newbie with a questions about rigid liners and insulation in old (1800's) chimneys

[nscarnati]

I have a few questions that I've searched the forums for answers to numerous times, and can't seem to find answers relevant to my case, so I'd appreciate any help .

Background:
I have an old house (1880) that has a straight down flue-less chimney with zero bends, and the interior dimensions of the chimney are approximately 18"x18" which will make a rigid liner install pretty easy. I'm new to woodburning and just bought a used jotul 100 woodstove. I repointed the brick at the top of the chimney that I had access too and added some more courses of brick to reach the 3' above the roofline code requirement. I'm planning to get a rigid liner, since it's a straight shot, but not sure whether to get a single or double lined for a few reasons that are unique to my situation. The stove will sit inside the fireplace (which is only 13" deep) a couple inches from the back wall of it (stove vents vertically)

Single-wall pro/cons for my specific situation:
- Since pipe is cheaper
- Since I would need insulation with single liner, I can get pour-in insulation like thermix to insulate the pipe, which will fill in all of the voids around the liner in the chimney. This I think would be important for me because what I've read, the pour-in insulation adds *some* structural integrity to the chimney and should get between bricks to help lock the brick together, which is very old with I'm sure a lot of deteriorated mortar joints. I have read and know that something like Supaflu would be the best option for dealing with the structural re-inforcement of the old brick, but it is out of my budget (less than $1000), and can only afford the materials and will do the install myself. I'm planning to go with Simpson duraliner single or double wall, and simpson DVL stove pipe for the interior pipe

Double-line pros/cons:
- Double lined would be a lot quicker to install
- I like the fact there's 2 rigid metal walls for safety sake
- concerned that with no pour-in insulation around the double-wall chimney, the space in the chimney around the new liner would heat up to a point where it would cause the old bricks in the chimney to possible expand/contract and cause structural damage (or worst case scenario collapse). I don't have any way of getting access to the chimney to repoint any brick prior to the new liner install, so I basically have to work with what's there.

I guess the big questions I have are:
1) does pour-in insulation really get solid and add some integrity to the chimney, or does it still stay kind of loose
2) how much protection to the old chimney would a single-wall rigid liner + pour-in insulation solution provide against chimney fires, etc versus a double-walled rigid chimney liner solution? In a perfect world with unlimited money, I would get the double-walled liner for saftey + pour-in insulation for chimney reinforcement/additional insulation, but I just don't have the budget for it.
3) Are there any issue putting the stove inside the fireplace a couple inches from the back wall of the chimney (which was originally used ot burn open fires)? I know there's clearances to combustible materials to take into consideration, but is there any typical clearance requirements to non-combutibles materials (fireplace walls) for the stoves?

Thanks in advance!

 

[backpack09]

I think you need to run atleast an insulated liner down any unlined (clay or otherwise) chimney. So I dont think that single wall is really an option for you.

Dan

 

[nscarnati]

I think you need to run atleast an insulated liner down any unlined (clay or otherwise) chimney. So I dont think that single wall is really an option for you.

Dan

I was intending to insulate no matter what -

If I ran single wall, I was going to use pour-in insulation (thermix or the equivalent) - which should meet code. The questions basically which of the 2 options (or something completely different) would be the best solution

 

[jtp10181]

We have used both simpson products, but not the thermix. With the flex liners we wrap them in 1/2" insulation plus a stainless steel mesh to keep it together. The rigid liner is very nice and faily easy to install. It is rated to 2100 deg and 0" clearance to masonry (even if the masonry structure does not meet current codes). You would be nuts to add MORE insulation around that (I know you said you are not, but would if you had the money). Anyway... I can answer any questions about that stuff you need.

Now we just need someone to let us know if the thermix will help reinforce your old chimney.

 

[nscarnati]

thanks jtp - were the chimney in good shape, it would be a no brainer to just use the double wall duraliner and nothing else... the longterm durability of the chimney as-is is what has me kind of concerned though, and was hoping the single-wall/thermix solution would help me out there too..

I priced out thermix, and since my chimney is pretty large (18x18 inside dimensions, 25' tall) and I only are using 6" chimney, it would take like 30-40 bags, which wouldn't be cheap. definitely would be more expensive than doublewalled pipe, or single + blanket insulation. but if there's some decent structural benefits to it, it would probably be worth it

 

[branchburner]

The house is 1880, but is the chimney 1880? Have you had anyone (pro mason/sweep) look at the chimney to really evaluate what state it's in? If it really is in bad shape then the thermix might not be enough to stabilize it, and I wonder if the thermal expansion of your liner material in that scenario may potentially cause problems. I was recently reading a thread that noted clay liners should not be motared to the surrounding masonry (to allow for expansion of the liner). But any idea how this applies to the thermix application? I have no clue.

