# undersize vs underinsulate new flue liner



## centaurcoach (Sep 3, 2011)

I am currently running a six inch stove pipe into a chimney lined with 7 inch ID terracotta. We are accumulating too much creosote at the top of the chimney.  The terracotta is insulated, but obviously not very well. 

I want to insert a stainless steel liner into the terracotta. I would like to insulate it as well but may have to undersize the flue liner just a bit to get it to go in. 

Would the benefit of insulation will offset the negative of undersizing? I know a woodstove flue should have 1/2 inch of insulation but that would be a tight fit in a 7" ID terracotta. Should I go with 1/4 inch insulation and a six inch liner, or go with 1/2 inch insulation and drop down to 5.5 inch liner? Any thoughts?


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## BrotherBart (Sep 3, 2011)

How tall is the flue?


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## cmonSTART (Sep 3, 2011)

Yes, how tall is the flue.  That is important.  

Personally I wouldn't undersize below 5.5 inches, but even then I don't think you will be able to get the 1/2" blanket or 1" poured around the liner.  Have you considered having someone local bust out the tile for you?  Most chimneys you should be able to bust and remove it.


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## cmonSTART (Sep 3, 2011)

Though, thinking about it more if you are unable to remove the flue tile a 5.5 inch liner with a poured insulation may be an improvement.  The insulation won't have the 1" minimum thickness, but there should be enough there to be of some benefit.


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## centaurcoach (Sep 3, 2011)

The flue is 35 feet tall and the 7" terracotta is insulated to the extent you can insulate a 7" ID terracotta flue inside chimney block. I don't think there was a whole lot of room there for insulation. The chimney drafts well but we did have some creosote inside the top 6-8 feet of the chimney.


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## laynes69 (Sep 3, 2011)

You should have no issues going to a 5.5" liner. We have a 5.5" rigid liner on our woodfurnace which is 32' tall. We have more than     
enough draft for the unit.


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## pen (Sep 3, 2011)

If it were me I'd do as comonSTART recommends and run a 5.5 inch liner and use a poured insulation around the liner.  That's a good tall chimney so I don't see the undersized liner giving you an issue.  

Nothing worse than buying the pre-insulated liner and buggering it all up trying to jam it down in there.  If it would fit, those tiles will have to be absolutely perfectly straight.

As others mentioned, if the chimney is structurally sound, the liner could be busted out.  However, for some reason I just prefer to keep them.

pen


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## BrotherBart (Sep 3, 2011)

I am running 20+ foot and a 30+ foot 5.5" un-insulated liners into 7 X 11 tile chimneys and the draft will pull the hat off your head. I can't prove it but I am firmly convinced that the smaller liner develops higher velocity.


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## Loco Gringo (Sep 3, 2011)

BrotherBart said:
			
		

> I am running 20+ foot and a 30+ foot 5.5" un-insulated liners into 7 X 11 tile chimneys and the draft will pull the hat off your head. I can't prove it but I am firmly convinced that the smaller liner develops higher velocity.


Interesting. Considering the physics of how siphoning works, it kinda makes sence. Imagine pulling the contents of a 5 gal bucket with a 2 inch hose vs a 1 inch hose.


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## Stump_Branch (Sep 3, 2011)

Loco Gringo said:
			
		

> BrotherBart said:
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Physics are the stepping down to a smaller size, more velocity. At the cost of volume. You want velocity with a fan in summer. A chimney is about volume.  Same with water, or fluidized object. Increasing a stack velocity doesnt draw more, it has to move faster to keep up with volume.


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## Loco Gringo (Sep 4, 2011)

Stump_Branch said:
			
		

> Loco Gringo said:
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Based on volume/mass created. Yes?


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## BrotherBart (Sep 4, 2011)

I skipped physics class. Would have probably failed it anyway.  :red: But I also have to question volume/velocity as it applies to passive chimney effect as opposed to active  pressurized air or fluid movement. Too big of a chimney gives lots of room for volume but creates a crappy draft.

I just know that the answer is gonna make my head hurt.  :lol: But I love to learn. When there isn't a final exam or grade involved.


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## laynes69 (Sep 4, 2011)

I have heard a whoofing noise before from our furnace on a high fire with the damper open. I don't know if it was the chimney maxing out, or the restriction of air on the intake of the furnace. I've wondered if it would happen if the liner was a 6". Our 5.5" liner has had draft speeds in excess of .12" of water during a high rate of fire. Draft speeds normally run .06"-.10" depending on the burn and weather. Low draft is something that was eliminated with the liner. We had very little room for insulation so I used vermiculite which I figured was better than none at all.


