What this video covers
The clip covers a specific and surprisingly common installation fault.
A dryer moves a large volume of moisture out of wet laundry. If the vent terminates in an attic or crawl space rather than outside, all of that moisture is being pumped directly into the building fabric, load after load.
The takeaway
Follow your dryer vent to its end point. If it does not exit the building, that single fault is generating more moisture than anything else in the house.
Read the full written guide: Dryer Vent Mold Prevention.