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creosote vs flue temp vs seasoning wood

Discussion in 'Firewood, Heating and Wood Burning Equipment' started by md1486, Jan 8, 2019.

  1. md1486

    md1486 ArboristSite Operative

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    I'm asking myself a question.
    What ultimately cause creosote build up in a chimney ?
    We often hear that flue pipe must be around 400-450F to have adequate airflow to force out smoke and gases.
    We also often hear that unseasoned wood create more creosote build up because of water particules.

    But if you can maintain a flue pipe at 400-450F, is this enough to limit creosote build up no matter if your wood is properly seasoned or not ? Or unseasoned wood by itself would create more creosote, no matter your flue temp.
    I only burn seasoned wood (max 20-22% humidity), but I'm curious about this issue.
    Thanks !
     
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  2. 4seasons

    4seasons ArboristSite Guru

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    450°? My chimney never gets that hot. For that matter guys using rocket mass heaters are running flue temperature of less than 200°.
    Creosote is caused my incomplete combustion. Whether it's wet wood or a poorly designed firebox.
    For me creosote buildup is no big deal as I can get on the roof without a ladder and brush my chimney twice a week of I want. The most I ever clean mine is once a month, and that is only when we are having warm winter weather so I choke my stove back during the day, and open it some at night. I am also burning 5 year old wood, so the only moisture in my wood is the bugs that have bored into the wood.
     
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  3. sunfish

    sunfish Fish Head

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    A smoldering fire is the biggest cause of creosote.
     
  4. NSMaple1

    NSMaple1 Addicted to ArboristSite

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    We often hear that flue pipe must be around 400-450F to have adequate airflow to force out smoke and gases.

    Don't think I've heard that before. Airflow would be a draft thing, not temperature. Creosote forms when temp drops to a certain point. That can happen with good airflow.

    Visualizing.

    The outlet of your stove or furnace or whatever is hooked to the chimney doesn't creosote. (Unless something is very wrong). All that should be there is fly ash. Because it is always way hot. The first place is usually at the other end, the cap. If your fires are hotter, the line in between the fly ash & the creosote at the top, will be further away from the stove. If you burn hot enough, you might manage to push that line quite far out. But it will cost you a ton of wasted heat (wasted wood) up the chimney. And it will likely never reach the top - you'd never keep that 400-450 all the way up.
     
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  5. md1486

    md1486 ArboristSite Operative

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    Sorry I guess my memory was faulty about "normal" flue temp. Anyways I have an insert so I can't even know flue temp of my stove. By looking at it I have a good idea if he's burning right or not. My question was more for my own personal knowledge. If someone can burn less than properly seasoned wood, lets say 25-30%, by mixing it with seasoned wood to maintain a good combustion (hot fire).
    i.e. If the only condition necessary to avoid creosote build up is flue temp (hot fire), regardless of the moisture of the wood.
     
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  6. Marley5

    Marley5 ArboristSite Operative

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    Back in the 80's I lived in a 2 story house that had a woodstove in the basement that struggled to keep the house warm.

    I burned that stove very hot and never needed to clean the chimney in the 11 years I lived there.
    A smoldering stove promotes creosote.
     
  7. merc_man

    merc_man Addicted to ArboristSite

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    I burn dead ash rite after its cut. It read any where from 17 to 25 ish depending on if its in a wet spot or not. I do smolder if worm out. Try to have a good hot.fire in tje evening.when im arpund to keep an eye an it. Clean my chimney once a year and maybe get a cup or little more of creasote.



    Sent from my SM-G950W using Tapatalk
     
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  8. CR888

    CR888 Addicted to ArboristSite

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    When smoke enters a cool flu it condenses and creosote is made. When hot gas meets cold in flu creosote is made. Smouldering fire or unseasoned wood are usual suspects. Burn seasoned wood and keep flu temp up & you minimise the issue. I'd inspect your chimney & clean it then change your burning behaviour if creosote is a problem.
     
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  9. md1486

    md1486 ArboristSite Operative

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    Thanks ! I have no creosote problem, I was just curious about the issue. I clean my chimney once a year and there's almost nothing. But I burn only 6-7 face cords a year.
     
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  10. Trapper_Pete

    Trapper_Pete ArboristSite Operative

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    creosote is un-burnt fuel, building up on the chimney wall.

    smoke is un-burnt fuel. burn in such a way that you can't see smoke exiting the chimney for more than a few minutes post startup

    if you have a hot fire you burn more of the fuel up.
    if you have a hot chimney because you have a hot fire there is less un-burnt fuel and it is too warm to condense.


    if your wood is wet it is hard to have a hot fire , so more un-burnt fuel going up the chimney and a cold chimney that it can condense on.

    sort of all of those things , but people focus one one or the other.

    burn dry burn hot burn clean.

    if you choke the stoves air control down don't do it till you have a fire box full of flame , the chimney is hot and burn hot open air controls for at least a load or two of wood , even if you have to open a window to not cook yourself out.

