Is preparing for an air conditioner worth it?

We have 3 split units on 150m². One in the living/dining/cooking area (open)

So are those then 3 outdoor units? I currently lack the imagination of where I should hang them on the upper floor. Although I forgot that I still get a carport under the bedroom, where I could definitely install something within 3m distance to the property boundary in the building window.

I have read so much about heat pump stuff – still, I currently lack any foundation for it.

We have the ventilation on the roof, integrating it there sounds too good to be true, but at least we have a condensate drain.

are those then 3 outdoor units?

No, one outdoor unit. Above the door could be a good place, if possible as centrally located as possible measured by your places of stay in the house.

2019/2020 was similar. The air conditioning supposedly would have resulted in a recalculation for the KfW. I just don't remember if that was just said or if it was actually the case. We then decided against it. I'm also keeping my hands off retrofitting for now, no desire to risk losing the subsidy because of it.

Last summer we bought a portable split air conditioning unit (Remko, about 1200€), which I hang out of our bedroom window when needed. I built a bracket for the blind rails and then place the outdoor unit outside on the bracket. Blinds down, window ajar, blanket around it, done. It blows into the hallway, the cold then falls down the stairs and cools the entire house to comfortable temperatures.

Not premium, but completely sufficient for the hot days.

The question is what you do with the thing the remaining 300 days of the year if you don't have a basement.

are those then 3 outdoor units? I currently lack the imagination where I should hang them in the upper floor. Although I forgot that I will still get a carport under the bedroom, where I could definitely attach something about 3m away from the property boundary in the construction area.

No, only one outdoor unit on the carport with us. The indoor units can practically be installed wherever you want, as long as you can route the pipes there. We have them above doors on the ground floor, and on the upper floor in the hallway relatively centered under the ceiling.

The question is what you do with the thing for the remaining 300 days of the year if you don't have a basement.

My wife heats with it because she likes the warm air ;)