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## centaurcoach (Sep 4, 2011)

Thank you. This is an interesting discussion. I need to learn something about poured insulation. Are there different kinds? What's the best? And how do you work it down around a 35 foot long flue liner? I am picturing lots of gaps without being able to grab the whole chimney and shake it or being able to bang on it with a giant bat. How is it done exactly?

Also, I am considering ordering my flue liner from ChimneyLinerDepot.com They said I should pick up the phone and call them to get my questions answered. That's ok, but I'd like to know my questions first. This forum has helped me think on it more better.


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## BrotherBart (Sep 4, 2011)

First, the liner won't be straight up and down in the chimney. Think snake here. If anybody knows how to get one in there straight first my hat is off to them and second "How the hell do you do that?". But you won't have to shake the chimney to settle the stuff. You shake the liner. Shakes easier starting out and as the lower part fills up the shaking slows down.

But make darn sure that you have a solid and sealed block-off plate installed. Or that stuff ends up in your fireplace and on your floor. AKA a mess.


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## laynes69 (Sep 4, 2011)

Theres Perilite, and Vermiculite. I know for sure some Perilite is treated for water resistance. If its installed in a chimney thats sealed properly and in good condition it will stay dry. Theres also a pour type insulation called Thermix, but I think things will be too tight for it. Perlite or vermiculite is a free flowing insulation. It will fill any voids.


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## leeave96 (Sep 4, 2011)

Several folks on this forum have had great success with the 5.5 inch liners.

I have/had a similar situation with a chimney with square tiles that measured about 6.5 inch ID.  I wanted a 6 inch SS liner with a full 1/2 inch insulation and simply had the tiles busted out.  For the install, busting out the liner was the easiest part!  The draft with the insulated liner was much improved.  Keep in mind that while the insulation helps keep the liner warm during a burn, it's real purpose (the full 1/2 inch) is to keep heat in the liner during a flue fire and away from adjusant combustables.

Something to consider.

Good luck,
Bill


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## centaurcoach (Sep 4, 2011)

> But make darn sure that you have a solid and sealed block-off plate installed. Or that stuff ends up in your fireplace and on your floor. AKA a mess.



This is an external 13x 13 chimney block chimney that runs up along side a two story house. The woodstove is in the basement and the thimble is about a foot above ground level. There is a 8x8 clean out door in the side of the chimney a couple feet higher than that.  The clean out obviously opens into the terracotta flue. 

When I put this liner in, I am guessing I will be cutting a hole in the side of it for the clean out.  Would I have to construct a sheet metal collar to keep insulation from pouring out the clean out door?


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## fraxinus (Sep 4, 2011)

You might also want to check into Supaflu (http://supaflu.com) or another brand of poured in place liner. In the case of Supaflu at least, the liner is self-insulated and does increase the draft because of its smooth, spiraled interior. Should be roughly equal in cost to an ss liner system.


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## Stump_Branch (Sep 5, 2011)

BrotherBart said:
			
		

> I skipped physics class. Would have probably failed it anyway.  :red: But I also have to question volume/velocity as it applies to passive chimney effect as opposed to active  pressurized air or fluid movement. Too big of a chimney gives lots of room for volume but creates a crappy draft.
> 
> I just know that the answer is gonna make my head hurt.  :lol: But I love to learn. When there isn't a final exam or grade involved.



I have a feeling some humor is involved BB. Yes too big not enough heat to cause the pressure differental creating draft. My comment  was i dont think a smaller diameter which may increase velocity, means much in regards to draft. Heat out put, outside temp, cross section of flue and height make up th inches of water column calc. For draft. 

That all being said, wood stove 20 something feet tall chimney, 5.5 probably isnt going to be noticable,maybe measured. I would think that insulating and keeping the flue gasses hot enough to create a good draft are more important. Im right sure ive read here pleanty that a 5.5 with 1/2 insulation will work fine for a 6 flue stove.  No?


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## centaurcoach (Sep 6, 2011)

I'm pretty sure I'm going with the 5.5 with a 1/2 inch insulation wrap. I think the 1/4 inch clearance will let me get it down the 7" ID terracotta. The chimney is only 3 years old and with a little work I can get that top part clean enough inside to make for a smooth install... I hope. This way I don't have to worry about poured insulation leaking out my clean out. 

