# Insulation around chimney liner?



## davis817

Hi, hoping someone can help resolve a question I've had for a while. I recently installed a 316Ti liner in my chimney for my wood stove. The stove sits in front of the fireplace and the piping runs through the damper plate opening and up the length of the chimney, about 20 feet. At the top I have a plate covering the flue with a cap on top . I packed some unfaced fiberglass insulation around the liner just under the plate at the top of the chimney. I was told by a local chimney sweep that this was acceptable. However, I have read elsewhere online that mineral wool or other such insulation should be used near the pipe. Anyone have experience with this? Thanks for any help.


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## cycloxer

Mineral wool is better as it does not burn and has a very high melting temperature. Fiberglass does not burn either, but it does melt at a lower temperature. So, it is not necessarily the right way to do it, but it also isn't going to burn down your house.


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## derecskey

You know, I was just going to post a related question about proper liner, etc. installation, less the insulation.  I have a small insert in my masonry fireplace opening, with an insert surround.  I did not self-install, rather I had the stove installed for me.  When my stove gets going good, the insert surround plate actually warps slightly from the heat and pulls away from the sandstone fireplace.  (My stove is a rather cheapish Buck 21, and I know the surround plate is not all that thick).  

So the gap there got me thinking... what if I just took the insert surround off and had a hearth stove installation, like yours?  But is there a plate blocking the flue where the damper once was?  My setup is just like yours.  Damper plate removed, flexible liner installed, plate siliconed to top of flue with cap on top.  But there's nothing blocking the flue where the damper plate used to be.  Should there be?

So I did the match test.  I lit a match, blew it out, and held it near the opening gap between the insert surround and the masonry and sure enough it really sucked the smoke (and even the flame from the second match I tried) right up the flue.  Is this just the convection of the heat?  Or am I leaking all my heat out right up the flue between the flue and the liner?  Is my insert and liner installed properly?


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## davis817

I used to have a 5' section of ovalized pipe that went throught the damper opening (damper plate removed) and up the chimney a few feet.  At that time I had a blocker plate on the damper opening with a hole for the pipe to pass through.  Never did seal it well though and had drafts when not using the stove.  I went with the liner for better stove draft and am guessing the plate at the top of the flue provides some protection against a draft.  I thought packing insulation either at the top or bottom would help with any remaining draft.  I went with insulation at the top thinking that any warm air from the house would make it part way up the chimney and help keep the liner warm since I didn't insulate the liner.


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## cycloxer

Seal, insulate, and block off both the top and the bottom with metal and a fireproof insulator for best results. Here is my lower block off plate.


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## oconnor

Fibreglass insulation is definately the wrong stuff to use, and most mineral wool batts actually aren't rated to the 2100*F temps that purpose built flue products need to be tested to.  If you want to insulate around a flue, I recommend you use the products that your liner manufacturer approves of in the instructions for your liner - most will refer to a ceramic fibre blanket, 1/2" thick.


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## DAKSY

davis817 said:
			
		

> Hi, hoping someone can help resolve a question I've had for a while. I recently installed a 316Ti liner in my chimney for my wood stove. The stove sits in front of the fireplace and the piping runs through the damper plate opening and up the length of the chimney, about 20 feet. At the top I have a plate covering the flue with a cap on top . I packed some unfaced fiberglass insulation around the liner just under the plate at the top of the chimney. I was told by a local chimney sweep that this was acceptable. However, I have read elsewhere online that mineral wool or other such insulation should be used near the pipe. Anyone have experience with this? Thanks for any help.



You will get answers both ways on this one. 
I, for one, agree with your chimney sweep.
I installed wood burning inserts (& stoves) for 5 years before 
moving to the sales floor & EVERY one of them - in a masonru fire place -
is installed with unfaced fiberglass insulation 
both UNDER the cap & in the damper area.
NOT ONCE has there been an issue with ANY of these installs.
Fiberglass does not melt. It does not outgas. It works, period.
I pulled my 3100L out of my fire place after 4 years of burning it 
as a primary heat source -  4 -5 cords per year - & the fiberglass looked 
& felt EXACTLY the same as the day I installed it. 
It was NOT melted. It was NOT discolored. It was NOT deteriorated
in ANY way.
We can battle this all we want & folks here will continue to disagree,
so you can take what you want from both sides of the argument.
I've worked for this company for 9+ years, & the owner started the business
in 1977 in his garage. He is one of the more respected voices in the field of 
wood burning & in fact his input is directly felt by anyone here who has taken the
NFI Certification Exam for wood burning. He is part of the board assembled to
develop the questions & answers, & under HIS direction,
we install with unfaced fiberglass, because it's safe to use
& it works very well...


