Why is the furnace filter alarmingly clean


I have central air and heat at my appartment I moved into about 6 months ago. Today I decided it was probably long past time to figure out how to change filters in the furnace so I poke around until I find the slot where the filter is.

However, when I pull it out, it looks like it was installed yesterday. It's perfectly clean, doesn't have a speck of dust on it. I've been using it for the past six months so I highly doubt it should look this way.

It's a really cheap fiberglass filter (Ace hardware brand), could it be defective? Could the landlord have placed it in the furnace incorrectly? Could something be wrong with the furnace? Or is this expected?

My last apartment had a permanent filter that had to be pulled out and washed every couple weeks or else it got filthy. Please help me figure out what's going on here.

Best Answer

The thin fiberglass filters (usually blue in color) are referred to as "rock catchers" by some of my fellow construction friends. They don't do much to catch dust, but they'll stop anything large from damaging the blower. It's entirely possible that it was changed before you moved in and just hasn't had enough time to catch the little dust that it will catch.

If you really want to filter the air, you'll want to upgrade this to the pleated filters. Just remember that these do require changing on a more regular basis.

The other possibility is that you may have filters at your return vents doing a majority of the air filtering, and the filter at the blower is simply redundant.