Refrigerator kiln?

[Mike Novak]

Hi

I’m considering building a refrigerator kiln. And most of the posts and videos that I’ve seen about building one of these, people are using up to 100w bulbs.

I was looking at the USDA website recommended Kiln schedules and I see that most of them go up to 180°. Can a 100 w bulb raise temp to 180? Do any of you actually go that high with temperature in your kiln?

It also says you need to get up to 140° to kill powder post beetles. Same question.

Thanks

 

[John Ames]

I’ll be interested in hearing these replies…
My guess is there would have to be a number of light bulbs but I have no idea how many and if the refrigerator needs to have a vent of some kind? Or can it be sealed up? I assume there should be a drainage hole to keep the humidity down….?

So many questions! Thanks for starting the thread

 

[Richard Coers]

I use a cheap hot plate with a large aluminum heat sink on it, with a small fan to heat the entire upright freezer equally. You never have to reach 180 degrees F. If you get the center of a block of wood over 133 degrees F for a couple of hours, the wood is sterilized. Note, that takes about 150 degrees F to make that happen. I start every charge around 90 degrees. Here is a chart taken during one charge in my kiln.

 

[Wally Crawford]

My kiln, used exclusively for bowls, is an old double commercial freezer. I cut a 4" hole low on one side and again high on the opposite side for a chimney effect and I use a 750W electric heater with built in fan as a heat source. I control temperature with a thermostat from Amazon, and it maintains temps very precisely between 100* and 102*, my set points. You can make the set points whatever you want, but I have found that higher will cause more loss due to cracking. My bowls usually take from 4-6 weeks depending on species and moisture content at the onset.

 

[Mike Shannon]

Some people use these reptile heat emitters in DIY fridge kilns.

https://www.amazon.com/s?k=reptile+ceramic+heat+emitter&crid=AKJ90KWV422C&sprefix=reptile+ceramic+heat+emitter%2Caps%2C109&ref=nb_sb_noss_1

 

[Mike Pindzola]

I'm not a physicist or whatever, but adding any amount of heat will make it hotter. The question becomes, how fast do you want it to change and how good is the chamber's insulation. Pretty sure 100w will work and that you'll need to add a vent to keep is cool enough. Or rig the lamp so it goes on and off via thermostat. But you'll want light on to keep mildew away. And some sort of humidistat to manage MC. Look for Inkbird controllers - https://www.google.com/search?sca_e...HRxYDMwQ0pQJegQICRAB&biw=1527&bih=817&dpr=1.1

This one is the one I plan on using: https://inkbird.com/collections/tem.../temperature-and-humidity-controller-itc-608t

 

[Richard Coers]

But you'll want light on to keep mildew away. And some sort of humidistat to manage MC.

A light will not keep mildew away. It may even increase the rate of mold growth. It's a perfect atmosphere to grow mildew with wood, moisture and heat. Air flow is the best way to reduce mold. A humidistat is a gauge, it won't manage MC. All your comments assume the wood is dead wet. I always dry my wet blanks in yard waste bags for weeks before going to the kiln. Then you won't have to deal with any mildew or mold at all. The OP didn't talk about bowls, so we don't know if he's talking about blanks or bowls.

 

[Mike Novak]

Richard, that’s very helpful seeing your schedule. I am mostly thinking about bowls, but also box blanks, and I have a stock of air dried cherry with some evidence of a beetle problem.

According to the USDA information, (https://www.fpl.fs.usda.gov/documnts/usda/ah188/chapter07.pd).
temps above 110 will stop mold growth even with high humidity and MC. The recommended starting point for all of the schedules is 100 degrees or more with very high humidity.

I already set up the kiln using an inkbird temp controller from another project. I’m eyeing the one with humidity control but don’t know what it would control to regulate humidity. Since it’s a newer fridge, it has a small fan inside as well as a 450w defrost coil. I hooked up the fan to run continuously. I have tested by running temp up to 100, but wanted to get real world experience from someone before going higher. I will push it higher today.

 

[Richard Coers]

Richard, that’s very helpful seeing your schedule. I am mostly thinking about bowls, but also box blanks, and I have a stock of air dried cherry with some evidence of a beetle problem.

According to the USDA information, (https://www.fpl.fs.usda.gov/documnts/usda/ah188/chapter07.pd).
temps above 110 will stop mold growth even with high humidity and MC. The recommended starting point for all of the schedules is 100 degrees or more with very high humidity.

