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Moisture content of wood question.

Post in 'The Wood Shed' started by oldspark, May 5, 2010.

  1. oldspark

    oldspark Guest

    I find all this talk of how long wood needs to cure (6 months, 1 year, 2 or more years) very interesting and have read about 15 or so articles about the subject plus my own expeirence. So far none of the articles have contradicted my own findings but for the people who have found it much better for the wood to cured 2 or more years I have a question. Do you know the difference of moisture content between fair and really good wood in your opinion? The 20% is the number used a lot so is 20% good but 15% better, of course you will have to have a moisture meter to have checked this out. I guess if you have noted the type of wood could also be of help in my quest for knowledge as that too could have an effect on the results.

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  2. quads

    quads Minister of Fire

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    I don't own a moisture meter, don't need one, but I know in my own decades of experience with oak (which is a different animal than other wood) the longer you can wait the better. After 2 years of seasoning, it is usually all good to burn. Of course, I can burn oak in 1 year if I was the impatient type. But, I can also burn fresh cut green oak if I wanted to. It's just simpler for me to eliminate the guesswork by planning to let it set 3 years before I burn it. Then I know it's all ready regardless.

    So, I can't help you with your % question, but I know that oak can't be put in the same category as other types of wood. When you read something about the seasoning time of firewood, unless it specifically refers to oak, it may not apply.
  3. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Like quads, I've never owned a moisture meter nor do I have the urge to get one. It simply is not needed if you have time for your wood to dry. quads burns his oak after 2 years but if you've followed many of his posts you also know that wood has been dead and some it down for many years before he even cuts it.

    As for the hangup on the moisture content I have to simply wonder why all the fuss. Get the wood so it burns good and don't worry. That wood, even if it sits around for 10 years will only get down to a certain moisture content....and will burn very nicely. So instead of trying to get all scientific and do studies on moisture content etc., most of us old wood burners have learned to simply give the wood time and then stick it into the stove and enjoy the heat.

    We've burned wood green, we've cut standing dead trees and burned them right away and even some fallen dead trees. We've burned wood that has seasoned 6 months, 12 months, 18 months, 2 years, etc., etc. up to 10 years. It has been our experience that if we burn wood that has been cut, split and stacked for 2 years we will not have problems, the wood burns great, no problem starting fires, no creosote problems, etc. We also have noticed many times over the years that we use a lot less wood if we let it season for 2 years or more (especially oaks).

    It has been said before that you can not lump all woods as the same as various times are needed for different wood. You certainly do not need the same length of time for ash, cherry, birch or soft maple as you do for any oak. You do not need the same time for white oak as you do for red oak.

    So if one does not want to have to be concerned about drying time, then just get 2-3 years ahead on the wood and sleep relaxed. If they don't have room to stack the wood on their city lot, perhaps they can find somewhere to store it until it is ready. Sure, that means an extra time handling the wood, but it is worth it.
  4. WoodPorn

    WoodPorn Minister of Fire

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    I'm not 100% sure of your question but I'l give it a go anyway. The difference between fair and really good is huge! fairly dry wood will not give you near the BTU ouput of properly seasoned (dry) wood. Now obviously this is subjective, and species will throw a curve as well. I don't know if the difference between 15 and 20% is noticeable as my opinion is based on experience and not through scientific data (Battenkiller chime in). I generally try to stick with Red/White oak, Hard Maple, and Hickory/Ash when available (never available enough) and find that if the Oak does not sit for a MINIMUM of 1.5 years I might as well be burning fresh Pine because there is 1/2 the heat output. Now the Maple I can burn in a year w/ no issues outside of a large amount of ash in the stove.
  5. WoodPorn

    WoodPorn Minister of Fire

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    Man...You guy must type at the speed of light, I thought I was going to be the 1st reply!
  6. oldspark

    oldspark Guest

    I need to ramble less, just looking for moisture readings on what people have have found to be their sweet spot with the EPA stoves. I have no issues with wood, burning for over 30 years and burn Oak, White Ash, Green Ash, Black Locust, Mulberry, and Silver Maple.
  7. Danno77

    Danno77 Minister of Fire

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    I haven't bought a MM yet, either. My wood is getting burnt whether it's ready or not. I'm not saying I don't want a MM, but it's a want, and not a need. I can tell what burns better and generally I know how long it seasoned and what it is and where it came from. It would be nice to have some numbers to go with it, but that isn't necessity.
  8. Battenkiller

    Battenkiller Minister of Fire

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    This is gonna be a tough one, oldspark.


