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DIY drying kiln... or dumb waste of time?

Post in 'The Wood Shed' started by Bunsen, Nov 12, 2012.

  1. Bunsen

    Bunsen New Member

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    Hi guys. Let me start by saying I'm totally new to wood burning. I've had a thread going in the wood stove forum about my first wood stove I'm having installed in a month or so. I'm a rather obsessive person so I've been thinking of nothing else but wood burning and how to occupy my time until the stove is in place. I've been thinking of putting together a drying kiln as shown in the image below, which would be made almost completely from free parts I have lying around. Would something like this be even remotely effective for anything other than occupying my time? The idea is to leave the black crate filled with wood (approx 68 sqft) in the sun to warm up, and constantly pull air through it using a duct fan (which would cycle all the air in the container about once every minute) and some duct work. I don't think it would cost much in electricity, and it might mean I have some more burnable wood this season.
    I'm toying with the idea of putting some light bulbs in the intake to warm the incoming air. This would mean I could have the contraption in my garage and pipe the exhaust out a window. Maybe this is a bit overkill. Can you tell I'm excited?

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  2. Standingdead

    Standingdead Burning Hunk

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    This is a very cool idea! I have had good luck over the years employing a simple solution. I stack my wood in a breezy location in north facing double stacks with 3-5 foot spacing between rows. These gaps between rows catch the western winds. I generally stack 8-10 feet high. I do all I can to get my wood into the wind. By getting a couple years supply ahead, the wood has time to season or dry to 15-18% moisture. Best of all stacking in the wind is free. The key is to get 2-3 years ahead. Some on this site, maybe most, cover their stacks with metal or poly. I choose not to, but bring a full winters supply indoors in late summer so it's not an issue. I have a bias and tend to favor simple things in life.

    Have you thought about a greenhouse design with venting? I have a friend who uses a small power vented greenhouse in summer to " bake" his wood. He claims he can season anything in 1 summer. He puts the wood in once the plants are out. I have never checked his wood with a MM so I still have some doubts.... Have fun building your supply!
  3. bogydave

    bogydave Minister of Fire

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    Could speed things up some. Gonna take energy to do it. Efficiency not gonna be there.
    Give it a go.
    Could be time well spent waiting for the stove. Seasoning wood takes time ;)

    What wood do yo have now.? How long CSS? Type of wood?
    Could also spend the time processing more wood for next year, get it stacked & seasoning.
    Find some dead standing & get it CSS. May be burnable this year, not great but burnable.
    Buy some dry wood to get thru this year. Hard to find but sometimes you get lucky.
    You location would help :)
  4. Todd 2

    Todd 2 Feeling the Heat

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    Might just work, One don't know till they try ! Good luck with the new stove and dry wood is the ticket,
  5. Slow1

    Slow1 Minister of Fire

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    The key to drying the wood seems to be airflow as much as anything. Relative humidity of the air of course if a significant factor, thus warming the air helps (i.e. it lowers the relative humidity of said air).

    I'd like to know how your design works out - I would suggest one change if you can figure out a way to do so have the air flow such that it passes through the stacks as much as possible so that all splits get some airflow over as much of the split as possible. However, if you are cycling the full volume of air every minute it may not matter all that much - you could save some energy perhaps and reduce the rate of airflow.

    If you do try this, please post your results as I'm sure there are several (if not many) who would be interested.
    Todd 2 likes this.
  6. Grisu

    Grisu Minister of Fire

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    If you want to quickly dry your wood you may want to take a look at a solar kiln. Here is one shown:
    http://owic.oregonstate.edu/solarkiln/plans.htm
    Btw. If your fans exchange the air completely within one minute a lightbulb will do little to heat up the incoming air.
  7. ScotO

    ScotO Guest

    Here's a great tutorial explaining the basics of a solar kiln. This one, of course, being setup to dry boards. But you could easily modify this setup to dry cordwood, I would think. Its on my bucket list of things to do someday......