I already set up the kiln using an inkbird temp controller from another project. I’m eyeing the one with humidity control but don’t know what it would control to regulate humidity. Since it’s a newer fridge, it has a small fan inside as well as a 450w defrost coil. I hooked up the fan to run continuously. I have tested by running temp up to 100, but wanted to get real world experience from someone before going higher. I will push it higher today.

You can follow any schedule you want, but I would be really surprised if the USDA tested those schedules on 4-6" thick bowl blanks and damp roughed out fruitwood bowl blanks that are close to the pith. 100+ degrees to start is very aggressive in my 10 years with my kiln experience. But what do I know.

 

[Brian Gustin]

temps above 110 will stop mold growth even with high humidity and MC. The recommended starting point for all of the schedules is 100 degrees or more with very high humidity.

You regulate humidity by controlling the fan and air moving in and out of the kiln - to ADD humidity, you would place a pan of water in there near the heat source, to release humidity you'd turn on your fan and open a vent to the outside

 

[John Ames]

You can follow any schedule you want, but I would be really surprised if the USDA tested those schedules on 4-6" thick bowl blanks and damp roughed out fruitwood bowl blanks that are close to the pith. 100+ degrees to start is very aggressive in my 10 years with my kiln experience. But what do I know.

Is your heat sink round or square or does it matter? I assume the heat sink just radiates the heat from the hot plate to a larger area?

Do you set a specific temperature on the hot plate (like an oven?) or just put it on high/med/low type settings?

 

[Wally Crawford]

I found that the addition of a fan, -In my face a computer fan-to the fridge increased my cracking significantly. I found that wrapping the outside of my green turned bowls with shrink wrap had had a positive effect.

 

[Scott Denneson]

I use the reptile ceramic bulb with a sheet metal shroud around it and the Inkbird temperature switch. I start the rough turned bowls in their shavings in paper bags for a couple of months then into the kiln. I start around 90F. I monitor the the weight and increase the temp as I go. The wetter the bowls the slower I go. Some of my wood comes from the Willamette valley and I’m in the high desert in Bend Oregon so it’s quite a shock. In those situations Anchor Seal is not enough to slow the drying process. So bagging has become my safest option to get things started. Locally harvested wood is not near as difficult to deal with.

 

[Mike Novak]

Richard, you are correct, the usda schedules only go to 8/4. They rely on high humidity to slow drying. For thick/ difficult wood the humidity starts at over 90%. Don’t think I could get that high with a water pan?

For those of you that check, what do you have for humidity at the start of a kiln cycle!

 

[William Rogers]

You can get a lot of humidity with a pan of water. the first chart shows the beginning of my cycle and the second shows where the pan of water is evaporating, usually in 4-5 days. This would have been in the summer as in the winter the humidity doesn’t get as high. I only do bowls in my kiln. I have a small fan that I run at all cycles and 4 1” holes in the top. This is what works for me. Start 90-95F. 95-100F. 100-115F, and 115-120F. Each cycle is a week except for the last one where I look for no weight loss for a week. Usually about 4-5 weeks to complete. I have three light bulbs in my kiln I can turn on or off any. I start with a 40 watt bulb for the first two cycles and then turn on one 75 in addition and finally all three (40,75,and 75w) for the last cycle. Having three bulbs speeds the later cycles.

 

[Mike Novak]

@William Rogers , I’m surprised you can get that humid with just a pan of water! What are you using to measure and make those charts?

 

[William Rogers]

What are you using to measure and make those charts?

I bought the temp/humidity indicator a couple of years ago from amazon. They don’t list that model, but the TP 359 is similar. I can get that high in the summer, From memory maybe 70% in the winter, could be less.

Similar indicator

Amazon.com

 

[Brian Gustin]

@William Rogers , I’m surprised you can get that humid with just a pan of water! What are you using to measure and make those charts?

Oh yeah - Same principle we go by in home heating - I got a humidifier for winter months (cold water and a fan blowing through wick filter) to maintain humidity in the house around 35% to 45% , it goes through about 4-5 gallons of water a day when it gets really cold and dry out. Adding the humidity makes the house feel much warmer and we save on heating costs. depending on the volume of your kiln, a pan or pot of water can really put a boost on your humidity levels and help slow drying at the start of things...

