I have a 1925 home in Philadelphia. Just purchased in January this year. It's a duplex with one unit on the first floor and one unit on the second floor. I had a new dusct system installed on first floor unit and a separator to get a thermostat on each floor and send the air where needed. The second floor vents run through the chimneys and the furnace now blows more air than ever through 1st and second floor as the furnace is powerful and focuses and the floor that needs it. The second floor ducts are run through old chimneys. There has been a white sut that has come out a bunch from the old ducts in the second floor. I don't know if the ducts in the chimneys are corroded or it is just old dust coming out. But it has come out in spurts over the past month. leaving piles of dust. Any ideas or suggestions? Thanks!