Thanks Jim and Steve for your input. The townhouse is 22 years old but the fireplace has not been used much during that time. The chimney is clean and I did clean the area where the damper sits when it is closed. We are considering a chimney sweep and cap. If that doesn't help I guess we will seal off the fireplace behind the glass screen. There is a hill behind our t/h and we think perhaps this could be one of the problems - the flow of air off of the hill.