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Firewood drying time

Discussion in 'Firewood, Heating and Wood Burning Equipment' started by Thechap, Jul 9, 2009.

  1. Thechap

    Thechap ArboristSite Operative

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    Here is some good information published by the US Forest Products Laboratory.

    Regarding Seasoning of Wood
    Freshly cut wood has a very high moisture content. As much as 60% (or more) of the weight of a tree is water. At least some of this water must be removed before trying to use it as a fuel wood. See Amount of Energy in Wood, for a discussion of why that is necessary. Several bad results can occur from burning wood that is not fully dried to below 25% moisture content. (Such wood is referred to as "green" wood). As that discussion mentions, the effective available heat is MUCH less, not just because there is less wood fibers in each pound of wood put in the woodburner, but that a good percentage of that heat must be used to evaporate all that water before those wood fibers can burn. Another VERY important consequence of burning green wood is that the presence of all that moisture tends to keep "putting out" the fire, and therefore making it burn very poorly, which tends to produce a lot of creosote and pollution. Don't Do It!
    Generally, the way this drying is accomplished is by "seasoning" it. Firewood is cut to length and then seasoned (dried) in a stack, with air being able to get to it, for at least 9 months before burning. The natural 60%-70% moisture content must be reduced to about 20% to burn well. The wood cells don't lose much moisture through the bark; the moisture is most effectively removed through the cut cells at the ends of each piece.

    That's why logs which have lain in the woods for years may still have a lot of moisture and may not burn well (unless cut and dried.) We have heard of people cutting up these downed trees and immediately putting them in a woodburner! And the wood burns poorly! Now you know why!

    OK! So, sometimes, it turns out to be NECESSARY to burn some green wood. Which species would be best under those conditions? It turns out that the desirability is NOT the same as for seasoned wood! While they are living, various species of trees have different moisture contents. If you suitably dry them all, that difference rather disappears. But, while still green, it becomes significant.

    It is possible to correlate both the heat-content of the wood fibers and the green moisture content to form a table of desirability for those situations when green wood must be burned.

    There are people who insist that wood should be dried (seasoned) for at least one or two years. Experimental evidence has established that that is nearly always unnecessary, as long as the pieces of wood are cut to length and stacked. Natural airflows through the stack, and particularly through the cut cells of the pieces of wood themselves, dries them sooner than that. Experimental evidence has established that one-foot long cut pieces generally dry to acceptable levels in just two or three months. Two-foot long cut pieces take about six or seven months for similar acceptability. Four-foot long cut pieces DO require at least a year.
    Associated with this, covering the woodpile with a tarp slightly improves this, but probably not enough to make the expense of a tarp worthwhile, except in a climate where rain and very high humidity is common. Similarly, split pieces of wood tend to dry slightly faster than full diameter logs, but again by minimal amounts.

    There appears to be no value in drying firewood more than about nine months.


    If wood is stacked in four-foot or longer lengths, the drying process is greatly slowed. In other words, if wood is cut to four-foot length and stacked, for nine months, and then cut to shorter burning length just before use, it will probably not burn well because it is still to wet (green).
     
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  2. howellhandmade

    howellhandmade Addicted to ArboristSite

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    Is that quoted verbatim from a USFS publication? Experimental evidence? What experiments? They don't mention climate as a factor in drying times, only in tarp necessity. They conclude that there is no benefit to seasoning firewood beyond 9 months. For some species and climates, that is true. For other species and climates, it is false. My experience has been that splitting does indeed speed drying. Et cetera, et cetera. I'm a little perturbed if tax dollars were spent writing that piece. Lots of exclamation marks are usually a bad sign.

    Jack
     
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  3. palmrose2

    palmrose2 ArboristSite Operative

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    Speaking as a 48 year old man that has about 30 years of using wood as a sole heat source I agree with almost all that was said. Splitting has minimal effect on dry time as the wood is just a bunch of tubes that run with the grain. Also concerning the tubal nature of wood, the shorter it is cut the faster it cures. You can cure a 2" cookie in a couple of weeks.

