7x11 clay flue woes

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beardley

Burning Hunk
Feb 5, 2009
102
Cato, NY
A couple years back I took on the daunting task of building my own house. Being a person not in the construction industry, occasionally some projects were farmed out to the "experts." Unfortunately my chimney expert wasn't so, and now I'm sitting here with a conundrum.

The problem:

-The mason set 7x11 tiles, which is oversized for my Keystone.
-It drafts fine because of the height, but takes an extended period of time to get the chimney hot, and I'm getting a LOT of condensation in the clean out on cold starts. (It's not the wood, I'm on the 3 year plan, fresh split face is ~15-18% MC.) After the chimney is up to temp, the condensation issues go away until the chimney is left to cool completely.
-Because of this condensation, I've found a number of joints where the tile must not be sealed because I've got staining/effluents on a few of the block mortar joints.

The solution:
-The obvious - Stainless liner.

I'm planning on dropping a liner down, but the 7x11 is making that a challenge. It hurts my heart thinking about breaking out tiles installed just 2 years ago. In hindsight, they wouldn't be there, but being an owner builder, you can only be an expert in so many things. . .

Some facts about the chimney
-It is centrally located in the house, almost dead center. Exits the roof at the peak.
-Approx 25' from the thimble to the cap.
-2" clearance 100% verified. This was one I item I DID know, and as I built the framing around this thing I KNOW there is at least 2" clearance from the basement to the peak.

I know it is strongly recommended to insulate, and with some manufactures, required. However I've seen many threads note that the insulation is to make it "Zero clearance" and I don't require that as the 2" clearance is maintained.

Is there a liner out there that doesn't require insulation? I understand the performance won't be "as good" as insulated, but it will be better than the clay, and being an internal chimney, that should help even more.

Regards
John
 
mellow said:
At that height I would try running a non-insulated 6" liner down it and see how it drafts, if it still gives you problems then I would pull it out and insulate it and bust out the tiles.

You will have to convert to 7" at the stove but plenty of adapters out there for that.
Click to expand...

In the house I'm already running Selkirk DSP 6" double wall pipe, so that part of the equation is set. Even in the oversized clay it drafted very well. I actually had to put in a key damper to keep things under control. I found to creeping up towards 700 too often for comfort.
 
Your set up sounds ideal for an un-insulated liner. Go with it and don't look back. You have the required clearance to combustables and an interior chimney that is kept warm by the house. Go for it!




beardley said:
A couple years back I took on the daunting task of building my own house. Being a person not in the construction industry, occasionally some projects were farmed out to the "experts." Unfortunately my chimney expert wasn't so, and now I'm sitting here with a conundrum.

The problem:

-The mason set 7x11 tiles, which is oversized for my Keystone.
-It drafts fine because of the height, but takes an extended period of time to get the chimney hot, and I'm getting a LOT of condensation in the clean out on cold starts. (It's not the wood, I'm on the 3 year plan, fresh split face is ~15-18% MC.) After the chimney is up to temp, the condensation issues go away until the chimney is left to cool completely.
-Because of this condensation, I've found a number of joints where the tile must not be sealed because I've got staining/effluents on a few of the block mortar joints.

The solution:
-The obvious - Stainless liner.

I'm planning on dropping a liner down, but the 7x11 is making that a challenge. It hurts my heart thinking about breaking out tiles installed just 2 years ago. In hindsight, they wouldn't be there, but being an owner builder, you can only be an expert in so many things. . .

Some facts about the chimney
-It is centrally located in the house, almost dead center. Exits the roof at the peak.
-Approx 25' from the thimble to the cap.
-2" clearance 100% verified. This was one I item I DID know, and as I built the framing around this thing I KNOW there is at least 2" clearance from the basement to the peak.

I know it is strongly recommended to insulate, and with some manufactures, required. However I've seen many threads note that the insulation is to make it "Zero clearance" and I don't require that as the 2" clearance is maintained.

Is there a liner out there that doesn't require insulation? I understand the performance won't be "as good" as insulated, but it will be better than the clay, and being an internal chimney, that should help even more.

Regards
John
Click to expand...
 
gerry100 said:
Ultimately I'd insulate the pipe because it maintains flue temps, which reduces creosote build up
Click to expand...


Perhaps some of the pourable insulation could improve things, but I doubt any of the insulated liners will fit. Heck I had trouble getting an insulated liner down my 10x10 clay tile.
 
I don't understand what you are so concerned about with your present set up. The only thing that seems to be a problem is some condensation you experience with a cold start up. How often do you let the flue get cold enough for this to happen? And how exactly is it a problem? Once a fire is going any condensation is going to dry up rapidly. The reason I'm asking is because I have a very similar set up for a Woodstock Classic that I burn on the lower level our home. It vents directly into a clay tile flue with a similar length run to your set up. My masonry/brick chimney also runs up the center of our house. The Woodstock Classic burns fine and drafts great. I've never noticed any condensation issues. I understand the principles involved in running a ss liner and have one for my Jotul F600 on the main level of our home. However, I did not insulate it because I wanted to shed some heat into the thermal mass of my chimney for a slow release back into the house when the fire dies down. My chimney is 8' x 4' and 25' tall. It has over 6000 bricks in it and holds a lot of heat.