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## cycloxer

In your own house you can use whatever you want. The key is to stay away from combustible materials. If you are going to use a board, watch out for those with paper foil backings. I almost built one out of that stuff and the problem is that the foil can burn as it is paper based and adhered with tar. 

Most insulations in and of themself are not combustible as they are made from glass, minerals, or ceramic. The temperature at which these melt is so high that the paint on your stove would literally be on fire before any of them were a problem. So if you come home one day and your paint job is on fire, then I would be concerned...

...also, this is a very good reason for having a lower metal block-off plate in your fireplace. It becomes a steel fire door for anything that may ignite inside your chimney. It's a good practice if you are willing to take the time to fabricate one.


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## oconnor

Daskey

Your experience with fibreglass is not at all what I have seen/smelled. When I used it to seal a gap between my thimble and the concrete wall in my old house (old oil flue with wood burner on it- not ideal) it smouldered, smelled like burning glycol antifreeze, and changed color, crumbling when I removed it. Even the Roxul AFB I have installed as a block off plate had discolored from the heat of the liner. 

If you stock with a product APPROVED for use around a flue, you will never by wrong or caught off guard ( think 2100*f chimney fire)


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## jtp10181

Under normal conditions yellow fiberglass insulation will turn white. The particulate that comes off it can get into the air and melt/burn and cause odors. The insulation itself can also cause odors when extremely heated. In abnormal conditions like a chim fire that pushes your liner to its limit the fiberglass should melt, and god knows what that would look or smell like, as I have never seen it.

The proper and tested way to install would be a SS liner insulated per mfg specs (ceramic blanket or pour in product). Chim is sealed at top or bottom (or both). Top  sealed with top plate of liner kit and bottom with a custom made block off plate. No fiberglass insulation anywhere in sight.


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## tickbitty

I'm a little confused on this issue, as it seems that the materials people mention using (ceramic fiber blanket, "rock wool" or the great board that cycloxer used in his plate above, are such specialty materials that seem quite difficult to find.  I have been checking the box stores and hardware stores as well as the online chimney liner stores, ebay, etc to see where I could get such a thing and have come up empty handed.  

The difficulty in finding this stuff makes me think that there may be few installs actually done "right?"

My insert's installation shows a full liner install to have an uninsulated block off plate at the top and no block off plate at the bottom.  The liner kit, with a pre-insulated liner, does not specify anything to stuff or insulate the kit.  The insert surround came with what looks like fiberglass to seal against the brick around it, but I am not likely to get a good seal with that since my surround will be slightly short of the fireplace opening and will require the mantel shield, anchored to the top of it, to fill that space.

I have a friend who is a handyman prepared to do the install as spec'd in the manual.  If I want anything additional to that I'm going to need to get pretty specific.  I am not likely to find these special materials by the time he does this (monday?)  So I am left with the question of whether to insulate the top plate or bottom connect area at all, and if so, whether to use unfaced fiberglass.  I have a large continuous damper that will have to be cut to allow the liner through.  This will leave the rest of the 4" wide slot open across the back of the fireplace.  I suppose I could stuff that with insulation as well, and if I end up having cold air coming in, I can still find some of this specialty stuff and make myself a separate block off plate that I can install later?

Advice welcome and appreciated, and my apologies to the Original Poster for the Hijack, but I hope he worked something out too!

Just want to reiterate that I AM using an insulated liner, I am just questioning what to use if I need to insulate at the top and bottom of the flue.


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## EatenByLimestone

I stuffed Kaowool around the top of my insulated liner.  I don't believe it was necessary since the liner was insulated but I figured it wouldn't hurt to keep any heat that escaped the liner insulation in the dead air space around it.  

Matt


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## jtp10181

tickbitty, with a fully insulated liner system, your min requirements would be to seal the flue at the top with the metal top plate, and thats it. Making a block off plate or putting insulation in the damper area is just extra to try and keep more heat in the house.


