Houston I think we have a problem - Cracked ceramic thimble

[PelletNJUSA]

Finally got around to removing the wall behind my pellet Stove to replace with backerboard or something. In opening the wall I found a cracked ceramic thimble, blackness on outside, and the paper backing on insulation tacked in the area between studs was black, Local fireman suggests it appears likely heat damage to insulation not actually ignition. I need guidance on how to proceed.

General info, ceramic thimble has a metal type insert inside it but seems like cheap single wall piping used to line the ceramic thimble. The thimble is long, it connects from the exterier chimney, through the home's cinder block wall, and through a studded sheetrock wall. The Pellet piping is the duravent double wall which travels all the way into the Chimney. Prior to the installation of the pellet Stove, a woodburning stove was in place using this same thimble. Because of the sheetrock wall (Which I think may be 5/8's X fireproof) was in place already, this could be old damage from the older Woodstove and not visible during pellet piping insert. The original barcodes on the 4" Duravent pipe were still on the piping in the wall inside the thimble suggesting this was old damage.

Anyway, what would cause this damage and what is the fix. I am selling the home and want to address this before I list. I removed the pellet Stove months ago and was just replaving the wall. The original wall with old brick vaneer was an eye sore. The plan was to replace the wall, cap the thimble, and then let the new homeowner decide what type of appliance they want.

Thank you. Here are some pictures.

 

[gthomas785]

Hold up. Is that brick veneer over drywall with fiberglass behind it butted right up to the chimney and clay thimble? Was there any clearance around the thimble?

I think the fire department's diagnosis is correct that what you are seeing is extreme heat damage from when the woodstove was there.

What they didn't tell you is that the heat damage likely has little to do with the crack, and more to do with the lack of clearance. A standard masonry thimble would need 18" of non-combustible (brick) all the way around it before you could have any combustible materials - drywall, studs, insulation etc. The previous owners or whoever was running that stove should count themselves extremely lucky that a fire did not start in the wall.

The other option available now is a stainless steel "insulated thimble," which has smaller clearance requirements.

If you were going to put a woodstove back then the way to fix this is to install a proper wall pass-through. Since the studs are so close, I'd recommend getting an insulated thimble which usually are about 10" in diameter and can butt right up against the drywall. However if you are going this route, you should also get the masonry chimney inspected to make sure it is safe, and probably put in a stainless liner. That's a lot of expense for a chimney that might not get used by the future owners. Pellet, gas, and wood stoves have different venting requirements that might not be compatible with whatever you put in. So if I were selling, I would just remove the cracked thimble and burnt insulation and plug the hole with some rockwool. Let them decide what they want to do from there.

By the way, "fire rated" drywall is not fireproof. It just means it will take a little longer to burn through if there's a fire on one side getting to the other side.

 

[PelletNJUSA]

Hold up. Is that brick veneer over drywall with fiberglass behind it butted right up to the chimney and clay thimble? Was there any clearance around the thimble?

I think the fire department's diagnosis is correct that what you are seeing is extreme heat damage from when the woodstove was there.

What they didn't tell you is that the heat damage likely has little to do with the crack, and more to do with the lack of clearance. A standard masonry thimble would need 18" of non-combustible (brick) all the way around it before you could have any combustible materials - drywall, studs, insulation etc. The previous owners or whoever was running that stove should count themselves extremely lucky that a fire did not start in the wall.

The other option available now is a stainless steel "insulated thimble," which has smaller clearance requirements.

If you were going to put a woodstove back then the way to fix this is to install a proper wall pass-through. Since the studs are so close, I'd recommend getting an insulated thimble which usually are about 10" in diameter and can butt right up against the drywall. However if you are going this route, you should also get the masonry chimney inspected to make sure it is safe, and probably put in a stainless liner. That's a lot of expense for a chimney that might not get used by the future owners. Pellet, gas, and wood stoves have different venting requirements that might not be compatible with whatever you put in. So if I were selling, I would just remove the cracked thimble and burnt insulation and plug the hole with some rockwool. Let them decide what they want to do from there.