Even though your idea seems perfectly reasonable to me, I'm guessing that a mason would not propose thermix as a way to stabilize your chimney. On the other hand, maybe the chimney is stable enough that you don't need to worry, and just go with the standard insulated liner. But I'd say if you are unsure of the longterm durability of the chimney, do you need to be sure of the longterm durability of the liner? You could probably just use flex.

Another question is do you think there will ever be other plans for the chimney? Once you pour the slop around that 6" liner I think you have a 6" flue for life (or at least the life of the chimney). From what I've read it will not only be solid enough to give support, it will have some permanence that you better make sure you want.

If you go that route, I wonder if anyone out there has a recipe for homemade thermix. The brand-name stuff seems pricy, but if the basic ingredients are mortar and perlite, those things are cheap as dirt (maybe cause they basically are dirt, I suppose). Based on the cost of raw ingredients, it should be the least expensive insulation possible.

Sorry, no answers, just more questions!

But what I'd do is get the insulated single wall or flex, sealed block-off at the bottom, fill all that extra air space between the liner and the chimney that is above the roofline (and maybe a bit below) with the cheapest, thickest mineral wool I could find (like Thermafiber safing insulation), and then seal off the top.

 

[oconnor]

But what I'd do is get the insulated single wall or flex, sealed block-off at the bottom, fill all that extra air space between the liner and the chimney that is above the roofline (and maybe a bit below) with the cheapest, thickest mineral wool I could find (like Thermafiber safing insulation), and then seal off the top.

Be careful adding "extra" insulation over the insulated liner. Check with the manufacturer of any product you use to see how they want it done (i.e. read the manual) If you take other "good idea" steps, you are not installing the product IAW thier instructions, and therefore you don't meet the appropriate specs (like UL 1777 or CAN ULC S 635).

Why is this important - your stove and flue is safe when installed IAW manufacturers instructions, and wasn't tested under the "good idea" conditions - you may not have a problem, or you might. Thermafiber is designed to stop fire spread, and doesn't burn when exposed to 2000F for a specific period of time (something in the order of minutes to hours). I have no idea how it would behave after 20 years of constant exposure to temps of 1200F, and then exposed to a chimney fire (2200F).

Here is an example from the Simpson manual

CLEARANCES

Simpson Dura-Vents DuraLiner (SDL) is listed by Underwriters Laboratories as a vent for listed wood burning stoves and inserts. DuraLiner (SDL) is designed and U.L. listed for installation in masonry chimneys only. The minimum clearance from pipe to masonry construction is 0". Never fill any required clearance air space with combustible or noncombustible materials. DuraLiner (SDL) shall be sized not less than that specified in the appliance manufacturer's instructions.


If you have doubts on the structural capacity of the flue, get it inspected. If you feel the flue won't take the expansion/contraction associated with wood heat, then don't use it until you feel it will.

Read the link in my signature on chimney liner best practices if you want a basic overview of liner installs.

 

[pgmr]

Last year I used a homemade batch of lightweight concrete (perlite and cement) to seal around the block off plate and single layer flex liner (keeps loose perlite above it from working through gap between plate and liner). Here's the link to the thread describing it: https://www.hearth.com/econtent/index.php/forums/viewthread/15558/.

The test batch of concrete seemed quite light and had decent compressive strength, though I didn't do any kind of strength testing as I was only interested in the thermal properties. I'd suggest doing test batches of different ratios of perlite/cement/water to see which works best for you.

I didn't notice how tall your chimney is, but if you fill the entire void area with a concrete mix of any kind, you will have a significant amount of weight bearing down on your block off plate. You might need to reinforce the plate with steel lintels underneath to prevent a blowout.

 

[branchburner]

Check with the manufacturer of any product you use to see how they want it done (i.e. read the manual) If you take other “good idea” steps, you are not installing the product IAW thier instructions, and therefore you don’t meet the appropriate specs (like UL 1777 or CAN ULC S 635).

The minimum clearance from pipe to masonry construction is 0". Never fill any required clearance air space with combustible or noncombustible materials.

Thanks for pointing out some very important things to consider, and the wisdom and safety of doing things by the book. I, too, was suggesting a professional opinion might be in order, and did not mean to suggest at the end of my post that just winging it would be the best way to proceed, but simply the way I might. I should indeed put a disclaimer on my posts when I say "what I'd do" that I mean that literally, and what you should do is question my logic - I could just as easily be doing it wrong!

