creosote

[Matt_W]

I have a general question about creosote. I am sure this varies with every configuration but where generally does the creosote collect first?
Top/Middle/bottom part of chimney?

I have 20’ + of straight double wall stainless and when I checked from the roof top I could only find ash.

 

[fossil]

Sounds like yer doin' it right. Creosote formation occurs when the steam that's transporting the combustion products up the chimney cools to the point of condensing out of the flue gas stream onto the interior surfaces of the piping. Absent any sort of unexpected "cold spot" along the way, the worst creosote buildup should occur in the coolest part of the chimney, which would typically be toward the top. The fact that your piping is all insulated double wall undoubtedly is a plus in your installation. Rick

https://www.hearth.com/econtent/index.php/articles/creosote_from_wood_burning_causes_and_solutions

https://www.hearth.com/what/guidelines.html

(broken link removed to http://chimneysweeponline.com/hobasics.htm)

 

[ScottF]

I have a general question about creosote. I am sure this varies with every configuration but where generally does the creosote collect first?
Top/Middle/bottom part of chimney?

I have 20’ + of straight double wall stainless and when I checked from the roof top I could only find ash.

I have the same question. Same exact situation. We have a cabin we just bought and want to check the chimney this weekend. I was wondering the same thing. Very difficult to access the roof. Steep pitch roof and cap way above the roofline. I was going to disconnect the pipe at the stove and look up. Was wondering if the creosote builds more at the top bottom or middle?

 

[bluefrier]

I have 20’ + of straight double wall stainless and when I checked from the roof top I could only find ash.

Good for you Matt, you must have been burning well seasoned wood. I am no expert, but I would say the cap and top of
the chimney collect the most creosote because gases are cooled before they exit.

 

[fossil]

Both my stoves have runs of single-wall stovepipe up to the ceiling support boxes. In my shop, that's about 7', in the house it's about 14'. The benefit I gain is a bit more heat transfer to the living space during stove operation. The price I pay for that arrangement is the flue gases are cooling more rapidly on their upward journey to daylight than they would had I used double wall throughout. My stovepipe/chimney installations, as a result, tend to accumulate more creosote during a season than they otherwise might. I find the distribution of the deposits to be fairly uniform, although they almost certainly must be a bit heavier toward the top than toward the bottom. Rick

 

[ScottF]

Thanks Rick, Both posts help a lot.
Scott

 

[Adios Pantalones]

Cleaned mine this weekend and found it fairly uniform- slightly heavier at the top. I have single stainless liner in an interior chimney.

 

[fossil]

The single most important factor, of course, is the moisture content of the fuel. If there were no moisture whatever, there would be no steam in the exhaust flow, thus no condensation. Regardless of the species of wood you burn, the lower the moisture content of that fuel, the less buildup of creosote you'll see. Rick

 

[Adios Pantalones]

Water is a natural combustion product of wood- so there will always be water- but we all know the combustion efficiency goes up without extra water and therefore there's less junk to stick.

I never heard anyone say that it was water condensing that caused the issue... I always just assumed that it was mass condensation (water, tar, particulate...). Many unburned products will also condense in that tarry mess.

 

[ScottF]

Why doesnt burning coal create creosote while burning wood does?

 

[ScottF]

i think there is a scenario where wood that is too dry & burns with inadequate O2 [pine?] will result in uncombusted creo going up the chimny

Is this true? Maybe this is where the old wives tale in the east that PINE = Creosote comes from??? Lots of people believe this in the eastern part of the country. Until I joined this site I thought it was fact.

 

[fossil]

Water is a natural combustion product of wood- so there will always be water- but we all know the combustion efficiency goes up without extra water and therefore there's less junk to stick.

I never heard anyone say that it was water condensing that caused the issue... I always just assumed that it was mass condensation (water, tar, particulate...). Many unburned products will also condense in that tarry mess.

Yes, H2O is a combustion product, so there will always be some, even if the fuel has 0% MC. But I think that, in practice, the moisture content of our wood fuel is far more significant (mass-wise) than the water byproduct of combustion. Water itself condensing isn't really the issue, just the mechanism...it's all the stuff that the water vapor's carrying along with it that deposits out and dries in place...at least that's my tenuous understanding. I'm sure I'm oversimplifying even as I'm speculating. %-P Rick

 

[Jags]

Why doesnt burning coal create creosote while burning wood does?

Coal, being a much closer form of pure carbon than wood, does not have all the nasty volatiles that cord wood has. Nasties + water + condensing = creosote.