By the way, "fire rated" drywall is not fireproof. It just means it will take a little longer to burn through if there's a fire on one side getting to the other side.

First, thank you for your response and forgive me if I have too many questions over the next couple of days as I educate myself a little so I know what to expect when I call in a pro. It must be done right, no shortcuts.

1. What do you think actually caused the crack ? It has been there for a couple of decades.

2. Just to clarify my exact structure here. From Stove, a 4in pellet piping traveled into the 4 inch adapter attached to the sheetrock wall, directly into the metal line clay thimble. The metal lined clay chimney sticks out 12 inches from the foundations cider block wall where it then enters the actual chimney which is exterior, attached to the house. I can't tell yet as to the actual length of the clay thimble but to stick out 12 inches from the cinder block was and still reach the actual exterior chimney, it would need to be long. Do they make them that long ?

3. The insulation was below the clay thimble, not to the sides or above it. The blackness was found on the bottom of the thimble, on the insulation closest to the thimble, and even where the thimble connection point with the sheetrock (Masonry sealant caulk like material was black.

3. You mention that a clay thimble would need 18 inches of non combustible brick all the way around it but how does one achieve that in the 12 inch empty space between the sheetrock and the cider block foundation wall ?

4. Is it possible there is additional damage inside the cinder block wall which is not visible to the eye yet ?

5. The stainless insulated thimble that you speak of does that also need non-combustible (Brick) all the way around it like you indicate a clay chimney does ? If so, how do I do that in the 1' air space between the sheetrock and the cinder block wall.


Thank you soooooooooooo much for your guidance !

 

[PelletNJUSA]

Hold up. Is that brick veneer over drywall with fiberglass behind it butted right up to the chimney and clay thimble? Was there any clearance around the thimble?

I think the fire department's diagnosis is correct that what you are seeing is extreme heat damage from when the woodstove was there.

What they didn't tell you is that the heat damage likely has little to do with the crack, and more to do with the lack of clearance. A standard masonry thimble would need 18" of non-combustible (brick) all the way around it before you could have any combustible materials - drywall, studs, insulation etc. The previous owners or whoever was running that stove should count themselves extremely lucky that a fire did not start in the wall.

The other option available now is a stainless steel "insulated thimble," which has smaller clearance requirements.

If you were going to put a woodstove back then the way to fix this is to install a proper wall pass-through. Since the studs are so close, I'd recommend getting an insulated thimble which usually are about 10" in diameter and can butt right up against the drywall. However if you are going this route, you should also get the masonry chimney inspected to make sure it is safe, and probably put in a stainless liner. That's a lot of expense for a chimney that might not get used by the future owners. Pellet, gas, and wood stoves have different venting requirements that might not be compatible with whatever you put in. So if I were selling, I would just remove the cracked thimble and burnt insulation and plug the hole with some rockwool. Let them decide what they want to do from there.

By the way, "fire rated" drywall is not fireproof. It just means it will take a little longer to burn through if there's a fire on one side getting to the other side.

Sorry, forgot 2 questions:

1. Which is typically hotter, my 45k max btu pellet stove or a wood burning stove.

2. The 4" pellet piping. As you know, it traveled into an adapter and into the thimble, all the way to the exterior chimney. I am lookin at all angle here so forgive me if I seem obsessive but fire safety matters to me ! If by chance the 4" Duravent 2 wall pellet piping got too close to the wall the wall thimble inner edge or was resting on the thimble at all, could than have been a contributing factor to the crack or the damage ? In other words, the pellet pipe has clearance requirements too, think it is only 2" but what if the pellet pipe was less than the 2 inches inside the thimble or potentially resting on the thimble ?

Thank you.

 

[gthomas785]

I'll do my best to answer your questions.

1. The crack could have been due to settling, or it could have been over heated for instance if there was a chimney fire.
2. Yeah, it's a common enough scenario to go through an exterior foundation wall and into a chimney.
3.
3. I meant 18 inches in the radial direction Picture a 18" radius hole in the wall, the thickness is not important just the distance away from the thimble. The block wall and chimney are fine because they are not combustible. The 2 studs as well as some of the drywall on the side wall on the right would be too close. But as I said there are ways available to reduce the clearance requirement.