    In my experience tarps are good for the fall and winter when there is lots of rain and snow. I've used tarps once.

    In my neck of the woods the best species of wood to cut and burn tomorrow is cherry. I don't mean orchard trees and I am talking about trees that are cut in the winter.

    I know that some climates and conditions effect wood curing. Throwing green wood in the basement in May invites mold and SLOW curing. If I do this I have to leave windows open and a fan going to have any hope of having it ready for winter. A buddy of mine lives in the trees on a small lake surrounded by swampy ground. Constant shade, little wind, and high humidity. My wood cures faster than his because mine is stacked in the sun on a hill that divides two watersheds surrounded by fields.
    Plenty-"O"-Wind.

    Nine months is a long time. Around here I discount Nov. Dec. Jan. Feb. and March as months of curing time. That only leaves seven months in a year for curing. Having said that, if I cut trees down in January and February when the moisture content is low, then cut them up by June, I'm good to go come October. That's only 4 or five months dry time. Basically when I have time my wood get's what most people call two years. That's two summers dry time which may only be nine of my curing months if I'm working in August. The wood I burn is 24" long so I need more time than others using 14"-18" wood.

    The time of year that the tree is cut down has a major effect on curing time. Curing time starts when the wood is cut to length. Shade coupled with low temps/high humidity and lack of wind extends dry time.
     
  4. J.W Younger

    J.W Younger ass kissing impaired

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    same
    Same here,all summer for the oak and hickory, 3-5 mo for the cherry, soft maple and gum. good to go
     
  5. CRThomas

    CRThomas ArboristSite Guru

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    Firewood drying

    I have a 20 foot container I burn my trash wood. I can dry 15 half ranks a week. Thats the only way I sell firewood wrapped. I can set 10 half ranks in my shop a week for back up. That gives me about 12 ranks to sell a week. Brings me in good chunk of change. No cost other than trash wood and my equipment. Try green wood in your shop or inclosed building with small air flow and heat. Do not put your wood close together. You can bring green wood down to 16 percent in a week. Take that out and put in another load. I do it time and time agin. My firewood is only 16 inch long. But if you are a big wood burner your pieces are 2 foot long and big around as your belly for get it. Later
     
  6. Ironworker

    Ironworker Addicted to ArboristSite

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    Thanks for the post, I have read that firewood will only get to a certain moisture content (about 20%) in about 6-9 months, then will not get any lower no matter how much you let it sit due to moisture in the air, I am sure this varies with region, in my experience I do not get any hissing after 6-8 month drying time except with my red oak and then that only hisses very little for the first few seconds. I have also read that wood can be too dry, I know this contradicts my first sentence, but I got that from this site.Can Firewood Be Too Dry?
     
  7. Whitespider

    Whitespider Lost in the 50s

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    I often read here on the board that it takes two years for oak to season, and it always makes me wonder what it is they do so different from me... because my oak has never taken near that long, one full summer has always been enough. I felled 4 really big oak last mid-March, started bucking in April, started splitting and stacking around mid-May. I placed the last split on the stacks on the last day of June... 10-cord in all.

    Just this last weekend I pulled some samples from the stacks and burned them in the fire pit. That oak is ready... no hissing, no smoldering, nice flame, easy lighting... only one summer, 6-7 months since bucking, 4-5 months since splitting depending on the stack, and I probably have at least another full month of seasoning time before solid freeze-up, maybe more. I just don't get where this "two years to season" comes from. This is how I stack my oak firewood for seasoning...

    [​IMG]
     
  8. Steve2910

    Steve2910 ArboristSite Guru

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    I agree, I stacked some Oak rounds last September from tops that were cut in June. I could tell when I picked them up this Spring that they were "close". That's w/ them being out in the weather all Winter. The green Oak I cut & split last May would be ready, if not for the ridiculous amount of rain we got in Sept. I know a guy who says Hedge takes 6 years, I guess opinions vary.
     
  9. J.W Younger

    J.W Younger ass kissing impaired

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    We had one of the wettest yrs on record in 09,,I stack mine like whitespider and keep a mo or so supply under a roof for wet weather. My wood never had a chance to dry much less season.
    Burned 9 cord where 7-7.5 is the norm.
    Stuff happens I guess. Need one of them prefab carport thingies.
     
  10. audible fart

    audible fart MS390 OAK CZAR

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    Are you "the woodsman?" Whenever i would get an oak score in the hot summer months, i'll usually at least half the rounds to get the process started. I'm so far ahead now halfing or quartering rounds will be just fine. One thing i noticed about the huge silver maple rounds i left unsplit all summer, they almost completely dried out without even messing with them. Oak sure wouldn't do that here.
     
  11. PMOWB

    PMOWB ArboristSite Lurker

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    Just curious whitespider....what are the dimensions of those stacks of wood you have? They sure do look nice!
     
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  12. woodman6666

    woodman6666 ArboristSite Guru

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    That sure is pretty!!!
     
  13. thombat4

    thombat4 ArboristSite Guru

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    I second that motion...!



    Those are some right purdy stacks!:eek:uttahere2:
     
  14. EXCALIBER

    EXCALIBER ArboristSite Guru

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    I would say you cannot reliably tell how much moisture you have left if a piece of wood by looking at it or even burning it. Yes you can tell somewhat how much moisture is in that pieces of wood by the hissing, smoke, lighting easy, but not exactly. I would say for the 10-15$ for a moisture meter I would just buy one then you have no question of if the wood is dry of not. This may also allow some people to burn wood they thought was not dry enough a little sooner. There is also a big difference on where you live and climate as to how long it will take in your area to dry wood. Moisture content of the air, average temps, wind and airflow, precipitation, and many other factors play into this equation.

    If you really want the most heat out of your wood buy a moisture meter (they are fun to play with and have many other practical uses), take one of your splits or rounds and cut it in half, test at the center of the piece of wood where you have just cut instead of the ends, and you might be surprised.
     
  15. Mntn Man

    Mntn Man ArboristSite Guru

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    Winter seems to be the best for drying around here when stacked in the sun.
     
  16. Whitespider

    Whitespider Lost in the 50s

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    That picture is from the first day in July. Now that they’ve had time to season, settle and even lean in a couple places they ain’t quite as pretty. Dimensions? Well, I didn’t get the tape measure out, but those are 16-inch splits (or the length of my 16-inch bar) stacked to eye level or a bit more with my boots on (or a bit over 5.5 feet) in rows that step-off at 13 paces (or about 35 feet long)… so, right close to 2-cord per row, maybe just a bit more on average.

    Well, I question the accuracy of a moisture meter, especially a 10-15 dollar one. And, just like burning a few splits, it can only tell you the moisture content of the piece actually tested… not the whole stack. Like with any piece of test equipment, at best, it would only be as reliable as its quality and the person using it. Mankind has been burning wood fuel as a heat source for over 3000 years… affordable, portable, homeowner type moisture meters have been around for what? Ten years at best? I’m sure they’re fun to play with; just not something I’m interested in… I’ll stick with what has worked since we left the cave.

    I’m not much into gadgetry and such… probably never will be.
     
  17. PMOWB

    PMOWB ArboristSite Lurker

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    Those are some impressive stacks. I was pretty close on my guess. I thought 30' x 6' x 20"
     
  18. Streblerm

    Streblerm Addicted to ArboristSite

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    I stack my piles of wood in 8' deep by 5' tall piles on the fenceline between my house and my neighbor's. He stacks wood on the other side. There are mature trees over the pile and some of it gets almost no sun. The trees soak up most of the rain before it gets to the pile in the summer but not so much in the fall/winter. One of the piles that gets no sun is a mix of hickory and maple with a few pieces of pine. This is wood cut and split last fall. It has never been under any kind of cover and we have had record rainfall this year. Pieces in the top 1/4 of the pile are noticibly wet on the outside after a rain, but dry out within a day or so of bringing it inside or within a few hours of being next to the stove. They feel dry by weight and burn clean and HOT! I stuck my cheap moisture meter into some freshly split pieces. It shows 17% moisture consistently anywhere other than the outer 1/2" of wood that is wet. I tried this with about ten different pieces from different places in the pile with the same results regardless of species. A piece of kiln dried 2X4 that has been in my garage measures 14%. Some pin oak that I cut and split late in August measures 30% moisture and it was over 40% (over limit on my meter) when I cut it.

    I had concerns about the shaded. uncovered pile but it seems to have seasoned just fine. Actually I prefer my wood a little less dry. Closer to 25% on my meter burns nice and hot with no smoke and I get a better burn time. I am starting to question the need for a woodshed or even tarping the wood in the fall/winter as I like to keep two weeks worth of wood in the garage rather than going to the woodpile frequently in the winter. That way the wood has always been inside a semi heated area for a week before going into the stove. This gives it plenty of time for the surface moisture to dry.

    I don't live and die by my $15 moisture meter but I do like gadgets. My senses told me that the wood from my uncovered pile was seasoned but maybe slightly wet on the outside and the meter confirmed the results. It seems that wood dries just fine within a year when uncovered and off the ground.

    [​IMG]
     
  19. borat

    borat ArboristSite Operative

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    I found the article about wood being "too dry" interesting. However, I can't totally agree with everything said in it. My old woodshed was destroyed in a wind event several years ago so I had to build a new one. When I transferred the wood from the old shed, that put the oldest wood first out in the new shed. Some of that wood is 25 years old and drier than a popcorn fart. It lights up without kindling. A piece of birch bark or newspaper can get it going. Like any other wood fire, it will smoke at first but once the fire is well established, it settles down to almost invisible exhaust while running hot. When I cut the fire back, it will smoke but certainly not to the extent to be considered excessive or abnormal. At least that's been my experience.

    The article was informative though.
     
  20. zogger

    zogger Tree Freak

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    one simple test

    This pretty much always works for me, whack two pieces together. If it clanks, it is good to go, if it clunks..it gets put on next year's stack. Subtle but noticeable pitch change. I smack 'em together from the stack before they go into the wheelbarrow anyway to bring them into the house, knocks the dirt off, and is a good last check for good dryness. I find a few ones once in awhile that way, not many, just some that haven't dried good enough for some reason.

    I've also noted that my inside pieces dry similar to the outside pieces, in a three row stack. The outside pieces get all the rain slop (top cover only on stacks). But the inside pieces don't get as much air flow. Seems to be a tradeoff on overall drying time that works out to "the same", so I can stack three rows wide instead of one or two. And two of my stacks I have made as deep as ten rows. It still dries, just a scosh slower than the narrower stacks, not so much to make much of a difference.

    I think living where we are and having beastly hot summers has a lot to do with it. I don't remember my wood drying near this good or fast when I lived up north. If I cut some green wood in the heat of summer in the morning, by the afternoon it is already cracking heavy. I have some now I cut..ohh..guess six weeks or so ago when we still had some wicked hot days, and dang if it ain't pretty much ready right now, I tried a few chunks just for fun. It's for next year anyway so should be pretty darn dry by then.(ya I would like a moisture meter because I am a nerd and like gadgets but it isn't high on my gadget need it now list either)

    Now I *prefer* to cut mid winter, cooler and more comfortable for me to work and the wood comes fresh with the least amount of moisture in it and weighs less, but beggars ain't choosers and I try to cut year 'round now anyway. It adds up more, and mo is bettah. Besides, mid summer cutting is the best time to beat the mud usually.
     

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