Bought my 45 year old house a few years ago. Had chimney cleaned this year. I have had 2 successful fires and 3 smoky disasters, downdraft? I notice inside the stove at the flue there are pieces of what look like patio block. The chimney sweep said they are shaped like a puzzle, and he had trouble putting them back after the cleaning. I don't know if there is a damper, I would have to remove the big trim piece above the stove (too cold). I wonder if these "patio blocks" are meant to be removed during heating season. Appreciate your help!