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Wasn't sure where to post this. We just bought our first home in WA out on the Olympic Peninsula and it had, apparently at one time, a wood stove. The piping was all gone, except for what was at the ceiling (15' vaulted). We purchased a brand new wood cook stove (wood burning upper, food cooking lower) and 6" double walled pipe to reach the ceiling and the pipe flange is for 8" double wall, so we simply added a 6"-8" adapter. We've only just started using the stove this season and have had a large amount of creosote falling back into the bottom of the stove. We purchased a wand cleaning system and used it to what we feel is a good success and then went up onto the roof to inspect the chimney, to find a very heavy amount of creosote present. We cleaned it to the best of our ability, as the wand is for 6" and the chimney is 8". Our question is, does having an 8" upper flue/chimney, affect the creosote issue we are having? I am concerned that the draft is too high at that height due to the increased flue size. We will replace the upper portion if need be, but we have a metal 10/12 roof and that is sure to be quite expensive. TIA.

-Damon
 

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Possibly a good suggestion from Neal. I do think you need 6" pipe all the way for proper draw And you see the difficulty in trying to clean two different sizes. With 6"all the way (the size the manufacturer recommended) you would be able to clean the chimney all the way from the bottom and not have to go on the steep roof.
 

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Hi MK19,
Despite chimneys having been in use for decades (if not centuries) their function is poorly understood. The height of the chimney determines the pressure that pushes the hot air up and out. Where it changes to a larger diameter the flow will slow a bit as the volume moving through the chimney has to be the same at all levels. The slowing could contribute to some extra cooling which is what causes creosote to form.

How much of the chimney extends above the roof into the colder air?
What kind of wood are you burning and is it dry?
Is the creosote you describe leftover from the previous use?

From my years of burning wood creosote forms when the fire is run very low, allowing the fumes to cool and condense on the inside of the chimney.

I'll wait for answers to the above.

Bud
 
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Hey Bud

Absolutely agree with everything you said.

Answers to your questions will also help determine a remedy.

I think you meant to address your post to Damon, the OP.
 

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I do better when I wake up :). Edit complete.

Bud
 
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I'm not seeing the diameter change to be much of a problem. Being you just purchased the home the creosote is likely to be from a previous owner as mentioned.



Chimney fires- the dry flaky residue that can be brushed out is no threat. Even though we sometimes see those flakes glow red, that has been spent. The creosote builds from the top down and when it becomes low enough in the chimney for a flame to reach it that's when the dreadful chimney fire starts. Chimney sweeps that attempt to brush or drag a chain to remove creosote are a joke.



The simplest way to remove the creosote from the upper portion is to choose a rainy day, fill the 8" section with crumpled news print and light a match to it. Otherwise use some kind of scraper or replace the 8" portion.
 

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I agree with SS but caution burning it out in the future, probably not needed now.

If the creosote is accumulating from your use i suspect it is from burning a low fire. One option is to use less and smaller pieces of wood and burn it faster. It will require adding more wood more often but will keep the exhaust hotter.

Pellet stoves use an even smaller liner to help move the exhaust faster so it cannot cool inside the chimney.

Bud
 

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If the creosote is accumulating from your use i suspect it is from burning a low fire. One option is to use less and smaller pieces of wood and burn it faster. It will require adding more wood more often but will keep the exhaust hotter.
Ayuh,..... 'n the biggest cause of creosote is burnin' non-seasoned wet wood,........
 

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When I was burning wood, I always fired the stove up really hot every morning, that way it burned any creosote out of it. I did have a chimney fire one time, it sounded like a jet it was roaring so loud, balls of fire were rolling down my roof. I had a damper in the flue so I shut it down and stopped it. That is the reason I burned the stove very hot every day at the start of the day.

Creosote will form if you are burning pine also.
 

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Ayuh,..... 'n the biggest cause of creosote is burnin' non-seasoned wet wood,........

And softwoods. Seasoned or unseasoned, it's full of resin. Great for starting but dirty and low on heat.
 

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When was the last time the flue was cleaned? You can buy the brushed [sized for your flue] and diy if you are so inclined. When I burned wood all winter I cleaned my flue every month, I still clean it at least once a year.
 

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Discussion Starter · #13 ·
Hi MK19,
Despite chimneys having been in use for decades (if not centuries) their function is poorly understood. The height of the chimney determines the pressure that pushes the hot air up and out. Where it changes to a larger diameter the flow will slow a bit as the volume moving through the chimney has to be the same at all levels. The slowing could contribute to some extra cooling which is what causes creosote to form.

How much of the chimney extends above the roof into the colder air?
What kind of wood are you burning and is it dry?
Is the creosote you describe leftover from the previous use?

From my years of burning wood creosote forms when the fire is run very low, allowing the fumes to cool and condense on the inside of the chimney.