But I am curious, and I'm not trying to be flip - if no clearance air space is required, how could required clearance air space be filled? And are you suggesting that the air space not be filled with thermix, either?

I was under the impression that safing was basically the same material as the mineral fiber insulation blanket that comes with a liner, so please let me know if I'm wrong. And that's not to say even if it is the same material that it should be used in this manner (even though I already have). I tend to make a lot of assumptions not based on hard facts, so facts are good when they come straight at me!

 

[nscarnati]

Here is an example from the Simpson manual

Never fill any required clearance air space with combustible or noncombustible materials. DuraLiner (SDL) shall be sized not less than that specified in the appliance manufacturer's instructions.

Thanks for spotting that - I missed that when reading the duraliner manual I found on their site.

If I go with a SINGLE wall 6" liner that of course needs insulated, centered in an 18"x18" chimney, and filled it with thermix type insulation, would ANY heat even make it through the insulation out to the brick? because we'd be talking about 6"+ of insulation between the surface of the liner and the surface of the brick, which is a lot more than the typical 1/2-1" of insulation typically wrapped around liners

 

[Hogwildz]

I used double wall preinsulated rigid, and would do it all over again the same way.

 

[oconnor]

Edit - I must apologoze for the long post - didn't realize how long it was until I posted it - and now it's longer 'cause of my apology. Sorry

If I go with a SINGLE wall 6” liner that of course needs insulated, centered in an 18"x18" chimney, and filled it with thermix type insulation, would ANY heat even make it through the insulation out to the brick? because we’d be talking about 6"+ of insulation between the surface of the liner and the surface of the brick, which is a lot more than the typical 1/2-1” of insulation typically wrapped around liners

Some heat will eventually make it to the brick regardless of the insulation - but it shouldn't get hot enough to need any clearances to combustibles. Thermix description of heat transfer from thier manual -
"TherMix® lowers temperatures on liners during over firing or chimney fires. Unlike ceramic blankets, TherMix® allows heat to be slowly absorbed into the entire mass of a chimney, where it is safely dissipated over a large surface area. To pass the 2100 degrees F test under the UL 1777 standard, foil-faced ceramic blankets rely on aluminum foil to reflect heat back to its source. Liners could be exposed to temperatures exceeding the limits of their respective stainless steel alloys."

I'm not sure how it can lower temps during overfires AND maintain temps the rest of the time, but many folks use it, and it works well from thier reports.

As far as single wall liner goes, there are a few manufacturers who allow thermix type insulation, but others don't - like Simpson, and I believe Selkirk as well - give thier instructions a read before you buy. Like Hogwildz, I am looking at having double wall insulated liner installed - I like the dual containment as well as the idea that a wrap can't get snagged or otherwise moved from an ideal position when getting shoved down my old brick chimney, 'cause it is encased in another steel layer.

And don't buy if you can't read thier instructions online. I currently have a flex liner installed (pro install) that should have been insulated but wasn't. My old inside chimney was built in 1936, and doesn't have any airspace clearance to combustibles around it, and is tight inside. Therefore, I need a zero/zero liner - nil clearance to combustibles inside and outside the brick chimney. I had to go thru 4 different install shops in the area I live, and still didn't find anyone who understood the requirement - in fact, most of them looked in shock when I read them the UL tag on the liner they installed - which stated the airspace clnc requirement outside the chimney - 'cause they had never even realized it was needed. My liner manufacture doesn't have thier instructions online, and still hasn't been able to get me a copy of the instructions for thier insulation kit - they can't find the file they say.

In the end, I wrote a letter to WETT INC - regulatory body in Canada - and got the confirmation I needed that my install was wrong and the installer, who is WETT certified, needed to fix it. That is another story - you can read my rant on it here.

Branchburner's question is very valid -

If no clearance air space is required, how could required clearance air space be filled? And are you suggesting that the air space not be filled with thermix, either?

I suspect that this line in the instruction manual is a standard line and could be better written. I would call Simpson and ask them - I suspect they would say that they don't want anything else around thier liner, 'cause there wasn't anything there when they had it tested - and thet probably wouldn't honour a warrantee claim if something else was installed around the liner.

The description I have seen on the liner wrap systems often speak of a "ceramic wool wrap" vice mineral wool. Doesn't mean that a liner designed for a wrap that doesn't require an airspace clearance after wrapping couldn't be filled with a mineral wool material - mineral wool is what I have so far for a block off plate (not done yet - waiting for the final liner install) - more research required on that one I think.