    I find if I can get 15% or under on the moisture meter I never hear any hissing , the wood lights easy with very minimal paper or kindling and burns well.
     
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  11. MAD MARK

    MAD MARK ArboristSite Member

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    You asked a multiple choice question with multiple answers. Ill give you mine if I had to pick just one, like you asked. I've been burning 33% moisture content wood most of December. When I cleaned on Jan 2, didnt really need to. Nothing but fly ash. I burned it hot and kept the temps up, nothing around 450. Mainly stayed around 300-350 on stove pipe temp gauge 18" up from stovetop.

    Flue temps.
     
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  12. Highbeam

    Highbeam ArboristSite Operative

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    I'm willing to bet that the 450 you remember is internal flue gas temperatures which correspond to about 225 surface temperatures on single wall pipe. That would be a logical minimum to prevent most creosote.
     
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  13. greenskeeper

    greenskeeper ArboristSite Operative

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    crank up the fire at least once a week....ZERO creosote issues
     
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  14. md1486

    md1486 ArboristSite Operative

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    Thanks, that answer my question. That kind of confirm my hypothesis. if, by any means, you can keep your flue temp high enough, you wont have creosote build up no matter if your wood is seasoned or not. But practically, to have a hot flue temp you need seasoned wood or a good mix between the two
     
  15. MAD MARK

    MAD MARK ArboristSite Member

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    Or leave the air open more with unseasoned wood. This will work but will eat through it quicker after done pissing and moaning. Its the price to pay.
     
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  16. Mustang71

    Mustang71 Addicted to ArboristSite

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    I have a magnetic flue thermometer and I usually usually read around 300 to 350 right before it hits the triple wall chimney. That doesn't mean there's no smoke. Once it is all burning and burning slow and hot there is no smoke. The point when the fire bricks are clean is when it doesn't produce smoke at all. Right after I get it going and loaded up my furnace will hit that chimney temp point but it smokes for a while until it gets good combustion. It's not a temperature thing it's a not efficent furnace thing.

    How ever at that chimney temp is when I know my furnace is burning correctly and making heat not just burning wood. It never gets hotter than that and my plenum temp never goes over 220ish. When I can maintain those temps I get the most efficent and cleanest heat but the process of getting there is dirty. I clean the chimney once a year and get a fair amount of creosote out but it's usually all at the top of the chimney. The stove pipe and lower chimney have no creosote.
     
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  17. NSMaple1

    NSMaple1 Addicted to ArboristSite

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    You're running things fairly hot. Those magnetic gauges read way lower than internal temps. Could be close to double. Also thinking 220 is pretty high for a plenum temp, but I dont have a furnace so not sure.
     
  18. Mustang71

    Mustang71 Addicted to ArboristSite

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    That's a thermometer stuck into the top of the furnace below the plenum. You can put your hand on the plenum and not get burned. It's about a similar temp to an old low boy furnace. The ones with the drum heat exchanger.

    As for the stove pipe temp it's at the low end of the yellow part of the magnetic temp gauge. No where near the red. So I would think it's ok? I'm running my air inlet wide open and nothing else open which is how it was designed to run.

    I think the efficiency has a lot to do with creosote. With no secondary burn you will get that smoke going out the chimney no way around it. Even burning a hot enough chimney wont eliminate poor inefficient combustion.
     
  19. Mustang71

    Mustang71 Addicted to ArboristSite

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    I looked at the magnetic temp gauge again and it's not 300 to 350 it's usually 250 and 300 at the hottest it will run. 300 is the middle of the yellow and 250 is the bottom of it.
     
  20. Trapper_Pete

    Trapper_Pete ArboristSite Operative

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    running the Quadrafire 3100 step top

    I have double wall strait off the top of the stove to the thimble in the ceiling.

    stove top lower step temp on a good fire down to glowing red wood that if hit with a shovel will break into lumps of coals 520 when I added another split it went up to 590 when that was fully engulfed in flame I choked it down to 1/4 air in and my numbers stay right about the same in the 500s stove top low 200s on the double wall pipe

    temps on the outside of the double wall pipe vary from 190 to 235 depending where it is measured

    with a fire like that most people never see any smoke from my chimney, 2-3 years after I got my stove the mail man commented I see the piles of wood I see them go away but I never see you burning. I said I have a good fire going right now look at the top of the chimney cap see the light bend , then he could see it , but he had never seen smoke so didn't think I was burning.

    when I clean it seams the 6 feet above the roof line are all that have any black , that is dry flaky powder that is a minimal amount every 2-3 years when cleaned.

    I would much rather split a little more wood than get on my 12/12 pitch roof , I actually clean it from the bottom when I do clean it I would just about need a bucket truck to get to my chimney cap I take the telescoping double wall pipe out and stand on a ladder over the stove with a bag around the thimble taped in place the bag has a hole just big enough for the rod I run up add a section run up add a section revers go up and down 2-3 times done
     

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