Insulating steel liners in internal masonry chimneys when relining

[Big Dan]

I'm just saying for the do-it-yourselfer which it seems like there's a lot on here its way safer to just put a stainless steel liner down their existing clay flue even if its cracked Than to break out all the flues and possibly causing a bigger problem. Remember no matter what you do it will never be totally "safe". I mean back in the day they made Chimneys out of wood

 

[begreen]

It is all about heat transfer and the masonry has very little r value.

That is an incorrect statement! 4" of brick has a respectable R=.8 insulation value. Brick has a high enough insulation value to earn a 33% clearance reduction in an NFPA 211 wall shield.

 

[Charles1981]

I have an internal masonry chimney in the center of my house (2 flues actually, one upstairs, one downstairs). The 6 inch liner is install in the larger flue which is lined by 10x13 clay tiles. The clay tiles are intact and the chimney was in good condition other than some creosote from a direct vent install the previous owners had (how they got draft into a 10x13 clay lined chimney is beyond me, but the glazed creosote in there was evidence of not very well.

Had the flue cleaned and a rigid 6inch liner installed. It is 27 feet tall to the basement. Drafts exceptionally well. There is basically at least 4 inches of air clearance on two sides of the liner and almost 6 on the other two sides. I have roxul stuffed in the top 4-5 feet of the flue and the bottom 4-5 feet of the flue.

Installer told me if i had an internal chimney insulation was not necessary. He did recommend it for external chimneys though.

So you are saying this is incorrect and to be to code the liner needs to be insulated? The general consensus here has been overall that internal chimneys don't need insulation in general either...

 

[oconnor]

Charles, that is exactly what I am saying, unless in exceptional circumstances you are able to determine that the chimney has an air gap all the way around it.

To be more precise, I am saying that liner manufacturers say that. Get the instructions that are published with your liner and see what they say. Let us know what you find please.

 

[Charles1981]

an air gap around the liner or the masonry structure?

 

[oconnor]

an air gap around the liner or the masonry structure?

Around the Masonry Structure. You can find this page here http://rumford.com/code/IRC12.html



R1003.18 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum air space clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum air space clearance of 1 inch (25 mm). The air space shall not be filled, except to provide fire blocking in accordance with Section R1003.19.

• 
  Exceptions:
  1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777 and installed in accordance with the manufacturer's installation instructions are permitted to have combustible material in contact with their exterior surfaces.
  
  2. When masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.
  
  3. Exposed combustible trim and the edges of sheathing materials, such as wood siding and flooring, shall be permitted to abut the masonry chimney side walls, in accordance with Figure R1003.18, provided such combustible trim or sheathing is a minimum of 12 inches (305 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).
  

 

[Big Dan]

I have an internal masonry chimney in the center of my house (2 flues actually, one upstairs, one downstairs). The 6 inch liner is install in the larger flue which is lined by 10x13 clay tiles. The clay tiles are intact and the chimney was in good condition other than some creosote from a direct vent install the previous owners had (how they got draft into a 10x13 clay lined chimney is beyond me, but the glazed creosote in there was evidence of not very well.

Had the flue cleaned and a rigid 6inch liner installed. It is 27 feet tall to the basement. Drafts exceptionally well. There is basically at least 4 inches of air clearance on two sides of the liner and almost 6 on the other two sides. I have roxul stuffed in the top 4-5 feet of the flue and the bottom 4-5 feet of the flue.

Installer told me if i had an internal chimney insulation was not necessary. He did recommend it for external chimneys though.

So you are saying this is incorrect and to be to code the liner needs to be insulated? The general consensus here has been overall that internal chimneys don't need insulation in general either...

If you understand everything is unsafe "from a certain point of view" Then it all will makes sense.

 

[oconnor]

If you understand everything is unsafe "from a certain point of view" Then it all will makes sense.

Not sure what you mean Dan. From a chimney fire point of view, I think code and instructions make sense.

 

[Big Dan]

Not sure what you mean Dan. From a chimney fire point of view, I think code and instructions make sense.

I'm just saying it can never be "Safe" no matter what you do.

 

[Charles1981]

My question is though how does having a liner in there change the equation. The clay liner is huge. There is 4-6+ inches of air surrounding the liner and the clay flue. Then the masonry structure.

That seems to be a schematic for a masonry structure with clay flue liner. I had my chimney inspected and no concerns were found with it and the current flue. I guess i don't understand... if the chimney inspects ok with the 10x13 clay flue why would it not be ok with a 6 inch rigid liner in place additionally?

 

[bholler]

Charles in the eyes of the code and the liner manufacturers no it doesn't. In all actuality yes it probably does help but regardless of that it doesn't meet code and doesn't comply with liner manufactures instructions. An your installer just took on a huge liability. And dan yes you are correct that you can defer make it totally safe but that doesn't mean that you shouldn't try to make it as safe as possible. I I am pretty sure that the people tat made and tested the liner have a better idea as to how to make it as safe as possible than any of us. As far as the break out issue I agree that most homeowners should not try to break out the clay liners. but I think they should understand that if they don't and don't get proper insulation they are not doing it to code and are probably voiding the warranty on their liner (as well as the safety and performance issues.) Further if the liner is has been cracked of has bad mortar joint there is usually creosote on the out side of those liners which causes a big safety concern.

 

[jatoxico]

I've read the back and forth here with some interest. I would like to try to better understand the construction of my chimney so maybe somebody can make a few educated guesses for me.

I have an external masonry chimney (red brick). The face is 24" OD (3 full bricks). The side that returns to the house is 21" (2 1/2 bricks). The chimney was added probably in the 80's. From the old damper up is just over 30'. Unfortunately I've never measured the clay tile but from memory I would say max 10" OD.