I'll wait for answers to the above.

Bud
Bud-

Approximately 6' above the roof (includes the hood)

Doug Fir, Alder & Ceder. 75% of wood is seasoned & dry, we are unsure as to the moisture % of all of the wood and believe it might have a higher content than 20%

Not sure if it's left over, they supposedly didn't use it much (we should have looked closer when we bought it)
 

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The Doug Fir and Ceder are both softwoods and should be avoided. Although Alder is listed as a hardwood it just barely makes out of the softwood class. I have burned some and when dry it burns fast and hot. I would say ok for getting a fire started but you wouldn't want a stove full of it.

Not everyone has the availability of nice hardwoods like we do here in Maine, but if you can get some that would be much better for avoiding creosote.

Being a cook stove you might be holding the fire down to control the temperature. If so try using less wood to see if you can get less heat while running with the stove vents more open. Just a wild guess.

Bud
 

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And the age old question "does size matter"? I think it might with wood stoves. If a large stove is positioned in a smaller living space, when up to a adequate burning temp, she may be throwing out too many BTU's for the space. So the tendency might be to lower the temps by closing the dampers a bit. But doing so, also lowers the temps in your chimney and allows for the build up. Smaller fires, fed more frequently and burning hotter and of course dry seasoned hardwood is the long term remedy.


Side note: I had a new small modern wood stove a few years back. And it just didn't burn very well at all. It was the strangest thing, I was checking my chimney, changing the cap, removing the cap. Nothing helped with one exception, opening the stove front door and it would burn fine. So I relined my old stove and installed that, and all is well. My conclusion with the newer stove is that the factory combustion intakes were insufficient to fire up decently. I am just wondering if MFG's are placing a little too much emphasis on efficiency and maybe being overly cautions about how hot a stove might get. But in doing so, may be creating chimney issues.
 

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And the age old question "does size matter"? I think it might with wood stoves. If a large stove is positioned in a smaller living space, when up to a adequate burning temp, she may be throwing out too many BTU's for the space. So the tendency might be to lower the temps by closing the dampers a bit. But doing so, also lowers the temps in your chimney and allows for the build up. Smaller fires, fed more frequently and burning hotter and of course dry seasoned hardwood is the long term remedy.


Side note: I had a new small modern wood stove a few years back. And it just didn't burn very well at all. It was the strangest thing, I was checking my chimney, changing the cap, removing the cap. Nothing helped with one exception, opening the stove front door and it would burn fine. So I relined my old stove and installed that, and all is well. My conclusion with the newer stove is that the factory combustion intakes were insufficient to fire up decently. I am just wondering if MFG's are placing a little too much emphasis on efficiency and maybe being overly cautions about how hot a stove might get. But in doing so, may be creating chimney issues.
In my opinion you are absolutely correct. Efficiency is the name of the game.
 

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So the tendency might be to lower the temps by closing the dampers a bit. But doing so, also lowers the temps in your chimney and allows for the build up.

I agree. I tend to have a slow burn in the wood stove inside my house and I do get a good bit of creosote build up which is why I clean the flue frequently. I also have a stove out in my shop. I burn most anything that will burn in it including a lot of pine. Because of the lack of insulation and the bldg not being as tight as my house I burn a hot fire out there and even though I only clean that flue once a year it gets very little creosote build up.
 

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I burned wood in an outside furnace for 20 years. Per the manufacturer's recommendation, I installed an insulated flue. This kept the flue temperature much more consistently hot and pretty much eliminated creosote build up.

The flue had an inner, 6" pipe, and an outer 8", with fiberglass or some other insulation between the pipes.

I ran a flue brush through it every 2 or 3 years, but there was never any real build-up.

I burned mainly oak and hickory, seasoned at least 6 months. I can't speak as to how softwoods would work.

20 feet of insulated pipe in 1996 was about 500 bucks; so it would likely be quite a bit more by now. It was worth every penny to me.
 

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If the chimney is as bad as you think it is, try burning one of those logs that cleans chimneys. It won't be perfect, but when I have done it, I have seen creosote fall to the bottom in small pieces. It's better than nothing.


What would burning bunched up paper in the fireplace do for a dirty chimney?
 

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The transition from 6" to 8" is a concern. It encourages anything dripping down to collect at the transition and the exhaust flow slows down right where the chimney gets cooler. If the new stove mfg recommends 6" all the way then that needs to be done.

The wood you burn has been mentioned and for cooking it won't take 10 cords. See what is available for a dry hardwood.

Note, draft is created by the total height and the temperature of air inside the chimney. Given that this is a cook stove a smaller chimney will get the burnt wood fumes out faster as the airflow for cooking tends to be cut back to control the fire. Moving the exhaust faster will reduce the time it has to cool.

Bud
 
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