I live in a 2200 sq foot house in Phoenix built in 1995 with all tile floors, A/C, heating, and multiple fans. I have no pets and clean once a week. The amount of dust I retrieve from the floor and see on top of shelves etc is amazing. Where does it all come from? The dust on top of shelves is a very light brown color and ulta fine, wheareas the dust on the floor form into little grey dustballs. I change the a/c and heat filter every month with the cheapest filter since I was told they don't block as much airflow and trap more dust. I have no pets and my dryer vent has no leaks. I notice more dust during the summer months when the A/C is working at least 12 hours a day here in Phoenix. I'm dusting every week with a Swiffer type product and pick up a lot of dust. As an experiment, I left town for two weeks this summer, cleaned thoroughly before I left, turned off the A/C and upon my return, I found very little dust. I air out the house during late fall and winter by leaving the front and back doors open in the morning for an hour to let in a cool breeze. Not much dust comes in over a weeks time. It's mainly in the summer for some reason. I was thinking it might be the a/c ducts or perhaps the old insulation. The insulation in the attic of this house is the kind that looks like hundreds of little hairballs were placed in the attic. I think it's called loose-fill insulation-not sure. It's definitely not board insulation that looks like at think roll of carpet pad that's fastened to the attic walls. My windows are single pane. I live next to a large grassy public park and golf course but all the homes around me have desert landscaping. You could get your car washed and a couple days later, there could be a tiny film of very fine dust on it. I think my house is well sealed. I'm just curious how it get in, in the summer. Any ideas on how to reduce dust?