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As far as clear, if the dew point is not undershot everything is fine... where and when moisture precipitates can be wonderfully checked in an Hx diagram. What if the ventilation system is in the unheated basement (15°C) or in the attic without insulation? Is that then a defect? I have already seen myself with some providers that devices were installed there.

Has anyone here who has had a controlled residential ventilation system for a longer time ever checked the exhaust air ducts and can confirm / relativize this statement (contamination does not occur at the intake but through house dust, etc. in the exhaust air ducts) or refute the whole thing?

Cleaning of the ducts (is necessary with regular filter changes about every 10 years) costs around 500 euros for a "normal" single-family house

However, decentralized systems should only be installed in rental buildings or during modernization... why settle for a half solution when the finished product is available...

Can anyone (possibly you @Mycraft) confirm or disprove the statement regarding contamination of the exhaust air ducts? To me, it sounds plausible since (probably) there is no filter upstream before the "air extraction" (in my opinion).

One of the reasons why we decided on the decentralized solution is the price. Our decentralized system will cost about half (possibly 40%) of the central one. (In my post on page 2, I exchanged information via private message with 2 members who have a controlled residential ventilation system regarding prices). It may not be representative, but it is a reference point.

As long as the dew point is not undershot, everything is fine... where and when moisture precipitates can be wonderfully checked in an Hx diagram. What if the ventilation system is located in the unheated basement (15°C) or in the attic without insulation? Is that then a defect? I have already seen this myself with some providers where devices were installed there.

Yes, that is a defect.

Yes, that is a defect.

Addition: Unless the system and pipes are properly insulated.

Very interesting @Mycraft. Thank you

If I understood correctly, the writer installed the system themselves or was primarily involved or at least planned it. They carry out the cleaning (except for the forgotten pipe) annually/biennially. Quite a bit accumulates each year.

Since I don't have much experience with central systems - are the pipes and components installed by a company in a new building just as (easily) accessible as in this example? I thought I once read that the pipes are often installed in walls/ceilings, etc. Regardless of the fact that companies may not always practice the simple and straightforward construction method.

No no, the pictures show 7 years of continuous operation...the heat exchanger further down then 14 years...he only changes the filters annually...

The laying of the pipes is a matter of planning...the ventilation company usually doesn't care how the pipes are laid later...therefore, as a builder, have the pipe layout explained before installation and express any wishes if necessary...

But I can get to pretty much everything on my system...for example, two of my exhaust ducts are only about 2 meters long, so cleaning later will probably be relatively quick in that area...