Need tip on extended pass through

I need to run 3" pipe from my new stove through an existing hole in my wall. The existing hole was from a wood stove that had 8" pipe running through the wall. On the inside wall I have a dry-stacked stone wall. The problem I am faced with is that the stone wall increases the distance from the inside to the outside that I have to run through the wall. Thus, the wall thimbles that I see online seem to be too short (10 in. max.). Any solid (but nice looking) suggestions on the best way to utilize the hole would be appreciated. I don't have the exact measurement at my fingertips, but I need to go through about 8 or 10 inch block plust maybe 7" of stone wall.

Thanks in advance!

I believe I read that to extend a thimble you can just use a ( Like ) material, sheet metal of a similar thickness. You would rolll the sheet metal to match the thimble pipe and you must overlap the joint I (think ) by two inches. If memory serves me I read this on a thimble manufactures website. If I"m wrong someone will correct me. I think I read it at Simpson dura vent website (but be sure before you do this).

Thanks BostonBaked!

Maybe this installation will turn out to be easier than I was antisipating

I did go to Duravents site and found this in their FAQ section:

Not very detailed, but at least it confirms what you suggested. The only possible problem yet, might be the very uneven surface of the stone wall for the thimble plate. I am conteplating maybe using a 3" to 8" adaptor on the inside stone wall, but I was not sure what I could connect on the other end.

Your very welcome Codebum, You may have to get creative with the stone issue. Maybe you could place the thimble on the stone draw an out line and then cut a (KERF CUT which is a cut that is just the thickness of the blade), with a diamond blade so the lip of the thimble can rest in the cut. Just a thought without seeing it.

Those are some good suggestions.

I'll be tackling the problem in a couple weeks. I'll try to repost here how I made out.

I did the same thing on mine, what i did was purchase a 8 in dia by 10 in length of woodstove pipe and used that. It was fairly easy.

I would even up the stone with some cement mix, where the plate sets.

treebeard did it right , this is what they mean by similar materials essentially the 8 inch sheet metal tube is a "heat shield" this keeps things inside the wall from laying directly on or getting too close to the pipe. by adding his piece of 8" which should have slipped in or over the shield just fine , he has created a shield for a thicker wall. easy fix.

They also have a 12" wall thimble made my silkeck?

If you're using Duravent, I bought a 4" to 8" adapter to go into an 8" thimble in an existing chimney. Got it online, when I went to hook it up, found out that O.D. on the adapter is 9 1/2". Went to a local sheet metal shop to get one made, another 50 bucks, now all I gotta do is try to get my money back from the online place. At least it's done, now.

the adapters such as mentioned above are for premanufactured class a flue systems , not for a wall thimble for a masonary chimney , this is the reason for the larger OD.

I am glad to see that I am not the only one with what I thought was an odd situation. I have only been reviewing pipe and adaptors online so far. I think my next step is to go to the store and see how all these connect. No matter how I end up completing this, I think I will insert the 8" pipe in the wall just as a heat barrier (as mentioned). It's a stone wall and block wall, nothing that should burn, but it should help isolate the area and keep insetcts and rodents out of the chamber that is created.