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Wet vs Dry Moisture Content?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Scottydont, Jan 10, 2011.

  1. Scottydont

    Scottydont Member

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    Like most first year burners I am having trouble getting seasoned wood. I know, I know, "you should have c/s/s this years wood year(s) ago" but of course I didn't know I would be burning wood a year ago... so all the guys who are 5 years ahead need not preach that.

    The wood I have seems to be a mixed lot; some reads under 20 and some over 30 on a moisture meter, when split and checked on the fresh exposed wood. It's extremely annoying to have to check every single split but it's better than burning green wood. I've ended up with some of the less then seasoned wood in the stove and while is does burn I have to keep the air at 75-100% or it dies out.

    I've searched here and read that there are different ways of determining MC; wet and dry. If I have it correct the EPA number of 20% is wet and my moisture meter number is dry? So what reading on my moisture meter equals the 20% that my stove is designed for? What would your cutoff number be if you were in my position?

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  2. Battenkiller

    Battenkiller Minister of Fire

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    There are different ways of expressing moisture content, which don't at all have to do with the method of determining them. The EPA test loads are Douglas fir that is between 16 and 20% wet-basis. That is expressed by taking the weight of the water present and dividing it by the weight of the entire split. Your moisture meter is calibrated for Doug fir as well, but the calculations done by the chip inside of it (or the width of the scale divisions if you are using an analog meter) are done using the dry-basis method of expressing moisture content. That is expressed by taking the weight of the water and dividing it by the weight of the dry fiber that would be present in the wood after all the water has been theoretically driven out (as would be done in a 215º oven in a lab).

    Naturally, you get very different numbers, and this effect grows increasing more substantial as MC rises. It's a mathematical thing, and has nothing to do with the actual wood, which always has the same amount of water in it.

    If you want a real easy way to convert dry-basis meter readings to the wet-basis used by the EPA tests, just divide the number on the meter by that same number plus 100, and you will get the correct wet-basis MC every time.

    For example, the meter says the wood is 25% MC. Add 100 to 25, then divide that number (125) by the original reading. 25/125 = 20% MC wet-basis. The high end of the EPA test range... perfect for you stove.
    In another case, the meter says the wood is 19% MC. Add 100 to 19, then divide that number (119) by the original reading. 19/119 = 16% MC wet-basis. The low end of the EPA test range... perfect for your stove.

    As far as a definite cutoff number, I don't believe it exists. The way you load the stove, the type of wood, the way the wood is split, the amount of coals in there, the internal stove temps, the timing and size of wood additions, the strength of your draft.... all things that can and sometimes do have a more profound effect on the burn then just MC and draft opening. For me, the theoretical cutoff is 25% MC wet-basis (33% MC on the meter). That's 5% more water in the wood than the maximum allowable MC in the EPA test loads. Above that, you will likely have a progressively harder time burning your wood without micro-managing the stove.
  3. begreen

    begreen Mooderator Staff Member

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  4. shawneyboy

    shawneyboy New Member

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    NOw that sir was an excellant, easy to understand, explanation. Hats off !!!
  5. Jags

    Jags Moderate Moderator Staff Member

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    BK - you da man. That was a great explanation.

    As for the OP's question of cut off MC%. You do what you gotta do, but be diligent with the stack maintenance and check/sweep on a regular basis (monthly, would not be out of the question).
  6. Renovation

    Renovation New Member

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    :)

    If it's any consolation, when it comes to being a new burner and wood, you get chided either way. I joined early enough to have wood seasoning beforehand, and I get teased for not having a stove! ;-)

    Welcome, and good luck!
  7. Martin Strand III

    Martin Strand III New Member

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    Scotty:

    FYI: "don't" need a moisture meter to know if your wood is dry or not.

    Good old common sense has worked over the ages well before electronic gadgets were developed.

