John I was thinking: Is the Harman coal stove vented in the same flue as it was in the cellar? Does that flue also have an cleanout door? Tell me it is blocked off and the ash dump door sealed? If not, then this could explain and agrevate the over draft situation. If the original outlet is left open in the basement all kinds of air is getting sucked in causing the overdraft. We see the front setup how did you connect the connector to the flue Do you have a liner? is it connected is it a tight connection. Just thinking about your situation trying to see if something simple was missed.