    Dune and PapaDave like this.
  8. Auzzie Gumtree

    Auzzie Gumtree Feeling the Heat

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    I have often thought about trying to utilize the heat going up the chimney - if you could somehow divert this into the inlet of the drying chamber......
    chazcarr likes this.
  9. Sprinter

    Sprinter Minister of Fire

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    I tried a temporary makeshift fan driven drier this summer. It only operated for a couple months, but I think it helped. I was getting worried about my first year's supply. I've given some thought to driers. Yours looks like a decent design and simple to make. Try to design for as much of the airflow to get evenly through the stack as possible. You will probably have to keep the structure completely full all the time to do that, or the air will just go around.

    Electrically heating the air would be ineffective and not cost effective IMO.

    You probably don't have to run the fans all the time. Consider putting them on a humidistat. Also, when you have very high humidity at night, air flow just won't help much anyway.

    What is your wood supply situation? If you have enough space for about three year's supply, then you probably would only need an active drier for the first year, like I did. After that, air drying is just fine, but you do have to have the space for a few years worth.
  10. Bunsen

    Bunsen New Member

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    Thanks for the encouragement guys! I think I'll give it a go just because I can, and its almost free to try. I'm not sure how I'll document my findings though. I guess I'll take a moisture reading every X days and compare to a group of control logs.

    Using the materials I have, I'm not sure I could increase air distribution any more than I am by offsetting the intake and exhaust (without spending money). Maybe it would just be better to put the intake and exhaust directly on opposite ends of the wood pile in the crate. This would hopefully draw the air straight through the wood. I have another idea involving drainage pipe that I have to think about some more.

    As far as heating the air via lightbulb, it's true that with my plan the air would be traveling too fast to heat up very much. Now that I'm thinking about it, if I remember correctly the 6" fan moves 250 cf of air per minute. That means the air would cycle more than 3.5 times a minute, which is probably enough on it's own.

    How is my wood supply now? Non existent!!! That's the problem. I'm having wood delivered this week and I'm really keeping my fingers crossed about its quality. I went to look at the dealers stock and it seemed decent, but I didn't have a moisture meter. I banged a few logs together and they clucked rather than thudded, but I don't really know what I'm doing. At least it's already all split.

    Unfortunately I live in suburbia (a bit north of Providence, RI), not in the wilderness, so I can't just walk in my back yard and start logging. I have room for several cords of wood, but I'm honestly not sure how much I'll use in a season. I'm going to buy 2 cords and see what happens this year. When I can afford it (or find it) I'll try to start stocking up for next year.

    Anyway, if I move forward with the kiln, I'll update you guys.
  11. Sprinter

    Sprinter Minister of Fire

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    That's as good a reason as any!

    Also, as I was reminded, "Pics or it didn't happen"
  12. Jack Straw

    Jack Straw Minister of Fire

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  13. peakbagger

    peakbagger Minister of Fire

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    I would recomend using a solar panel but avoiding Harbor Freight panels. They have a high failure rate and are relatvely expensive. There are all sorts of 12 volt fans on ebay or any auto junkyard should have radator fans that are used on front wheel drvie vehicles. When you do buy a panel make sure its a "12 volt" panel which is actually about 18 volts, many of the grid tied panels out there are higher voltage and could cook the DC motor. No need for a battery or charge controller just hook the fan direct to the panel. Air circulation is good but you do want to set it up with a snap disk on the air inlet so that the air temp entering doesnt get too low. Getting the fan to have a good flow without a lot of cycling is going to requires some adjustments, you want it sized so that it runs much of the time.

    Shipping on single panels is pricey but if you need some sunelectronics in Miami usually has panels on sale.
  14. Dune

    Dune Minister of Fire

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    Insulate the heck out of it and duct your stove exhaust pipe through it. Should season half a cord in a couple weeks.

    Since you clearly will not be doing that, consider the solar kilns. They work very well. With the solar kilns, convection provides air movement, no electricity needed.

