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Thread: My Low Cost Dehumidfication Kiln

  1. #1
    Join Date
    Dec 2010
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    My Low Cost Dehumidfication Kiln

    I mill much of the lumber I use for my furniture and cabinet work. Milling your own lumber can save you a lot of money if you have a source of free logs - I do. But milling is only half the battle; you still have to dry the wood before you can use it. Air drying to 6 - 8% MC is a very long term proposition and I'm not a patient man so I wanted a means to finish dry lumber after air drying outside to the EMC of my area of around 12 - 14%. I decided on a dehumidification kiln after reading an article in Fine Woodworking (1991). A dehumidification kiln is pretty simple to build at relatively low cost, and is safe because it operates at low temperature. I modified the design, dimensions, and some of the components outlined in the FWW article to suit my needs and the components I could source.

    Here's a photo of the kiln as I'm loading it with some very nice red oak I milled last Fall. The kiln is made from OSB, plywood, and 2 x 4's. The internal seams are all caulked and interior surfaces were painted with a couple of coats of oil based paint. Overall it's about 10 ft long so it can handle 8' long boards, and can hold about 275 BF.

    IMG_4203.JPG

    A closer view of the drying chamber shows the vertical slots from in the rear air plenum where the dehumidified air exits and flows through the stack of wood.

    IMG_4204.JPG

    Here's a photo after the kiln has been fully loaded and the dehumidifier installed in the right chamber. Note the catch pan under the cooling cools and hose that ducts out of the kiln to a collection bucket. That allows me to measure the amount of water removed every day.

    IMG_4209.JPG

    Above the dehumidifier are 3, 100W light bulbs that provide the primary heat source. That's all it takes to heat the chamber to it's operating temperature because it's so well insulated with the 1-1/2" foam board. Behind the dehumidifier is a squirrel cage blower that puts out about 500 CFM.

    IMG_4205.JPG

    The fan blows heated and dehumidified air into the rear plenum, which flows through the stack and returns to the right chamber. Here's a photo of the control system.

    IMG_4206.JPG

    On the far right is a high limit temperature switch. Just to the left and almost hidden from sight is the analog humidistat, which is only thing I adjust during a drying run. To the left is the primary power switch, and then switches for Heat, the Dehumidifier, and the Humidifier. Top left is the digital temperature control which is always set to 110 F. In the center below the switches is the wiring rats nest, which is all done through a DPDT relay. Just below that is an alarm below that will ring if the high limit temperature switch is tripped. At the lower right is the ultrasonic humidifier. It's used for reconditioning the lumber at the end of the drying cycle, but I've found there's no case hardening if I follow the drying rate schedule given in the FWW article so I never use it.

    The door seals to the chamber against a foam seal to create an air tight seal.

    IMG_4211.JPG

    Drying takes about 2 weeks with a full load of wood at about 14% MC, and costs perhaps $20 in electricity. Operation is as simple as checking how much water is removed every day, and adjusting the humidistat to stay on but not exceed the drying rate schedule. If I have to leave town for a few days, I just let the kiln idle at the last setting and then resume lowering the humidistat when I get back. As long as you don't try to dry faster than the schedule allows you really can't do anything wrong.

    I built the kiln 12 years ago at a cost of about $300. I've dried at least 3000 BF of lumber in it over the years.

    John

  2. #2
    Join Date
    Feb 2003
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    Hayes, Virginia
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    John,

    Your kiln looks a lot like the Ebac kiln I built over 20 years ago. Mine dried 400 BF at a time and I ran the kiln for over ten years.
    .

  3. #3
    I'm still running an Ebac - 26 years old and on the 4th blower but still works.

  4. #4
    Join Date
    Feb 2003
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    Hayes, Virginia
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    The Ebac dehumidification system produced the best quality lumber I ever had. The drying cycle was slow but worth the wait IMO, I dried my lumber down to 8-10% and put it in the kiln soaking wet.
    .

  5. #5
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    I'm sure the Ebac is a great kiln, but I didn't have the space or money for one. This little kiln is of a size and cost that fits many hobbiest woodworker's space and money constraints. Speaking of space, I need more. I have so much wood in my basement shop that it's getting hard to move around. I really need another building for drying and storing wood but no good alternatives come to mind looking at my very narrow property. Anyone have any clever solutions?

    John

  6. #6
    Join Date
    May 2004
    Location
    Tyler, Texas
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    No clever (or stupid) solutions here for wood storage. I'm in the same boat.