4. I think its unlikely the blocks are damaged they can withstand quite a bit more heat than fiberglass insulation. There's nothing wrong with passing the thimble through the non-combustible cement wall.
5. No. Most of the insulated thimbles are rated for zero clearance, that's why they're insulated. You could put one of those in and then drywall right up to it. It comes with a trim ring to cover the rough edge of the drywall.
Like this:

Insulated Chimney Thimble for Thimble and Wall Pass Thru Installations - Rockford Chimney

An Insulated Chimney Thimble protects the wall from overheating where the flue pipe passes through. Includes installation instructions. Free shipping.

www.rockfordchimneysupply.com

1a. I think, typically wood stoves have the hottest exhaust temperatures. Pellet stoves use a forced draft (=more air) and are listed to hook up to a different class of venting pipe specifically rated for pellet stoves. Those pipes have their own clearance requirements and wall pass-thru arrangements.

2a. If the pellet pipe was not installed according to the manufacturer's instructions then anything is possible. A pellet pipe touching insulation would be bad just as a clay thimble of a wood stove would be. However I suspect that due to the multiple layers as well as the air space around the pellet piping and the fact that it's a pellet stove and not a wood stove, that the damage was probably due to the wood stove. But it's impossible to say for sure.

 

[PelletNJUSA]

I'll do my best to answer your questions.

1. The crack could have been due to settling, or it could have been over heated for instance if there was a chimney fire.
2. Yeah, it's a common enough scenario to go through an exterior foundation wall and into a chimney.
3.
3. I meant 18 inches in the radial direction Picture a 18" radius hole in the wall, the thickness is not important just the distance away from the thimble. The block wall and chimney are fine because they are not combustible. The 2 studs as well as some of the drywall on the side wall on the right would be too close. But as I said there are ways available to reduce the clearance requirement.

4. I think its unlikely the blocks are damaged they can withstand quite a bit more heat than fiberglass insulation. There's nothing wrong with passing the thimble through the non-combustible cement wall.
5. No. Most of the insulated thimbles are rated for zero clearance, that's why they're insulated. You could put one of those in and then drywall right up to it. It comes with a trim ring to cover the rough edge of the drywall.
Like this:

Insulated Chimney Thimble for Thimble and Wall Pass Thru Installations - Rockford Chimney

An Insulated Chimney Thimble protects the wall from overheating where the flue pipe passes through. Includes installation instructions. Free shipping.

www.rockfordchimneysupply.com

1a. I think, typically wood stoves have the hottest exhaust temperatures. Pellet stoves use a forced draft (=more air) and are listed to hook up to a different class of venting pipe specifically rated for pellet stoves. Those pipes have their own clearance requirements and wall pass-thru arrangements.

2a. If the pellet pipe was not installed according to the manufacturer's instructions then anything is possible. A pellet pipe touching insulation would be bad just as a clay thimble of a wood stove would be. However I suspect that due to the multiple layers as well as the air space around the pellet piping and the fact that it's a pellet stove and not a wood stove, that the damage was probably due to the wood stove. But it's impossible to say for sure.

THANK YOU SO MUCH. I decided that I just want to pass this on to the next homeowner to manage depending on which appliance they install, if they install anything at all. In the mean time I want to close it up/cap it off properly but in a way that is easy for the next homeowner to reopen or in a way that it is permanently safe should they never use the chimney again. I need guidance on this:

1. The exposed part of the clay chimney is cracked in multiple places. Can I shave everything down flush with the cinder block wall, put rockwool in and cover/cap it somehow ? What is the best way to cap/cover the hole ? I really don't want to pull the entire clay thimble out if I don't have to because it is in there really tight.

Thank you Sir !

 

[stoveliker]

As a side remark from a bystander here: I would not just put rockwool in there; the humid air from the chimney stack can still get in/seep through the rockwool, eventually leading to mold behind the drywall.
I'd seal it off one way or the other (after putting in rockwool). My uneducated mind would simply put a piece of sheetmetal with adhesive over the hole.

