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Adding a small wood burner into an existing extra chimney in the basement. It has 8 inch clay thimble, stove is 6 inch.

For draft purposes, is it better to using reducer to convert 6 in stove pipe into 8 inch to go through the thimble, or run 6 inch through the thimble and then close up the air gap with (furnace cement/rock wool/etc?)

This was going to be for supplemental heat for new office, but with coal around $400/ton going to be burning more often.

Tightly packed fiberglass insulation would allow so little air thru it with the tiny pressure differences in our chimney systems that I doubt there be a measurable benefit between the two. Although, using an adapter might look better. Just my opinion.

I hate to say it---BUT---I'm with Lee!!!!!!!!!!!!!!!

That's the part I'm trying to figure out. That chimney used to under perform 40 years ago, but we added a few chimney block to the top when we moved back and bought the house. I don't want it to be too slow or hard to light before warming up the large outdoor masonry and clay liner chimney. It's about 27 feet.

I'm wondering if the velocity in the pipe is a major factor of draft? The horizontal 6" in to 8 in adapter route would be nearly 2X volume, so does this drop to 1/2 velocity?

Is there much difference between changing diameter in HORIZONTAL, or the VERTICAL as it dumps into the inside of the chimney liner instead?

I've never compared them and don't remember reading about a comparison?

FYI. If 6 inches straight through and dumping inside the chimney, I'd probably do something like this video and use some ceramic insulation between the 6 in and 8 inch, then maybe use some furnace cement to "cap" the gaps at the end.

https://youtu.be/yfY3QI3hIwg

freetown fred wrote: ↑

Fri. Nov. 25, 2022 11:40 am

I hate to say it---BUT---I'm with Lee!!!!!!!!!!!!!!!

What is happening? It's like the laws of the universe have been suspended. Lol

I run 6" out an elbow off the stove, 3' pipe up, elbow 6' horizontal into 6"to 8" adapter through 8" tile into 10" ss liner.

CCW,
I had a Jotul with a 5" flue into a 6" adapter into a 8" adapter into an 8" thimble of a 8" x 12" clay chimney liner, burning wood for years.........no problem, and easy to run the brushes through about every 6 weeks.
Cheers

Thanks for all the replies. If I can get 8" piece of pipe into the thimble without too much trouble (some pipe seams are pretty flat), I'll go with that original plan. Much simpler and if not going to cut the draft, all the better.