Is a ventilation system cost-effective? Does it save money?

I assume that you installed the decentralized system during a renovation. It is clear that the threshold here is lower than running pipes throughout the entire house (as with a centralized system). Of course, this comes at the expense of efficiency.

I can only agree with my predecessors that the calculation here is not quite that simple and depends on too many factors to make reliable statements. If we assume that in the end (perhaps after about 15 years) you break even, it has still been a good investment, because you have significantly better air, no mold/pollen/dirty air in the house, and very likely have done something good for your health.

I assume that you installed the decentralized system during a renovation. [...], because as a result you have significantly better air, no mold/pollen/dirty air in the house, and very likely did something good for your health.

Decentralized is better in the sense that every piece of duct is also a breeding ground for everything that the filter lets through. See

Another point besides mold prevention and heat recovery: There is a residential area nearby where there is definitely above-average fine dust and soot development. I know a few people there. Those who built or live with ventilation (whether central or decentralized) have completely inconspicuous walls. Everyone without ventilation has to paint the walls every few years because otherwise, they really look worn out.

I don't know how significant this effect is in a normal residential area. Certainly much less. However, I found it impressive and can imagine that depending on the location, one might also have to paint the walls less over the years.

I don't know how big this effect is in a normal residential area

Living in the countryside, I can confirm it. Much less dust in the house - you still notice when the tractors are in the fields and/or straw and hay are being made.

Well, that might fit if you built in the London East End of the 1870s.

On the topic of whether it’s worth it... is it worth building a new single-family house? Is an energy-efficient renovation of an existing property for 200, 300,000 EUR worth it? Nope. For 300,000 EUR you can heat for 50 years at 6,000 EUR per year.

The advantage is that you hardly have to ventilate anymore. The disadvantage, especially with the decentralized solution, is that in summer you constantly let in the heat and especially the humid air, while in winter the air is usually too dry.

The disadvantage, especially with the decentralized solution, is that in summer you constantly ventilate in heat and especially moist air.

Is it completely different with central? Even decentralized there is a crossflow heat exchanger and bypass.