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## tickbitty

Thx jtp - since we want to get this done soon, we are going to skip the block off plate at the bottom to start with.  If we find we have a draft problem or underheating, etc, we may decide to add one.  I think I might like to just to feel all sealed up but we would like to get this up and running as soon as possible, so...
Anyway thank you for clarifying.


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## k3c4forlife

What type of regular home insulation is safest for the damper area if you are not going to build a block off plate?


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## mellow

Soft block off "plate" would be Kaowool or rock wool.  I ordered my kaowool from ebay, a guy sells it by the foot, but then again that was a few years back.


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## k3c4forlife

Would like R-30 insulation work?

Does the local Home Depot of Lowes have insulation that would work between the insulation kit and the masonry wall?  

I just installed my insert on Saturday. 15’x0.014” thick 6” chimney liner insulated with 1/2” insulation kit.


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## bren582

There is plenty of the correct product to use available on Ebay.. That is Ceramic Fiber Blanket.. No binders, oils, Formaldehyde etc  mixed in.. Its 100% spun ceramic material plain and simple..  Yeah you could use regular fiberglass and probably never have an issue with it but why chance it when you can get 100% comfort level with ceramic fiber?  

This is just one of many listed:
http://cgi.ebay.com/Kaowool-Ceramic...emQQptZLH_DefaultDomain_0?hash=item1e58fd6580


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## k3c4forlife

The guy in the local hearth store said any insulation at home depot would be fine as long as you took the paper off of it.  I dont feel comfortable with that...


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## jtp10181

That guy should crack open an install manual once and a while. The ones I have seen specifically state NOT to use fiberglass insulation around the liner for wood inserts.


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## k3c4forlife

How about around the insulation kit around the liner?


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## jtp10181

Never seen it recommended in a manual, doubt it is proper. The wood liners are rated for up to a 2100F chimney fire. Fiberglass batting would melt at that temperature.


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## gizmos

yes, rock wool (mineral wool)


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## k3c4forlife

That is exactly what I want to do Gizmo.  How is that connected to the walls of the chimney flue and liner?


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## Black Jaque Janaviac

OK.  I see a lot of folks do not recommend fiberglass insulation because it melts at 2100*.

For the expense and the simplicity of finding the material - it might still be worthwhile.

I guess I just don't see any great danger in fiberglass melting.  I can imagine it would make for a mess to clean up, but not a hazard.

Or am I missing something?

The other question I have would be is there any great difference between the fiberglass gasket the manufacturers use in these stoves and the batting?


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## 53flyer

DAKSY said:
			
		

> You will get answers both ways on this one.
> I, for one, agree with your chimney sweep.
> I installed wood inserts (& stoves) for 5 yrs before
> moving to the sales floor & EVERY one of them - in a masonry fire place -
> is installed with unfaced fiberglass insulation
> both UNDER the cap & in the damper area.
> NOT ONCE has there been an issue with ANY of these installs.
> Fiberglass does not melt. It does not outgas. It works, period.
> I pulled my 3100L out of my fire place after 4 yrs of burning it
> as a primary heat source -  4 -5 cords per year - & the fiberglass looked
> & felt EXACTLY the same as the day I installed it.
> It was NOT melted, discolored, ordeteriorated
> in ANY way.
> We can battle this all we want & folks here will continue to disagree,
> so you can take what you want from both sides of the argument.
> I've worked for this company for 9+ yrs, & the owner started the business
> in 1977 in his garage. He is one of the more respected voices in the field of
> wood burning & in fact his input is directly felt by anyone here who has taken the
> NFI Certification Exam for wood burning. He is part of the board assembled to
> develop the questions & answers, & under HIS direction,
> we install with unfaced fiberglass, because it's safe to use
> & it works very well...



Hi DAKSY,
I read your reply to a forum Q irt insulating top cap and damper area with unfaced insulation.  I actually just bought some Johns Manville R-30 unfaced fiberglass to use and wanted to ask a few follow up Q's relating to it.

I called the manufacturer and he said the only thing that will break down in their insulation that's made for home construction is the binding agent.  He said that could occur around 400 deg.  He said they make another version of their insulation for commercial and OEM use that doesn't have that binder and is a much higher temp product.  

