Chimney & Creosote Question

 
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Old 11-17-2006, 12:53 PM   #1
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Chimney & Creosote Question


Hey ya'all,

Anyone have a less-than-pleasant client in their past?
One of our's just called. We rebuilt their chimney & siding last year after a small fire damaged that area.

Apparently, there's creosote leaking out of the clean-out door on the chimney. They've been told by folks driving by their house, that it's a poorly built chimney, and that's why it's leaking creosote out this door.

If it's wrong, and it's my fault, I'll fix it. But there's this nagging thought in my mind... I keep thinking about how poorly they kept their house up, and the fact that it's a wood burning stove on the other side of the wall that hits an exhaust pipe that's vented to my chimney. I dunno guys, but isn't creosote a product of wood either not burning correctly, or inferior wood being burnt?

Any help & advice is as always, much appreciated.

Thanks!
~Matt

PS. Pics of chimney before, & after (mostly) rebuilt are attached.
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Old 11-17-2006, 03:40 PM   #2
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Re: Chimney & Creosote Question


Makes you wonder if they burn a lot of green wood. The flu looks functional with plenty of clearance above the ridge. Flu pipe all the way from top to cleanout , right? Wonder if the top being uncovered lets rain in and it is a mixture of rain and creosote leaking or being flushed out. Might be covered, I cannot tell from the pic. I would think if they burn a lot of green wood, they might need to call a sweep and burn more seasoned wood. Maybe a green log at night to burn longer and slower. Be interesting to see the responses to this.

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Old 11-17-2006, 03:47 PM   #3
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Re: Chimney & Creosote Question


Bo,

It's just a wood burning stove attached, and the flu goes all the way down.

I'm wondering about the green wood myself, and one of my employees just mentioned that their chimney leaks as well, because of the rain. It does, however, keep the chimney cleaner. (He suggested getting it cleaned once a year if you add the cover).


Anyone else have a thought?

~Matt
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Old 11-17-2006, 05:10 PM   #4
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Re: Chimney & Creosote Question


Creosote is a by-product of all wood. Good seasoned wood, (cut and dried at least 6-9 months) will produce very little creosote if the chimeny is vented properly. This is because god dry wood burns hot, whereas green, or just as bad, wet wood burns slow and takes a long time to reach max heat levels.
During that time, there is a lot of smoke full of unburnt moist particles depositing themselves on the inside of the chimney, and not a lot of heat. As a result there's not of lot of oxygen feeding the firing and exhausting it quickly out the chimney. So you got a slow exhausting moist smoky fire when you burn wet wood.
That said, if they have been using wet wood for a while, they should not switch to dry wood before having the chimeny cleaned. The heat from a proper fire could very possibly start a chimney fire, (been there, very scary).
The secret to a clean chimeny is to burn hot as quickly as possible.
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Old 11-17-2006, 05:35 PM   #5
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Re: Chimney & Creosote Question


I agree with the above. I would see what kind of storage they have for their firewood before I asked them about it. I am surprised more fires aren't started from creosote buildup. Dry cracks in the end of the wood sticks can be a good indication if it is seasoned or not. The dryer the wood, the more pronounced the cracks usually. If there wood is cut in wedge shaped pieces, might advise them to stack in way that allows air circulation between the wedges. Each layer layed ouy witht he narrow part of wedge up. On top of that lay the next row with the wide side across the v's on the row below. Helps keep seasoned wood dry and helps green wood to dry out.
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Old 11-18-2006, 03:21 AM   #6
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Re: Chimney & Creosote Question


re: creostoe buildup; if they are having enough creosote build up to cause visible leaking from the cleanout door I would bet that the type of stove is the first problem. Age of stove? Does it meet current EPA standards? There have been tremendous advances in wood stove construction over the last few years. The other obvous problem is that an exterior masonry chimeny is the worst of choices for an airtight stove. If you have a choice in the future go to insulated metal. It can usually be installed straight up or close to it, so it has better draft and it is insulated so the gases stay warmer and exit the chimney quicker leaving less chance for creosote build up. Masonry chimneys are cold because masonry is dense and gives up its heat quickly to the outside, so of course, problem is more severe in colder weather. This heat loss causes the gases at the top of the flue to become heavier than the gases entering the flue at the thimble and creates a cold air plug that impedes draft. This happens most when the stove is shut down to smolder through the night and the gasese entering the chimney are already cooler than with a hotter fire.
As a builder you can not be responsible for the owners choice of or use of stoves and burninng habits. You can check the stove and perhaps suggest a newer model if necessary. You can check the breaching, the pipe from stove to chimeny, and the thimble, th epart going through the wall, to make sure they are intact not sucking in air and that the connections are tight. You can check to see that their firewood is not soaking wet, yes dry wood is 90% of successful wood burning, the type of wood does not matter. Your area or state might have a brouchure available that explains good burning habits that you can give to the owner.
Hope this helps, MH
Almost forgot, make sure that the cleanout door is tight fitting and isn't letting excess air into the chimney to interrupt the draft, I sometimes silicone them on. A little sand in the bottom of the chimney will collect some of the cresote/water drip, and do add a rain cap.
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Old 11-19-2006, 07:59 AM   #7
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Re: Chimney & Creosote Question


I have a very old pot belly stove from the 1800's we have it vented into a masonary chimney, What I do each year is burn one of those paper logs that will treat the creosote in the chimney, But creosote is organic chemicals phenol and cresol is obtained during the destructive distillation of coal or wood, I also use a wire chimney brush each year too. The Homeowner needs to clean the chimney each year no matter what they burn that's the rule to pervent a chimney fire.
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Old 11-27-2006, 11:42 AM   #8
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Re: Chimney & Creosote Question


Guys, Thanks so much for the wealth of info!

