by Tom

I am constructing a chimney for a (my home) wood stove using an 8" flue inside 16" block. Without using an adapter pipe, how do I connect the round and square pipes where the horizontal 8" round flue meets the vertical 8" square so as to have the best structural support for the column and air tight seal? Is there a diagram online you can point me to? My supplier says they stopped selling the adapter since no one buys them. With all the concern about chimney fires I want this done to code...


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Aug 05, 2011
by: F.J.N.

There is just such a product to address your need,it is called a thimble.There is a supplier i believe in iowa called copperfield chimney supply who sells several types.They ship all over the US.& CANADA.Ihave had good results whith all of my dealings with them.

Sep 05, 2008
Handcrafted Thimble

The best way to make the thru wall connection is to have solid masonry from your drywall or inside finish straight to the chimney's vertical flue liner. As in the diagram, there needs to be 12" of masonry all the way around the
stove pipe.

The stove pipe needs to be ran to the flue liner inside the chimney, all you have to do to connect them is to cut a hole in the flue liner and slide the pipe into the hole barely protruding into the vertical flue approx 1/2 inch.

Butt the horizontal flue into the vertical flue and mortar around inside with your hand filling in any holes that may be due to cutting. To help you understand why the flue liner needs to be around the stove pipe, is to protect the masonry around the flue. The flue takes the heat, and the masonry around the flue reassures nothing combustible will ever be near the hot spot.

Note; in the side view there is an air gap, I would fill that in with masonry to make for certain that nothing combustible will ever fall down in there.

Thanks for visiting and I hope this will help you out.


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