1. Do you know if the fiberglass insulation you use is the typical home insulation or perhaps the other (higher temp rated) fiberglass insulation the Johns Manville rep described?

2. When you pulled your 3100L was the fiberglass you referred to used around the surround, up in the damper area, or even higher up in the smokeshelf area?  I imagine the fiberglass used between the surround and the fireplace exterior rarely experiences temps above 150-200 deg whereas insulation used in the damper area (in direct contact with the exterior of the SS liner) may routinely experience temps much higher (perhaps as high as 400-500 deg 18" up at the damper level and 300-400 deg 24-30" up at smokeshelf level?).  Do those temps seem like good estimates to everyone?

I'm not concerned about the temps under the top plate.  I doubt it ever hits 150deg 17ft up from the stove top in a masonry fireplace that's exposed to the outside air for the last 8ft (first 6.5ft is in the middle of the house, next 2.5ft goes through an attic space).  The smokeshelf area is where I'm wondering how hot I should expect the exterior of the SS liner to get to.  Since my smokeshelf is 3ft above the stove top I figured the exterior of the SS liner would be hard pressed to get to 400deg.  

*Could someone tell me how high the temps are 3ft up on the exterior of their single ply liners/pipes?* 

Thanks,
53flyer


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## oconnor

53flyer said:
			
		

> ....snip
> 
> *Could someone tell me how high the temps are 3ft up on the exterior of their single ply liners?*
> 
> Thanks,
> 53flyer



During a chimney fire - 2100*F

*And that is the temp you need to concern yourself with.  Nothing other than ceramic fibre will meet that temp - not fibreglass insulation, nor rockwool. * If you use a technique other than what is expressly stated in your instructions for the liner, you are operating outside of the realm of tested and approved and are becoming your own engineer, system designer and safety expert.

My guess is none of us wouldn't think of using a non-code compliant method to meet clearances around our stoves, so why do I keep reading about folks doing the exact same thing around their flue liner?  You might as well say that you don't need ember protection in front of your stove because you've never had a problem with sparks before - that may be true for a given person, but somebody did have problems, and the standards were upgraded, and now we all have ember protection that is larger in front of our stoves than we had 10 years ago.

So, follow the instructions and use the right materials. Period.


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## Black Jaque Janaviac

Cleanburnin,

I understand your point.

I agree with you that fiberglass insulation will not hold up to 2100*.  But the question is what will happen to the fiberglass when the temperatures reach 2100*?

It melts, is all I've ever understood.

So yes, we become our own engineers when we use a non-approved material.  And we may very well accept the fact that if we ever have a chimney fire we will have a mess of melted glass to contend with.

From the appearances it doesn't sound like this is the worst idea in the world.  Probably not the best either.  But it doesn't sound like those who know something about chimneys (i.e. chimney sweeps) are telling folks that using fiberglass batting is a good way to burn your house down.


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## k3c4forlife

I had looked into this idea and have since moved on, accepted to fact that it is cutting corners, and bought the ceramic insulation.  You spend hundreds of thousands of dollars on your house, $3000 on a nice stove, $500 on a liner, $300 on an insulation kit... What is a little more to do it right.  I am an engineer and decided not to cut this corner.


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## oconnor

Black Jaque Janaviac said:
			
		

> Cleanburnin,
> 
> ....snip....
> 
> But it doesn't sound like those who know something about chimneys (i.e. chimney sweeps) are telling folks that using fiberglass batting is a good way to burn your house down.



As with any trade, there are good tradesmen and bad tradesmen.  I would assert that as a whole, chimney sweeps aren't the most likely folks to be reading up on the latest in code revisions and engineering advances.  Most sweeps or installers I dealt with in my install didn't even understand why insulating my flue was a good idea, let alone neccesary to meet code.  there are good ones, many of them post here, but there are also bad ones that post here too.

Really, they are no different than many plumbers, mechanics, or carpenters who spend most of their career doing exactly what they learned to do when they became a tradesman, with little intentional skills updating or training/professional development, unless it is thrust upon them.  Even membership in a recognized body (like W.E.T.T. Inc in Canada,) doesn't mean they have learned anything, just that they passed the test at the end of the seminar.

