It doesn't have a trap door. Is a flue the same as a damper? If so it doesn't have one. The chimney company was supposed to install a damper and clean it. The first guy who came didn't have what he needed. A second guy came to do it and he said what the first guy was going to do was silly and he recommended leaving it alone or ordering one that fits in the bottom of the chimney from the internet. I couldn't find them. I'll do a search under flue. Neither of them cleaned it. Thanks, you have given me some hope!