    That DH kiln is impressive and I've seen pics of your work so it must be doing a good job drying your lumber. I saw a similar DIY kiln in American Woodworker years ago and always thought I would build it one day but went with a solar kiln, instead.

    Thanks for the great pics and detailed description of the components.
    Cody


    Logmaster LM-1 sawmill, 30 hp Kioti tractor w/ FEL, Stihl 290 chainsaw, 300 bf cap. Solar Kiln

  7. #7
    Join Date
    Feb 2003
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    John,

    I meant to say that your design is very similar to the Ebac kilns and I expect it does a great job producing high quality lumber. For a hobby woodworker to be able to produce and use the good stuff is pretty rare so your design is pretty slick.
    .

  8. #8
    Join Date
    Nov 2013
    Location
    Western Australia
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    145
    Add one more wh0o ran an ebac dehumidifying kiln for about 12 years or so.

    I put ~13 M^3 of wet hardwood in and it took 3 months and $3000 worth of power to bring it down to 10% EMC. I had a feature grade saw log contract and ran the kiln 4 x 3 month cycles a year. Loaded strip stacked timber in & out with a fork lift.

    I selected the best boards that I wanted for furniture manufacturing, the next best for joinery work and the rest I sold on to pay for the logs and milling + power bills.

    In essence all my wood was "free" and I had the run of the mill in terms of what timber I personally kept to use.

    Most of the 13M^3 charges were Jarrah species.. but I also dried Marri and Blackbutt.

    One charge a year was Coastal Sheoke - which I sold into the commercial boat building trade because its very stable when dry in humid environments (i.e. on the water). One of our local naval architects his design signature was using sheoke to trim out the cabin berths bunks etc.







    This was one vessel trimmed with some of my sheoke.. that I sold to the builder.

    The Ebac was a good kiln evap unit - however after a number of years, the refrigeration mechanic almost lived at oiur factory repairing the ebac unit & re-gassing it frequently!

    The condensation on the evap coils - being from our timber was acidic in Ph and corroded little pin holes in the copper - especially the fine thin copper tube near the TX valve.

    Probably should have just bit the bullet and bought a new one... it had earned it's keep many times over!.

    Sold up and retired before it got to that tho. Used to pull 23 or 24 liters in a 24 hour period for ~ 3 months.

  9. #9
    That's a nice kiln John. I like the speed and low operating cost.
    I'm curious, how long does it take to air dry down to the 14% EMC you start from?
    Fred

  10. #10
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    Hi Fred,

    Well, there's no hard and fast rule of how long it takes to dry to 14% MC because it depends upon the species of wood, how thick it is, where you live and when you saw/stack it. But to give you an idea, if I saw most any wood in March/April at 4/4 thickness, it will be down to 12 - 14% by Sept or October. 8/4 stock takes about 2-1/2 to 3 times as long, so at least a year. The old rule about it take one year per inch of thickness is pretty conservative for where I live. Here's a link to an article that can give you an idea of the required drying time in most parts of the country: http://sbisrvntweb.uqac.ca/archivage/030108539.pdf

    John

  11. #11
    Thanks John. I was hoping you'd found a magic approach to shorten the air drying too. No such luck I guess.

    It's still a darn nice setup. Wish I had access to logs and a bit.more room. I'd copy your design in a minute!

    Fred

  12. #12
    hi john
    was wondering what dehumidifier you used
    great job

  13. #13
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    WNY
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    An old General 30 pint per day. It's far larger than needed but I had it so that's what I use. New dehumidifiers seem to die in no time. This one is at least 30 years old and just keeps running.

    John

  14. #14
    Did you find a storage solution? A shipping container sounds about right

  15. #15
    Join Date
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    Quote Originally Posted by kent wardecke View Post
    Did you find a storage solution? A shipping container sounds about right
    Yes, I did. I built a 14 x 18' shed:

    20181027_155829.jpg

    Here's a shot as I was loading wood into it. I store lumber on edge, so I can pull out any board w/o digging.

    IMG_5620.JPG

    I planned to put my kiln in the shed, too, but the more I thought about it the less I liked that idea, so I built a solar kiln:

    20190820_192251.jpg

    Can't dry in the Winter anymore, but when the weather is warmer it dries 750 bf essentially for free.

    With the shed as my primary wood storage now, I only keep a couple hundred BF of wood and sheet goods in my shop. It's a pleasure to work in my shop again, with plenty of space to move around and assemble projects.

    John
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