 

[Matthew Ferriter]

I use a cheap hot plate with a large aluminum heat sink on it, with a small fan to heat the entire upright freezer equally. You never have to reach 180 degrees F. If you get the center of a block of wood over 133 degrees F for a couple of hours, the wood is sterilized. Note, that takes about 150 degrees F to make that happen. I start every charge around 90 degrees. Here is a chart taken during one charge in my kiln.

133F is not a "sterilization" temperature.

 

[Richard Coers]

133F is not a "sterilization" temperature.

Lethal Temperatures- Before wood is used for construction or manufacturing, most of the water is removed by air-drying or kiln drying. Kiln-dried lumber is heated for a period of hours to a temperature of about 125-140°F. This is sufficient to kill all stages of powderpost beetles that might be in the wood prior to heating. However, even wood that is properly kiln dried may become infested during subsequent storage and transit. The longer wood sits in a vulnerable condition, the greater the chance beetles will find and lay eggs on the lumber. https://entomology.ca.uky.edu/ef616

The current international standard for heat sterilization of solid wood packaging materials is the International Standard for Phytosanitary Measures (ISPM) 15, “Guidelines for Regulating Wood Packaging Material in International Trade,” which requires heating wood to a minimum core temperature of 56 °C (133 °F) for a ... https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr282/chapter_20_fpl_gtr282.pdf

Manufacturers of hardwood pallets are faced with the prospect that they will be required to sterilize their pallets or pallet parts prior to export to Europe. The proposed regulations stipulate that the interior of the wood used in the pallets has to be heated to 56°C or 133°F for 30 minutes. https://content.ces.ncsu.edu/heat-sterilization-of-hardwood-pallets-and-pallet-material

Where did you get your information that 133F doesn't sterilize wood?

 

[Paul Paukstelis]

True sterilization would mean killing all organisms. There are plenty of microorganisms, including fungi, that can survive temperatures above 133F. Are those likely to be in pieces wood? Probably not. So its mostly an argument of "sterilization" vs "effective sterilization".

 

[Richard Coers]

True sterilization would mean killing all organisms. There are plenty of microorganisms, including fungi, that can survive temperatures above 133F. Are those likely to be in pieces wood? Probably not. So its mostly an argument of "sterilization" vs "effective sterilization".

It's not an argument at all. It's the final result that you want. I don't want to sell wood with bugs in it, so I use the USDA recommendation for wood sterilization. It would be ridiculous to sterilize it to kill fungi since ambient air is filled with it. As soon as I took it out of the kiln, or even touched the wood, it would be contaminated again. This wood is not for implantation into the human body.

 

[Mike Novak]

I did a test run to sterilize some air dried wood. I wrapped it in a garbage bag so it wouldn’t lose moisture and baked it overnight at 140. I let it cool completely before removing from the bag. I can’t verify it killed anything, but it did not damage the wood or change MC.

I could only get 40% RH, probably Because I’m using the defrost coil. it doesn’t heat the water directly. I suspect Richard’s setup would be best for raising humidity because he can put a pan of water directly on the hot plate.

I’m now debating getting a hot plate like Richard’s, or a cheap vaporizer.

 

[Richard Coers]

Here's a couple of pictures. Believe it or not, that little plastic fan has worked through about 15 loads in the kiln. It was included with the free freezer from a friend. It vibrates a little, so the splitting wedge keeps it away from the hotplate. Unbelievable it handles 150 degrees F

 

[John Ames]

Thanks for the pictures, @Richard Coers ! It looks like a very simple but very effective set up.

It looks like you drilled 3 (at least) holes in the top and added a vent on the right side wall?

I assume the wire running from the top coils leads to a temperature sensor?

Is the hot plate then run on a timer/thermostat?

Do you run the cord for the fan and hot plate through the wall of the kiln by drilling a hole? Or do you just close the door and let the cords run out the magnetic seal?

Thanks for entertaining my newbie questions!

 

[Richard Coers]

6 holes in the top and each side. There is a metal outlet box and outlets on the lower side panel. I use a meat thermometer and run the thermocouple down through one of the vans holes in the top. The hot plate runs 24/7, and I use the adjustment knob on it to set the temp. I could use a much more sophisticated temp control, but it's pretty easy to tweak, and it holds the temp very well. It's running around 145 went I went out and checked it earlier. Tiny tweak tomorrow to get it to 150. I got it a little hot in an early charge, and the plastic shelves in the door and plastic tabs that hold the bottom shelf in softened and sagged. So now I have pieces of 2x4s to support the lower shelf in the back. After that, I used a marker to put a mark on the hot plate knob where it runs at 150. But easy to be a few degrees off.