 

[Adios Pantalones]

Scott- I speculate that people would pick up pine and thiunk it's dry because it's so light- then burn it too wet. It burns so fast that it may be harder to get it adequate oxygen as well, exacerbating the issue with wet wood.

I know in firing the kiln- if I want incomplete combustion (to suck up all the oxygen on purpose)- then throwing in copious pine is a safe bet.

 

[ScottF]

Scott- I speculate that people would pick up pine and thiunk it’s dry because it’s so light- then burn it too wet. It burns so fast that it may be harder to get it adequate oxygen as well, exacerbating the issue with wet wood.

I know in firing the kiln- if I want incomplete combustion (to suck up all the oxygen on purpose)- then throwing in copious pine is a safe bet.

Makes perfect sense! So it is really a compound issue. Wood burned too wet and maybe not enough oxygen due to the fast burn rate. It is much easier to prevent the problem now that I understand it much better. Thanks

 

[fossil]

I burn Pine almost exclusively...along with some Fir, Larch, and Juniper. All softwoods. I have a moisture meter. I won't burn anything in excess of about 20% MC, which is not difficult to achieve because of our dry, high desert climate and the nature of the wood. I don't think I'm burdened with any worse creosote deposition than the hardwood burners might be just by virtue of the species of my fuel. Seasoning and burning practices have more to do with it. Rick

 

[kjsnooks]

I burn mostly pine with a little doug fir mixed in. Creosote isnt really an issue i have had. Those are the wood available to us in these parts and the three other families that use it also dont have an issue with creosote. Some of us even go 2 yrs before cleaning the chimney. If the wood is dry the isssue isnt there.

 

[gyrfalcon]

OK, so last winter was my first burning seriously, and most of my wood wasn't fully seasoned (not green, but not bone dry) and I also struggled for some time learning how the stove works, secondary burn, overnight burns, etc.

The super-competent chimney guy who put in my chimney and installed the stove can't get to me to look in the chimney until November. Argh.

The chimney and stove pipe are double-walled stainless-- inside about 6 feet from stovetop to just below the ceiling, then a 90-degree angle to go out the wall, another 90-degree angle and straight up about 10 feet outside. The draft is really superb,. and even with all the fussing I had to do with the fire, I rarely got more than a faint whiff of a wood fire smell in the house.

Getting up on the roof to look down is not possible for me. Would I learn anything at all useful about creosote deposits from last year by having a look at the interior pipe?

(Yes, some of the wood was unready enough to sizzle, but I only once or twice ended up with black crap on the glass door, but maybe the superior draft just sucked it all up the chimney. The first month, I struggled to get the stove temp over 300, but got somewhat better wood after that and learned how to operate the stove more and managed 400-450 most of the time for the rest of the season. I'm also very uncertain about my overnight burns.)

 

[fossil]

You should be just fine waiting for your name to come to the top of the sweep's list, raptor. Rick

EDIT: Just make sure the stove's cold at the appointed hour for him to show up!

 

[gyrfalcon]

You should be just fine waiting for your name to come to the top of the sweep's list, raptor. Rick

EDIT: Just make sure the stove's cold at the appointed hour for him to show up!

Thanks for the reassurance, old bones.

But could you explain why? I read on this forum all the time folks talking about cleaning their chimneys every month, checking them more often, and these are people with good wood and who know what they're doing.

So why would I be exempt? Is the double SS chimney the key thing? I'd really like to have a better handle on all this than I have.

 

[begreen]

There are all sorts of stoves, flues, locations and experiences here on the forums. Many of the posters that come here have problems. We probably only hear about 1% of the successes.

The folks you read about that need to clean their flues every month are typically dealing with a problem situation. It's rare to have to clean every month with an EPA stove connected to an interior flue system that is burning good dry wood. For instance, I've gone several years without cleaning, burning 2-3 cords of softwood a year. The chimney gets checked annually and the sweep kept getting only a cupful or two from the flue. I finally stopped asking him to come and now check the pipes myself. But if I was living in a cold climate, burning 2-3 times as much wood and had an exterior flue, then I might be cleaning a couple times a season or even monthly. It depends on the setup, wood, stove operation and location.

You're wise to be cautious and check the flue regularly. Many of us have decades of burning behind us and have developed a sense of how the system is working. You will get this over time as well. But at first, ask lots of questions and check things frequently. They are data points of experience that you are accruing. And even us old-timers can learn a thing or three. The new Alderlea is my latest education. It burns quite differently from previous stoves I've owned. So I'll be watching the flue more closely for a season or two until I get to know the stove a lot better.

 

[fossil]

...So why would I be exempt?

