New Installation - III; Thimble Question

Should have my new (first) coal stove next week. It's an Alaska Channing III stoker with top vent and standard Auto-Heat control setup. My exterior masonry chimney has an 8-inch clay thimble as the former owner of our house was a wood burner. I have obtained the impression from reading through a lot of posts that I should install a 6-inch clay thimble inside the existing 8-incher, as opposed to using a steel vent pipe adapter. I don't have the 6-inch thimble yet, but it's looking to me as though it will be a pretty close fit inside the existing 8-inch, and I'm worried about getting it properly cemented in place so it will be properly sealed. Has anyone else done this job? What do I use for cement?

I'll appreciate any wisdom the group can offer.

I'm not an experienced coal burner, but I did build a chimney recently. The mortar that glues tiles together is special high heat stuff. $35 for a one gallon pail! One pail did do all my tile so it wasn't so bad. What I want to say is: If you do try it, you'll have to do two things, figure a way to lower the tiles gently down, then release them. I have no good ideas there....and you'll have to put mortar on the tiles as you go. I discovered that if you smear the mortar hard at first, it will allow you to put a finger formed "bead" on the ends and have it stay there. If you just put a bead on, it doesn't want to stay. Making that smear gives it the stick-um it needs.

Freddy may have thrown you for a loop, as he went from the "thimble" to the "flue liners".

If you are needing a 6" stove pipe, but have an 8" thimble, IMO, I'd get a 6" to 8" adapter and a length of 8" pipe to slide into the 8" thimble a ways.

I just used hi temp Silicone sealant on my thimble/pipe going into the chimney, It's rated for 500 degrees, your stove exhaust shouldn't get anywhere close to that, expecially on the outside of the pipe (Hopefully). Either way should work, either a smaller thimble or 8" to 6" adapter piece.

Thanks to Freddy, Dallas and WNY for your help . The idea of using a half-joint of 8-inch inserted in the thimble followed by a reducer to 6-inch dia. for my stove connector is MUCH more appealing than the thought of trying to cement a 6-inch clay thimble inside the existing 8-incher. It's the reducer route for me unless someone else out there in Coal Country wants to talk me out of it. Whatever is going to happen happens early next week—it's getting downright cold here in NE Ohio and they're predicting snow showers for Monday, Tuesday and Wednesday. Also, I'm getting really eager to light my first fire!

6" to 8" black stove pipe increaser is the way to go. Why make it any harder than it needs to be? I have mine set up in two stages. 5" to 6" and then 6" to 8".

Make sure you make it easy to clean out the 6" to 8" expander/adapter.. the air velocity will slow down in the flue when the diameter increases, and this will allow the fly ash to settle in the larger diameter pipe... not a problem,, it will probably be the area of the most fly ash accumulation,, that and elbows..

Make sure you use at least 3 screws for every pipe slip-joint.

Greg L.

Thanks Greg.
Plan to top off the vertical pipe from the stove with a tee having a clean out cap in the end facing the room. The run the opposite way, from the tee to the thimble, will be fairly short. Is there any reason why I shouldn't have the tee with the baro damper be the first piece following the reducer/adapter?
Chal

The baro damper just before it increases to 8 inch would be fine.
I would try to limit the amount of 8 inch pipe and go with 6 inch as much as you can and, as Greg said, you should frequently check for ash build up where it increases to 8 inches.

Hunts...

I too am faced with a similar install... 6"stove going into an 8" existing thimble in a masonry chimney.

I'm making sure if I am reading this correctly... is it 1) or 2)?

1) 8" to 6" reducer on the pipe going into the thimble where reducer is outside the chimney trim ring and visible?
2) put the reducer + pipe "assembly" into the thimble where the reducer would be hidden behind the chimney trim ring?

I wasn't even sure if reducers could be installed horizontally...

8" tee
8" baro bullhead position
8" reducer to 6" on the vertical
6" tee on the bottom for cleanout
If you do the reducing on the vertical then the ash will drop to the bottom tee cap
cleanout is easy and it is like an ash pit.