 

[Mike Novak]

Here’s an update on my kiln experiments:

Since I’m concerned about bugs and mold, I wanted to heat treat my wood before storing in basement shop. Most common heat treatment is to heat in 160deg kiln until internal temperature is 135 deg for at least. 1/2 hour. Not wanting the wood to dry and crack, I wrapped each piece in a plastic garbage bag and put end grain sealer before putting into kiln. Then bake at 160 for 24 hours just to be extra sure. I’m happy to report that after 2 full loads, not one blank developed checks.

I have a load of white oak drying now. Mostly spindle blanks, and three large bowls. I wanted to use the usda drying schedules. These generally start at 110 with very high humidity to slow drying. In order to add humidity, I’m using a cheap Vicks vaporizer plugged into an inkbird humidity controller. I’m using the most conservative USDA recommended schedule. It’s for 16/4 red oak viral infection that makes it especially prone to splitting. It’s been in for about a week now.

The good:
The bowls had some pretty significant cracks forming from air drying before the kiln was ready. About as thick as a dime. After 48 hours at 110 degrees, 92% humidity, the cracks closed up completely ( even though the bowls got lighter). I hit them with thin CA, hopefully they won’t open up again.

The bad:
This is going to take a lot longer than I expected. Over a week to bring MC from 40% to 30% 2inch spindle blanks.

I can’t just set the controls when starting up. If the heater and vaporizer run at same time, it heats up too much. When starting, I need to raise humidity first, then slowly raise the temperature.

Because of the super high humidity, I’m getting condensation dripping on the floor. I’m doing 2 things to try to help this. First, I moved the humidity sensor to a cavity in the pile of wood. It’s cooler there. Second, I think I need to stop checking progress so much. Every time I open the door the temperature drops and it starts raining in the cabinet.

Here is a link to the usda heat sterilization guidelines.

Chapter 20: Heat sterilization of wood | US Forest Service Research and Development

www.fs.usda.gov

Here is a link to the usda kiln operation book.

Dry kiln operator's manual

This is the humidity controller.

https://www.amazon.com/gp/aw/d/B07XGQ7Q53?psc=1&ref=ppx_pop_mob_b_asin_title

This is a link to the vaporizer

https://www.amazon.com/gp/aw/d/B0000TN7ME?psc=1&ref=ppx_pop_mob_b_asin_title

 

[Mike Pindzola]

raining in the cabinet ? Grow some ferns or toadstools perhaps ?
This is a great report and it sounds like you're getting dialed in. And the pre-treatment of sealing in plastic is clever. Thanks for the update.

 

[DON FRANK]

I have a kiln for drying bowl made out of a dishwasher. The motor assembly was removed from the bottom and you have about an 8" hole. I used one of the cheap metal utility lights with a 100w bulb in it. I load the kiln full with as much as many bowls that I can get into it. Turn it on, shut the door and forget about it for two-3 weeks. There is no fan inside to move the air around. I get very few cracks and things generally dry well. There is a thermometer probe inside so I can monitor the temperature.
The dishwasher works really well because they maintain a very high humidity as the temperature builds up to about 100. That moisture escapes slowly over time so the bowls don't dry out too fast. Before this I had another style with heat and moving air and I got lots of failures with that. With this kiln I am not anchor sealing the end grain generally unless it's oak.
Once turned bowls for bowls that will be twice turned can dry in less than a month compared with the 6 month to a year routine. It works very well for me.

 

[Richard Coers]

Here’s an update on my kiln experiments:

Since I’m concerned about bugs and mold, I wanted to heat treat my wood before storing in basement shop. Most common heat treatment is to heat in 160deg kiln until internal temperature is 135 deg for at least. 1/2 hour. Not wanting the wood to dry and crack, I wrapped each piece in a plastic garbage bag and put end grain sealer before putting into kiln. Then bake at 160 for 24 hours just to be extra sure. I’m happy to report that after 2 full loads, not one blank developed checks.

I have a load of white oak drying now. Mostly spindle blanks, and three large bowls. I wanted to use the usda drying schedules. These generally start at 110 with very high humidity to slow drying. In order to add humidity, I’m using a cheap Vicks vaporizer plugged into an inkbird humidity controller. I’m using the most conservative USDA recommended schedule. It’s for 16/4 red oak viral infection that makes it especially prone to splitting. It’s been in for about a week now.

