I burn a Buck Stove as a fireplace insert. We have an internal chimney made of masonry. When we burn the stove for more than a day the wall above the mantel and the wall upstairs gets very warm. My house is very old and I assume that the plaster and lathe was applied over the brick chimney. Not sure about that though. I sweep the chimney annually and have expressed my concern to my sweeper but he thinks it's just radiating heat from the brick chimney. My concern is not necessarily about a chimney fire but more about combustion of the wall, espcially upstairs because the wall is adjacent to bedrooms. Does anyone have a similar situation or any thoughts on this?
Internal Chimney Question / Concern
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I have observed this many times on many different chimneys. It takes a ton of BTUs to heat a block/brick chimney but once hot it is like a heat sponge. If it were me, I would not worry as long as it does not get hot to the touch and that inspection confirms that the chimney is in proper working order. ie no cracks or missing mortar.
Runner
I assume you have a stainless steel liner? or clay tiles?
If you think you have wood within the required 2" of airspace that is supposed to be around a brick chimney, I would recommend you get your liner insulated. Insulating your liner will give you a zero clearance chimney, which means that you won't need to worry about the heat transfer, as the insulation will limit it enough to keep it below what can damage the walls.
With a chimney liner heating itself to 1200*F, over a few years of heavy use, the amount of heat exposure can have significant effects to the exposed wood. That is why any flue that you can't determine is fully up to code should get the insulation treatment when the liner is installed. Lots of threads even in the last few days about insulating liners, and a good one about fireplaces and heat transfer to wood nearby that can cause fires. While the heat amounts in a liner are lower than a fireplace back wall, over time the principles are the same. Do a quick search on "insulation" and "liners" in this forum, and you will get a good reading list.
I assume you have a stainless steel liner? or clay tiles?
If you think you have wood within the required 2" of airspace that is supposed to be around a brick chimney, I would recommend you get your liner insulated. Insulating your liner will give you a zero clearance chimney, which means that you won't need to worry about the heat transfer, as the insulation will limit it enough to keep it below what can damage the walls.
With a chimney liner heating itself to 1200*F, over a few years of heavy use, the amount of heat exposure can have significant effects to the exposed wood. That is why any flue that you can't determine is fully up to code should get the insulation treatment when the liner is installed. Lots of threads even in the last few days about insulating liners, and a good one about fireplaces and heat transfer to wood nearby that can cause fires. While the heat amounts in a liner are lower than a fireplace back wall, over time the principles are the same. Do a quick search on "insulation" and "liners" in this forum, and you will get a good reading list.
O'Conner - Thanks for the reply. That is good advice and I will follow-up on it. I do have a stainless steel liner but I don't believe it's insulated. Do you know if it's expensive to do? Somebody did suggest I insulate between the stove and the chimney. There is space due to the fact that it's a fireplace opening. Thanks again.
Cost will depend on how much flue you are insulating and if you do it your self. I would look into ceramic fibre blanket kits for liner insulation - most manufacturers have a kit for their liner system. Insulating between the stove and the chimney isn't needed - a block off plate can keep some of the heat from escaping up the flue - here is a link to a good how to article - https://www.hearth.com/econtent/index.php/wiki/Why_damper_seal_is_needed
oconnor said:
Oconner, not real sure where your getting the code for a two inch space around a brick/block chimney??? I am pretty up on NFPA code but I may have missed it???? Also the heat transfer you talk about is actually called pyrotechtonics (not to be confused with fireworks) were they conducted a rather large investigation into fires being caused manly by hot water pipes from boiler systems having contact to wood. Over time, the wood that has contact to these hot water pipes actually lowers its ignition temperature to the point were the wood will ignite around 120 degrees F. The wood itself that has been exposed to these temps actually looks chard from the heat. I dont remember the exact particulars about the investigation But I do know it takes a very very long time with constant exposure to the hot water pipes for this to happen.
The requirements vary by country - I am Canadian, so I get 2 inches of airspace. Sorry for the mixup. In the end, it isn't the NFPA 211 code that matters, but the instructions for the liner system in use. Here is a sample from a Metalbestos (Selkirk) liner install instructions. You will see that the internal and external airspace needs vary from US/CAN and inside/outside flues. In the end, code requires we follow the manufacturers instructions, and requires at least 1 inch of airspace around the outside of a masonry flue.
The point is, that pyrolysis occurs when wood is exposed to radiant heat - time and temps may vary, but the result is the same eventually. If you read most liner install sheets, they will mention the need for airspace outside the brick structure, and some include the need for airspace inside the structure from the liner to the brick. Some actually don't permit insulation - that is a testing issue, as a product can't be installed in a manner not tested to follow UL1777/CAN 635 specs - so if a liner company can't afford a second test with insulation, then there won't be insulation instructions, and in theory there is no approved way to install the liner if the chimney doesn't meet code specs.
Main problem is, most installers, both pro and DIY, never read that part of the sheet, and if they do, they come up with reasoning like this "Everyone does it this way, so I don't know why this manufacturer thinks we need it..." That is exactly what my certified installer did, and now I wait for him to come back and reinstall the liner - with code required insulation this time.
edit - from NFPA 211 -
4.3.2 Clearance. The space between the chimney and the enclosure shall be at least the minimum air space clearance specified in this standard (see Table 7.2) or the clearance specified in the manufacturer's instructions for listed chimneys.
