Stainless steel thimble out of round

[woodlumn]

Several years ago I had my chimney relined. It's an old brick chimney in rough shape, so we had a Ventinox lining system installed. Basically it's metal pipe with a hardened insulating cement-like material that surrounds it and strengthens the chimney. We had this work done years ago during the renovation, and it's not until now that we're actually getting ready to use it.

The thimble is just a T off the metal pipe (6"), and it's flush with the face of the chimney. I went to dry fit some stove pipe and noticed that the thimble is out of round. So when I slip the stove pipe into it, there's a decent gap on one side (about .25" to .5"). I can't reshape the thimble because it's surrounded by that cement-like insulation.

Am I doing this correctly? The stove pipe is supposed to slip inside this thimble, right? It's also really difficult to make the 6" stove pipe fit in. I've got the kind of pipe that is open until you close it up with the interlocking seam.

Thanks in advice for whatever help you can offer

 

[trophyhunter]

If it's any help I hated hooking up new stoves to thimbles like that but if the dimensions force you to use an inside fit you have the seam at the connection reversed at that point and have to take precautions to make sure the pipe you insert gets sealed and secured.

I used pipe crimpers to make the fit better than the factory crimp allowed for in most cases, I always chipped some mortar away in three places outside the pipe on those flush thimble pipe openings to drill a hole so self tapping fasteners could secure the pipe inserted into the opening.

I would insert the pipe until it was fitting to a good depth, then reach inside with a short pencil and scribe a line at the end of the pipe inside the receptor piece. Pull it out, and apply a generous amount of high temperature silicone just before the line. Put your pipe back in, secure with screws and reach inside and smooth out that silicone to seal the gaps at the end.

I would usually finish up by using stove cement on any gaps around the outside perimeter of the two pieces. However you choose to seal the gaps, don't rely on sealants to secure the connection, get some screws in there any way you can!

-On Edit, your using a short piece crimped on both ends for this scenario so the rest of your stovepipe seams are joined correctly from the wall thimble towards the stove.

 

[woodlumn]

Thanks so much for the detailed response. I've never installed a wood stove indoors before, so please bear with me.

So you're saying that I should insert the male end of pipe into the thimble and crimp the other end (or use a male coupling), seal with silicone, and chip out some mortar in the thimble so I can get a couple of screws in there?

Where the pipe enters the thimble, how big of a gap is too big to be plugged with furnace cement?

It really bothers me that the thimble is out of round. Seems like sloppy work to me...or is this normal?

Thanks again for all your help.

 

[BrokenToys]

They should have put a plug in it when seating/sealing the thimble when they did the work. but trophyhunter's solution is the way to correct it.

 

[savageactor7]

That gap won't matter when the stove is running ...the draft will suck the smoke right up the chimney.

Actually the gap is way smaller if you could do the math on the real tolerance. Do you have any wood burning neighbors you can consult for some reassurance?

 

[trophyhunter]

Thanks so much for the detailed response. I've never installed a wood stove indoors before, so please bear with me.

So you're saying that I should insert the male end of pipe into the thimble and crimp the other end (or use a male coupling), seal with silicone, and chip out some mortar in the thimble so I can get a couple of screws in there?

Where the pipe enters the thimble, how big of a gap is too big to be plugged with furnace cement?

It really bothers me that the thimble is out of round. Seems like sloppy work to me...or is this normal?

Thanks again for all your help.

Yes, you want a short male coupling crimped on both ends. Don't sweat the out of round issue, I did several hundred installs to those and not a single one was as perfectly round as one would want. You just want to expose some of the outer metal edge where it's flush so you can drill three holes to add some metal screws. To many people get the crimped end tapped into the hole and it's so tight they just blow it off and don't bother with the screws.

Use high temp silicone on both the inside seam and outside gaps if you wish, if for some reason it doesn't hold up on the outside just get some furnace cement in the gap it will hold up to higher heat. You absolutely don't want those gaps drawing air into the chimney, that draw needs to bring all the moving volume of air in the chimney system through the stove inlets to maximize stove performance and your ability to control the amount of combustion air to the fire.

If you need any more help at all don't be shy, better to get it right the first time and enjoy having it up and running right.

 

[woodlumn]

Trophyhunter, a million thanks. I'll be sure to post back with the results, or any questions I have along the way.

 

[trophyhunter]

Trophyhunter, a million thanks. I'll be sure to post back with the results, or any questions I have along the way.

You are welcome! I'll PM you my number and if you need anything while your planning the rest of the chimney pipe and components just give me a shout and I can talk you through the rest of it if you need more help. It will all seem so easy after you get it all in there and fitted properly.

 

[woodlumn]

I'm wondering about where the stove pipe attaches to the top of the pot belly stove. On the stove side, it's oval. The pipe is round. Can I just form the round pipe around the flange on the stove, or should it go inside the flange? Does this need to be air tight for carbon monoxide or anything? The stove itself is far from air tight