I believe it's fair to say that every situation is different which causes certain outcome. Knowing masonry chimney is by far the best for coal burning, some look at SS 304 316 and black pipe. Here comes the debate on SS or black pipe, but you'll need to remember why some get better results then others. Location of piping from what I've been reading is a factor, wet basement,damp area your going to have issues. Poor maintenance of not cleaning fly ash out of pipe during shut down season. The members who has good results do they burn year round, dry location,good maintenance? Friend used SS chimney and one season it looked like Swiss cheese, following season he decided to just get black stove pipe. Black stove pipe after one season looks new, so you ask why. First year he wet coal with water to keep dust done, now he uses oil.