Is the dust coming from the ventilation? How did it get in there? Was the system a closed system during the construction phase? That would be my question if you hadn't already had five clean months...
Looked at the two filters today. One was completely clogged with the stuff. It fills up like crushed chalk. Replaced it immediately. According to the plan, it was due only in 9 months.
The system was not in operation during the construction phase, and the ends were covered with a cap.
We need to narrow it down further and simultaneously ask the customer advisor.
The existing system will need to be cleaned, but the origin of the contamination ... just wipe your hand over the plastered (?) wall - white? A friend once had the issue that his interior plaster was crumbling. On the other hand, the controlled residential ventilation system must first manage to suck something like that in. Strange.
Lime! Here they lime the forests in autumn, where do you live? But 9 months for filter changes? I change mine every 2 months and am already amazed. Fortunately, all the construction sites in the area are now finished.