The good:
The bowls had some pretty significant cracks forming from air drying before the kiln was ready. About as thick as a dime. After 48 hours at 110 degrees, 92% humidity, the cracks closed up completely ( even though the bowls got lighter). I hit them with thin CA, hopefully they won’t open up again.

The bad:
This is going to take a lot longer than I expected. Over a week to bring MC from 40% to 30% 2inch spindle blanks.

I can’t just set the controls when starting up. If the heater and vaporizer run at same time, it heats up too much. When starting, I need to raise humidity first, then slowly raise the temperature.

Because of the super high humidity, I’m getting condensation dripping on the floor. I’m doing 2 things to try to help this. First, I moved the humidity sensor to a cavity in the pile of wood. It’s cooler there. Second, I think I need to stop checking progress so much. Every time I open the door the temperature drops and it starts raining in the cabinet.

Here is a link to the usda heat sterilization guidelines.

Chapter 20: Heat sterilization of wood | US Forest Service Research and Development

www.fs.usda.gov

Here is a link to the usda kiln operation book.

Dry kiln operator's manual

This is the humidity controller.

https://www.amazon.com/gp/aw/d/B07XGQ7Q53?psc=1&ref=ppx_pop_mob_b_asin_title

This is a link to the vaporizer

https://www.amazon.com/gp/aw/d/B0000TN7ME?psc=1&ref=ppx_pop_mob_b_asin_title

I'm really confused about your thinking on heat treating the wet wood first in plastic bags? No way the center of the block of wood reached 133 degrees. Heat treating is done when the wood is dry. Of course you aren't seeing cracks, your kiln is like a sauna.

 

[Kent Reisdorph]

Here’s an update on my kiln experiments:

Since I’m concerned about bugs and mold, I wanted to heat treat my wood before storing in basement shop. Most common heat treatment is to heat in 160deg kiln until internal temperature is 135 deg for at least. 1/2 hour. Not wanting the wood to dry and crack, I wrapped each piece in a plastic garbage bag and put end grain sealer before putting into kiln. Then bake at 160 for 24 hours just to be extra sure. I’m happy to report that after 2 full loads, not one blank developed checks.

I have a load of white oak drying now. Mostly spindle blanks, and three large bowls. I wanted to use the usda drying schedules. These generally start at 110 with very high humidity to slow drying. In order to add humidity, I’m using a cheap Vicks vaporizer plugged into an inkbird humidity controller. I’m using the most conservative USDA recommended schedule. It’s for 16/4 red oak viral infection that makes it especially prone to splitting. It’s been in for about a week now.

The good:
The bowls had some pretty significant cracks forming from air drying before the kiln was ready. About as thick as a dime. After 48 hours at 110 degrees, 92% humidity, the cracks closed up completely ( even though the bowls got lighter). I hit them with thin CA, hopefully they won’t open up again.

The bad:
This is going to take a lot longer than I expected. Over a week to bring MC from 40% to 30% 2inch spindle blanks.

I can’t just set the controls when starting up. If the heater and vaporizer run at same time, it heats up too much. When starting, I need to raise humidity first, then slowly raise the temperature.

Because of the super high humidity, I’m getting condensation dripping on the floor. I’m doing 2 things to try to help this. First, I moved the humidity sensor to a cavity in the pile of wood. It’s cooler there. Second, I think I need to stop checking progress so much. Every time I open the door the temperature drops and it starts raining in the cabinet.

Here is a link to the usda heat sterilization guidelines.

Chapter 20: Heat sterilization of wood | US Forest Service Research and Development

www.fs.usda.gov

Here is a link to the usda kiln operation book.

Dry kiln operator's manual

This is the humidity controller.

https://www.amazon.com/gp/aw/d/B07XGQ7Q53?psc=1&ref=ppx_pop_mob_b_asin_title

This is a link to the vaporizer

https://www.amazon.com/gp/aw/d/B0000TN7ME?psc=1&ref=ppx_pop_mob_b_asin_title

Perhaps it's your nature, but it appears you are way overthinking this. Put them in the dryer and check them in a couple of weeks.

 

[Mike Novak]

Richard

The link to heat sterilization talks about both wet and dry methods. It also has times for the core to get to temperature.