Neither one of my flues, the ss liner or the clay tile flue, get much of a creosote buildup. In fact, I've never even had to sweep the clay tile flue, just the single wall pipe between the stove and the thimble. Most of the soot and creosote in that flue seems to just fall down the flue and build up in the clean out below my thimble. If you do feel compelled to install a ss liner inside your clay tile flue I wouldn't worry about insulating it since you said your chimney goes up the center of you house. If you are burning dry wood like you say you are I don't think you would have problems with excess creosote building up inside the liner.
 
i have almost the exact setup with an uninsulated liner, drafts too good actually
 
Nick Mystic said:
I don't understand what you are so concerned about with your present set up. The only thing that seems to be a problem is some condensation you experience with a cold start up. How often do you let the flue get cold enough for this to happen? And how exactly is it a problem?
Click to expand...

In the shoulder season it would be everyday for weeks. The main problem is the clean out is in the basement, so the condensation collects down there and soaks into the base blocks. They're stained and when it was happening, it didn't smell great. Being 10 feet below the thimble it would never dry out. We're talking about a cup of gross black water each time.

Also there are a few joints on 2nd floor and attic that I can see and smell the same staining, so I know the tiles are leaking somewhat.
 
Condensation forms when warm moist air comes into contact with a cold surface. A clay tile flue can get cold in the winter when the stove isn't being burned, but where are you getting the warm moist air if you are burning wood with less than 20% moisture? Is your house exceptionally damp with a high humidity level in the winter? Most homes have the opposite problem in the winter with too little humidity in the air. What sort of rain cap do you have over the top of the clay flue? Is it possible that you aren't getting condensation, but rather rain water down the flue?

As for the cup of nasty water in your clean out staining the block down in the basement, perhaps you can put some sort of waterproof container inside the clean out to collect the water and then just dump it out periodically before it overflows. The staining up in the attic could be from the wicking out of the mortar joints and not necessarily indicative of an active leak.
 
Nick Mystic said:
Is it possible that you aren't getting condensation, but rather rain water down the flue?
Click to expand...
even properly dried wood is 15 to 20% water that can still give you quite a bit of condensation. The bigger problem i see is the leaking at the tile joints. I would line it and insulate with pour in insulation. Due to the fact that you dont need the zeroclearance the pour in even though you wont have enough in spots will still help allot to keep the temps up.
 
bholler, are you saying that you think wood dried down to 15% - 20% moisture has enough water in it to produce a cup of water in the bottom of the clean out? If so, I find that hard to believe because many of us burn wood much wetter than that from time to time and rarely do you hear of complaints about a cup of water dripping out of the bottom of a T-connector, etc.
 
Nick Mystic said:
bholler, are you saying that you think wood dried down to 15% - 20% moisture has enough water in it to produce a cup of water in the bottom of the clean out? If so, I find that hard to believe because many of us burn wood much wetter than that from time to time and rarely do you hear of complaints about a cup of water dripping out of the bottom of a T-connector, etc.
Click to expand...
Ok nick think about it how much does a load of wood weigh that you put in your stove? Lets say 20lbs i know that probably isn't right but anyway if 20% of that 20 lbs is water you would have 4lbs of water right? that is about 1/2 gal. So the potential is there. The problem with this setup is it takes to long for the flue to get up to temp and therefor the water condenses out when it hits the cold walls. I see water stains running out of cleanout doors pretty often
 
i think the reason most don't have the issue is they either have a properly size chimney, or its SS. SS heats up nearly instantly compared to the teracotta. Hence folks with liners don't run into this issue often.

The pour in may be a good compromise. I have a cleanout in the basement. Would I just build a block off plate down there to hold the insulation back?
 
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Reactions: bholler
3fordasho said:
Your set up sounds ideal for an un-insulated liner. Go with it and don't look back. You have the required clearance to combustables and an interior chimney that is kept warm by the house. Go for it!
Click to expand...
Agreed ^ ^ ^
 
In my 7 X 11 ID 21' fireplace chimney (top of stove to the cap) where my stove is located I had to go to 5.5" un-insulated just to get a liner down it. 10 years ago. Drafts like a vacuum cleaner and the walls behind the the chimney, from the first floor to the upstairs ceiling, have never measured a degree over the room temp even after the stove has been cranking for days. And accumulations is powder. Drop the rope, pull the brush into the stove and done. Yes, it is more than a cup full. I think the ones that say they get a cup full use these cups.

cup of creosote.jpg
 
Last edited by a moderator:
Condensation won't go away unless it's lined. We fought that for a season and it's not fun. I was removing a gallon every other day or so. Once we lined, the problem was history. We didn't have the issue with the old furnace, but 600-800 flue temps weren't uncommon. Do that chimney a favor and line it.
 
And with the uninsulated liner you can stuff some rockwool around it above the roof line for good measure.

BTW, nice job on the house!
 
branchburner said:
And with the uninsulated liner you can stuff some rockwool around it above the roof line for good measure.
BTW, nice job on the house!
Click to expand...
Why not insulate it then. It will help allot believe me
 
Another little piece of math/chemistry related to the source of water. Coaly posted this in response to a thread about my creosote problem. 1 lb of dry (0% moisture) wood creates a little over 1/2 lb of water when it burns as a product of combustion. There will always be water going up the chimney, it's just a matter of keeping it hot enough to exhaust as vapor.
https://www.hearth.com/talk/threads/reversed-flue-collar-creosote-leak.150046/#post-2013948
 
The Keystone is an easy breather; Might be able to go with 5.5" insulated?
 
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