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Thread: A New Dehumidification Kiln

  1. #1
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    7,441

    A New Dehumidification Kiln

    I have a solar wood kiln that I use to dry rough sawn lumber. It works well from May to October. So what about the other 6 months of the year? Well, it's pretty useless here in western NY. Wood I've put in it in November has dried about 1%/month through the winter months. Like I said, pretty useless. So to add some much needed drying capacity I recently built a dehumidification kiln in the back of my wood storage shed. I designed the shed for it when I built it 3 years ago but never added the kiln until I became desperate for more dry wood.

    A dehumidification kiln is a pretty simple affair. All you need is a well sealed and insulated box to hold the stickered wood, a low wattage heater, a small dehumidifier, a fan to circulate the air, and a couple of simple controllers to regulate the RH and temperature. My new kiln is about 11' long x 4' high x 4' wide inside. I built it by first insulating two walls of the shed with fiberglass insulation, then covering it with 6 mil plastic to form a vapor barrier. I added an insulated knee wall to give me the third wall and then added an insulated roof. The roof has a layer of 2" foam on the inside and then 3-1/2" fiberglass in the stud cavities of the framing.






    The floor is insulated with more 2" foam over a layer of plastic. There are sleepers every 2' to support the wood that will go on top. I made the door in three sections. More 2" foam backed up with a 2 x 4 frame. BTW, I made all of the lumber from some fir logs I got for free last Fall and cut into 2X stock. I had no idea what I would do with it at the time, but it came in very handy for this project and saved me some money. Lumber prices right now are nuts. Anyway, the doors seals against the rubber gasket around the perimeter of the box and give a pretty good seal. I can easily maintain the 75% RH needed at the start of a drying cycle for partially air dried wood.

    Here's a shot of the kiln loaded.






    I should have made it a foot longer because I didn't have room at the left end for the dehumidifier and heater with the 9-1/2' boards I had. With 8' lumber it will be fine. So I had to get creative in how to load the kiln. The fan is on the left and circulates air to the back and than across the back face of the lumber where it travels through the lumber stack to the front side and then repeats. The heater is just a 1500 W oil filled room radiator set for 1000W.

    All buttoned up the kiln looks like this:





    The RH and temp controllers sit on the outside and are easily adjusted to follow the EBAC drying schedules I use. They are Inkbird brand I bought at Amazon; just over $100 for the two of them IIRC.





    The kiln holds 400 - 500 BF of lumber. Air dry wood at 20% or less should take 2 to 3 weeks to dry. I'll let you know; this is the first load.

    I already had the dehumidifier, oil filled radiator and fan, so the cost to build the kiln was around $300. It's going to pay for itself very quickly.

    John

  2. #2
    Join Date
    Nov 2014
    Location
    West Granby CT
    Posts
    755
    That looks pretty cool! My solar kiln can only do 400 or so bd foot at a time. That’s a good amount for that space, cool design.

  3. #3
    Join Date
    Feb 2003
    Location
    Hayes, Virginia
    Posts
    13,998
    I operated an EBAC dehumidifier for ten years and it produced the best quality lumber I have ever seen. Your kiln is very close to the one I built, you are going to enjoy the fruits of your labor I guarantee.

  4. #4
    Little did I know that I was operating a dehumidification kiln in my shop by adding a couple of dehumidifiers. I have successfully dried a lot of treated pine to a level that does not trip the Sawstop by just bring it into the shop. Stringers and clamps are helpful to keep that stuff reasonably straight while drying out.

  5. #5
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    7,441
    To give you an update, the load dried from 18.8% to 7.0% in 25 days, a little longer than I had guessed but still acceptable for 8/4 stock.

    John

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