undersize vs underinsulate new flue liner

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centaurcoach

New Member
Sep 3, 2011
13
Central PA
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?
 

BrotherBart

Modesterator
Staff member
How tall is the flue?
 

cmonSTART

Minister of Fire
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.
 

cmonSTART

Minister of Fire
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.
 

centaurcoach

New Member
Sep 3, 2011
13
Central PA
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.
 

laynes69

Minister of Fire
Oct 2, 2006
2,598
Ashland OH
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.
 

pen

There are some who call me...mod.
Staff member
Aug 2, 2007
7,958
N.E. Penna
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
 

BrotherBart

Modesterator
Staff member
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.
 

Loco Gringo

Feeling the Heat
Jan 17, 2011
416
Western North Carolina
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.
 

Stump_Branch

Minister of Fire
Nov 12, 2010
878
MD
Loco Gringo said:
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.

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.
 

Loco Gringo

Feeling the Heat
Jan 17, 2011
416
Western North Carolina
Stump_Branch said:
Loco Gringo said:
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.

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.
Based on volume/mass created. Yes?
 

BrotherBart

Modesterator
Staff member
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.
 

laynes69

Minister of Fire
Oct 2, 2006
2,598
Ashland OH
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.
 

centaurcoach

New Member
Sep 3, 2011
13
Central PA
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.
 

BrotherBart

Modesterator
Staff member
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.
 

laynes69

Minister of Fire
Oct 2, 2006
2,598
Ashland OH
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.
 

leeave96

Minister of Fire
Apr 22, 2010
1,113
Western VA
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
 

centaurcoach

New Member
Sep 3, 2011
13
Central PA
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?
 

fraxinus

Feeling the Heat
Aug 3, 2007
341
coastal Maine
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.
 

Stump_Branch

Minister of Fire
Nov 12, 2010
878
MD
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?
 

centaurcoach

New Member
Sep 3, 2011
13
Central PA
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.
 

BrotherBart

Modesterator
Staff member

centaurcoach

New Member
Sep 3, 2011
13
Central PA
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.
 

pen

There are some who call me...mod.
Staff member
Aug 2, 2007
7,958
N.E. Penna
Perlite or Vermiculite. http://www.homedepot.com/webapp/wcs...1&storeId=10051&catalogId=10053&Ntpc=1&Ntpr=1

d95aaa76-85e2-4bef-acd6-d3c9eaec8fd8_400.jpg


2172735c-272b-4a80-8e41-2eb406c6bdc3_300.jpg


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
 

BrotherBart

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