I was wondering if I could be having a bigger problem then what I think. I have to change out my air filter in the house about every 3 weeks. It is black/gray and thick with dust all over it every 3 weeks. The house was empty for a little while and not sure if I missing something. Want to make sure its safe for me and my kids. I have the ductwork cleaned, the a/c unit serviced and no one said anything when I showed them the filters. Now I noticing dust blowing onto fans and a 3/4 wall where vent blows onto. Thanks for any help anyone can offer.

Filter catching the dust is good. If the house is old, the time line of filter change is about right. Each life style of home owner will change and so with the filter change. Investigation of all ducts is the place to start. Supply and return.