    Not too many folks have meters, mostly new burners who don't seen to be using them correctly. I don't believe any of them are using high-quality resistance meters that correct for various species, between which there are some significant differences in electrical resistance at the same moisture content. Even if they did have fancy $300 Delmhorst meters, many of them don't yet have a clue exactly what species they are burning anyway. Also, new burners can't provide accurate observations about combustion differences between various woods of different MCs because they haven't had the opportunity to burn them yet. They may tell you that the wood that they measured at 35% is burning great, when the cheap meter they are using doesn't correct for the fact that it is oak and not doug fir (the wood that all meters are calibrated with), and then they may think it's burning great because they never burned really dry oak. So for these and a bunch of other reasons that haven't popped into my head yet, I'd take all such MC/burning reports with a large grain of salt.


    I never knew for sure what the moisture content of any of my wood was until this winter. There was so much over-emphasis on this aspect of burning that I decided to investigate it myself. I used the oven-drying method because I know it is 100% accurate and all I needed was a kitchen scale and a microwave, which I already owned. Using the same test that scientists use in a lab doesn't make you a scientist anymore that a using a thermometer to measure your flue temps does (I never did that until this year either). When I did the test, it confirmed many things that I already suspected from long experience with burning wood:

    Green wood was drying rapidly in the desert-like air in my basement where the stove is because the temps were so high (85-90ºF) that the relative humidity was very low (<20% RH) . I also confirmed that my wood was drier on the outside than on the inside (just like everybody else's), but that on the average, for an entire cross-section of firewood:

    - Green cherry that started at about 50% MC (high for cherry) got to 30% MC in 10 days, 24% in three weeks, and 18% in two months.

    - Green bitternut hickory that had been cut in December and stored outside started at about 42% MC (very low for hickory). There was absolutely no difference between rounds and splits of the same size, both measured at 42% MC. It got down to 31% MC in two weeks inside the stove room. Burnable, but not highly desirable. I never determined the MC of hickory after two months inside, but I'll hazard a guess that it was in the low 20% range by the way it burned.

    - Green oak (not northern red, but a red type) dried to 53% MC in two weeks in the stove room (I didn't try to determine the initial MC, but was likely up around 70-80% MC), and got to 36% in two months. It about burned as good as green ash at that point, maybe even a bit more heat from it. Several big rounds dropped on top of a large coal bed ignited nicely and burned cleanly (sorry, no smoke when I looked up there with a flood lamp) and evenly, with a lot of heat produced. The stove and flue pipe were nice and white on the inside the next morning, and a good bed of coals present to get the next day's fire going. No, I didn't measure the BTUs lost in evaporating the surplus water in the wood (not much according to the laws of physics). The house was 72ºF in the morning... why should I care?

    - All of the wood seemed to lose a lot of its initial moisture very quickly, but drying slowed down to a crawl after some time. The drier is got, the slower it released the remaining moisture. I'm sure that the same thing would be true for wood stored outside to dry. You quickly get to a point of diminishing returns where it doesn't make much sense to store it any longer. I'd guess that would be after about 9-12 months outside, properly stacked in single rows in sun and wind.


    BTW, I took all of the samples left from the experiment and tossed them on about 2" of very hot coals. There was about 4 1/2 pounds of wood at 0% MC. Ignition was instantaneous, and the stuff was positively incendiary. Frightening, actually. I can't imagine putting 20 pounds of that stuff in there because it took off like a rocket ship. But it smoked like crazy when I tried to shut the air down at all. It was gasifying so rapidly that it needed all the air I could provide to get it to flame. A full box would have either sooted up the works or overfired the stove. I shut the bypass damper and the secondary combustion just roared. You can't see the secondary flames in my stove, so all you can tell is by the sound. Even then, every time I tried to shut down the intake air, smoke came pouring out of the chimney. This continued until the stuff was reduced to charcoal. At that point, the coal bed was so hot it was near white in spots. Trust me, wood this dry has no place in a wood stove of any type.


    Nothing scientific about any of this. The scientists I worked with would have laughed at calling this "science". I merely determined and recorded the MC of my wood and then observed how it burned, recording those observations only in my memory. I know damn well how faulty that is at this point in my life, but nothing groundbreaking or eye-opening came out of it. It was all exactly as I expected based on what I know about wood combustion and what I have experienced over a lifetime of combusting the stuff. OK... burning the oven-dried wood was eye-opening, but only like in "eyes opened in horror".