My only other concern is the cap on top. The mason finished the chimney with just mortar built up to the terracotta that sticks up a couple inches at the top. I guess I will have to break that off and chisel the top flat to place a proper cap to go with the new liner.  Any thoughts on this would be appreciated. And thanks to everyone for taking the time to comment.


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## BrotherBart (Sep 6, 2011)

When you buy the liner get it with a "terra cotta top plate". I didn't at first and when I finally switched my two out last year I could have kicked myself for not doing it in the first place.

These guys aren't the cheapest, just to give you an idea what it is. All all the liner vendors have them these days.

http://www.chimneylinerdepot.com/st...-Deluxe-Terra-Cotta-Top-Plate-Flex-Liner.html


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## centaurcoach (Sep 18, 2011)

Today was chimney stuffing day, and a very frustrating day it was. Wrapping the 5.5 stainless steel liner with 1/2 inch insulation, taping it with the foil tape, putting on the wire mesh wrap, and the stainless steel binding wire... all pretty much a waste of time and money. There was no way this thing was going down the chimney... not a chance. I ended up stripping all of the above off the ss liner and putting in just plain. 

We have everything hooked up down below at the T-connector. Still have to install the cap. But I do want to insulate this thing, so I am now looking for the most pourable, easy flowing insulation material available. There isn't a whole lot of space in there, even without the fiberglass wrap... maybe a half inch all around and it has to pour down 30 feet. 

Feels good to have the bulk of the work done.


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## pen (Sep 18, 2011)

Perlite or Vermiculite.  http://www.homedepot.com/webapp/wcs...1&storeId=10051&catalogId=10053&Ntpc=1&Ntpr=1












It appears that Home Depot only has it listed in 2cu foot bags.  4 cu foot bags can be had from other retailers.  Call around your area, particularly older privately owned hardwares / concrete block / brick supply houses / large garden centers.  I paid only a tad more than 20 bucks for the 4 cu foot bag I picked up from an old time local hardware in my area.  If they didn't have it I would have had to order it as nobody else within 75 miles carried any.

You'll have to do the math to figure out what you need.  Here's a 6 cu foot back of vermiculite for $44 bux.  Don't know what shipping would be.  Stuff is bulky, not heavy.

http://www.amazon.com/Vermiculite-6-cu-ft-bag/dp/B0002IU95Q/ref=sr_1_1?ie=UTF8&qid=1316308457&sr=8-1

pen


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## BrotherBart (Sep 18, 2011)

Thanks Pen. Not sold at my store but free shipping makes that alright with me.


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## branchburner (Sep 18, 2011)

A good masonry supply store should have perlite, big bags cheap.

In addition to a well-sealed blockoff plate, if you stuff some rock wool good and tight up around the liner at the bottom it will make a seal that the perlite shouldn't sift through. An easy way to put some redundancy in the system. 

I'm not sure on this, but it is possible by using perlite instead of wrap that the liner won't technically be to code, since that application is probably not listed for the liner you're using. 

Didn't stop me.


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## pen (Sep 18, 2011)

branchburner said:
			
		

> I'm not sure on this, but it is possible by using perlite instead of wrap that the liner won't technically be to code, since that application is probably not listed for the liner you're using.
> 
> Didn't stop me.



If that's the case it's news to me.  That liner was sold bare and could be installed bare.  I've worked w/ both vermiculite and perlite and they'd do less damage to a SS liner than a cloth diaper.  

Did you see this on a manufacturer's website?  Code enforcement?  The only problem I could see with having less than a 1/2 in insulation would be if the chimney were structurally deficient and did not meet clearance requirements on its own.?

pen


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## branchburner (Sep 18, 2011)

pen said:
			
		

> That liner was sold bare and could be installed bare.  I've worked w/ both vermiculite and perlite and they'd do less damage to a SS liner than a cloth diaper.
> 
> Did you see this on a manufacturer's website?  Code enforcement?  The only problem I could see with having less than a 1/2 in insulation would be if the chimney were structurally deficient and did not meet clearance requirements on its own.?
> 
> pen



Well, for example, on the first one I happened to pull up on google, check out the caution on page 7:
http://www.hartandcooley.com/Libraries/Product_Installation/SLK_5_to_8_Liner.sflb.ashx
CAUTION
DO NOT FILL THE SPACE BETWEEN
THE LINER AND THE MASONRY
CHIMNEY WITH LOOSE INSULATION.

And my understanding is that even if there was no caution, the liner instructions would have to specify that loose insulation is listed among the acceptable insulation applications for that specific liner. Again, I'm not sure on this - I recall it from a thread long ago, but could be mistaken.