That is why we have standards and instructions that get approved for hearth products - or most other products for that matter. I work in aircraft software development, and we have more specs and best practices than I care to follow, but when I do, nobody gets hurt needlessly.  And when problems arise, we implement changes to processes to make sure the risk is managed.

All of that, and pilots still crash planes by using technology the wrong way, like trying to land in bad weather using the handheld GPS they bought at Future Shop.

So, make sure you get your advice from a good tradesman, not one who does what he has always done - one day that guy will get bitten, except it will be your house not his.


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## 53flyer

CleanBurnin said:
			
		

> Black Jaque Janaviac said:
> 
> 
> 
> 
> Cleanburnin,
> 
> ....snip....
> 
> But it doesn't sound like those who know something about chimneys (i.e. chimney sweeps) are telling folks that using fiberglass batting is a good way to burn your house down.
> 
> 
> 
> 
> As with any trade, there are good tradesmen and bad tradesmen.  I would assert that as a whole, chimney sweeps aren't the most likely folks to be reading up on the latest in code revisions and engineering advances.  Most sweeps or installers I dealt with in my install didn't even understand why insulating my flue was a good idea, let alone neccesary to meet code.  there are good ones, many of them post here, but there are also bad ones that post here too.
Click to expand...


I called 3 chimney sweeps (that's about half the sweeps in this area) and they all said they either "have used" or "exclusively use" unfaced fiberglass insulation.  One said a person had a fire in their liner (the liner was ok afterwards) and the insulation simply had to be replaced in some areas where it had fallen apart and turned into little glass fiber “leftovers”.  I also talked to the 2 largest fireplace/stove/hearth stores and heard that they've used it as well.  It would seemingly be a large leap (in my opinion) to assume they all don't know what they're talking about. 



			
				CleanBurnin said:
			
		

> All of that, and pilots still crash planes by using technology the wrong way, like trying to land in bad weather using the handheld GPS they bought at Future Shop.



In some situations (in an emergency for example) that can actually be a potential lifesaver.  My old helicopter squadron was flying (I was in back resting for that leg) below the clouds (around 500ft AGL if I recall correctly) when we went inadvertent IMC (into the goo which is slang for clouds).  It was in an area that had no VOR/TACAN services (used for instrument navigation) and the nearest airport's radar approach service was down.  One of the aircrews used their GPS (we didn't have actual GPS approaches for these aircraft) to navigate towards the airport (they popped out of the goo along the way and did a rapid decent iot stay out of the clouds).  Anyway, it was a lifesaver in that situation with relatively low fuel (at that stage of the flight) and lots of mountains in the area.  I was just happy not to have known what was going on at the time because if I'd known I wouldn't have gotten the nice nap that I did.  Btw, "YES" weather briefings were obtained but the weather doesn't always unfold as forecast.


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## k3c4forlife

Doesnt your gut say that its a bad ideal to use insulation that is only rated to like 400* in an area that will receive temperatures over 2000* during the even of a chimney fire.  It's not like it costs $1,000 to be on the safe side.  I dont see what the big deal is.


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## 53flyer

Just a few thoughts:

1.  Sometimes it sounds like people talk about chimney fires like they're a routine part of burning wood.  That may have been closer to true many yrs ago but nowadays it's much less probable.  If you look at someone who uses well seasoned wood, burns correctly, has an EPA stove, and does routine liner/flue cleanings, a chimney fire is an extremely rare occurrence to be sure (1 in a million perhaps?) and would be very short lived due to the good burning/cleaning habits previously referred to.  If it should happen, you wouldn't want to have something that readily burns but fiberglass insulation doesn’t burn it simply deteriorates over time; the 400deg ref isn't some temp that it spontaneously ignites at or suddenly goes poof and falls apart.  A lot of people (sweeps and stove shop installers) use fiberglass insulation and if it was a big problem we'd have heard of al kinds of problems by now.

2.  We're talking about under the top plate and down around the smoke shelf so 90% of the liner will have no insulation around it.  A chimney fire inside a SS liner (that's inside a full masonry chimney) isn't going to subject the inner chimney area to the kind of heat and possible damage that an unlined chimney would experience.  If, due to a chimney fire, the fiberglass insulation completely deteriorated, you'd end up with a lined chimney with no insulation (which many people do when installing SS liners anyway.