    Dry wood, ready to burn, shows characteristics such as

    * the bark is stiff, loose, missing and/or separates easily
    * the exterior color has darkened, especially the ends
    * the ends show radial cracks
    * two pieces "clink" rather than "clunk" when struck together
    * a piece feels light compared to an equal size known green piece

    Aye,
    Marty
    Grandma used to say, "Your brain best work as man's gadgets eventually fail."
  8. Renovation

    Renovation New Member

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    Unfortunately, man's brains eventually fail too. Some's sooner than others'. :)

    Harbor Freight has a moisture gauge for $12, that some folks have had good luck with.

    Another gadget-less test is to resplit a piece and see if it feels cool (moist) against your cheek.
  9. Lumber-Jack

    Lumber-Jack Minister of Fire

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    You know those points don't always apply. I've seen very wet wood with loose, or missing bark.
    Darkened ends (caused by black bacteria/mold) doesn't readily develop on wood that was cut and split from dry logs.
    Same goes for end cracks, if the wood was cut dry and stacked in the shade you will not get a lot of end cracking.
    "Clinking" and "clunking" is hard to define. Different types of wood sound different (eg. hardwood vs softwood)
    Sure wet wood is heavier than dry wood, but like banging two pieces of wood together, it's pretty hard to say what the exact MC of two particular pieces of wood might be just by holding them in your hands, other than to be able to tell which one is wetter or dryer, but just how much % difference? You'd just be guessing, especially if you had no previous experience.

    For years I burned wood in an old wood stove and never had a stove top or flue thermometer, you don't really need them, you can tell a hot stove from a cold stove just by feeling the warmth with your hands. However, that was then, This is now, and now I've got both thermometers, and I'm glad I do,
    Besides a pack of matches, or a stove top thermometer, a moisture meter has got to be one the cheaper tools a wood burner could have. I've never understood the reluctance of some in this forum to use one, especially for novice wood burners who are often so unfamiliar with seasoned wood.
  10. Martin Strand III

    Martin Strand III New Member

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    You can always find exceptions...
    My list has worked for me over 40 years without the need for "gadgets".
    For me, loose bark on a green log spells "birch".
    Not being able to tell a "clink" from a "clunk", is ,well, just sad.
    And, you're right. When the brain fails, not much matters. Eah?

    Aye,
    Marty
  11. gyrfalcon

    gyrfalcon Minister of Fire

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    Well said. If you're a first-time woodburner, how the heck are you supposed to know whether what you're getting is a "clink" rather than a "clunk" if you don't have dry wood to compare the sound with? I mean, really.

    Also, not all bark falls off easily when the wood is dry. I have some small rounds of sugar maple that have been outside for two years, and they're still trying mightilly to hang onto their bark. Ditto for beech.

    I think folks who've been doing this for years need to stop and try, try to remember what it was like when they started before disimssing newbies' difficulties with this.
  12. Renovation

    Renovation New Member

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    Hi Scotty, and welcome.

    The short answer is that moisture meters read dry-basis moisture content, and 20% is the generally-accepted cutoff for sufficiently dry wood.

    So a cheap moisture meter is a very effective way of getting your bearings in the mysterious world of dry-enough wood.

    Harbor Freight has a moisture meter for only $13, that folks here have reported good luck with:

    http://www.harborfreight.com/digital-mini-moisture-meter-67143.html

    As I recall, it goes through the batteries quickly, so keep that in mind if it begins to act weird.

    Seems like a small price to pay for a little knowledge and confidence.

    HTH. Burn long, and prosper.

    Edit: Oh, you already have one. So the (even shorter) answer is 20%! Remember check by resplitting a piece, and testing the newly exposed surface.
  13. Boozie

    Boozie Feeling the Heat

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    I observed one of my logs "oozing" white stuff on the end as it was burning. Wet wood?
  14. Renovation

    Renovation New Member

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    I think the OP is confusing EPA testing moisture values with the moisture levels that this group generally recommends.

    Doesn't this forum generally recommend that wood read 20% or less on a moisture meter for convenient, clean burning--particularly in modern, EPA-compliant stoves? And don't moisture meters read dry-basis moisture?