It's the same with a stove, right? Deviation from installation specs or alteration of the stove not only voids warranty, but could violate code (if code says follow manufacturer instructions).


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## nola mike (Sep 18, 2011)

I wouldn't mess with perlite again. If you have ANY gap in your block off plate, the perlite will find a way out. All of it. I made that mistake twice.  Just did some pour in thermix type stuff and it war much more forgiving.


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## branchburner (Sep 18, 2011)

nola mike said:
			
		

> I wouldn't mess with perlite again. If you have ANY gap in your block off plate, the perlite will find a way out. All of it. I made that mistake twice.  Just did some pour in thermix type stuff and it war much more forgiving.



Yeah, having something besides a blockoff as a backup (like the rockwool I suggested) makes things safer. Even if you start with no gap, someday...


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## pen (Sep 18, 2011)

Hmm.  Time to do some new research.  I just found the same warning on metal-fab's instal sheet.  

I wonder if something has changed.  I'd like to know the reasoning here.  When I purchased my liner the company said that using vermiculite was just fine (last summer).

pen


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## branchburner (Sep 18, 2011)

pen said:
			
		

> I'd like to know the reasoning here.
> pen



CYA? Kind of like putting instructions on a hammer "do not hit self in head" so you don't get sued when someone hits self in head because NOT instructed not to.

Not that Homer would sue.


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## centaurcoach (Sep 18, 2011)

So Thermix is mostly vermiculite or not? If you use straight vermiculite, do you mix it with water or just pour it in dry? Since I have an external 8x8 clean out door, which will now not be used for anything because the liner is all that is in there, I definitely don't want anybody to open that door and let loose insulating material pour out. I think I need something that will solidify.  Can you get that with vermiculite, or should I go with Thermix? Thanks.


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## pen (Sep 18, 2011)

branchburner:  I think you hit the nail on the head but I'll wait to hear back from the companies I emailed.  

Here is the clearance to combustibles with and without insulation guides that metal fab gives (bottom of post).  I would imagine that their issue with loose fill insulation is that how much is where can't be measured and as a result they assume the worst and don't want to consider that any insulation is better than none for an otherwise safe masonry chimney that happens to have a SS liner in it.  In other words, so long as the loose insulation doesn't hurt the liner, and your old chimney is sound with 1 inch clearance to combustibles, then it should be fine.  Another issue they may be dealing with is the last time I tried to buy vermiculite the only chain store I found who had it was Lowes and it was laced with miracle grow.  God only knows what that would do in a chimney.  

Centaur:  If it is OK with your liner to install vermiculite or perlite on its own, then it goes in dry.  In the articles I read tonight regarding SLK and metal-fab liners I couldn't find a yea or nae regarding that type of insulation.

This stuff has been common practice for years, I want an explanation and hope to get it soon.

pen


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## branchburner (Sep 18, 2011)

pen said:
			
		

> branchburner:  I think you hit the nail on the head but I'll wait to hear back from the companies I emailed.



pen,
I'm pretty sure I gleaned that general code-disclaimer info from a thread by CleanBurnin (Brent) - it may even be in one of the ones i linked tonight in this thread: https://www.hearth.com/econtent/index.php/forums/viewthread/79115/


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## btuser (Sep 18, 2011)

I saved my left-over insulation for behind the stove and plan on using the rest for a block-off plate(mine as well try it to see if it is an improvement).  My own 5.5" liner is only 17' and still pulls a decent draft for a Lopi Freedom (3cf) firebox.   I've had 2 instances of backdraft (smoke into the hosue) that were both my fault.  One I had a large box fan in the kitchen window blowing out and the other was a shoulder-season fire that just kind of billowed till I lit some paper on the top of the fire.  

That must be a hell of a job to bust out a clay liner.  I'm guessing regular chimney sticks wouldn't cut it.


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## branchburner (Sep 18, 2011)

centaurcoach said:
			
		

> So Thermix is mostly vermiculite or not? If you use straight vermiculite, do you mix it with water or just pour it in dry? Since I have an external 8x8 clean out door, which will now not be used for anything because the liner is all that is in there, I definitely don't want anybody to open that door and let loose insulating material pour out. I think I need something that will solidify.  Can you get that with vermiculite, or should I go with Thermix? Thanks.



If you are using perlite/vermiculite, just pour in dry (again, making sure it won't sift down - I actually mixed a small amount with cement to make a plug at the bottom, in addition to a small amount of rock wool).