My brother is stopping by this customer today, and will check things out. He'll be sealing around the door & adding a bit of sand inside, as well as educating the customer about proper burning.

Again, thanks for the wisdom!

~Matt
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Old 11-27-2006, 03:23 PM   #9
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Re: Chimney & Creosote Question


John just got back from this job, & I asked him to grab a few pictures.

Something is wrong with this.
He talked over proper burning w/ the homeowner, & it didn't seem to sink in w/ her. Look at these pics!

That crack is new- and for "barely using" this chimney... the ash & soot!!!

I don't know for sure, but it looks like these was some small fire in the chimney already.

BTW, I'm not sure if the earlier pics showed it, but when we rebuilt this, there is a brick wall on the inside, fully insulated wall sheathed w/ plywood, covered by a continuous piece of aluminum flashing, with the chimney block outside of that. The flues are set in the middle of the block, and the space around them was packed tight with mortar (& the inside joints were packed as well).

Any thoughts?

~Matt
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Old 11-27-2006, 03:24 PM   #10
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Re: Chimney & Creosote Question


more pics
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Old 11-27-2006, 05:37 PM   #11
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Re: Chimney & Creosote Question


There should be a space between the flue liner and the chimney block to allow for expansion of the liner when it heats up. If you filled this space with mortar then when the liner expands it has nowhere to go and cracked the block to relieve the stress.

You need a cap on the chimney to reduce the rain getting into it which washes the creosote down and out the clean out. Even with the cap you might get some dripping of water from condensing water vapour in the smoke.

I can tell from the debris under the cleanout that they have had a chimney fire at some time, not a real bad one, they might not have noticed. Often it is the neighbours (if anyone) who notices the fire first.

Keep teaching them that they need to burn the thing hot at least once a day
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Old 11-27-2006, 07:22 PM   #12
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Re: Chimney & Creosote Question


Do not pack the mortar around the flue. That alone is what caused the block to crack. Judgine from the last pic, they are burning green, sappy wood, but that isn't what caused the failure.
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Old 11-27-2006, 07:30 PM   #13
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Re: Chimney & Creosote Question


Much also depends on what they are burning. I once had a list of BTU's by type, can't find it. Basically, the more dense and dry, the more BTU's. Pine can really screw it up, loads of resins.

At the NC house, I burn Hickory, Red and White Oak and some Persimmon. Poplar is used to get everything started, it burns hot and fast.

Think ahead. I ring trees in the fall when the sap is down and fell/split them the following late summer allowing a few mos. to dry before they are to be used. I also keep a good pile and often have 1 to 1/2 cord left from the previous year. When I lived there full-time, 3 cords would get me through the winter including the stove in the garage.
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Old 11-27-2006, 09:35 PM   #14
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Re: Chimney & Creosote Question


why is the cleanout door so high up. how much higher does the thimble enter the chimney or is the cleanout door right in the back of the thimble.
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Old 11-27-2006, 10:29 PM   #15
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Re: Chimney & Creosote Question


I'll bet the thimble goes in right in the middle of that crack where it jogs, that is where the heat expanded the liner.
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Old 11-27-2006, 10:37 PM   #16
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Re: Chimney & Creosote Question


The Thimble enters just above the cleanout.
I just checked the pix of the inside.

~Matt
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Old 11-27-2006, 10:39 PM   #17
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Re: Chimney & Creosote Question


Would anyone see a significant problem with pressure washing the chimney, then applying a 50 year paintable silicone to the crack, then painting the chimney again?

Wash it to get rid of the crap.
Silicone would shrink & expand.
Paint to make it look good again.

Anyone want to step up & shoot me down?

~Matt
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Old 11-27-2006, 10:49 PM   #18
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Re: Chimney & Creosote Question


Consider yourself shot. There needs to be an airspace between the flue liner and the chase, period.
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Old 11-27-2006, 11:40 PM   #19
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Re: Chimney & Creosote Question


The chimney is shot, you might be able to run a ss liner through it all the way to the stove, but the real fix is to rebuild it properly with an air space like Ts says.
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Old 11-28-2006, 01:10 PM   #20
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Re: Chimney & Creosote Question


Alright guys.

I just made a difficult call.
I'll tear down the chimney to the thimble, and rebuild it from there on up. This will take care of a lot of the mess issues internal & out, and will address the structural integrity concerns.

I don't want to spend the time & $$, but it seams like the right thing to do here, so we'll do it ASAP.

Next question, if you don't anchor the flue liner w/ mortar packed around it, how do you keep it secure- won't it want to, for lack of a better term, "rattle around" in there, letting exhaust gas escape?

(Can I use a brick tie embedded in the mortar joint between the flues extending & embedded in the mortar joint of the chimney block?)


Thanks again,
~Matt

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