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Semi dry vs. 20% ish

Post in 'The Wood Shed' started by James02, Nov 2, 2011.

  1. James02

    James02 Feeling the Heat

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    As a noob I don't have the greatest wood, but it still burns. My question is since my stash is higher in moisture content and it takes more to get hotter and keep going, am I still getting the same results with less (quantity) dryer wood? So would 10 wetter splits = 5 dryer splits? Make sense?...

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  2. krex1010

    krex1010 Minister of Fire

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    You will definitely get longer burn times, and longer periods of higher temps with dry wood verses wet wood, so yeah dry wood is more efficient than wet wood.
  3. James02

    James02 Feeling the Heat

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    Dang I can't wait....
  4. Gasifier

    Gasifier Minister of Fire

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    Hard to say. I understand your logic. But the fire is using so much energy just to get the water out of the wood I would say it is even less than 10 wetter splits = 5 dryer splits. Mix some dry stuff in with the wet stuff. I know it is easier said than done if you don't have any. But I believe you can find some if you look hard enough. Think finding scrap lumber from construction jobs, lumber yards, craigslist, etc. Talk to people. I find scrap lumber around and keep it for kindling and just supplementing into my fires when it gets really cold. Good luck man. Happy burning. And have a good one.
  5. Battenkiller

    Battenkiller Minister of Fire

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    No, that is not correct. You cannot make any sort of split vs. split comparison. Once you get that lesser stuff burning well there won't be any noticeable heat loss.

    A ten pound split of wood that is 20% water by weight contains eight pounds of wood fiber. That fiber will produce about 64,000 BTUs and will use 1920 BTUs of that heat to evaporate the water within it. That's a 3% heat loss after complete combustion.

    Earlier on in the drying season, that same split was at 27% and weighed 11 pounds. It still had all eight pounds of wood fiber, but it had an additional pound of water in it that needs to be evaporated. So, it had the same potential energy - 64,000 BTUs - minus 960 additional BTUs to evaporate the extra pound of water. It will have a 4.5% heat loss after complete combustion. Not that much extra at all.

    Can you really sense a 1.5% heat difference in the course of a several hour burn?
  6. James02

    James02 Feeling the Heat

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    Hard to say. I understand your logic. But the fire is using so much energy just to get the water out of the wood I would say it is even less than 10 wetter splits = 5 dryer splits. Mix some dry stuff in with the wet stuff. I know it is easier said than done if you don't have any. But I believe you can find some if you look hard enough. Think finding scrap lumber from construction jobs, lumber yards, craigslist, etc. Talk to people. I find scrap lumber around and keep it for kindling and just supplementing into my fires when it gets really cold. Good luck man. Happy burning. And have a good one.[/quote]

    I've been lucky enough to come across some scraps to supplement my wood issue. The good part is when I go outside I don't see any noticable smoke. I'm happy bout that. I'm putting oak on the side as I come across it, I know that ain't dry.
  7. shawneyboy

    shawneyboy New Member

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    Battenkiller, man you and your numbers. You freaking amaze me. That is meant as a compliment.

    Shawn
  8. Battenkiller

    Battenkiller Minister of Fire

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    Thanks, man, but they're really not my numbers. This stuff is plastered all over the Internet if you look for it. Of course, if someone tells you that most of the energy in wet wood is used to dry it out and you believe this, you won't go looking. ;-)
  9. jimbom

    jimbom Combustion Analyzer

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    James, You have nothing to worry about. Think of it this way.

    I use five gallon spackle buckets to carry in my wood. One filled up with oak splits of bone dry(0%moisture) weights about 20 pounds. Bone dry. No moisture. This 20 pounds when burned will generate 10 pounds(10 pints) of water of combustion. 10 pints up the flue.

    If this 20 pounds of dry wood fiber carried 5% moisture, then one more pound of water would be sent up the flue. So 11 pints up the flue.
    If this 20 pounds of dry wood fiber carried 10% moisture, then two more pounds of water would be sent up the flue. So 12 pints up the flue.
    If this 20 pounds of dry wood fiber carried 15% moisture, then three more pounds of water would be sent up the flue. So 13 pints up the flue.
    If this 20 pounds of dry wood fiber carried 20% moisture, then four more pounds of water would be sent up the flue. So 14 pints up the flue.
    etc
    As a practical matter, the difference in pints of water between 15% moisture content and 20% moisture content is not significant to your heat output.

