District heating KfW55 - KfW70 costs Ventilation system/Exhaust system

Expensive in KfW55 is unfortunately not the material, but the name and what the general contractor charges for it. Triple-glazed windows, slightly thicker ceiling insulation, and facade insulation practically cost almost nothing extra since the work has to be done anyway. That’s why it can still be worthwhile with individual contracting or doing it yourself. If central controlled residential ventilation is used, I would also take it with heat recovery. Otherwise, in case of doubt, the cold outside air is distributed everywhere and destroys the only financial advantage of controlled residential ventilation.

I don't have much experience in this area but I believe that to put a ventilation system with heat recovery into operation, the pipes must be installed. Apart from the resulting costs, I am afraid that after 5 or 10 years, fungi and bacteria will form in the ducts that can never be completely cleaned out again.

It is not an air conditioning system, where should the fungi and bacteria come from?

There are two options for controlled residential ventilation with heat recovery: decentralized and centralized. In decentralized systems, a fan with a heat recovery function must be installed in individual rooms. Many say that it becomes too noisy. In centralized systems, pipes must be installed for the transport of exhaust and supply air. It is often criticized that after years germs CAN form there, and it can never be cleaned as well as before. I don’t know what it costs, but I estimate it should cost over €10,000, and when does the whole investment pay off? Because it has to be maintained and whether it never breaks down! Isn’t that so? I will still talk to our property developer, but I plan the following: old air will be sucked out from the kitchen, bathroom, and utility room (fan with electricity or wind-driven) and fresh air will come from the bedrooms and living room through valves with filters and sound insulation. It should run when CO2 or humidity is too high. The valves will not allow much air through if there is a large temperature difference between the house and outside. What do you think?

That is exactly our system. The simple solution. Should also work.

Do you happen to know if you can also get KfW55 with it? As you wrote, it is about low-interest loans and of course better thermal insulation.

We also build KFW 55 with decentralized ventilation (exhaust air: bathroom, WC, kitchen). Supply air elements in the rooms: Lunos ALD-S (sound-optimized) with pollen filter. Possibly additional soundproofed external hoods.