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?
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.
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.
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?
It needs to be on a small scale and simple.
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
That sounds like a great approach.
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!!!
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
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.
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.
Quote from: YellowHammer 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.
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
popcorn_smiley
Good Topic!
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.
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.
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 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
When I sterilize fully dried walnut at 150 degrees for 24 hours in my DH kiln, it does not affect the color.
Quote from: losttheplot 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.
Does the dehumidifier run ok at the higher temps?
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.
Heat in a kiln does not change the walnut structure. You observations reflect differences in moisture content.
Quote from: 69bronco on December 04, 2017, 07:30:36 AM
Does the dehumidifier run ok at the higher temps?
[/quote]
Seems to, I've only put around 10 loads through it.
Its mostly Maple and Alder, the water comes out crystal clear and odorless.
I don't know how it would do with something like Oak.
I dont know if it has an over temp cutout.
I was quite surprised when I saw how hot it was getting in the Kiln.
I just set the dehumidifier to 35% relative humidity and let it do its thing.
I bought some temp/humidity meters, with the sensors on 6 ft of wire, and put them at different places through the stack.
Thank you to all who took the time to contribute to this topic. As I have said before, this sawmill hobby has become a slippery slope with a learning curve.
Have any of you quantified what kind of money youre spending on these kilowatt hours? Are they as expensive as it sounds?
Im surprised that with the proliferation of outdoor wood boilers being fed slabwood, that they dont go hand in hand with kiln chambers.
Quote from: losttheplot 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.
how does it get this hot without additional heat source? Does the dehumidifier have a heat source in it? is it the process of the water leaving the wood?
And is it staying at the 140+/- constantly? Thx.
We need some pictures of that sucker. 8)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0219.JPG?easyrotate_cache=1512694686)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0218.JPG?easyrotate_cache=1512694806)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0216.JPG?easyrotate_cache=1512694818)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0206.JPG?easyrotate_cache=1512694938)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0210.JPG?easyrotate_cache=1512695454)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0213.JPG?easyrotate_cache=1512695523)
I bought the Styrofoam from a neighbour for $10 a sheet.
The sheets are stitched together with old chainsaw files and the inside joints were sprayed with a can of expanding foam.
For the first couple of runs I used borrowed box fans made from plastic. They work fine but I had to give them back so I bought a couple of attic fans from Amazon.
I got some temp/humidity meters from e-bay and placed them through out the stack, as long as I load it "loose" it does fine.
If the plastic vapor barrier is not sealed tight it will never stop putting out water, as it will suck in air/humidity.
It takes a couple of days to warm up and a few days to cool down.
I leave the wood in there untill I need it, keeps it dry.
I got fed up with making stuff for the house with air dried wood, then having it warp and shrink. We heat with a wood stove which makes the house very dry.
I put 6 and 8 inch Douglas-fir flooring in the house, the boards right in front of the stove have shrunk a tiny bit, the rest shows no sign of shrinking.
14 inch red Alder just went in so I will see how it does.
Outstanding and thanks for the pictures. I will start looking for parts that I will need to build a box like yours. ;D
I am curious, have you run it with wood which was pretty green? Just wondering how long it took to dry it out and what the quality turned out to be. That is a great set up!!!
I have never tried it with green wood.
If I was gonna try, I think I would sticker stack it in the kiln then leave it open on the ends and just run the fans for a week or two first.
That is just an assumption and you know what they say about those :) :) :)
(https://forestryforum.com/gallery/albums/userpics/20959/DSCN0220.JPG?easyrotate_cache=1513210669)
My gosh that is some awful purdy wood there!! Really held it's color.
For a fast drying wood, like pine and poplar, leaving the kiln open and blowing air through the pile and then having itexit (single pass dryer is the technical name) can be very efficient. Run the fans when the humidity is under 90% RH only. Higher humidity will waste electricity and achieve little drying.
For harder to dry woods, if they go into the kiln green, then keep the vents fairly much closed so you control the humidity inside at a high level, which will give you slow drying and high quality.
For white woods like hard maple, aggressive air drying, protected from rain, will get the whitest color.
So, I been kicking a few ideas around in my head for a sterilization box.
Building it like the OP's box, but adding even more heat by using stove heating elements. Reason is that down here in the south, the humidity runs high about 95% of the year above 70%. Using the stove Tstat and controls, I think I could get it dialed down to about 150F. With a dehumidifier in the works, that just might speed things up some.
Am I thinking this would help out or am I wrong? Like I said, just kicking this around. ;D
We are concerned about the average relative humidity. A good source of values, in terms of EMC is
www.woodweb.com/knowledge_base_images/zp/equilibrium_moisture_content.pdf
As an example, in July, Alexandria, LA has 15% EMC which is about 75% RH average for the month.
Hey, thanks. ;D
Quote from: E-Tex on December 06, 2017, 12:08:01 PM
how does it get this hot without additional heat source? Does the dehumidifier have a heat source in it? is it the process of the water leaving the wood?
Don't know if you ever got an answer so here's mine. The heat gain comes from the resistive motor windings of the
compressor. (If I turn the DH unit off and leave the circulating fans on I can still get a heat gain due the same principle). The evaporation and condensation of water inside the kiln yields a net heat gain of zero so there is no help there.
I used to run my kiln up to 140°F and the unit lasted about a year. Home DH units (as mine is) aren't designed to operate at that temp. Now I try to keep it under 100 and just wait longer. OK for a hobby.
Bob
Thinking this would be great in my store room. Is the styrofoam the blue dow board foam? I have a few sheets of 1" and now they are selling 2" at Menards. Probably would have to use a few boards and some kind of long screws with big washers to put this together.
Not all foam boards are the same with respect to their durability to heat. Some disappear at 130 F. Check the temperature rating if used for a kiln.
Just looked up blue Dow board. Appears dow board will only handle up to 160 degrees. The foam pictured in lost the plot's pics must be of another type.