    What is significant is burning small loads of fuel in a hot fire. Do that, and creosote will not be a big problem. Heat off the stove will be great. Future years when you are using dryer wood things will be easier, but don't give up on this year because your wood is a little wet.
  10. smokinj

    smokinj Minister of Fire

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    The way I look at it, keep feeding the thing until its warm. Hope you have lots of good stuff for Jan-Feb.
  11. krex1010

    krex1010 Minister of Fire

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    Batenkiller, in my experience temps come up quicker with dry wood and I can cut my air back quicker with dry wood, I tend to have to give wet wood a bit more air in the early part of a burn which I think tends to decrease my burn times with a full load of wet wood, also giving that extra air seems to get wood to the coaling phase faster, so with wet wood you tend to have the issue of a stove with massive amounts of coals. So wet wood essential has the same btu potential, but I find that with wet wood you end up feeding the stove more often than with dry wood. I think that's what the op was asking.
  12. CTYank

    CTYank Minister of Fire

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    Moisture content of a split is not a constant. Stacked near the stove for x days, it can drop substantially.
    Then, as previously noted, it'll light and let you reduce draft much more quickly. That's the most important stuff, to me.
    Efficiency increment from reduced water vapor sent up the flue is a plus.
  13. James02

    James02 Feeling the Heat

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    Krex....That was kinda what I was going for, I cannot even wrap my head around those number this early into my wood burning career....I do have to keep the air open a bit longer than I'd hoped on my insert at this point. Even last night after work in the dark I was splitting for next year....


    CTY....I am going to bring a few days in once the temps have been down for a bit, don't want bugs or mold after all the rain this year....
  14. pen

    pen There are some who call me...mod. Staff Member

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    The numbers may say 1.5 percent but if the stove top isn't geting much over 450 degrees as many guys find w/ less than ideal wood, I'd say there is more going on here as your home will be more than 1.5 % colder.

    pen
  15. zzr7ky

    zzr7ky Minister of Fire

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    Hi -

    My observations:

    Battenkiller's numbers are fine... However they don't take into account the time factor... The added pounds of water turn to water vapor, which slows combustion, which changes the user's peception of stove performance.

    It appears to me watching by my modestly enthusiastic daughters run the stove that they use about 20/25% more wood when it's not good dry wood. My son loves to unload limbs (stuff under 6" of so) right into the garage... since it will burn ; ( He is responsible for bringing up most of the wood. The girls do notice. They're starting to process some wood themselves.

    I really enjoyed burning the second season. It was so much nicer having wood that acted consistantly, lit off easily, and fit in the stove properly.

    Enjoy!
    MikeP
  16. krex1010

    krex1010 Minister of Fire

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    James, you may not want to wrap your head around batenkiller's numbers right now, but I would pay attention to them , his numbers are always spot on as far as I have seen. To keep things simple, dry wood makes for a much more enjoyable wood burning experience which you have figured out already. Which puts you way ahead of a lot of wood burners, happy burning!
  17. jerseykat1

    jerseykat1 New Member

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    wet wood is just harder to get going. but it will burn just as long as dry wood, in fact dry wood burns up a bit quicker because it goes up into full flameage (is that a real word lol) sooner. while wet wood takes some time to reach that point, but you will get your BTU's faster with the dry stuff.
  18. ewdudley

    ewdudley Minister of Fire

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    I assume you're trolling your audience by ignoring the heat needed to raise the water vapor to flue gas temperatures, not to mention the heat needed to heat the extra air required to maintain high enough oxygen concentrations for vigorous combustion as the combustion air is diluted by water vapor.
  19. jimbom

    jimbom Combustion Analyzer

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    And in BTUs, what would those numbers be?
  20. ewdudley

    ewdudley Minister of Fire

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    Your google is as good as mine. Can't tell you in BTUs, but it varies from 'not so bad' for fluidized bed combustion of high-moisture biomass to 'yikes' for a smoldering gasifier designed for dry fuel.
  21. krex1010

    krex1010 Minister of Fire

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    I kinda disagree with what you are saying. Wet wood will burn longer if you throw it in and damp your stove and let it smolder. But I am not comfortable cutting my air until I see certain things happening inside my stove, and I have to let a lit more air into the stove for a longer period with wet wood, which makes the wood get to the coaling phase faster than with dry wood. I definitely get noticeably longer periods of useable heat with dry wood than I do with wet wood. Im not you can't heat your house with less than ideal wood, but my preference for dry wood is great enough to make me do the work of getting ahead on my wood stacks and believe me I'm not doing all that work if I can't see a pay off.
  22. jimbom

    jimbom Combustion Analyzer

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    Of course my google is as good as yours. But this is a call for the numbers behind your statement. I would like to evaluate them. You either have them or you don't.
  23. ewdudley

    ewdudley Minister of Fire

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    I never claimed to 'have the numbers', I claim only that they're being ignored.

    IIRC the specific enthalpy of dry steam is about 2 kJ / kg K, depending on temperature, but I don't recall what that is in parochial units.

    And as I said the amount of excess oxygen, and therefore excess nitrogen, varies wildly depending on the combustion technique, and therefore throwing around idealized numbers as if they applied across the board doesn't help me much in evaluating what high moisture fuel means for my boiler.
  24. krex1010

    krex1010 Minister of Fire

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    This is the only formula anyone needs on this subject

    Dry wood=good
    Wet wood =not so good
  25. zzr7ky

    zzr7ky Minister of Fire

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    +1 Krex!!

    ; )

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