    All in all, I don't think it's a bad idea to own and occasionally use a cheap meter. It's a tool, just like a chain saw or a hydraulic splitter. Using it as a tool to rough check the MC of your wood before you burn it doesn't mean you are claiming that wood must be burned scientifically anymore than using a draft meter or an IR thermometer does. Understanding is the key to good burning, and these tools can help to give that understanding. As I've said before, you can't buy, sell, steal or transmit experience. New burners will benefit the most from all of this information and old burners will likely ignore it and remain stuck in the ways that work for them.
  9. Got Wood

    Got Wood Minister of Fire

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    I bought a meter last winter, used it maybe twice and it confirmed what I already knew - the wood needed more time to season. Now, I'm ahead with next years wood having 2 full years of seasoning time. That moisture meter is buried on my workbench somewhere and not likely to be used again....
  10. oldspark

    oldspark Guest

    Very interesting and thanks battenkiller, some of your observations are what I would have expected, I read an article about an expierment on drying wood and that guy stated wood loses 40% of the total moisture it will lose in 2 weeks and 60% of the total in 4 weeks, Very much the same as what you said with the drying slowing down after a shor perion of time. A lot of chatter about the wood drying out a lot in the winter months with the dry air but one guy stated it did not dry much after the temps dropped below 45 degrees (not sure I agree with the numbers but I do not think it drys much in winter). I think a lot of this ifno would be helpful to the new burners and people who have limited storage and time for wood collecting (even buying the wood). Some of the information on this site is misleading but the intentions are good (road to he!! is paved with good intentions), I am a old burner but have a new EPA stove so I hope I can keep an open mind.
  11. oldspark

    oldspark Guest

    I just want some referance numbers for people to use, I know I can get wood seasoned quicker than 2 years, learned that a long time ago, wondering why you will not be using the meter again. I think they have there place for a lot of people, I am 2 years ahead and cut a lot of dead oak that is already on it way of having a low moisture content but I still would like to see numbers as some of the posts on here are not rational IMHO.
  12. wooddope

    wooddope Member

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    My hats off to you BK. Esp. liked the 0 percent wood burn characteristics part. It's amazing how complicated this heating with wood thing can get.For me, I can say that I thought wood seasoned 1 year was ready to burn before finding this forum.Now I've realized that the oak sizzle is not "just the way it burns" and can give it the proper time to dry.
  13. Lumber-Jack

    Lumber-Jack Minister of Fire

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    I started using my Moisture meter regularly when cutting and drying my firewood. I don't have the luxury of the kind of space that Quads and BS have, so storing up years worth of firewood is not practical for me. Fortunately I have access to a lot of well seasoned standing dead trees, but not all of them are as seasoned as others, and even the trees that are well seasoned usually have wood near the trunk that is not as dry as the rest of the tree. So having a moisture meter not only helps me decide what wood is fine for burning right away and which wood could be split smaller and stored a bit longer if need be, but it also lets me monitor any stuff I have drying.

    Yah, I have a pretty good idea of which wood is which too, but having a M. meter is like the fuel gauge in a car. I can tell when the gas tank is full or empty or somewhere in between without the gauge, but the gauge lets me know EXACTLY where I'm at at any particular time.
    And even if my meter is out by a couple % due to temperature or different wood species, it's still close enough for my purposes.
  14. Nonprophet

    Nonprophet Minister of Fire

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    There's a couple things that need clarifying here. One, LOTS of people here use moisture meters, and not just newbies. I've been burning for 20+ years, I'm happy to spend $30 or so on a tool that can help me with my burning. It's nice to know what species dry faster, it's nice to know which of my stack locations and methods dry faster, it's nice to know that the wood I'm buying or trading for is actually well seasoned.

    Second, if you read the directions carefully for the top-end meters, you'll see that species variation (among common US tree species) means maybe 1-2% +/- in variability in terms of moisture content, hardly anything to get too worried about.

    Yes, it's nice when you're an established wood burner in one location with ample storage space where you can cut and stack and then let it sit for 2-3 years or more, and have a 5-6 year supply on hand an not worry about it. But the truth is that maybe a third of the people here fall into that category, so dismissing a moisture meter as a tool only for the newbie is neither accurate nor realistic. Lots of wood burners seem to lean towards the stubborn, curmudgeony "I've always done it this way so that's how it's done" side of the spectrum, and that's unfortunate. From electric chain sharpeners, to newer splitting tools (i.e. Fiskars SS) there's a lot of innovation out there that makes gathering and burning wood a lot easier and more efficient--even if that's "not the way my pappy did it................."