Sorry, couldn't find table 7.2.
The point is, that pyrolysis occurs when wood is exposed to radiant heat - time and temps may vary, but the result is the same eventually. If you read most liner install sheets, they will mention the need for airspace outside the brick structure, and some include the need for airspace inside the structure from the liner to the brick. Some actually don't permit insulation - that is a testing issue, as a product can't be installed in a manner not tested to follow UL1777/CAN 635 specs - so if a liner company can't afford a second test with insulation, then there won't be insulation instructions, and in theory there is no approved way to install the liner if the chimney doesn't meet code specs.
Main problem is, most installers, both pro and DIY, never read that part of the sheet, and if they do, they come up with reasoning like this "Everyone does it this way, so I don't know why this manufacturer thinks we need it..." That is exactly what my certified installer did, and now I wait for him to come back and reinstall the liner - with code required insulation this time.
edit - from NFPA 211 -
4.3.2 Clearance. The space between the chimney and the enclosure shall be at least the minimum air space clearance specified in this standard (see Table 7.2) or the clearance specified in the manufacturer's instructions for listed chimneys.
Sorry, couldn't find table 7.2.
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I do agree a steel double or old triple wall chimney is a different animal all together from a masonry style chimney. The NFPA 211 does require a two inch space to combustibles around the double and triple wall chimneys. Whether its the closest wall to your stove or any chimney to combustibles its going to contract an amount of radiant heat. So I am sure the idea behind all of this is to keep the temp to a safe and manageable level.
firefighter29 - the table above is for a liner, not double wall chimney. So it applies to the given manufacturers liner system in a brick chimney.
Here is a better discussion on the code from rumford.com - http://www.rumford.com/training/codeissues2006.html#chimneys - specifics on clearances. It tells us that the latest code revisions (2006) would require 2 inches on internal chimneys and 1 inch for ecternal chimneys.
All that to say - Unless you have a good reason not to, then insulate your chimney liner.
Here is a better discussion on the code from rumford.com - http://www.rumford.com/training/codeissues2006.html#chimneys - specifics on clearances. It tells us that the latest code revisions (2006) would require 2 inches on internal chimneys and 1 inch for ecternal chimneys.
All that to say - Unless you have a good reason not to, then insulate your chimney liner.
Based on my inspection from the attic, I don't believe I have the 2" between the chimney and the wall. Remember, this is an 1850's house and chimney. The previous owner installed an insert stove and a stainless steel liner. Based on your comments, I should consider insulating my liner to limit that radiant heat to the internal walls. Correct/
who is this oconner from the warm north? i agree with him again 
! 2' minimum clearance from any framing member in the structure. I have seen charred framing as close as 3/4" from clay lined chimney.
! 2' minimum clearance from any framing member in the structure. I have seen charred framing as close as 3/4" from clay lined chimney.
Runner
One thing to note in all of this - If you read thru the Rumford site, there is some merit to the idea that the older chimneys were better built, and that the increased thermal mass they possess can decrease the chance of fires related to thermal radiation. To counter that, fireplace chimneys rarely got as hot as your liner will, so while they may be able to deal with a given amount of heat better than a modern built brick unit, the given amount of heat may be alot higher.
So, yes, you should insulate your liner for 2 reasons -
1 - to limit radiant heat to the walls
2 - in order for it to be installed IAW the manufacturers instructions, therefore meeting code.
Another great 3rd reason is this - once you install a liner to meet zero/zero clearances (by insulating it) you can air seal and insulate around it without violation of code/rules, as it can then touch combustibles. That will keep more heat in the house, and is in the end a very large advantage. I recall the space around my unused flue beeing quite warm last winter just because of the massive amounts of rising air that were escaping around the chimney. So even if my flue had the required air clearances, I would still insulate it just so I could air seal around it.
One thing to note in all of this - If you read thru the Rumford site, there is some merit to the idea that the older chimneys were better built, and that the increased thermal mass they possess can decrease the chance of fires related to thermal radiation. To counter that, fireplace chimneys rarely got as hot as your liner will, so while they may be able to deal with a given amount of heat better than a modern built brick unit, the given amount of heat may be alot higher.
So, yes, you should insulate your liner for 2 reasons -
1 - to limit radiant heat to the walls
2 - in order for it to be installed IAW the manufacturers instructions, therefore meeting code.
Another great 3rd reason is this - once you install a liner to meet zero/zero clearances (by insulating it) you can air seal and insulate around it without violation of code/rules, as it can then touch combustibles. That will keep more heat in the house, and is in the end a very large advantage. I recall the space around my unused flue beeing quite warm last winter just because of the massive amounts of rising air that were escaping around the chimney. So even if my flue had the required air clearances, I would still insulate it just so I could air seal around it.
Thanks again O'Conner. What you are saying makes sense. Afterall, isn't that what we are really after....keeping the most amount of heat in the house as possible and doing it safely.
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