3.  I'm actually planning on stuffing the fiberglass insulation 2-3ft (if I can get it down that far) from the top plate.  That'll be 14-15ft up the chimney from the stove and in the 9ft of exposed (outside the home envelope) masonry chimney.  I'm comfortable that the temp won't get high enough to be an issue at hat level.  In the smoke shelf area I'm actually going to use rock wool from the stove shop that sells the blankets (made with rock wool) that goes inside my Quad stove (it's the same material).  They've got a 24"X48"X4.5" (8ft²) piece for $26.  I think that's a pretty good price and it should be enough to stuff around the liner in the smoke shelf area.  I won't have a bottom block off plate but I think stuffing the smoke shelf area and the area under the top plate should do a decent job of stopping air movement.  Roxul, which refers to 2150°F, looks good as well but it's hard to find it locally (unless you live near the great lakes or in Canada).


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## oconnor

53flyer said:
			
		

> I called 3 chimney sweeps (that's about half the sweeps in this area) and they all said they either "have used" or "exclusively use" unfaced fiberglass insulation.  One said a person had a fire in their liner (the liner was ok afterwards) and the insulation simply had to be replaced in some areas where it had fallen apart and turned into little glass fiber “leftovers”.  I also talked to the 2 largest fireplace/stove/hearth stores and heard that they've used it as well.  It would seemingly be a large leap (in my opinion) to assume they all don't know what they're talking about. ...snip



Well, I spoke to 4 shops here in the Annapolis Valley of Nova Scotia, (That would be all the retail stove stores for a 40 mile radius) and NONE of them had heard of insulating a liner, even when I read them the instructions for the liner system they used that specified when it needed to be insulated.

As for knowing what they are talking about - the guy who simply replaced the insulation after a chimney fire is stupid - liners aren't to be reused after a chimney fire, especially if you had to take it out the replace the fiberglass.  No such thing as a liner being OK after a fire like that from where I stand.

But, based on what you are describing, I'd say they don't know what they are talking about.  Just my opinion.


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## oconnor

53flyer said:
			
		

> Just a few thoughts:
> 
> 1.  Sometimes it sounds like people talk about chimney fires like they're a routine part of burning wood.  That may have been closer to true many yrs ago but nowadays it's much less probable.  If you look at someone who uses well seasoned wood, burns correctly, has an EPA stove, and does routine liner/flue cleanings, a chimney fire is an extremely rare occurrence to be sure (1 in a million perhaps?) and would be very short lived due to the good burning/cleaning habits previously referred to.  If it should happen, you wouldn't want to have something that readily burns but fiberglass insulation doesn’t burn it simply deteriorates over time; the 400deg ref isn't some temp that it spontaneously ignites at or suddenly goes poof and falls apart.  A lot of people (sweeps and stove shop installers) use fiberglass insulation and if it was a big problem we'd have heard of al kinds of problems by now.
> 
> 2.  We're talking about under the top plate and down around the smoke shelf so 90% of the liner will have no insulation around it.  A chimney fire inside a SS liner (that's inside a full masonry chimney) isn't going to subject the inner chimney area to the kind of heat and possible damage that an unlined chimney would experience.  If, due to a chimney fire, the fiberglass insulation completely deteriorated, you'd end up with a lined chimney with no insulation (which many people do when installing SS liners anyway.
> 
> 3.  I'm actually planning on stuffing the fiberglass insulation 2-3ft (if I can get it down that far) from the top plate.  That'll be 14-15ft up the chimney from the stove and in the 9ft of exposed (outside the home envelope) masonry chimney.  I'm comfortable that the temp won't get high enough to be an issue at hat level.  In the smoke shelf area I'm actually going to use rock wool from the stove shop that sells the blankets (made with rock wool) that goes inside my Quad stove (it's the same material).  They've got a 24"X48"X4.5" (8ft²) piece for $26.  I think that's a pretty good price and it should be enough to stuff around the liner in the smoke shelf area.  I won't have a bottom block off plate but I think stuffing the smoke shelf area and the area under the top plate should do a decent job of stopping air movement.  Roxul, which refers to 2150°F, looks good as well but it's hard to find it locally (unless you live near the great lakes or in Canada).