    NP
  15. Shari

    Shari Minister of Fire

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    Well, I'm a newbie. Started stashing wood before I got the woodstove. I'm not hung up on what the MC is although out of curiosity I did purchase a MC. The types of wood I'm burning need at least 12 months of seasoning. I have that. Why worry? My wood doesn't sizzle when it burns. I'm happy. There are tons of other things to worry about in life, MC is not one of mine.

    Shari
  16. Battenkiller

    Battenkiller Minister of Fire

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    1-2% variation across all species? That may be true for wood at the furniture grade spectrum of kiln-dried wood (<10% MC), but the variation increases as MC rises. At the range of moisture that wood burners are interested (20-25% MC), there can be over a 5% variation. That can lead to cases where wood at an actual MC of 25% gives a reading of 20% or 30%, further adding to the confusion of how wood at different moisture contents burns.

    I'm not dismissing the use of a MM as a tool for newbies at all. In fact, I am saying the opposite, that newbies will likely get the least accurate results from it. If they really want to know exactly what the MC of their wood is at different stages of drying, the cheap kitchen scale and microwave drying method will give near 100% accuracy of the entire split, at all moisture contents and for all species anywhere in the world. It only takes about half an hour or so, and could be done with a few representative samples each season to establish the drying rate of the various wood species and drying locations.
  17. djlarson77

    djlarson77 Member

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    I think my cheap little moisture meter is useful....when I feel like taking the time to use it. This past weekend as I was splitting some wood near my various piles of dry to wet Oak, elm, cherry, cottonwood, and box elder I decided to split and check some of the wood in these various piles, writing the moisture content on the ends of the splits. I then burned them on a bed of hot coals in my patio fire pit as a test that evening. As I came down from OL (over limit) towards 20%, the wood definitely ignited quicker and burned much better. I did have an idea based on my experience with wood (newbie with my own wood stove but many years of experience with burning wood other ways), but having a way to quantify my observations and then test them with a burn is definitely useful in my opinion - though I will probably use it less and less as I approach being two years ahead with my stacks.

    The main lesson I learned during my testing is that I'm not going to have much wood to burn this winter unless I buy some, which I really don't want to do since I have loads of wood on my property (damn two-lined chestnut borers). Outside of losing some BTU's and adding some creosote, should I be worried if I burn the occasional 27% oak or black cherry split in my pretty new stove? How much am I going to screw up my secondary burn chambers, the viewing window, and the inside of my excel pipe? I plan to check and clean the chimney quite often, but should I avoid putting any wet wood in my expensive new system?
  18. ckarotka

    ckarotka Minister of Fire

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    Very intersting thread we have here. I've been burning for about 5 years now, this will be my second year post hearth.com. I don't have enough room to get too far ahead with my stacks but 2 years is good enough for me. In all reality I have the room to season about 17 months worth, better than I can buy. In the begining hearth days I bought an MM and went nuts because my wood was marginal. Now I'm in the "let it sit for at least 1.5-2 year catagory".

    I have some red oak, cherry, poplar, maple and pine that will have dried for about 12-17months (the pine being the shortest oak the longest), and it's getting burned this year nomatter what. I have to. I will wait and see how the winter goes to see if I need the oak, if I can make thru then that will sit another year.

    I checked a few splits this weekend and found this, poplar small splits 17months dry read 30%, I find that hard to be true.
    Cherry read 22% and the oak small splits again read 33%, yes I did resplit some of the biggest ones and checked the middle with the prongs with the grain. I hope these readings are wrong.

    My point is, this is the last time I want to have to worry about it, because I will have over 3 cord stacked for next year before mid august, lots of maple, some locust, sycamore and more crapenwood(cottonwood). I live in an area with lots of oaks but do you think I could scrounge some of that?.....none this year. Silver maple seems to be species for 2011/2012
  19. Backwoods Savage

    Backwoods Savage Minister of Fire

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    If you have some marginal wood, then mix some with the better wood. In other words, throw an oak on top of other wood. You could even throw an oak right on top of a good bed of coals and leave that draft open a good ways and you probably will not notice much difference. However, fill that stove with that marginal wood and you might very well have some problems to deal with.
  20. smokinj

    smokinj Minister of Fire

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    What he said! +1
  21. Skier76

    Skier76 Minister of Fire

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    I've got a meter; comes in really handy. I usually have a cord or so on hand at any time. We just don't have room to stack a lot of extra wood. So it's good to know how the splits are doing every so often. You can certainly tell by weight/feel, but I like knowing exactly.
  22. Cash Wiley

    Cash Wiley New Member

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    By the end of the season this year, I could pretty much tell by feel and weight which splits were good to burn and which were going to hiss and steam. As a few have mentioned, some of us don't have the luxury of a lot of wood. I'm just starting and have to buy in wood because I can't afford a saw and trailer, which also means I can't afford to get a year ahead.

