AC filter gets dirty after 2 weeks - duct need cleaning?

[George P.]

Just wanted to see if anyone had this problem, too.
I installen an AC filter (rating 800 or something) and after 2 weeks I checked it and discovered that it is very dirty. Is that the duct dirt that I need to address or something else?

Thanks!

[Steve Babiak]

Just some random thoughts to be condsidered...

The AC filter is installed on the return side of the ductwork, just before the air handler. That means the air coming from the rest of the house contains the dirt you are seeing (just for you to understand the source).

There is some national body that deals with ductwork cleaning; they recommend that ducts be cleaned (both return and supply ducts) every 4 years or more frequently.

Have the ducts been cleaned within last 4 years? If not, then it's over due for cleaning.

Before cleaning, I'd make certain that the whole house was not supplying that dust that is accumulating in the filter. Recent repairs to things like drywall or woodwork or flooring that involved any sanding would contribute dust. Also, find the return vents and see if they are filthy, and whether they are actually sucking air from the room (by holding tissue in front of the vent and seeing if there is suction). Any filthy vent that is found points to a room where I'd give this added attention.

Leaving windows open might also contribute dust from the outside.

Sometimes the return "ductwork" isn't what you might think (it is not really sheet metal within walls, it just uses the space between studs and floor joists with a cover of metal or foil). This allows for air infiltration into the returns from many sources (not just through vent openings). Sometimes carpet can get really filthy where a return isn't tightly sealed, because the room air gets sucked through the return's gap near the floor.

As an aside, much of the dust that gets newly created is skin being shed off by the occupants.