on top of the large double radiators around the house. Tbh that has to be one of the best features of it, flow temperatures low enough that a cat can comfortably sleep on it.