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Thread: heater for small sterilization kiln?

  1. #1
    Join Date
    Sep 2013
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    Wayland, MA
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    heater for small sterilization kiln?

    I have a few hundred feet of cherry and walnut that I need to heat treat to kill powderpost beetles. I was figuring to build a foam box ca 4x4x12 ft that I could use to heat the wood to ~140 deg. I'm terrified, however of burning my barn down if I mess up. One solution is to make my mini-kiln outside, away from the barn, but then I'll need an even bigger heat source, as it is cold outside!

    I have a temperature regulating electrical outlet with a thermoprobe I can bury in the woodpile and control the heating from outside the box, I have a couple of small fans that are rated for use in ambient temperatures up to 200 degrees, so they should be fine inside the box, the component I haven't been able to find is some sort of electric space heater rated for use over about 105 deg ambient. Most of them incorporate thermal cutoffs that turn them off when the ambient temp is too high, and none of the ones I've found for a reasonable price carry a rating for elevated ambient temp use. (I did find commercial kiln heaters rated to thousands of degrees for thousands of dollars, I was hoping for something under $100.

    I've thought about 500 w halogen flood fixtures, but they too often have thermal links to turn them off when they get too warm and/or aren't rated for higher ambient temperatures. They also generate very high temps locally, increasing the chance of setting my wood pile or the foam/wood enclosure on fire

    Are any of you aware of a small (1500 W) heater or electric baseboard that is safe to use at 140 deg ambient temps?

    Thanks!

  2. #2
    Roger,

    Have you considered using a bank of 250W heat lamp bulbs, or possibly repurposing the heating elements from a toaster oven?

    Regarding your "temperature regulating electrical outlet with a thermoprobe". Which unit do you own? Do you trust it enough to prevent a fire by cutting off the heat before it gets too hot for ignition?

  3. #3
    Join Date
    Sep 2013
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    The temp controller is of these: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1, It appears to be of reasonable quality and had good reviews.

    Light bulbs would be the easiest, but I was kind of hoping for a real product with a heating element and fan inside a metal box (like a milkhouse heater) designed so that it would heat the air without itself becoming hot enough to be an ignition source. If I dig around I can probably find a bunch of porcelain light bases, I'd worry about the plastic ones.

    I'm increasingly thinking I will do this outside, away from the buildings.

  4. #4
    I have considered a heat box as well, but do not wish to do it in my shop. Have a cargo trailer that would probably work. Checked on the proper foam, found you should use R max, a poly something. Just a board with a few porcelains and maybe 4 light bulbs will give you enough heat, make your stack to keep the lumber away from the bulbs. You also need fans and a dehumidifier.

  5. #5
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    The wood is already quite dry (air dried for 10-15 years), is the dehumidifier really needed? I'm just wanting to do a relatively short heat treatment to make sure the bugs are dead.

  6. #6
    Join Date
    Dec 2010
    Location
    WNY
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    An old sauna heater and controller would work great. Their high temp. limit is far higher than 140F.

    John

  7. #7
    A hot plate
    I used one in a smoker. I took it apart and put the head element on the bottom and the controller/thermostat at the top .Then I calibrated the unit and it would reliably hold temps 150-250.
    The hardest part was finding a good old fashioned hot plate

  8. #8
    Air dried wood is usually not below 11 or 12%. Test it if you have a moisture tester. I tested some air dried lumber a month or so ago, it was about 11 %. Has to be moved into a heated room to go below that, but takes a while to get on down to 6%.

  9. #9
    Join Date
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    Peoria, IL
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    Best idea I've seen is an oven element from a discarded oven, mounted to an aluminum plate. I think the guy had it hanging from one end, with a steel plate spaced off the end to isolate the heat from the box. Use the oven controls to regulate the temp. I have a hot plate in my freezer kiln for drying bowls. I have this giant aluminum heat sink sitting on top of it. Got the heat sink off an ancient industrial motor controller.
    Last edited by Richard Coers; 02-10-2019 at 10:14 PM.

  10. #10
    Join Date
    Sep 2013
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    Thanks for that idea-- I have both a heavy duty lab hot plate and a big piece of heat sink saved from a different project. I see a plan emerging here!

  11. #11
    You can just buy heating wire and make any shape or wattage you want..

    https://www.ebay.com/itm/15FT-KA1-Re...egA:rk:11:pf:0

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