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Thread: Hobbyist dehumidification/sterilization kiln questions

  1. #1
    Join Date
    Dec 2006
    Location
    Madison, Wisconsin
    Posts
    317

    Hobbyist dehumidification/sterilization kiln questions

    This subject has been covered in various wood forums and Youtube videos but I canít seem to find consistent recommendations for a small and inexpensive dehumidification/sterilization kiln equipment for a hobbyist. Insight from anyone who has built such a system would be most welcome. I have a lot of air dried lumber and would like to further dry a few hundred bf at a time as needed for projects as well as sterilize as I have a powder post beetle problem with some of the wood.

    My thought was to build a 4íx4íx10í box (in my garage) from 2"- 4" rigid foam insulation that could be disassembled when not needed. I intend to include a home dehumidifier and fans for water removal. My question has to do with the best, and safest heat source to elevate temperatures to the necessary 130F to kill powder post beetles.

    The many threads I have read suggest using heat lamps as a heat source as conventional space heaters have cut off switches at 100F or so. Others suggest a sauna heater, which is intriguing. A 3KW sauna heater capable of reaching temperatures well in excess of 130F can be had for about $100 on Ebay. In both cases, controlling temperature, as well as preventing ignition of the wood or foam, is important.

    Anyone out there built such a kiln? If so, what type of heater did you use and what safety precautions did you take? Obviously, I donít want to burn down my shop or house in the process so any insight would be appreciated. Thanks, bob

  2. #2
    Maybe you should consider building a small storage building for such a task. I was considering using a old cargo trailer for that, as also don't want to burn my shop down. Finally decided to buy a old reefer trailer, which is insulated, and the seller offered to deliver it and remove the wheels, so I bought 2 4x8 prestressed concrete panels, leveled them and had him set the trailer on those. Turned into a lengthy project, as I decided to set up a track, so as not to have to pack the lumber in a board at a time, and got some old solar panels from neighbors, then had to wire the trailer and hook it up to the grid to power a furnace blower to push air through the solar panels. Am getting heat up to about 115 degrees in the afternoon, and plan to run a sterilizing for about 24 hours soon, using heat lamps to push the air up from the 115 to about 140. The inside of the trailer box is lined with a fiberglass coating over the insulation, and will only tolerate up to 160 degrees, so have to be careful. The panel has several breakers, and each receptacle is on a separate breaker, so I can plug in several, get the heat up, and then turn some off to maintain the heat.

  3. #3
    Join Date
    Dec 2006
    Location
    Madison, Wisconsin
    Posts
    317
    Thanks for your input Jim. Your ideas are good ones and I wish I could build a system like yours, however I am in an urban neighborhood and can't add another building to my lot. I got approval to built a shed in which I store my lumber, but I doubt I would get approved for another. However, you got me thinking....perhaps some type of temporary trailer would be the ticket. The only issue is that it gets COLD here in Wisconsin and if I put the kiln outside I am fighting the ambient temps during the winter months. My garage is heated so would not be as difficult to reach temperature. I have a 6x10 dump trailer (with a cover)....perhaps if I get some thick foam insulation, I could use my trailer as the kiln???......I love this forum....always gets me thinking!

  4. #4
    On forestry forum, there are some threads of guys building a solar kiln on a trailer. Just like a kiln on skids, but on a car trailer. The 6' wide by 16' long works pretty well.

  5. #5
    I know this is an older thread but it still seems like a popular topic with many so I'll share my slab drying set up and maybe others can use it or improve on it. I mainly build tables using large slabs up to 13 ft long so I do spend time in trying to keep my wood straight after milling it. In TN the lowest it air dries down to is 13%-15% after a year or so. My kiln is a simple Rigid foam board Insulation box using 4x8 sheets of 2" pink for the walls and ends. I used cheaper 1" for the top to save some money but it does sage when set up more than 60" wide. Tape the seams with tyvek tape, plastic on your floor if it's concrete, dehumidifier on low or medium and a box fan. Temp stays around 85-90F for 2-3 weeks and the MC is down to 8%-9%. I'll take out the dehumidifier and add on oil heater to bring it up to 100F for a day or 2 when I'm working close by to keep an eye on it which brings MC down to 6%. Wood is stacked well, stable and stays straight. Even after putting many loads of bug infested slabs through this I've not had a problem with them coming back. Hope this helps.

  6. #6
    Join Date
    Dec 2010
    Location
    WNY
    Posts
    6,131
    While foam panels alone are convenient as far as disassembly/storage goes, it's not something I'd do with a sauna heater nearby. Foil faced fiberglass duct board would be a safer choice. Perhaps make a two layer system to improve the R value, foam on the outside and duct board on the inside. Electric sauna heaters are controlled by an integral thermostat, so there's little risk of over shooting the desired temperature. If that's a residual concern, however, you could wire an adjustable high temperature limit switch in the system to trip out the main sauna relay if it does happen.

    3 KW seems like plenty of power. I used to heat my 275 bf indoor dehumidification kiln to 110F with 3, 100 W lightbulbs.

    John

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