For your first point, you are right, we haven't seen the reports of big problems concerning poor insulating techniques, and I don't know why. But I do know that when I used fiberglass around a piece of stainless insulated chimney, it smoked me out of my basement.  I suspect if we worked in the industry though (in the design shops of major manufacturers) we would have lots of stories to tell.

For your second point, a chimney fire inside a stainless steel lined but not insulated masonry chimney can transfer enough heat to adjacent timbers to burn the house down - just ask a fireman.  That is why you need a 2 inch airspace between the bricks and combustibles according to codes.   Wood will ignite on its own at around 600*F, and a chimney fire can reach 2100*F inside the liner - doesn't take to long for that 2100*F to raise the temp of the bricks to a point where the adjacent wood ignites on it's own.

For your third point - the stuff inside your stove isn't rock wool, but ceramic wool.  That is the right stuff to use around your liner. Roxul refers to 2150*F as the melting point of the Basalt they spin out to make it, not the working temp of the product. The highest Roxul product temp I've seen for an intentional design is 1200*F.  the Roxul you buy at the hardware store (mostly Roxul AFB) isn't intended to be exposed to heat other than the single time that it functions as a fire stop inside the wall it was installed in.

I have a bat of Roxul AFB in my flue now as a lower block off - it has discolored, and gave off fumes when it got hot the first few times, and is disintegrating around the liner. I will be replacing it with a steel plate this summer.


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## bren582

Well, I'm a bit anal when it comes to exposing my family to environmental hazards within a relatively confined air space as a house offers. I did a good deal of reading before preparing for my installation and I found the following to be fact for most, maybe not all but most of the current fiberglass products available today:

Fiberglass Insulation intended for home insulation purposes is not just glass. Most commercially available spun glass fiber products contain binders, lubricants, anti-static compounds, corrosion inhibitors and sizing agents. Some of the older fiberglass products also contain formaldihyde. These compounds having various melting points much lower than the point where fiberglass begins to soften and melt (approx 2000 Def F). At these lower temperature these fiberglass products will off glass these compounds into the air so unless the fiberglass is sealed up real well above a metal block off plate there is a good chance you will be breathing in these compounds

Kaowool brand or Ceramic Fiber blanket is a product made from 100% naturally occurring alumina-silica clay refractory fiber. it is white and odorless and resists temperatures as high as 2300 deg F. It will not go moldy or loose its effectiveness when exposed to moister. It will not off gass anything. It is the product of choice for high heat applications and thus lends itself very well to fireplace projects. 

Much has been written of the dangers of exposure to heat induced off gassing of compounds of every sort. Bottom line its not good for you or your family to breath it..

Just consider this before you stuff that fiberglass insulation into a high heat application that it was never designed for..


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## bren582

And one more thing before jumping off the soap box..

Make sure you wear breathing protection when working with the stuff.. preferably a 3M respirator like the ones they sell at HD and lowes.  Ceramic Fiber is far worse than regular fiberglass as the needle like fibers become air born very easily when worked with. Once it’s in place no problem but the slightest movement of the stuff makes the fibers go air born. Big itch factor to the skin and no good for the lungs..  Be safe during installation of the stuff!!


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## cycloxer

Rockwool and rockboard are fine. They are not combustible. It is made from rocks. Even insulation is okay. It just gets messy and smells a bit when it melts. So if you were to have a chimney fire, it would melt all over your stove and fireplace. If you have a steel block off plate sealing everything off from the hearth, then none of this matters.


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## Brian in Michigan

Back when I built my house 20 years ago I was debating whether to put fiberglass insulation in or blown in insulation. (walls and ceiling) I was interested in the blown in type but it was nothing more than ground up paper and then treated with some fireproofing additive. The video showed a welders torch heating up a coin that was sitting on fiberglass and then sitting on the paper. The coin melted thru the fiberglass but just sat there on the paper and just smoked a little. The paper never caught on fire.


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## Black Jaque Janaviac

"The coin melted thru the fiberglass but just sat there on the paper and just smoked a little. The paper never caught on fire. "

And neither did the fiberglass?

I tested a piece of fiberglass in my garage.  I touched the blue flame of a propane torch to it.  The fiberglass melted and shrank away from the flame.


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