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Author Topic: Heat box for sterilization help  (Read 3516 times)

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Offline Prinnie

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Heat box for sterilization help
« on: October 08, 2015, 09:12:28 AM »
We build a lot of things from reclaimed wood harvested from structures all over Southwest Georgia.  While this wood is clearly, at the very least air dried, a good bit of it has various signs of previous or current powderpost beetle activity.  We need to build a "kiln" intended solely for sterilization.  I've read where a lot of people turn their kiln systems up above 150 at the end of a drying cycle to achieve sterilization, but I can find very little on a simple setup that would achieve just the sterilization.  I am hoping for some experience/knowledge on best practices regarding structure, heat source, controls etc in the construction of such a heat box.  This does need to be as cost effective as possible.  Anyone have any experience?

Online beenthere

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Re: Heat box for sterilization help
« Reply #1 on: October 08, 2015, 12:51:43 PM »
Welcome to the Forestry Forum.

What size packages are you thinking of sterilizing? Will they be uniform, or of all lengths and sizes?

Let us know your limitations... "cost effective as possible" doesn't give much to go on.
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Offline WDH

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Re: Heat box for sterilization help
« Reply #2 on: October 08, 2015, 08:37:31 PM »
Welcome Prinnie Dew! 

Prinnie is a good customer of mine, and I suggested that she join to solicit some advice on building a simple heat chamber to sterilize air dried and reclaimed wood without the added expense of building a full blown kiln.  The key question is what would be the simplest and safest heat source to heat a small chamber framed out of lumber and well insulated, like a solar kiln chamber or small dehumidification kiln chamber like I have.  A chamber that could hold maybe 500 BF of stickered lumber, say one that is 12' long x 6' wide x 6' high with a door for loading.  The goal would be to heat the wood to kill insects, basically a sterilization chamber. 
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Offline samandothers

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Re: Heat box for sterilization help
« Reply #3 on: October 11, 2015, 09:02:41 PM »
I am glad to see this thread and hope there will be some feedback.  I too have some wood structures I would like to dis-assemble and 'sterilize' the wood. 

Do you use strip heat of some sort and blow it in and recirculate to the strips?  What would supply the 165 or so degree heat to get the chamber up and keep it at the correct temps for 24 or so hours?

Offline WDH

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Re: Heat box for sterilization help
« Reply #4 on: October 12, 2015, 07:11:43 AM »
It needs to be on a small scale and simple. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5640SU, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Offline Tom L

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Re: Heat box for sterilization help
« Reply #5 on: October 12, 2015, 07:34:54 AM »
piney woods helped me big time with the element,when I did this to my small kiln, I tried 10 different things that didn't work well.

I have a thermometer hooked up to a mag starter to power up a simple oven element, element cost me less than 10 bucks

I hang the element from the power supply wire on top of the kiln set it for 150 degrees and turn it on.

I also have a  6" round duct fan that is in some 6" stove pipe. that sits in the corner , it draws air into the bottom and circulates the air up to the top of the chamber.I put a 45 degree elbow on the top end. the one I bought is rated for 300 degrees.

takes around a full day to get the box up to 150 degrees. I let it sit there for another day and then shut it off
and let it cool on it's own.

has worked very well on pine and cedar to kill bugs and set the pitch

Offline WDH

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Re: Heat box for sterilization help
« Reply #6 on: October 12, 2015, 07:45:14 AM »
That sounds like a great approach. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5640SU, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Offline Prinnie

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Re: Heat box for sterilization help
« Reply #7 on: October 12, 2015, 08:31:36 AM »
That's a great idea! Very simple and efficient for sure. We are starting construction on the box today so I will keep you posted on our progress and methods. I'm going to order an oven element now. Big thank you to WDH for all your help clarifying our needs!!!

Offline MattJ

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Re: Heat box for sterilization help
« Reply #8 on: October 12, 2015, 04:23:04 PM »
Tom would you mind giving more details on the setup with the thermometer, mag starter and element.  Maybe a picture and/or part numbers if you have a chance?  That sounds like what I am looking for as well.

