coalkirk wrote:The screws are essential, you don't need to goop except maybe wher ethe pipe connects to the boilers thimble.
looking at the light coming thru where the pipe seam is, no amount of screws are going to seal that.
This black pipe is very thick and the seam is very thick putting a screw on each side of that seam will not close up that hole.
if you have a very tall chimney with extra draft, then you can afford to lose a little draft thru the poorly fitting chimney pipes.
I have a ranch with the minimum height chimney so I don't have any extra draft that I can afford to lose.