    While my cheap meter may not be the pillar of scientific accuracy, it's been spot-on within a purchased stack. Last year I bought late and got relatively lucky, 3/4 of the wood was good. At the end of the season, I'd sift through the last quarter, tossing the stuff that felt right into one pile. Then I'd split and check the interiors of the ones that felt wet and use the meter for the final sorting. It was very useful for that.

    I'm trying to not get my hopes up, this might be the year I can get ahead. My mother's landlord was asking her to look into tree services, she has over a dozen 60'+ oaks. Even if he takes two out, it's going to be a nightmare trying to process all the wood, I've only been doing around 2 cord. Luckily I have the room to dry it, but that will mean building a shed next year...

    Don't know where to mention this, so I'll put it in this post, I got a Fiskars super splitting axe off Amazon, new, for $12 shipped ($25 gift card from my credit card) :) Went out in the rain last night after work to re-split some big chunks just to compare it to my old maul. I'm in love.
  23. Battenkiller

    Battenkiller Minister of Fire

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    I think you are over thinking this whole issue.

    For one thing, you should realize that moisture meters are calibrated to the way moisture content is assessed by the wood products industry, a method that is not very intuitive to us, but works for the industry just fine. From a previous thread:



    All MMs are set to use this method as the basis for their internal calculations. Otherwise, they would all disagree with each other.


    For example, a chunk of wood that weighs 127 pounds and reads 27% MC on the meter actually only contains 27 pounds of water. 127 minus the weight of the water is 100 pounds. 27 pounds divided by the fully dried weight (100 pounds) times 100 = 27% MC on the MM. But the actually amount of water in that 127 pound block of wet wood represents only 27/127, or .21 or 21% water by weight.

    A similar block of wood that weighs 120 pounds and reads 20% MC on the meter actually only contains 20 pounds of water. 120 minus the weight of the water is 100 pounds. 20 pounds divided by the fully dried weight (100 pounds) times 100 = 20% MC on the MM. But the actual amount of water in that 120 pound block of wet wood represents only 20/120, or .17, or 17% water by weight. Don't trust me, see below (in blue type):


    http://extension.missouri.edu/publications/DisplayPub.aspx?P=G5450


    So, for a 10-pound split, there is really only 0.4 pounds of extra water in a split that measures 27% MC compared to one that measures 20%. That is a total difference of about 6.4 ounces of water in a 10-pound split. This much water represents a heat loss of only about 390 BTUs out of a potential 70,000 BTUs of sensible heat in the split. Pretty small difference IMHO. And as far as all that extra water going up the stack and condensing on your flue walls? Well, a 10-pound split of wood that is at 20% MC and, therefore, contains 8.3 pounds of wood is creating 4.5 pounds of water (steam) as a product of combustion. That is huge compared to the 0.4 pound difference between woods at 20% and 27% MCs. And if you don't recover any of the latent heat in that steam (which you really don't want to do) by condensing it back into a liquid, you always lose 4365 BTU for every 10-pound split at 20% MC that you burn. Does that 390 BTU difference seem all that bad in comparison?


    Folks should take it easy on themselves and stop obsessing over the finer points of moisture control and do as Dennis and many others here recommend: Take any wood that you feel is marginal (whether you are using the "heft", seasoning time, or MM method of assessment) and mix it in here and there with the good stuff during a hot fire. Your stove will be just as happy, and you won't be able to tell the difference.
  24. muncybob

    muncybob Minister of Fire

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    My MM tells me one thing, is this wood going into the burn it this year pile or not. I'll check a couple of splits and if they are in the same ballpark I'll assume the rest of that tree will be too. After cutting down a tree and splitting is about the only time I use the MM. In my woodpile I like to take the top of a dog food can and mark it with date split/MM reading & tack it to an end of a split. Most of my wood is one of four types so I'll have a good idea based on the date and which pile it's in as to when I can actually burn it.

    I do this now as this is only my second year burning but I can see a day coming when I'll skip this because by then I too will be more "seasoned".
  25. Battenkiller

    Battenkiller Minister of Fire

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    What species are you cutting? Bet you're getting a lot of "OL" readings on your LCD screen.

    The vast majority of woods won't even register on a MM when freshly cut because they are way above 40% MC. Not only is 40% about the cutoff for most moisture meters, they are very inaccurate in that range. Better to wait until the wood has been sitting for six months to a year and the MC has dropped considerably.

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