How is the clay tile typically installed? Freestanding or is masonry/mortar typically layed up right to the tile? Is there likely another layer of brick behind the outer layer?
Are air gaps typically provided between the different components?

Should probably have asked this first but are there any typical installs or is a free for all?

 

[bholler]

well most of the chimney is probably single coarse thick once you get up past the smoke chamber. and there is supposed to be air space between the liners and the other masonry many times there is not. also if there are multiple flues there is supposed to be a wythe wall separating them.

 

[oconnor]

My question is though how does having a liner in there change the equation. The clay liner is huge. There is 4-6+ inches of air surrounding the liner and the clay flue. Then the masonry structure.

That seems to be a schematic for a masonry structure with clay flue liner. I had my chimney inspected and no concerns were found with it and the current flue. I guess i don't understand... if the chimney inspects ok with the 10x13 clay flue why would it not be ok with a 6 inch rigid liner in place additionally?

Charles, from a technical point of view, the instructions can't deal with all install scenarios. So the manufacturers tend to work from the most restrictive situation, which would be a much smaller flue size.

Also, with a 10 x13 tile, I assume this is a former fireplace. They had much lower flue gas temps. Once you line it and block it top and bottom, the chimney will experience much higher temps than it did in its original use.

Also, I believe the testing for relining systems is just more strict than the criteria used for masonry chimneys.(I May be wrong here though)

In the end, the local Authority Having Jurisdiction (specific term used in the codes) has the final say as to what is OK. If they say it is OK, then it meets code.(NFPA 211 even has a statement to that effect in it, if LAHJ approved it then it is deemed to meet NFPA 211, even if it is outside the details the code contains.)

I don't think you have anything to worry about, but I've never seen your chimney.

 

[Rudyjr]

[quote="oconnor, post:

In the end, the local Authority Having Jurisdiction (specific term used in the codes) has the final say as to what is OK. If they say it is OK, then it meets code.

I don't think you have anything to worry about, but I've never seen your chimney.[/quote]


Finally! Exactly the point some on here have been trying to make all along.

 

[tcassavaugh]

ok, I have a question..........in the brochure, I see a flex liner being installed. how prone are they to "trapping" or "collecting" more creosote vs. the smooth liner variation of the chimney liner. just wondering.....and don't tell me to burn dry wood..... I already know that has a direct relation to creosote production. just curious.

 

[bholler]

They can collect a little more creosote yes but as long as it is not glazed it will usually brush off pretty easy. We usually use heavy wall flex for wood liners which is pretty smooth inside (it is classified as smooth wall) but we use it for the added durability of the thicker metal not necessarily for the smooth wall.

 

[branchburner]

[quote="oconnor, post:

In the end, the local Authority Having Jurisdiction (specific term used in the codes) has the final say as to what is OK. If they say it is OK, then it meets code.

I don't think you have anything to worry about, but I've never seen your chimney.

Finally! Exactly the point some on here have been trying to make all along.[/quote]

Not quite exactly, because I don't recall anyone mentioning the "Local Authority Having Jurisdiction" earlier in this thread. The distinction is, without some kind of official word that your install is acceptable, it may very well still be in violation of code even though it might reasonably be considered "safe" -- and nothing to worry about -- by just about anyone.

Here's how it worked for me, and I assume this is common: the Local Authority Having Jurisdiction had no interest in actually inspecting my install... he simply said as long as all manufacturer specifications were met, I was fine. As a technicality, however, the specifications set forth by my liner manufacturer were NOT met. Until I return to the Local Authority Having Jurisdiction and get this officially okayed, I have not met code.

So my install remains technically in violation of code, even though I am quite confident it is "safe" to my standards, and COULD be code-approved by the LAHJ. What will the insurance company say, in the event of a house fire? I don't know. Is that something to worry about, even if I'm not worried about a fire? Maybe.

So I think the overriding point of this thread is that many installs, though reasonably considered "safe," remain in technical violation of code due to failure to exactly follow liner specification AND failure to have the LAHJ sign off on that fact as being acceptable.

 

[begreen]

Our house had two chimneys one original, from the 1920s and one added for an oil furnace at some point, maybe the 60s? Both chimneys had the required 1" air gap. I know because I removed both of them, brick by brick. Surprisingly they were build correctly in spite of us being in a rural area where I know inspection did not occur back then. However, the house had a significant remodel around 1984 and the contractor clearly didn't know or care about clearances. They built right up to the brick with framing. Also, we found 2 stove takeoffs in the chimney, one being plugged by plaster and nothing else between it and newer wood framing.This was not evident until the tearout.

Unless your home has never been lived in by multiple families and never suffered a remodel how can you be sure that the chimney was installed correctly and has not had later changes that compromise safety? Adding a full liner increases the margin of safety and improves stove performance. An insulated liner is the safest and will help reduce creosote build up.

 

[Big Dan]

They can collect a little more creosote yes but as long as it is not glazed it will usually brush off pretty easy. We usually use heavy wall flex for wood liners which is pretty smooth inside (it is classified as smooth wall) but we use it for the added durability of the thicker metal not necessarily for the smooth wall.

How many heavy flex liners have you seen fail?

 

[bholler]

I have seen a couple heavy flex liners fail but the only 2 I can think of were after 25+ years of heavy use. I have seen many more light wall liners fail. But both are good products I just feel that the heavy wall is worth the extra money. I have also seen a few failed rigid liners anything over enough time or with abuse will fail.

 

[begreen]

Hard to imagine properly installed rigid failing. Were the rigid failure due to the pipe or due to poor installation (like poorly attached sections)?

 

[bholler]

One was after 26 or 27 years of burning coal and there were lots of pin holes The other was with a big wood furnace and according to the homeowner many chimney fires over 19 years. That one was burnt out at the bottom it was ok from about 6 feet up.