I don't know much about Thermix, other than it will obviously cost more and it will be much harder to remove if you should ever have the need to. And more likely to comply with any code technicalities.


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## centaurcoach (Sep 18, 2011)

I'm leaning toward the vermiculite because I do like the option of removing this liner at some later date. 

Couple more questions: 1) I like the idea of the clean out door. It is a very direct way to get a shop vac down into the bottom of the chimney. I am thinking of opening that 8x8 door and cutting a hole in the side of the liner to preserve this clean out function. Otherwise I would have to somehow clean out through a 36" horizontal snout and making a 90 degree bend to get down to the bottom of the liner. 

I could make a collar of metal and cement/vermiculite mix to keep the insulation from leaking out that door. What do you think? 

2) I understand I should get a nylon brush to clean the ss liner... is that right?


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## branchburner (Sep 19, 2011)

One more suggestion: instead of insulating the entire liner, maybe do just the top section, since that is where the creosote is. That could be done by stuffing some rock wool in from the top and tamping it down as far as possible (6, 8, 10 feet?) so it is tight between the tile and the liner. Then pouring in a small layer of cement/perlite to rest on top of the rock wool plug (thin enough that it could be broken out if needed). Then filling on top of that plug with loose perlite to the top.

Anyone have thoughts on that? Again, not likely to be technically code compliant.


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## nola mike (Sep 19, 2011)

The problem with the loose fill stuff is that it's tough to totally seal the gap. With a block off plate, a gap formed on both of my installs over a number of burn cycles as the liner expanded/contracted.  Then the perlite all came out.  With the thermix,  it should set up and not run out.  It actually wasn't much more than perlite/vermiculite at a local chimney installer.  Also, all the vermiculite I found was for gardening and was mixed with other stuff.


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## centaurcoach (Nov 14, 2011)

Just to follow up. I purchased the 5 1/2 inch stainless steel liner with a 1/2 inch fiberglass/aluminum foil wrap insulation. BIG MISTAKE that last bit. There was no way this combo was going down the 7" terracotta chimney. After endless struggle on the rooftop with a man down below pulling, we gave it up. We stripped off the insulation and put in down bare.

Then, thanks to the info I gained here, I poured 4 cu ft of vermiculite down and around the stainless steel liner. Awkward, but doable. Success.

The chimney works very well. Good draft and the stove maintains 300 degrees F damped down for hours and hours. Last year with the 7" terracotta, the stove would cool much faster and need to be fired up more often to keep things going.

Thanks all. I learned my lesson and I will never try stuffing a fat wrapped liner down a skinny flue again.


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## pen (Nov 14, 2011)

I do hope you read the posts after mine which explained that most manufacturers don't recommend it.

After this thread, I contacted a several companies.  All told me the only problem is that it hadn't been tested.  None considered actually doing it a hazard or problem.

I can't see how it could hurt a damn thing unless an even layer of insulation were needed to maintain a certain clearance to combustibles that the original chimney was lacking.  Even then, it would be damn hard to be sure that the pour around vermiculite mixes which set hard that are approved could be kept evenly spaced either.

I chose to do it on my chimney because of the same reason you did for the right or for the wrong.  

pen


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## centaurcoach (Nov 14, 2011)

Pen, the chimney is on the outside of the house and there was no problem with proximity to combustibles to start with. The only problem was cooling at the top of the chimney, which has now been eliminated. Because I poured slowly and shook the liner continually, I have to believe the vermiculite is as uniform as anything else could be. Also, there is no place for it to go. My clean out door is sealed and the bottom of the chimney is filled. So I am happy and, as I said, the chimney is performing very well indeed.

Thanks again.


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## WoodpileOCD (Nov 14, 2011)

pen said:
			
		

> Perlite or Vermiculite.  http://www.homedepot.com/webapp/wcs...1&storeId=10051&catalogId=10053&Ntpc=1&Ntpr=1
> 
> It appears that Home Depot only has it listed in 2cu foot bags.  4 cu foot bags can be had from other retailers.  Call around your area, particularly older privately owned hardwares / concrete block / brick supply houses / large garden centers.  I paid only a tad more than 20 bucks for the 4 cu foot bag I picked up from an old time local hardware in my area.  If they didn't have it I would have had to order it as nobody else within 75 miles carried any.
> 
> ...



This has been a most informative thread for me.  I'm getting ready to pull the trigger on an 8" liner for my Buck 91 insert.   Pen, thanks for the links to the HD page for the vermiculite/perlite.   Is there any difference between the two for this application except the $4/bag diff in price?   

