Seasoning Firewood: A Scientific Approach

By , August 27, 2014

After a fairly wet summer, I’m beginning to see the end of this year’s firewood gathering. Obviously, wood gathering, and perhaps more important, wood drying has been on my mind a lot lately.

Apparently, there’s a group of people at the Cold Climate Housing Research Center in Fairbanks, Alaska who spend a lot of time watching firewood dry. Even for a firewood lover like me, that seems like a bit of a bore. They learn a lot from it, though, providing information that we can use.

In an article by Ned Rozell, Science Writer for the Alaska Science Forum, Geophysical Institute, University of Alaska Fairbanks (Dry Wood is Good Wood, August 12, 2010) I learned more about firewood in Alaska—at least their part of Alaska.

Air quality is extremely important, particularly in Fairbanks. Their air remains quite still during most winters. They often exceed Environmental Protection Agency air quality standards, largely because of wood smoke emissions. Burning unseasoned wood makes the problem worse.

The article sites expert findings that firewood is at its best as an energy source when it contains 20% moisture or less.

Fairbanks fourth-grader Linnea Schultz studied drying birch for firewood as a science project. She concluded that split birch dried for 16 months had more than 20% moisture remaining. She found that split birch dried for 28 months “had a moisture content below 16% and was dry enough to burn properly.” The Cold Climate Housing Research Center cross-stacked green, split firewood on pallets and covered it with a sheet of plywood. It dried to about 16% moisture during one hot Fairbanks summer.

This led them to predict that air drying takes much longer in damp, humid regions of the state—meaning mine, Southeast Alaska.

While this makes sense if one considers the amount of moisture in our air, I don’t think that the conditions in Fairbanks can be directly compared to Southeast Alaska. We seem to get far more wind than they do. Air flow seems to be a much more important factor in wood drying than low humidity. After eight years of drying birch on the homestead, I’d say the firewood we dry in the wind probably matches or exceeds Fairbanks’s calm drying conditions (see A Day at the Beach: Passive Solar and Wind Power at Work). Specifically, we often dry birch very well in a single summer.

The point is good, though. Firewood, birch in particular, should be dried at least two years before burning whenever possible.

Since most of us lack the skills and resources to check moisture content in wood, the Cold Climate folks offer simple ways to estimate moisture levels in wood:

  • Dry wood checks, splits and cracks in cross section.
  • If knocking two pieces together makes a hollow, ringing sound, that indicates 25% moisture or less.
  • Dry wood also doesn’t hiss or bubble when burned.

To this, I would add:

  • Visible smoke coming out of the chimney (after the fire is burning well) indicates a higher than 20% moisture content.

4 Responses to “Seasoning Firewood: A Scientific Approach”

  1. al frascoia says:

    Check out this site. It has how to build a solar wood dryer.

  2. Mark Zeiger says:

    Hi Al, thanks for the link! This looks great, although if I were to make one, I’d probably make the sides translucent as well, or at least have panels of that material in them.

    We have long known a way to make something similar to this with visquine, but I’ve never made one, as it would be too fragile to hold up in our winds. This shed would hold up just fine, I’d guess.

    Of course, what really made me drool was the idea of moving firewood around with a front loader! After tripping a couple times yesterday. falling flat out with a full load of wood on my back, that looks really good!

  3. Beth says:

    Mark, thanks for this – we’re excited to have a wood stove and fireplace this year and want to do the best we can with it. This info will really help!

  4. Mark Zeiger says:

    Hi Beth, I forgot your new place has a wood heat option! You’ll likely want to buy your firewood, which is a luxury we don’t have here. Just remember to ask for “mixed cords”. That means that instead of a cord of more or less same-size rounds, they need to fill the gaps between them somewhat with smaller wood. A mixed cord provides much more wood, often for the same price as a regular cord, which looks like what a suburban wood burning home wants, but isn’t, really.

    If you can find them, mill ends can often be delivered, too. Much less stackable, but way cheaper than good looking firewood. When we shared a house in Portland with Dave and Kathleen, that’s what we did. It was very inexpensive!

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