The best advantage I see to insulating the liner is that you get zero clearances to combustibles outside the brick chimney - you could concievably wrap the chimney in paper mache and be safe (not what I recommend, but just to say...) That means I don't have to worry about combustible clearances when I insulate and air seal, and I don't have to worry about running wiring alongside the chimney in the chase during renovations and upgrades. You can even expose a portion of the brick chimney if your design style likes the look - you can't do that if you have clearance requirements.

I can't imagine how I would ever replace a liner if I had a loose fill perlite insulation around it - what a mess. I know we think that our stoves are lifetime installs, but so did folks who installed the original fireplace, and first generation inserts that didn't even have flue pipes (aka slammers)- they just let the smoke rise out the hole on the appliance, and hoped all would be good. I suspect in 20 years, we wil have discoved some sort of flaw with the best installs going in today, and we will be changing them too - I want to be able to get my liner back out when that day comes.

I plan on the doublewall preinsulated liner going down my chimney real soon (as soon as I can get my installer back to fix his mistake).

I got some good info from details on this site here. I am not affiliated with them, and have never bought from them, but I liked how you could get great info on each product they sell right off thier site.

 

[nscarnati]

thanks for all of the long and thorough replies, it's been very helpful in trying to decide which route to go. the only question I have that's still unanswered is how much, if any, structural re-enforcement does using a thermix type product add the the chimney. I realize a loose fill like perlite/vermiculite wouldn't since it doesn't harden, so I'm referring more to a wet-mix pour-in inuslation. My chimney doesn't seem like it's in any danger of falling down (it's stood there fine for 120+ years), but I always like to over-do it when possible for safeties sake

 

[begreen]

When we removed our 84 yr old fireplace and chimney I was amazed how easily the chimney came apart. Old mortar can get very crumbly and turn to sand. In some places it seemed like only gravity was holding our chimney together. One good earthquake can point this out quickly.

 

[nscarnati]

When we removed our 84 yr old fireplace and chimney I was amazed how easily the chimney came apart. Old mortar can get very crumbly and turn to sand. In some places it seemed like only gravity was holding our chimney together. One good earthquake can point this out quickly.

It was like for some of the bricks near the top of the chimney that I removed and rebuilt (above the roofline). I'm wondering whether a chimney cleaning before the liner install might actually do more harm than good to the structural integrity of the chimney if that's the case and the mortar has turned to sand

Luckily I don't have any earthquakes to worry about in maryland

 

[oconnor]

If cleaning it hurts it, then so be it - you need to clean it first. Don't want any old creosote or debris catching fire outside of the liner. At least then you will know that it needed repair. Avoiding the cleaning to avoid breaking something doesn't seem ideal.

Have you had a Mason/Sweep look at it yet? You seem concerned, and smart enough to know that problems need to be fixed before you light that first fire.

I am going to guess that if the flue was going to come apart, then it would most likely do so once you fill it with wet heavy Thermix. The instructions say that in a 18.5 x 18.5 flue interior, using a 6 inch liner, assuming a 20ft flue, you will have 43.5 cuft of mix @ 20lbs/cuft - that's 870 lbs of mix inside the flue to hold up until it dries. (Real strong block off plate). I'm sure Thermix was designed to avoid the concern you have, but why attempt to find out.

Your call, but I'd get the double wall preinsulated and be done - I have no idea how much weight would be needed to blow out a flue.

That said, Thermix should add structure to your flue - it has to if it's 870 lbs heavier.

Wow, that's a lot of weight up and down a ladder

 

[NHFarmer]

I have a house built in 1850, original chimneys.Mine were in similar condition.I repointed the brick above the roof,I also parged the exterior of the chimney in the attic and the cellar.I dropped a 7" SS flex liner in and filled around it with pour in insulation.The insulation pours in and mixes to the consistancy of potting soil.It does set up as there is portland cement in the mixture.It hardens but is somewhat soft.You can push a screwdriver into it.I felt that it does help to hold the chimney together.It seemed to be the most cost effective solution short of tearing down and starting from scratch.Now the earthquake issue,I am going to take my chances.What I now have is far better than what I started with.

