How to seal a non used thimble in exhaust chimney.

[Blvayer]

Hi All, I have a 1955 farm home which has a chimney currently being used to exhaust an oil furnace. The furnace is in the basement, and on the main floor there was a thimble extending out on each side of the chimney. When I had a chimney expert out to inspect the chimneys, he suggested I brick/mortar one side up and place a thimble cover plate on the other side. In case the next owners move away from the oil furnace and want to put in a wood burning stove. So I followed his advice and blocked in one side and mortared it up. The side that still has an accessible thimble is in the kitchen and it currently has an original thimble cover plate (tension rods on back that slip into thimble) on it that was hand painted. I also have carbon monoxide detectors which have never gone off.

Problem: home inspector said I have to remove the cover plate and seal the thimble to prevent carbon monoxide leaks.

I reached out to the chimney guy that I originally worked with and he said that he knows of no building code regulations that say how to seal the thimble so the thimble plate w silicone caulk should be fine or to just brick/mortar the hole (which I don't want to do).

Question: can I use a high temp silicone caulk around the thimble cover plate so it's not permanent like brick/mortar but still air tight. Is there other methods of sealing a thimble so carbon monoxide doesn't escape but aren't permanent?

 

[bholler]

Hi All, I have a 1955 farm home which has a chimney currently being used to exhaust an oil furnace. The furnace is in the basement, and on the main floor there was a thimble extending out on each side of the chimney. When I had a chimney expert out to inspect the chimneys, he suggested I brick/mortar one side up and place a thimble cover plate on the other side. In case the next owners move away from the oil furnace and want to put in a wood burning stove. So I followed his advice and blocked in one side and mortared it up. The side that still has an accessible thimble is in the kitchen and it currently has an original thimble cover plate (tension rods on back that slip into thimble) on it that was hand painted. I also have carbon monoxide detectors which have never gone off.

Problem: home inspector said I have to remove the cover plate and seal the thimble to prevent carbon monoxide leaks.

I reached out to the chimney guy that I originally worked with and he said that he knows of no building code regulations that say how to seal the thimble so the thimble plate w silicone caulk should be fine or to just brick/mortar the hole (which I don't want to do).

Question: can I use a high temp silicone caulk around the thimble cover plate so it's not permanent like brick/mortar but still air tight. Is there other methods of sealing a thimble so carbon monoxide doesn't escape but aren't permanent?

It needs to be firebrick and refractory mortar

 

[Blvayer]

It needs to be firebrick and refractory mortar

Can you elaborate on why it needs to be firebrick and refractory mortar?

 

[bholler]

Can you elaborate on why it needs to be firebrick and refractory mortar?

Because that is required by code. Regular brick and mortar is not acceptable as a lining material

 

[Blvayer]

Because that is required by code. Regular brick and mortar is not acceptable as a lining material

I've already used fire brick and refractory mortar on the other side of the thimble, not regular brick & mortar. That wasn't what was in question.

According to VA chimney experts there is no code stating how I have to seal the thimble. If you could provide a link to VA code that says otherwise I'd be appreciative. Seems pretty extreme and unreversible.

The goal is to not permanently seal it with fire brick and refractory mortar - but some other means.

 

[bholler]

I've already used fire brick and refractory mortar on the other side of the thimble, not regular brick & mortar. That wasn't what was in question.

According to VA chimney experts there is no code stating how I have to seal the thimble. If you could provide a link to VA code that says otherwise I'd be appreciative. Seems pretty extreme and unreversible.

The goal is to not permanently seal it with fire brick and refractory mortar - but some other means.

The problem is that you are not allowed to have more than one breach in the chimney. Now that one breach can be a thimble and cleanout but you cannot have a second thimble. Your inspector has already told you that your chimney expert was incorrect. It needs sealed and the only way to properly seal it is with firebrick and refractory mortar.

 

[Blvayer]

The problem is that you are not allowed to have more than one breach in the chimney. Now that one breach can be a thimble and cleanout but you cannot have a second thimble. Your inspector has already told you that your chimney expert was incorrect. It needs sealed and the only way to properly seal it is with firebrick and refractory mortar.

Oh, actually, the inspector never said any of the experts I've spoken with in the last 2 days were incorrect he said I needed to seal it and didn't specify how, just that his concern was carbon monoxide leaking. So, I'm just looking for all my options. The previous 2 home inspectors were fine with a tension rod cover plate and multiple thimbles so it seems to be a matter of opinion.

I'm just looking for the building/fire code or link that backs up what your saying or anyone for that matter as to further educate myself.

I found an thimble insul-plug that seals unused thimbles from gases and would work as well apparently. Seems a lot like the first suggest I got on this thread.

But I thank you for your time and opinion.

 

[coaly]

NFPA 211 is the standard used for chimneys and venting. Codes adopt standards, and VA uses the ICC family of codes which references NFPA 211. (Same as many other states including PA) Local codes can be more strict, but that's the norm.

https://www2.iccsafe.org/states/Virginia/Mechanical/PDFs/Chapter 8_Chimneys and Vents.pdf

4 inches of cement (the thickness of a chimney block wall) is the minimum required around (and between) flue liners, so using firebrick and refractory mortar (due to contact of flue gasses) of that thickness would suffice solid fuel codes. (oil is NFPA 31) I'm not a chimney expert in the business like bholler, so he may know if that 4 inch spec comes from the International Building Code, or Mechanical Code which is intertwined with all the other International Codes.

I can tell you that I have multiple brick chimneys in a double house that have had multiple breeches plugged by filling a piece of steel connector pipe with firebrick and mortar and plugging the hole tightly with it. Mine fits so tight there is no silicone or sealant used, but you could if it were a concern. I don't see that type of plug being any different than the flue and chimney construction. I recently opened a wall to find this and it had been done by a previous owner before 1960. No sign of rust or corrosion of the steel and a Nat. gas furnace and Nat. gas water heater are vented into them.