 

[johneh]

Here are some ideas

chimney hole plug - Google Search

 

[PelletNJUSA]

I'll do my best to answer your questions.

1. The crack could have been due to settling, or it could have been over heated for instance if there was a chimney fire.
2. Yeah, it's a common enough scenario to go through an exterior foundation wall and into a chimney.
3.
3. I meant 18 inches in the radial direction Picture a 18" radius hole in the wall, the thickness is not important just the distance away from the thimble. The block wall and chimney are fine because they are not combustible. The 2 studs as well as some of the drywall on the side wall on the right would be too close. But as I said there are ways available to reduce the clearance requirement.

4. I think its unlikely the blocks are damaged they can withstand quite a bit more heat than fiberglass insulation. There's nothing wrong with passing the thimble through the non-combustible cement wall.
5. No. Most of the insulated thimbles are rated for zero clearance, that's why they're insulated. You could put one of those in and then drywall right up to it. It comes with a trim ring to cover the rough edge of the drywall.
Like this:

Insulated Chimney Thimble for Thimble and Wall Pass Thru Installations - Rockford Chimney

An Insulated Chimney Thimble protects the wall from overheating where the flue pipe passes through. Includes installation instructions. Free shipping.

www.rockfordchimneysupply.com

1a. I think, typically wood stoves have the hottest exhaust temperatures. Pellet stoves use a forced draft (=more air) and are listed to hook up to a different class of venting pipe specifically rated for pellet stoves. Those pipes have their own clearance requirements and wall pass-thru arrangements.

2a. If the pellet pipe was not installed according to the manufacturer's instructions then anything is possible. A pellet pipe touching insulation would be bad just as a clay thimble of a wood stove would be. However I suspect that due to the multiple layers as well as the air space around the pellet piping and the fact that it's a pellet stove and not a wood stove, that the damage was probably due to the wood stove. But it's impossible to say for sure.

So I decided I don't want to remove the entire length of the clay thimble. I just want to shave it back near even with the cinder block wall and cap it. How do I cut/shave it ? Thanks.

 

[stoveliker]

So I decided I don't want to remove the entire length of the clay thimble. I just want to shave it back near even with the cinder block wall and cap it. How do I cut/shave it ? Thanks.

Angle grinder imo. Don't want to whack it with anything lest it cracks more.

 

[PelletNJUSA]

Finally got around to removing the wall behind my pellet Stove to replace with backerboard or something. In opening the wall I found a cracked ceramic thimble, blackness on outside, and the paper backing on insulation tacked in the area between studs was black, Local fireman suggests it appears likely heat damage to insulation not actually ignition. I need guidance on how to proceed.

General info, ceramic thimble has a metal type insert inside it but seems like cheap single wall piping used to line the ceramic thimble. The thimble is long, it connects from the exterier chimney, through the home's cinder block wall, and through a studded sheetrock wall. The Pellet piping is the duravent double wall which travels all the way into the Chimney. Prior to the installation of the pellet Stove, a woodburning stove was in place using this same thimble. Because of the sheetrock wall (Which I think may be 5/8's X fireproof) was in place already, this could be old damage from the older Woodstove and not visible during pellet piping insert. The original barcodes on the 4" Duravent pipe were still on the piping in the wall inside the thimble suggesting this was old damage.

Anyway, what would cause this damage and what is the fix. I am selling the home and want to address this before I list. I removed the pellet Stove months ago and was just replaving the wall. The original wall with old brick vaneer was an eye sore. The plan was to replace the wall, cap the thimble, and then let the new homeowner decide what type of appliance they want.

Thank you. Here are some pictures.

View attachment 294428 View attachment 294429 View attachment 294430 View attachment 294431 View attachment 294432 View attachment 294433 View attachment 294434 View attachment 294435 View attachment 294436 View attachment 294437

 

[PelletNJUSA]

THANK YOU ALL for the guidance here ! I really appreciate it. I was able to easily chisel the clay thimble flush with the block wall and in doing so, the short piece of metal liner came out with ease. I am either going to stuff the hole with gonna stuff the inside with rockwool or insert a flueblocker (See pic) and then close the hole with the original 4" adapter I have. I will fill the 4" whole with a piece of sheetmetal and glue. Thanks again ! By the way, the remaining clay thimble that will remain in the wall had not cracks or damage.