 

[nscarnati]

I have a house built in 1850, original chimneys.Mine were in similar condition.I repointed the brick above the roof,I also parged the exterior of the chimney in the attic and the cellar.I dropped a 7" SS flex liner in and filled around it with pour in insulation.The insulation pours in and mixes to the consistancy of potting soil.It does set up as there is portland cement in the mixture.It hardens but is somewhat soft.You can push a screwdriver into it.I felt that it does help to hold the chimney together.It seemed to be the most cost effective solution short of tearing down and starting from scratch.Now the earthquake issue,I am going to take my chances.What I now have is far better than what I started with.

thanks, that was kind of my thinking... the only issue now is what occonnor brought up, that'd I'd need 40 bags of the stuff. It's a lot of weight, but I would think I could pour some in, let it harden, pour in more and harden, etc. When wet, it should not "fill" but at least indent into any brick joints missing mortar, and when that dries should provide some structural support to the thermix to hold it up and keep it from falling through the chimney into the hearth

 

[oconnor]

Here is a thought - if it is 18 x 18 inside, you could run a prefab flue (Stainless like Selkirk etc) inside the brick and use the brick as a chase - you wouldn't even have airspace clearance problems (6" inside plus 4" total thickness), and you would reduce almost all heat transfer to the brick.

Think outside the box (actually inside it, but...)

Or, I may be having a really dumb idea.

 

[NHFarmer]

My chimney is 35' tall only 12"x12"inside .I used 12 bags.You don't pack it in,just pour it in and jiggle the liner.I didn't worry about the weight.

 

[BJN644]

I have a house built in 1850, original chimneys.Mine were in similar condition.I repointed the brick above the roof,I also parged the exterior of the chimney in the attic and the cellar.I dropped a 7" SS flex liner in and filled around it with pour in insulation.The insulation pours in and mixes to the consistancy of potting soil.It does set up as there is portland cement in the mixture.It hardens but is somewhat soft.You can push a screwdriver into it.I felt that it does help to hold the chimney together.It seemed to be the most cost effective solution short of tearing down and starting from scratch.Now the earthquake issue,I am going to take my chances.What I now have is far better than what I started with.

thanks, that was kind of my thinking... the only issue now is what occonnor brought up, that'd I'd need 40 bags of the stuff. It's a lot of weight, but I would think I could pour some in, let it harden, pour in more and harden, etc. When wet, it should not "fill" but at least indent into any brick joints missing mortar, and when that dries should provide some structural support to the thermix to hold it up and keep it from falling through the chimney into the hearth

If I remember this stuff is like $50 to $60 a bag, X 40 bags, wouldn't having someone pour a Supaflue or similar be cheaper and achieve the same result?

 

[nscarnati]

If I remember this stuff is like $50 to $60 a bag, X 40 bags, wouldn't having someone pour a Supaflue or similar be cheaper and achieve the same result?

If using the pour-in brings the total cost up to the cost of supaflue (whom I can't even get someone to come and quote me on), then I would definitely go supaflue.. trying not to do that though, because of the cost

 

[nscarnati]

My chimney is 35' tall only 12"x12"inside .I used 12 bags.You don't pack it in,just pour it in and jiggle the liner.I didn't worry about the weight.

wow.. seems like it should be more than that.. what brand and type (rigid/flex) did you use? was it 6"?

 

[nscarnati]

Here is a thought - if it is 18 x 18 inside, you could run a prefab flue (Stainless like Selkirk etc) inside the brick and use the brick as a chase - you wouldn't even have airspace clearance problems (6" inside plus 4" total thickness), and you would reduce almost all heat transfer to the brick.

Think outside the box (actually inside it, but...)

Or, I may be having a really dumb idea.

I was looking on google for the selkirk pre-fab flue and couldn't find anything that I think you're describing.. can you provide a model name of the right product, or better yet a link? what I think you're saying is that I could put some type of metal flue in the chimney, that's bigger than the 6" doublewall chimney liner pipe, and run the liner inside of it? (which would basically provide a secondary metal liner for additional safety)

 

[oconnor]

Caveat - my idea may be a dumb idea - I have those once in a while, and I am willing to take the hit, so if someone has a good reason why my proposal is stupid, please let the fellow know.

http://www.selkirkcorp.com/

The idea is to run a chimney inside your current chimney - the only reason you need a liner is to complete the old chimney you have now. If you ran a new chimney (even if you did it inside the old one), you wouldn't need a liner.

This of course assumes that you can install the chimney inside the 18 x 18 space and secure/support it properly.

Again - could be dumb idea - but I don't think Thermix is the best idea. It was great in 1983 when not much else was available, I'm sure, but there are other products on the market that do the same for less money effort, like Simpson double wall insulated liner.

Just my opinion...