Question: recently installed an older stove into an existing 5" stovepipe in my home. The stove smokes pretty badly, especially if I use the screen that was with it. I read most of the Q&A on the site and it seems that a 5 inch pipe is way too small for any woodstove. But the flue collar on the stove is only slightly larger than the squished 5 inch pipe - it MIGHT accept a 6 inch pipe at most. I can't see it making a big difference if I increase the pipe size by 1 inch for a length of, at most, 4 to 5 running feet. Any suggestions you might have would be greatly appreciated. Answer: The difference in size between an 5 inch and 6 inch is quite a bit. If I remember my geometry..... pi times the radius squared...so 6" pipe has about 30 sq inches of flow 5" pipe has about 20 sq inches of flow So, 6" pipe hold 50% MORE smoke than 5". It may be be that the oval collar on the stove is designed for 6" pipe to fit over it instead of in it. Also, use furnace cement to seal all seams in the pipe...and also the seams of the stove.