Initially, we thought it might be the furnace sucking smoke down the ash trap that empties in the lower fireplace. We plugged up the ash trap, and that did not solve the problem. Based on the repair person's report, there does not seem to be any damage to the fireplace. It is pulling air in through the basement chimney. The fireplace dampers may be closed, but they are not air tight.
Smoke going out the first-floor chimney is sucked into the basement chimney.
Put on rubber gloves and apply the cleaner with a sponge. Wipe off with a squeegee. Clean up any drips with a 100-percent cotton towel. Include your name, city and phone number with question.