Comment by munk-a

Ventless temperature control units are extremely popular there so it's probably not an unwise investment but you're not really ahead of the curve. The construction of most European buildings[1] lends itself poorly to anything that requires knocking a hole in a wall but the systems that can exhaust heat through water lines are usually quite reasonable to set up.

1. Though this is significantly less prevalent in Spain due to a lot of reconstruction happening after the civil war - that isn't to say buildings there are perfect, they just have different problems than the classic German 30cm thick stone wall.