Currently running metal chimney through ceiling. Will be converting to a thimble thru wall with a new interior masonry chimney on the other side of the wall. Don't want to mess with the bricked overlaid heat shield behind the stove. If my installer thimbles through above this shield, the pipe will be about 2' below ceiling where it goes through the wall. Hard to say until they tear into the wall. Could be a little less. What's the minimum allowed from ceiling down to pipe? Am guessing 24". If so, is there insulated pipe which would allow you to get closer. Thanks for your ideas.