    I realize situations vary and what works for one person may not work for another, but isn't that the rule of thumb around here?
  15. gzecc

    gzecc Minister of Fire

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    "Ignorance is bliss" "What you don't know won't hurt you"
    I bet you would be surprised of the moisture reading you would get! You would probably be close to actual, but you would also be surprised occasionally.
  16. Martin Strand III

    Martin Strand III New Member

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    A number on a meter is of limited value.

    What counts is what works well, is dependable, etc.

    I have no problems igniting and burning fires hot with split wood (without kindling) I've ID'd as dry per the above.

    Putting a number on that wood is meaningless.

    Throwing money at gadgets is your choice.

    "Clink".

    Aye,
    Marty
  17. oldspark

    oldspark Guest

    I have burnt wood for about 34 years and never had a MM until last spring, I think they are useful for some people, not sure why some think they are useless, so do you guys who do not like gadgets start your fires by rubbing two sticks together.
  18. Battenkiller

    Battenkiller Minister of Fire

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    The EPA sets the bar at the height that it chooses and the stove companies have to design stoves that will successfully clear that bar. The EPA testing protocol stipulates the use of a specific size test load made of Doug Fir, and having a moisture content of between 16% and 20% by weight - wet-basis. The stove companies have to design stoves that successfully burn that test load cleanly under carefully controlled and very demanding conditions (i.e. low burn rates with minimum air).

    So.... You are telling me that we should recommend fuel that is outside the MC range of the EPA test fuel just because you feel that is the consensus opinion on an Internet forum?


    Really. :-/
  19. Battenkiller

    Battenkiller Minister of Fire

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    Judging by the times I read that it takes to get their stoves up to operating temperature, I think maybe some do. ;-P
  20. Lumber-Jack

    Lumber-Jack Minister of Fire

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    If putting numbers on wood is so meaningless then why do all the professionals recommend only burning wood that is less than 20% MC?
    You see, even unseasoned wood will burn. You can burn hot fires even with wood that is well over that 20% MC mark, and thousand of people burn wood like that every year, and some even manage to heat their homes with it. Thing is it's just not very efficient. That's why they put a number on it, because wood that is less than 20% MC burns so much better.


    Marty you are right about one thing, buying usefull gagets is a personal choice, just like burning questionable or unseasoned wood is your choice.

    "Clunk".

    Carbon
    :)
  21. jlove1974

    jlove1974 Member

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    OK when I started burning, I thought that you could split wood and burn it that day (you can...).
    But I always wondered why some wood that I considered "seasoned" took soooo long to light.

    Then I noticed the bark falling off on some of the older stuff, and it would burn and light faster.

    THEN I hit my wife over the head and dragged her into the cave to make some biscuits.

    Seriously, the moisture meter thing is strictly for it's appeal to my gadget-nerd side. But this year it's helped
    me split and stockpile dead and dry hickory and ash, while I managed to burn hot fires.
    my fresh cut green Oak sits by the wayside. Unlike in years past.

    After a while, you kinda get where you can pickup a piece of similar size to another piece, and tell whether or not it's got less water.
    Knocking the wood together makes a certain sound (like bowling pins knocking together) and you can become the 'wood whisperer' like some of these guys.

    NOTE I don't have an 'EPA' stove, so I burn what I what when I have it basically. And lately I have been getting either punky@$$ oak, or green willow oak.
    So I have to seek out faster drying or dead trees to supplement the hard to season stuff.
  22. Todd

    Todd Minister of Fire

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    You guys have it all wrong! There is only one true method for figuring if your wood is dry or not, the bubble test. Take some liquid soap and smear it on one end of the split then put your lips together on the other end and blow, if the other end with the soap starts to bubble up the split is dry. I'm serious, this actually works, just hide behind the wood pile when you do it so nobody thinks your insane. :lol:
  23. oldspark

    oldspark Guest

    Do you think any one is going to take the bait on that one? :)
  24. Boozie

    Boozie Feeling the Heat

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    I observed white bubbly ooze coming from the end of one of my smaller rounds while burning last evening. Was the log Wet? or dry?
  25. Todd

    Todd Minister of Fire

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    They already have. This actually came out of a Morso manual. Crazy Europeans!

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