Thanks

Offline YellowHammer

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Re: Heat box for sterilization help
« Reply #9 on: October 12, 2015, 09:42:55 PM »
I've had very good success adding auxiliary heat using inexpensive halogen worklights, such as sold at Lowes, Home Depot, or Wal Mart.  I had my heat strips burn out in my kiln and needed a quick way to get heat.  They cost about $20 each, are mounted in their own metal stand, and are in a weatherproof enclosure so will last a long time in a kiln environment.  They are about 500 to 1000 watts each.  I have used as many as 4 at once and they will put out some major heat and easily get to 145F for sterilization.  I use 4 to get up to temp, then unlug 2 to maintain.  I put them right next to some fans to keep the heat circulating, and if a light ever burns out, the halogen bulbs are easy to replace and cost about $7.  Of course, the hot box itself must be able to take this kind of heat, and not melt or worse.

I've also heard that the passive baseboard heaters will work well, but I've never tried them. 
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Offline GeneWengert-WoodDoc

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Re: Heat box for sterilization help
« Reply #10 on: October 12, 2015, 10:51:03 PM »
Most baseboard heaters have a high heat cutoff, so will not reach the higher temperatures.

Always have a smoke alarm.  The lights or strip heaters do get hot enough to ignite fine wood dust.  Do not use inside a house...too risky wrt fire.  When using a hot source for heat, we usually use a plenum so the wood does not "see" the high heat.  Special note:  if the kiln is a business venture, and it burns your home, your homeowners insurance will not cover you, as it usually has a business exemption.
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Offline caveman

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Re: Heat box for sterilization help
« Reply #11 on: December 03, 2017, 09:01:59 AM »
I've had very good success adding auxiliary heat using inexpensive halogen worklights, such as sold at Lowes, Home Depot, or Wal Mart.  I had my heat strips burn out in my kiln and needed a quick way to get heat.  They cost about $20 each, are mounted in their own metal stand, and are in a weatherproof enclosure so will last a long time in a kiln environment.  They are about 500 to 1000 watts each.  I have used as many as 4 at once and they will put out some major heat and easily get to 145F for sterilization.  I use 4 to get up to temp, then unlug 2 to maintain.  I put them right next to some fans to keep the heat circulating, and if a light ever burns out, the halogen bulbs are easy to replace and cost about $7.  Of course, the hot box itself must be able to take this kind of heat, and not melt or worse.

I've also heard that the passive baseboard heaters will work well, but I've never tried them.

Robert, I remember discussing the use of halogen lights with you at the Sycamore Project but I do not remember many of the specifics (I am plagued with CRS).

How big is the kiln or box that you were heating with the lights?

Is the box store weather station what you are using to monitor the temperature?

Do you have the lights controlled by a thermostat or do you just know from experience that if you burn x number of lights for a certain time with a given load of wood for your space that sterilization temperatures are reached?

Do you store all of your dried and sterilized wood in the showroom/barn separate from all of your unsterilized wood? 

We now treat all hardwoods with solubor before sticker stacking but we also want to be able to heat sterilize.
Thank you,
Kyle
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Offline E-Tex

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Re: Heat box for sterilization help
« Reply #12 on: December 03, 2017, 09:42:28 AM »
 popcorn_smiley

Good Topic!
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Offline Savannahdan

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Re: Heat box for sterilization help
« Reply #13 on: December 03, 2017, 11:23:11 AM »
I'm glad this is being discussed.  My small solar kiln is just about complete but I'm sitting in a backyard where it isn't going to get good sunlight this time of year.  I figured I'd have to put some heat source in it to get things hot.  It includes a solar fan which runs just fine even with no so much sun.  I need to seal up some joints, paint it, install the solar panel on the outside and load with lumber.  I'll post some pictures when it's completed.  I also built a foam chamber box which is good for working with a very small load of slabs.  I didn't have a good heat source for it and have been eyeballing a larger heater.  The heater sits outside the box and the heat is directed into the box with an old heat duct.  The wood sits on top a couple of saw horses.  I insert a thermometer through the foam and have a small vent at the top.   
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Offline GeneWengert-WoodDoc

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Re: Heat box for sterilization help
« Reply #14 on: December 03, 2017, 06:12:22 PM »
When using a heater in a kiln, we are cooncerned about the fire hazard.  Fine wood dust can ignite in the 220 F range.

