Dark lines along carpet close to the walls
Updated: Sep 21, 2019
Those are often called filtration lines because they are made up of fine particles that get sucked through the walls by negative pressure provided by your HVAC forced air system. I find that hard to believe. There have got to be places sealed better than others, so how do you explain the uniform dirt? And all floors are glued down now anyway. Also why don't I have dust lines on my hardwood floors?
My guess is that the problem is caused by the tack strips underneath which provide ridges and valleys for the dust. Most carpet cleaning heads can't get that close to the baseboards so who's to say where which particle came from? It's all dust. I have also heard some people say it's caused by holes in your air ducts so those should all be inspected. This doesn't make any sense because then the dark lines would only be near the hole in a return vent.
The origin may be disputed but their presence can't be. Here is a video from a company that has the best solution I've seen for getting rid of them. However you do it be careful because those tack strips will rip the meat off your body!