Question: Just had a certified sweep clean and inspect my masonry chimney. He used a video system to check for damage. We found a few small voids in the grout between the flue tile joints, and one crack running vertically from the bottom to the top of the third tile up. My chimney is approximately 18'high, with nine (13" x 13") tiles.My question is, how serious is this condition? The one crack didn't seem to be separated very much at all. Should I install a stainless steel liner, if I'm installing a Wilkening Heat Exchanger? Or an insert liner if I decide on an insert?I have asked questions in the past, and want to thank you very much for all your help. Answer: It would be my guess that the great majority of masonry chimneys have cracks and voids similar to yours. Clay tile is very fragile and houses shift and settle. Based on your description, I'd guess that the Wilkening Heat Exchanger would be fine. If you do get a different insert, you might consider lining both for performance and safety. In addition, a liner makes it easier to sweep the chimney. In summary, I doubt that your described condition represents an immediate fire hazard.