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Does wood that is too dry produce creosote buildup?

Post in 'The Wood Shed' started by mskif, Jan 20, 2009.

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  1. mskif

    mskif Member

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    I thought I was doing good in my with my wood moisture content until I stumbled upon this article from the US EERE. Most of my wood is between 12% and 18% in moisture content. It is a mix of Ash, Maple and Cherry that has been split stacked and covered for over 18 months. What are your thoughts on this article.
    http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12570

    Wood and Pellet Fuels
    Selecting and Storing Wood
    Because a lot of energy can be wasted burning wet wood, you should use wood that has been properly seasoned. Properly seasoned wood is harvested in the spring and allowed to dry throughout the summer. Look for wood that is of even color, without any green. It should have a moisture content of just over 20%–25% by weight. Some well-seasoned wood can in fact be too dry for today's airtight modern stoves. If you place wood that is too dry on a bed of coals, it will instantly give up its gases as smoke, wasting unburned smoke and producing creosote buildup.

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  2. wolfkiller

    wolfkiller Burning Hunk

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    Should I be concerned?

    No.
  3. Nic36

    Nic36 Feeling the Heat

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    This post is interesting to me because this is my first year of burning and I have amassed a large supply of wood. It should last me easily 3 years or maybe much longer. I plan to continue to scrounge good wood like oak when I run across it. Because of that, I have wondered what the negatives of having wood seasoned over 3 years might be. Until now, I assumed the worse thing would be a fire that is too hot and may burn too fast. The very dry wood I burned early on (like some pallets) didn't produce any smoke except at start up. I assume no smoke means little or no creosote.

    Personally, I am not putting too much stock in it. I'm curious to see what the experts here say about it.
  4. jebatty

    jebatty Minister of Fire

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    Not being a pyro-scientist, let me speculate. I think a well-engineered wood stove will be optimized for a specified MC in the wood. Air will be admitted to sustain a particular burn rate based on the assumed MC. Higher MC will produce a cooler fire due to the air limited burn rate using more energy to dry the wood. Drier wood will produce a hotter fire due to the air limited burn rate using less energy to dry the wood. Ideally the air limited burn rate with fuel at the assumed MC will result in near complete combustion.

    If the smoke/gas emissions are free to escape up the chimney, then with regard to creosote it seems to me that the cooler fire is more the problem than the hotter fire. A cooler fire may allow condensation of the smoke/gas emissions in the chimney = more creosote. A hotter fire, on the other hand, should allow the smoke/gas emissions to escape without condensing = little creosote. The hotter fire will lose some efficiency due to the escape of more heat and maybe hot unburned gases resulting from limited air. The cooler fire will lose some efficiency due to heat being used to dry the wood and escape of cooler unburned gases because of insufficient heat and limited air to produce near complete combustion.

    In either case, if you are able to adjust the air intake rate to maintain an optimum flue temperature (on my stove that is about 350F exterior flue temp 18" above the stove top) and interior chimney temperature high enough to prevent condensation, there should be little creosote, as adjusted air will have been sufficient to allow near complete combustion and escaping smoke/gas will be hot enough to exit the chimney without condensing.

    Speculation or theorizing by others is welcome.
  5. Wet1

    Wet1 Minister of Fire

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    You're right, your stove has a cat on it so you really don't need to be concerned. ;)


    To the OP, don't worry about your wood being over seasoned, dry wood is good wood. The pellets I burn in my pellet stove(s) are dryer than your wood is and I have never had any issues with any buildup.
  6. cityevader

    cityevader New Member

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    I'm thinking that's probably something that started out from the days before secondary air systems, and the idea simply stuck around.
    Perhaps folks used to over-damper down too much trying to control the output of the super-dry wood!
  7. savageactor7

    savageactor7 Minister of Fire

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    I suppose extra dry wood if allowed to smolder would produce creosote...or if a chimney cap were partially plugged to restrict the smokes exit.

    But I take exception to the article and say it would be more difficult to do in the newer stoves which can't be shut down all the way. Especially so if the said extra dry wood were to be put on an a established bed of coals.

    Been burning 24/7 here for 30 years, have aged wood piles stashed here and there, recently burned some 10yo woodshed splits drier than popcorn and it burned fine, just like you would expect seasoned wood to burn.

    For the average wood burners like most of us I wouldn't worry about wood to dry. It's usually the opposite you have to worry about.
  8. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Do not believe everything you read....especially if it is something printed by a government agency!

    How can wood be too dry?! What harm could it possibly cause to a chimney? Too hot would be the only thing and too hot will not cause creosote.

    If wood can be too dry then we have and have had a big problem because this year the wood we have cut will not be burned before the year 2015. Are we worried? Absolutely not and we'll probably cut even more so will be into the year 2016 or further.

    The only wood we have now that we must be careful with is soft maple. It is so dry that it ignites almost instantly. Is that a problem? NO. Does our dry wood cause creosote? Well, we put up a new chimney in 2007 before the burning season and it has not been cleaned yet nor does it need cleaning. And this chimney is all outside; that is, it runs up the side of the house and there is no chase. We live in Michigan too.

    When people talk about their wood being too dry I usually laugh. I've never seen wood too dry to burn but I have seen wood so dry that you have to be careful. For example, someone who burns only pallet wood maybe gets some pallets that are quite old. If they fill their firebox full with that, they could have an overfire situation, but creosote? Bull.
  9. Jags

    Jags Moderate Moderator Staff Member

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    Less moisture = greater energy = higher burn rate = less creosote.