If the hot burner gases go into the kiln, especially when burning wood, the fire risk is high. The kiln atmosphere can lack oxygen too, so do not go in without airing out the kiln.

When the outside air is heated as the burner burns, or for any reason, this lowers the humidity substantially.  Foggy air heated about 30 F drops to 30% RH or so.  A burner of propane, wood, etc., will have even lower humidities, as the air is much hotter.  Such low humidity can damage the lumber being dried...by drying too fast, or by getting the outside and ends, or maybe the whole piece, too dry and brittle.

For flame burners that need oxygen, it is best to use a plenum between the burner and kiln, so the air in the kiln can be recirculated and thereby heated but humidity controlled.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline losttheplot

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Re: Heat box for sterilization help
« Reply #15 on: December 04, 2017, 12:01:02 AM »
I built a 4 ft by 4 ft by 16 ft box out of used 4 ft by 8 ft by 4 inch Styrofoam sheets.
Its wrapped in 6mil Polly and sealed with tuck tape when its full.
With 2 fans and a 70 pint dehumidifier it gets up to 140 +/- degrees.
No auxiliary heat.

Air dried wood takes less than a week to get the remaining water out of it.
I put some spalted maple in it, that was full of white grubs.
The bugs turned to powder.


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Offline PA_Walnut

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Re: Heat box for sterilization help
« Reply #16 on: December 04, 2017, 05:39:33 AM »
Does anyone know how/if this high heat changes the structure of walnut. I prefer using air-dried walnut due to the way it tools and works well. Also, the colors are more to my liking than kiln dried.

However, some areas of PA are currently under quarantine due to Thousand Cankers in walnut. So, may be necessary to sterilize.

Anyone comment about how just a short sterilization period effects is as compared to a complete kiln drying cycle?

Thx
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Offline WDH

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Re: Heat box for sterilization help
« Reply #17 on: December 04, 2017, 07:27:06 AM »
When I sterilize fully dried walnut at 150 degrees for 24 hours in my DH kiln, it does not affect the color.
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Offline 69bronco

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Re: Heat box for sterilization help
« Reply #18 on: December 04, 2017, 07:30:36 AM »
I built a 4 ft by 4 ft by 16 ft box out of used 4 ft by 8 ft by 4 inch Styrofoam sheets.
Its wrapped in 6mil Polly and sealed with tuck tape when its full.
With 2 fans and a 70 pint dehumidifier it gets up to 140 +/- degrees.
No auxiliary heat.

Air dried wood takes less than a week to get the remaining water out of it.
I put some spalted maple in it, that was full of white grubs.
The bugs turned to powder.
Does the dehumidifier run ok at the higher temps?
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Offline YellowHammer

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Re: Heat box for sterilization help
« Reply #19 on: December 04, 2017, 07:48:45 AM »
I've never had any heat discoloration at all due to the moderate heat of a DH kiln sterilization cycle, either. 

Caveman,
I use the halogen lights to augment the heat strips in my Nyle 53 kiln, as it only has 1 KW heat strips, and I like to reduce the heating time with up to 4 of the 500 watt halogens.  I use the kiln controller to monito temps, and since the kiln heat strips are thermostatically controlled, once up to temp, I turn off all but one halogen which is all it takes to maintain temp, and the Nyle controller will cycle the strips off.  So for my kiln, it takes a constant 500 Watts to maintain sterilization temp°.  If it's a cold night or the temps drop, the the controller will cycle in the kiln's heat strip back on to boost the temps back up, then will shut it back off.  So it's very easy to control. 

I don't have any sterilization capability in my solar kiln, it leaks too much.  All it's loads go into the Nyle for sterilization.  Once they come out, I plane and dead sick and put in a protected place.

The kiln building is approximately 10 foot x 8 foot by 8 foot high with a concrete floor. 

Yes, I alsways separate my kiln dried sterilized from air drying or non sterilized and store it either in my barn or showroom building.  I look at it as a process, and the end of the processing is when the sterilized and dried wood is planed and resting comfortably in a sheltered protected place.  When that happens, all the risk is over.  If stored with other non sterilized wood, or in an exposed place, the wood becomes at risk again.

 
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