6" stove to 8"thimble - adapter or "just stuff with insulation"?

[grommal]

Our masonry chimney has an 8" thimble. This was just fine with our old VC stove, which used 8" pipe.

I'm in the process of piping our new Jotul, which naturally has a 6" outlet like almost all stoves these days. I was planning to use an adapter at the wall to transition to an 8" piece of stovepipe for inside the thimble, but the stove shop suggested I not bother with that and just run the 6" pipe through the thimble, and stuff the gap full of fireproof insulation. That would be cheaper and perhaps a little easier, but it seems a little hokey to me.

Any thoughts on which way to go?

 

[Todd]

Go with the adapter. Those stove shop guys should know better. Also be advised that 8" chimney may work just fine or could be a little sluggish since it's larger than the stove collar. You may want to look into a full 6" liner to the top if it doesn't draw to your liking.

 

[grommal]

Go with the adapter. Those stove shop guys should know better. Also be advised that 8" chimney may work just fine or could be a little sluggish since it's larger than the stove collar. You may want to look into a full 6" liner to the top if it doesn't draw to your liking.

I almost decided to go for the liner right out of the gate, but I figured I'd try it for a season (next) first. In the past I've had decent draft once the chimney warms up. I think the stove shop said what they did at least partially because they were out of 6"-to-8" adapters.

 

[jtp10181]

Someplace there is a PDF or wiki article on how to properly do a thimble / crook. You cant just jam any old pipe into the clay flue and expect it to be safe, unless the entire brick chimney wall is exposed in the room.

 

[Backroads]

Someplace there is a PDF or wiki article on how to properly do a thimble / crook. You cant just jam any old pipe into the clay flue and expect it to be safe, unless the entire brick chimney wall is exposed in the room.

Ok, I'm ready to learn something new...Why is it safe if the entire brick chimney wall is exposed in the room?

 

[colebrookman]

Go with the adapter. Those stove shop guys should know better. Also be advised that 8" chimney may work just fine or could be a little sluggish since it's larger than the stove collar. You may want to look into a full 6" liner to the top if it doesn't draw to your liking.

I almost decided to go for the liner right out of the gate, but I figured I'd try it for a season (next) first. In the past I've had decent draft once the chimney warms up. I think the stove shop said what they did at least partially because they were out of 6"-to-8" adapters.

I used the adapter with little problem. It sometimes seems a little sluggish, as Todd mentioned, but keep the wood nice and dry with good dry kindling and you should be very happy with the Oslo. Be safe.
Ed

 

[grommal]

Someplace there is a PDF or wiki article on how to properly do a thimble / crook. You cant just jam any old pipe into the clay flue and expect it to be safe, unless the entire brick chimney wall is exposed in the room.

It is all brick in the room, 4 feet wide either side of the thimble, floor to ceiling, for whatever reason that's important.

I just didn't like the idea of that insulation maybe getting wet from the little bit of rain that blows past the cap, and then rusting the heck out of the pipe over time. Also, it seemed like there'd be more chance of chimney smell creeping into the room through all that non-airtight insulation.

 

[ansehnlich1]

I mortared a 6 inch clay thimble right inside the 8 inch clay thimble, works fine.

 

[grommal]

[/quote]
I used the adapter with little problem. It sometimes seems a little sluggish, as Todd mentioned, but keep the wood nice and dry with good dry kindling and you should be very happy with the Oslo. Be safe.
Ed[/quote]
Yep, this concerns me a little, as we used to have some backpuffing with the old VC cat stove when the bypass damper was closed. That always seemed to be related to gases building up in the firebox, and then igniting, and then not having an easy-enough passage through the cat channel to the chimney to absorb the pressure spike. Even if the chimney will be a bit more sluggish because of the size transition, I'm hoping the Oslo design, with less internal restriction, won't have this issue. We also had some downdraft problems because of some trees and the shape of the house, so I'm also going to switch to a VacuStack cap to fix that specific issue. Maybe with all that, and well-seasoned wood, I won't need to reline the chimney.

 

[Jags]

Use the proper adapter and don't look back. Its the right way.

 

[jtp10181]

Someplace there is a PDF or wiki article on how to properly do a thimble / crook. You cant just jam any old pipe into the clay flue and expect it to be safe, unless the entire brick chimney wall is exposed in the room.

Ok, I'm ready to learn something new...Why is it safe if the entire brick chimney wall is exposed in the room?

Uhh... cause if its a combustible wall there are special penetration requirements.

 

[Backroads]

Ah, I think I know what you saying. Obviously I'm not a installer. :coolsmirk: