Is there such a thing as too dry wood?

ohlongarm Posted By ohlongarm, Nov 29, 2011 at 10:29 PM

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  1. oldspark


    From thechimneysweep post in the other forum, just to show that we are not alone in our thinking.
    "I’m surprised nobody has jumped on the reported 7% - 12% moisture content in your wood. We shoot for 20% - 25% moisture content because at that point most of the free moisture (water) has evaporated away, leaving the bound moisture (wood resins) behind. When a fresh load reaches about 500 degrees, these wood resins begin to gasify, and the gases ignite, which provides the fuel for Stage 2 of your burn. This is when the secondaries light up, and provide up to 50% of the heat from that load.

    If your wood is truly at 7% moisture content, much of the bound moisture has evaporated away, taking its fuel value with it. When fueled with wood that dry, your fire progresses rapidly from Stage 1 (kindling the load) to Stage 3 (charcoaling), resulting in disappointing heat output and short burn times (sound familiar?). Yours is a common complaint we hear from folks who burn mill ends, because much of the resin content has been baked out in the kiln.

    The solution? To start with, do exactly what you’ve been doing: chop the extra-dry pieces into small splits, and use them to start your fires. But from now on, try this: once the fire is going, fuel it with larger pieces that aren’t so over-seasoned."
  2. Battenkiller

    Minister of Fire

    Nov 26, 2009
    Just Outside the Blue Line
    OS we may be alike in our thinking, but I don't agree with that post (who wrote it?)

    Wood resins do not evaporate out of the wood with the bound water. Basically all of the wood energy remains even down to 0% MC. I have different reasons why I like wood at a slightly higher MC. The bound water helps to regulate the burn so combustion efficiency increases, but there is a penalty is latent heat due to evaporation, even though the wood will burn cleanest just at the point where there is no free water left and only bound water remains.

    Also, there is more heat transfer loss at these higher moisture contents, so it is better to get it down near 20%MCdb as this has been shown to provide the best overall efficiency. That's why 20% has been the gold standard since folks started examining these phemomena in the lab. Before that, one year c/s/s got you to the same point in most locales without anybody actually knowing it, so that still works fine.
  3. oldspark


    I wondered about the resin thing because I had never heard that before, it came from the poster "the chimneysweep" who is from the site of the same name I believe.
  4. hughmyster

    New Member

    Feb 20, 2009
    central ct
    I get low burn times when the wood is too dry. I can't close the air control all the way down or I will get backpuffing. I store all my firewood in a greenhouse and been using the same wood I stacked for 4 seasons. The first year no problems. Every year after the back puffing got worse. I called the manufacturer and he said if the wood is too dry, back puffing can happen more frequently on cat stoves. I will only burn wood now seasoned for no longer than a year.
  5. oldspark


    hughmyster-I love the personal expeirence stories, it seems like the only way you are going to have wood that is "too dry" would be by having in a greenhouse, wood room, or a old barn giving it a kiln dried cure, left outside in will not be any where near that dry IMHO.
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