Can one of you math geeks out there check my math on this because the calculations I make are different than the poured insulation calculator on Rockford Chimney Supply page:  http://www.chimneylinerinc.com/insulation_kits.htm

I have a 25' chimney with 12"x12" tera cotta flue and need an 8" liner.  Soooooooo.... 
25' x 12" x 12" gives me 25 cu ft for the vol of the flue
25' x 8" :  radius 4" : pie r sq. x length gives me 3.14 x 4" x 4" x 25' x 12in/ft  gives me 15,072 cu in.  
15,072 cu in / 1728 cu in/cu ft = 8.72 cu ft for the vol of the liner 

25 - 8.72 = 16.28 cu ft of insulation needed yet the Rockford calculator tells me I need 12.5 cu ft.    I'm pretty decent at math and think I have everything right here so I'm confused about the Rockford calulator.  Does this stuff they sell and mix with water swell up so I don't need as much dry volume?  (their mix is crazy expensive compared to the vermiculite/perlite)  

I'm pretty sure I'm going to go this route because it will save me over $200 on the cost of a insulation sleeve for my liner.  

Thanks for any help on this.


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## pen (Nov 14, 2011)

OCD, make sure you continue to read through the post.  This may not be an approved method to follow when insulating that liner. 

pen


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## laynes69 (Nov 14, 2011)

4 cu ft isn't much insulation, that was one tight liner. We used 16 cu ft on our chimney when we insulated our liner. I cannot see how the wet and pour insulation would flow around the liner in a tight install? Seems like there's a better chance of air pockets around the liner which could cause uneven temps up the liner.


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## WoodpileOCD (Nov 14, 2011)

BrotherBart said:
			
		

> When you buy the liner get it with a "terra cotta top plate". I didn't at first and when I finally switched my two out last year I could have kicked myself for not doing it in the first place.
> 
> These guys aren't the cheapest, just to give you an idea what it is. All all the liner vendors have them these days.
> 
> http://www.chimneylinerdepot.com/st...-Deluxe-Terra-Cotta-Top-Plate-Flex-Liner.html



BrotherBart:  What specifically are you kicking yourself.  What is the biggest difference or advantage of the terra cotta top plate that you see.  Obviously you think the money was worth it but why?  Thanks


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## branchburner (Nov 14, 2011)

WoodpileOCD said:
			
		

> Is there any difference between the two for this application except the $4/bag diff in price?



I was told vermiculite has more potential to absorb water, making perlite the better choice.


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## BrotherBart (Nov 14, 2011)

WoodpileOCD said:
			
		

> BrotherBart said:
> 
> 
> 
> ...



- No mess with sealing the top plate to the top of the flue tiles. 

- Easy to remove for inspection or for whatever reason. 

- Ya just flip it open for inspection and cleaning the liner. No screws to remove. No cap glued to the top plate collar by creosote etc. No cap rooling off the roof while you are brushing the liner.   :red: 

- I can tell from two hundred yards away, on the ground, if anything is starting to clog the screens in the caps. 

- Chimneys just look like everybody else fireplace chimneys. No particular reason for liking that. I just do.


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## WoodpileOCD (Nov 14, 2011)

Looks like everyone else's chimney?   And I took you for a rugged individualist...   ;-) 

Points all well taken.  Thats what I was looking for.  Thanks


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## centaurcoach (Nov 14, 2011)

"4 cu ft isnâ€™t much insulation, that was one tight liner. We used 16 cu ft on our chimney when we insulated our liner."

Well it's a 5 1/2" liner inside a 7" terracotta x 30 feet. The question of undersizing the liner a bit to get the maximum insulation-- that's what started this whole thread. I was NOT going to bust out the terracotta; that much I knew. Like I said, I'm a happy little Lopi watcher.


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## Battenkiller (Nov 15, 2011)

branchburner said:
			
		

> One more suggestion: instead of insulating the entire liner, maybe do just the top section, since that is where the creosote is. That could be done by stuffing some rock wool in from the top and tamping it down as far as possible (6, 8, 10 feet?) so it is tight between the tile and the liner. Then pouring in a small layer of cement/perlite to rest on top of the rock wool plug (thin enough that it could be broken out if needed). Then filling on top of that plug with loose perlite to the top.
> 
> Anyone have thoughts on that? Again, not likely to be technically code compliant.



My thoughts are that you get creosote up top because the gases started cooling below.  If you're gonna insulate, insulate the whole thing IMO.


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