Air Duct Cleaners

how do my air ducts/vents work?

done asked: I have 3 vents in my room (all on the ceiling). One is larger than the other two. That one seems to be taking in air and has a filter. It is square and looks like this: http://www.wholehousefan.com/grill2.jpg The other two are smaller, less than half the size of the first. I think [...]