    Air inlets at the bottom, vents at the top.
    ScotO and PapaDave like this.
  15. jharkin

    jharkin Minister of Fire

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    I'd be leery about any contraption to direct your stove exhaust into this. There is nothing for free in physics, the heat in your stovepipe is what drives the draft - redirect this heat to the kiln will either kill the draft or gunk up your pipe or both.

    Same reason why none of us would use a magic heat....
    LEES WOOD-CO likes this.
  16. Grisu

    Grisu Minister of Fire

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    What I was wondering whether you can build a contraption to channel the warm air from the blower through the wood. I just do not see a way to get that looking nice somehow. Plus, you will probably have to leave the wood in there for weeks to have any substantial effect.
    Another great place to dry wood would be our attic in the summer. I am just way to lazy to carry it up there. :p
  17. Sprinter

    Sprinter Minister of Fire

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    Okay, I gotta ask, what's a magic heat?

    BTW, I would hope that was a tongue-in-cheek suggestion above.!!!
    Dune likes this.
  18. Sprinter

    Sprinter Minister of Fire

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    I've actually heard of that being done. I imagine it could be pretty effective, if rather impractical, if the attic is well ventilated. I think they used a hay conveyer to get it there. Floor loading could be an issue:eek:
  19. jharkin

    jharkin Minister of Fire

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    The magic heat a.k.a. creosote formation accelerator.


    [​IMG]
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  20. Sprinter

    Sprinter Minister of Fire

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    Good grief.
  21. scotvl

    scotvl Burning Hunk

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    You say you bought a couple of cords to try for this year, I would suggest you add a couple more to your order for next year and try for a discount on quantity. The best way to get seasoned wood is to season it yourself.
  22. jdp1152

    jdp1152 Minister of Fire

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    Looks like a similar concept to a basement dehumidifying system called the Humidex only the fan on it runs extremely slow and constant rather than cycling. They claim the cost is 2.00/month to run it. Have a friend who made his own version for incredibly cheap and the results in his basement were pretty profound. I imagine this could similarly be applied to your device. The air movement is likely slow enough to still allow heat accumulation.

    http://www.humidex.ca/products/hds-209/
  23. Sprinter

    Sprinter Minister of Fire

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    It's true that it doesn't need much cfm to do the trick. Just enough to pick up the water vapor as it leaves the wood, which is slow, and to expose the wood to the RH of the air provided.
  24. Dune

    Dune Minister of Fire

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    Induced draft.
  25. Bunsen

    Bunsen New Member

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    Well I plugged in my contraption today. It follows my original plan for the most part with a few changes.

    1- instead of 1 fan, I used 4 arranged in a square on one end of the crate. They are not duct fans, they are cabinet fans from a job site we demolished a couple of weeks ago. Each has a similar CFM to the fan I originally planned on using. So really, there is a whole lot of air moving through the box.

    2- the box is a bit smaller. Maybe 1 or 2 feet shorter. I haven't measured. It's the one I had available for taking at work.

    3- I layered the wood crisscross, in hopes of maximizing wood surface area exposed to the moving air.

    4- Instead of an inlet duct, I cut the entire end of the crate open and affixed a wire screen, to keep mice and chipmunks out.

    I have the fans plugged into a timer set to operate during daytime hours. I'm assuming humidity is lower while the sun is out, but that is a complete guess and I need to research this a bit more. I know I can purchase a plug that is humidity controlled, intended for use with a dehumidifier. I may get one of those instead.

    I also have a remote kill switch on it, so I can manually turn it off from inside the house, if it's raining, or if the relative humidity is high.

    This is a completely unscientific experiment. I'm planning on opening the box in a month and maybe do some moisture readings and compare to the stacked wood I have. Probably I'll just see if the wood is noticeably drier by observation rather than readings. I'm not expecting much, but it'll be fun.
    ScotO and milleo like this.

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