 

[PelletNJUSA]

Here are some ideas

chimney hole plug - Google Search

THANK YOU ALL for the guidance here ! I really appreciate it. I was able to easily chisel the clay thimble flush with the block wall and in doing so, the short piece of metal liner came out with ease. I am either going to stuff the hole with gonna stuff the inside with rockwool or insert a flueblocker (See pic) and then close the hole with the original 4" adapter I have. I will fill the 4" whole with a piece of sheetmetal and glue. Thanks again ! By the way, the remaining clay thimble that will remain in the wall had not cracks or damage.

 

[PelletNJUSA]

I'll do my best to answer your questions.

1. The crack could have been due to settling, or it could have been over heated for instance if there was a chimney fire.
2. Yeah, it's a common enough scenario to go through an exterior foundation wall and into a chimney.
3.
3. I meant 18 inches in the radial direction Picture a 18" radius hole in the wall, the thickness is not important just the distance away from the thimble. The block wall and chimney are fine because they are not combustible. The 2 studs as well as some of the drywall on the side wall on the right would be too close. But as I said there are ways available to reduce the clearance requirement.

4. I think its unlikely the blocks are damaged they can withstand quite a bit more heat than fiberglass insulation. There's nothing wrong with passing the thimble through the non-combustible cement wall.
5. No. Most of the insulated thimbles are rated for zero clearance, that's why they're insulated. You could put one of those in and then drywall right up to it. It comes with a trim ring to cover the rough edge of the drywall.
Like this:

Insulated Chimney Thimble for Thimble and Wall Pass Thru Installations - Rockford Chimney

An Insulated Chimney Thimble protects the wall from overheating where the flue pipe passes through. Includes installation instructions. Free shipping.

www.rockfordchimneysupply.com

1a. I think, typically wood stoves have the hottest exhaust temperatures. Pellet stoves use a forced draft (=more air) and are listed to hook up to a different class of venting pipe specifically rated for pellet stoves. Those pipes have their own clearance requirements and wall pass-thru arrangements.

2a. If the pellet pipe was not installed according to the manufacturer's instructions then anything is possible. A pellet pipe touching insulation would be bad just as a clay thimble of a wood stove would be. However I suspect that due to the multiple layers as well as the air space around the pellet piping and the fact that it's a pellet stove and not a wood stove, that the damage was probably due to the wood stove. But it's impossible to say for sure.

THANK YOU ALL for the guidance here ! I really appreciate it. I was able to easily chisel the clay thimble flush with the block wall and in doing so, the short piece of metal liner came out with ease. I am either going to stuff the hole with gonna stuff the inside with rockwool or insert a flueblocker (See pic) and then close the hole with the original 4" adapter I have. I will fill the 4" whole with a piece of sheetmetal and glue. Thanks again ! By the way, the remaining clay thimble that will remain in the wall had not cracks or damage.

 

[PelletNJUSA]

As a side remark from a bystander here: I would not just put rockwool in there; the humid air from the chimney stack can still get in/seep through the rockwool, eventually leading to mold behind the drywall.
I'd seal it off one way or the other (after putting in rockwool). My uneducated mind would simply put a piece of sheetmetal with adhesive over the hole.

I definately am going to cover the whole with an adapter. Instead of rockwool, you think I can just stick ordinary Batts insulation inside ? I have a bunch sitting around. Thanks.

 

[stoveliker]

I definately am going to cover the whole with an adapter. Instead of rockwool, you think I can just stick ordinary Batts insulation inside ? I have a bunch sitting around. Thanks.

I think that would be fine, if none goes thru the wall and falls out of reach - i.e. if it's clear that all can be removed before the system is set back up for burning. Makes sense to use something you have rather than buying something (way too much) for this job.