Nobody's exempt, avian rodent hunter. You've got an installation that sounds like a good one and you report no draft problems...and you're learning & paying attention. All I'm saying is that in one season of burning, even burning less than ideal fuel, it's not likely that you've managed to load your system up with so much creosote that lighting a fire in it now is a hazard. You've got a sweep scheduled, you're doing what you should be doin'. You'll learn a bunch more about your system when the sweep does his job. My shop stove has single wall from the stove to the 10' ceiling, and I'm sure that contributes to more creosote formation than I might experience with double-wall. Even so, I clean it but once a year, and yes, I get a non-trivial amount of the black, sooty stuff out of there, but not enough so's I think I need to sweep more often. Rick

 

[gyrfalcon]

There are all sorts of stoves, flues, locations and experiences here on the forums. Many of the posters that come here have problems. We probably only hear about 1% of the successes.

The folks you read about that need to clean their flues every month are typically dealing with a problem situation. It's rare to have to clean every month with an EPA stove connected to an interior flue system that is burning good dry wood. For instance, I've gone several years without cleaning, burning 2-3 cords of softwood a year. The chimney gets checked annually and the sweep kept getting only a cupful or two from the flue. I finally stopped asking him to come and now check the pipes myself. But if I was living in a cold climate, burning 2-3 times as much wood and had an exterior flue, then I might be cleaning a couple times a season or even monthly. It depends on the setup, wood, stove operation and location.

You're wise to be cautious and check the flue regularly. Many of us have decades of burning behind us and have developed a sense of how the system is working. You will get this over time as well. But at first, ask lots of questions and check things frequently. They are data points of experience that you are accruing. And even us old-timers can learn a thing or three. The new Alderlea is my latest education. It burns quite differently from previous stoves I've owned. So I'll be watching the flue more closely for a season or two until I get to know the stove a lot better.

Thank you, sir. A couple other questions? I understand why the folks with those decorative all-exterior masonry chimneys have trouble, but I think I'm unclear on the concept of why the interior pipe leading to a chimney that then sticks 10 feet above the roof in the cold winter air isn't also a problem. What happens between my stove and the ceiling that makes creosote formation inside the actual chimney stick up above the roof much less?

And why would Fossil's single-walled interior flue be more of a creosote former than my double-wall? We used the double-wall inside in order to have a shorter clearance requirement to wall and ceiling. I don't get why the extra insulation indoors should make a difference in creosote formation.

Elementary physics and chemistry were not my strong suit, and it was a loonng time ago. So I'm struggling a bit to understand the processes.

 

[gyrfalcon]

...So why would I be exempt?

Nobody's exempt, avian rodent hunter. You've got an installation that sounds like a good one and you report no draft problems...and you're learning & paying attention. All I'm saying is that in one season of burning, even burning less than ideal fuel, it's not likely that you've managed to load your system up with so much creosote that lighting a fire in it now is a hazard. You've got a sweep scheduled, you're doing what you should be doin'. You'll learn a bunch more about your system when the sweep does his job. My shop stove has single wall from the stove to the 10' ceiling, and I'm sure that contributes to more creosote formation than I might experience with double-wall. Even so, I clean it but once a year, and yes, I get a non-trivial amount of the black, sooty stuff out of there, but not enough so's I think I need to sweep more often. Rick

I asked above and want to ask you, too, why it is that your single-wall interior flue would be more problematic than my double-wall. I understand, I think, why the double wall on the exterior portion reduces the creosote problem, but not why it would inside in the warm air.

And about the draft-- is my intuitive sense right that because the draft is so good, the stove gasses get whisked rapidly up and out, so there's less time for them to condense and deposite gook? (That's a technical term)

You've allayed my anxieties, now I'm just trying to get a handle on the way the processes work, just for the sake of adding to my general knowledge base.

 

[fossil]

The flue gases exiting my stove into my single-wall pipe begin cooling more rapidly than yours going into your double-wall pipe. The benefit I gain (at least in my imagination) is a bit more heat radiating into the living space from the stovepipe. The price I pay is the fact that creosote formation occurs when the moisture in the flue gas stream that's carrying along with it nasty other combustion products cools to the point of condensation. That probably happens lower in my system than in yours...but I can't say for sure, because my system has but 2 45-degree direction changes, no 90's. Your intuition is correct...gook deposition is a complicated phenomenon, but among the factors that are signifianct in exacerbating it are decreasing temperature and decreasing mass flow rate...this is why we're always harping on folks not to dump a 6" flue into a gaping 8" x 8" chimney...everything s l o w s w a a a y d o w n when you do that. Rick