I have a house that was built somewhere in the 60's. I purchased the house (cape cod, unfinished attic and basement) last year after it was abandoned and someone renovated the major items. Replaced before I purchased the house: roof, all windows, electrical, furnace (not the duct work), hardwood floors.

After I purchased the house, I ripped down a few walls, added crown molding throughout, high hats in a few rooms, added additional outlets, had the duct work cleaned and a microbial spray and painted the entire first floor (all walls and ceilings, trim, etc...)

Currently my attic is not insulated, which I am in the process of pulling out the t&g flooring, vacuuming between the floor joists, installing R-19 (2X6 framing) and putting down 3/4" plywood.

Now my issue, the house is VERY dusty. I have a cleaning person who comes in and cleans the house (900 sf), and the next day you can see dust on all the wood furniture. My attempts to resolve the problem, as noted above, the ducts were cleaned, I have vacuumed the entire basement three times, I have replaced the four return ducts and replace the HVAC filter (merv 10) every month. I went as far as covering the return grills with a cheap oversized filter in each room and within a few weeks it was dark gray from the dust.

As far as I can see, the ducts down stairs are all sealed with no leaks. I am at my wits end, and am looking for any suggestions.