thanks energy rater La...I will try to respond to all your questions. I appreciate your help.
We had the subfloor in our living room tested to rule out asbestos in it and it was safe, but was composed of a lot of cellulose. It is a type of particle board most often used to insulate walls I guess. I can see it is our walls as well. Our home was built in 1950 and has plaster walls and ceilings. Our ducts are in the walls that lead down to the basement where we have a forced air furnace. The go into the attic briefly for the two vents we have up there. Mostly hard ducts. One small line of flex duct that is newer and small area of insulated cardboard type product for cold air returns to two bedrooms which is also newer. We have return air ducts in both downstairs bedroom and in the living room which is the largest and most efficient one. No recessed lights or fireplace. The mold in the basement was from water intrusion. The basement was finished with drywall, carpet, ceiling and we had to rip it all out before we moved in. The home had set closed up for several months as well, which made the mold problem even worse. (at least we got a good deal on it, ha ha!) It was remediated for the 2nd time this past December 2012 by our air quality guy using a thyme based product to kill the mold and then with an application of a mold resistant sealant over every inch of the basement (mild safe antifungal but cannot recall the name of it.) Testing reveals no mold at all on first and second floors (which really did not have a huge mold issue to begin with per testing.) and basement current mold test reveals a very low amount of mold there. The basement is under the entire first floor, no crawlspace. I have noticed that when the furnace is on, I happened to be reaching up to check something and there are several areas along the basement ceiling where it meets the first floor subfloor and outside wall where I could feel cold air just streaming in from the outside. However, as I said, the basement does not have a high level of dust particulate at this time. Not sure if this outside entry of unfiltered fresh air would affect the overall dust problem though? The attic, which desperately needs a cleaning, may have had cellulose insulation blown in previously but the air quality guy said all he could see was some fiberglass insulation. I am seriously considering whether we need to get a water baseboard heating system as I have read that forced air heating systems are not recommended for those with allergies and asthma. Would like to take care of the dust regardless though. I think it accumulates whether the furnace/AC is on or not, but definitely worse with it on. It kicks on and I start to sneeze and nose starts running. But I can be out of my home for hours and be okay but when I step in, whether furnace is on or not, I start to itch my nose, feel irritated. Thanks for your help!