    The only negative side I could see would be a harder to control fire. The stuff may really want to "Burn". As long as you have control over the stove temps, I would pick 18 % MC wood over 25% any day of the week.

    To the poster concerned with 3 years worth of wood - no problems mate. Your just gonna know what good seasoned wood is supposed to burn like.

    One dudes opinion.
  10. slowzuki

    slowzuki Feeling the Heat

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    Actually too dry wood does produces lots of tars and such from burning too "rich". Its like burning kiln dried lumber or finely split wood, the volitiles are produced to rapidly for the amount of oxygen in the stove. If you damper down to stop the overheat you likely will have, you can end up cooling the smoke to the point where the cresote sticks in the chimney.

    Many modern stoves with secondary air or cat's would be fairly ok with some minor use restrictions:

    Don't overload the stove, don't split so finely, mix with normal moisture wood etc.
  11. Jags

    Jags Moderate Moderator Staff Member

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    Hmmm....ya got me scratching my head on this one. Is it possible that with a given amount of oxygen that volatiles can be produced at a greater rate than can be burned??? Somehow I can't get the science through my head on this one. SOMEBODY HELPPPP!!!!
  12. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Can't help you there Jags as I am a bit confused too. As I've stated before, my wood is well seasoned and very dry. No, I have never used a moisture meter as it is something I have no use for....but I have burned wood over 10 years cut and stacked with no problem. And never have I gotten creosote from dry seasoned wood....nor would I expect any.

    As for the fire burning hot, well, fire should be hot. We intentionally burn some soft maple which burns fast and hot without problems. If we use all soft maple, we do have to close the draft a bit sooner and further, but that's all. The stove top has never reached the critical point nor do we expect it to. But then, we've only been at this for around 50+ years....
  13. savageactor7

    savageactor7 Minister of Fire

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    I don't think you'd have any tars in leafed trees would you? Tars=pitch and early seafarers would occasionally beach their boats and reseal the hulls with pitch made from the sap out of conifer trees. I'm speculating that any leafed tree that's cut and split can't get too dry to burn in a stove.

    This house was built when they put in the old Erie canal about 1826. The 2x4's were real thick and different remodeling jobs over the years have yielded plenty for the wood stove. They burned a little on the hot side but way less hot than the seasoned willow I've burned over the years.

    Even the old smoke dragons would smoke burning real hot but I can't believe the newer stoves that reburn the smoke couldn't burn that same super dry wood with no problem and no creosote. After all if there's no smoke there's no creosote right?
  14. John the Painter

    John the Painter Member

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    After buying our first house last year and installing a wood stove I was lucky enough to get 3 cord of well seasoned maple.It caught within 5 seconds and I had very little build up in my flue.
  15. RedRanger

    RedRanger New Member

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    When I place a bunch of super dry red cedar to start the burn cycle, it takes off like a "blow torch". Flame,flame, and more flame and no visible smoke in the firebox.

    Whoever wrote that nonsense, is smoking too much of what they should be burning ;-P
  16. Andre B.

    Andre B. New Member

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    Just because you have no creosote buildup in the chimney does not mean you are not producing creosote.

    Creosote is made in the fire box not in the chimney. If the wood is gasifying faster then it can be burnt with the available O2 you are sending unburned hydrocarbons up the chimney, they are very likely so hot that they will not condense in the chimney. But the fact remains that you are sending some very nasty crap into the air around you house.
  17. Jags

    Jags Moderate Moderator Staff Member

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    But wouldn't you see that nasty crap??

    Still trying to get my head wrapped around how fire/heat can create more volatiles than can be burned and why very dry wood, could cause this over med MC% wood. THATS the part that still does not make sense to me.
  18. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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  19. Jags

    Jags Moderate Moderator Staff Member

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    Yee Haw. Thanks Daksy, that brings it full circle.

    " The dryer the wood, the more dense is the smoke at a given heat input rate."

    That was the missing piece of the puzzle for me. I didn't realize that smoke density would increase with dryer wood.

    And once again, thanks John Gulland.

    Edit: and for those that choose not to read it, John also stated that it would be difficult to get firewood down too far without a unique environment such as desert or under barn roof (I would assume that this would take some time as well).
  20. MacPB

    MacPB New Member

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  21. Jags

    Jags Moderate Moderator Staff Member

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    If "dry" equals "kiln dry" then it would fall in line with the other post. If "dry" is in reference to "properly seasoned firewood", then I don't buy it.

    Being the gubment, they probably stacked kiln dried 2x4s in the stove for the test.
  22. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Right Jags. And I'd bet you a case of the finest beer that even my wood that sits around doing nothing for years still has a moisture content of 15-20%. In other words, regularly cut firewood is not going to be too dry even after 10 years. However, Erik might have a problem with his 40 cords in his barn...but I doubt even that. I would not be afraid to burn it at all. If he lived closer I'd trade him some just to see the difference, if any.
  23. savageactor7

    savageactor7 Minister of Fire

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    government tests of chimney fires, the dry wood produced slightly more creosote.

    ^reason #47 why you can't trust them anymore.

    Well I'm just gonna have to throw down and call BS on this government report. People that put the governments stamp of responsibility on this should be severely and harshly dealt with.

    Of course I'm the heretic here cause I didn't do an official study.
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