Yes, it’s a sauna in there, but the wood is losing weight faster than outside the kiln, and it’s not splitting. 😊

Kent

Yes, I have gone a little overboard, but there is a reason. I have some nice figured white oak. Over the last year I have lost everything I tried to make from it to catastrophic splits. So far 6 20” bowls and a number of smaller pieces. This is despite anchorseal + bagging + paying close attention to thickness + no sharp corners etc.

My nature is if I keep failing using “good enough “ methods, then I switch to what’s scientifically proven. In this case, that means following the USDA kiln operation book. If I can’t get a good result from this, I will burn the rest of the log.

I’m hoping my experience can help someone else who has some especially difficult wood they don’t want to lose.

 

[hockenbery]

So far 6 20” bowls and a number of smaller pieces. This is despite anchorseal + bagging + paying close attention to thickness + no sharp corners etc.

Hope your kiln works for you.
Drying large bowls is more difficult than drying smaller ones because the shrinkage is proportionally larger.
White oak. Has radial shrinkage of 5.6% And tangential shrinkage of 10.5%
5.6% of 10” is a bit over half an inch. 5.6% of 20” is about an 1 1/8”

I notice you did not mention curve of the bowl. From my experience curve has a big impact on successful drying.
Hemispherical shaped bowls highly successful. Classic “dog dish” least successful.

These are some slides I use in my working with green wood demo
I show two 12” bowls from laurel oak. Both were dried in paper bags.
The one on the right in the photos with the flat bottom cracks because the wood cannot move
The one on the left with the curve through the bottom lets the wood move to a crack free dry state.

 

[Richard Coers]

Richard

The link to heat sterilization talks about both wet and dry methods. It also has times for the core to get to temperature.

Yes, it’s a sauna in there, but the wood is losing weight faster than outside the kiln, and it’s not splitting. 😊

Kent

I would have to see measured results that thick wet wood in a plastic bag had the center reach the desired temperature. Here are the instrumented results of air dried wood reaching the desired temps.

 

[Mike Novak]

Richard

Now you have me curious? Next load I put in for heat treatment I will drill a hole in one of the larger blocks so I can measure it. I will post the results here.

 

[Jacob Browning]

Some people use these reptile heat emitters in DIY fridge kilns.
[URL The ceramic heaters work great. Inkbird I think is the name of the temperature controller I use. It's got a digital display and you can set the temp you want. Works great. I use the 150w ceramic elements because there's no heat in my shop so the 100w doesn't cut it when it gets in the teens or colder.

 

[DON FRANK]

Lots of people boil their bowl blanks and are certain it aids in the drying process. It would most certainly kill any powder post beetles in the wood as well. I have not tried boiling blanks before turning but I would think that would do the same thing. I'm pretty sure you could achieve an internal temperature high enough even in a 4" blank.

 

[Richard Coers]

Lots of people boil their bowl blanks and are certain it aids in the drying process. It would most certainly kill any powder post beetles in the wood as well. I have not tried boiling blanks before turning but I would think that would do the same thing. I'm pretty sure you could achieve an internal temperature high enough even in a 4" blank.

I thought they only boiled rough turned bowls? They actually boil 4" thick blanks? Wood is a pretty good insulator, it would be a long boil to get the heat to the center of a big blank, not to mention a huge pot for a 16" diameter. Then consider how many blanks could you boil at one time. I'd look like a Halloween witch stirring to boil this much wood!

 

[Mark Jundanian]

Lots of people boil their bowl blanks and are certain it aids in the drying process. It would most certainly kill any powder post beetles in the wood as well. I have not tried boiling blanks before turning but I would think that would do the same thing. I'm pretty sure you could achieve an internal temperature high enough even in a 4" blank.

Interesting idea. It certainly would get rid of any Anchorseal or wax that was where you didn't want it.

 

[William Rogers]

This is so interesting. I have a kiln, but suspect many don’t and use the good old paper bag method as I did for years. I don’t remember any problem with insects using the paper bag method. From my understanding insects need moisture to survive. I think insects need moisture to survive and once the wood is dry they dye. I built my kiln for quicker drying, not really for killing insects. I guess killing insects is a bonus. I do four cycles using my kiln. Start slow 90-100F with a pan of water for 7 days, 100-120F for 7 days, 120-130F for 7 days, and 130-140F for 7 days. I keep it on the last cycle until I have two 3 day reading the same. A little over a month. Now I have no idea if my internal temperature reaches the 133F as described by the USDA. Mostly bowls, but some blanks. However, I don’t expect there are any live insects once my wood is dry in my kiln. Is this a big problem experienced by many that I am not aware of?