Kiln killing bugs?

[Stevenjohn21]

I recently (4 weeks ago) loaded my kiln for the first time since it was built and today I decided to test sone of the slabs and see what MC they were reading. I noticed a few new holes with sawdust around them which is an obvious sign of PPB but I'd this them going in or coming out? 
The kiln has hit 136 degrees about 4 times. The kiln has been hitting around 120 on average everyday. 

I'm hoping the bugs were in the wood, felt uncomfortable with the heat and decided to come out to which they eventually died? 
Although I didn't inspect thoroughly on each slab, I did notice one PPB upside down with X's on its eyes, so I know I killed at least one! 

Are these fresh holes caused by them going in to hide from the heat or coming out because of the heat? 

[fishpharmer]

Stephen I found some good info from Purdue on PPB.  https://extension.entm.purdue.edu/publications/E-73/E-73.html
It says the holes are caused by emerging beetles.  What type of kiln do you have?

[YellowHammer]

The holes are generally caused by them coming out due to the heat, not just as beetle, but also as larvae.  Unfortunately, it puts more holes in the wood, but on the other hand it's killing the bugs.  

That's one reason I like to sterilize at higher temps, it has a tendency to kill the bugs faster, before they have a chance to emerge and do more damage by leaving holes.

I like to look for dead bugs, they will look like little black pepper specks or pencil leads, depending on species, generally hard to recognize.  The legs will typically be burned off.

Yellowhammerism: Bugs is bugs and bugs is bad.  Kill them all.   

[Stevenjohn21]

Stephen I found some good info from Purdue on PPB.  https://extension.entm.purdue.edu/publications/E-73/E-73.html
It says the holes are caused by emerging beetles.  What type of kiln do you have?

I have a solar kiln. Thanks for the link, I will take a look later today. 

[scsmith42]

You're going to need to get your temps up higher. USDA specs call for heating all portions of the lumber to 133F or higher.  

A short time of air temp at 136 is not hot enough to soak all of the way through the lumber for sterilization.  

Many kiln operators turn the temp up to 150F or higher and leave it there for 12 - 24 hours.  This is after finishing a load at 120F.  It takes longer to fully heat 8/4 lumber than 4/4 too.

[YellowHammer]

Yes, I hold at 150 for at least 24 hours. 

[Stevenjohn21]

You're going to need to get your temps up higher. USDA specs call for heating all portions of the lumber to 133F or higher.  

A short time of air temp at 136 is not hot enough to soak all of the way through the lumber for sterilization.  

Many kiln operators turn the temp up to 150F or higher and leave it there for 12 - 24 hours.  This is after finishing a load at 120F.  It takes longer to fully heat 8/4 lumber than 4/4 too.

Problem is I'm running a Solar kiln so I'm dependent on the weather. 
The kiln hit 136 when outside temp was 89 degrees so I'm hoping here in the next few weeks we will get mid 90s which should easily get 140+ however, it's never going to be for 24 hours. From what others have said, the fresh holes I'm seeing are from the beetles coming out so they're obviously uncomfortable. Hopefully 140 degrees for a few hours will be good enough 🤞 

[scsmith42]

I added a propane torpedo heater to one of my solar kilns just so that I could run a 24 hour sterilization cycle.  It works great and will easily maintain 150F.

[Stevenjohn21]

I added a propane torpedo heater to one of my solar kilns just so that I could run a 24 hour sterilization cycle.  It works great and will easily maintain 150F.

Interesting! Do you have the heater outside and run a dryer hose into the kiln? Do you have any pictures of the setup? 

[scsmith42]

I added a propane torpedo heater to one of my solar kilns just so that I could run a 24 hour sterilization cycle.  It works great and will easily maintain 150F.

Interesting! Do you have the heater outside and run a dryer hose into the kiln? Do you have any pictures of the setup?

Here is my setup.  A LP torpedo heater is installed on a covered shelf added onto the side of the kiln so that it's discharge is directed behind the circulation fans.  There is a metal baffle on the inside of the kiln to protect the first few feet of air baffle.
We used a double wall stove pipe through the kiln wall to protect it from heat, and the heater outlet is inside of the double wall pipe.
Placing the heater near the top of the kiln helps keep the hot discharge air from blowing directly onto the lumber, and allows for the most consistent circulation through the kiln.


 


 


 


 
We are seeing around a 5 degree delta in temperature across the top of the kiln when the heater is running.  Typically we're averaging 150 on low and 172 on high - measured behind the fans, during the early spring.  
We typically run the heater on it's lowest setting to keep from overheating the kiln (and melting the solar collector), although during a cold winter day we may have to run it on medium.

[Stevenjohn21]

I added a propane torpedo heater to one of my solar kilns just so that I could run a 24 hour sterilization cycle.  It works great and will easily maintain 150F.

Interesting! Do you have the heater outside and run a dryer hose into the kiln? Do you have any pictures of the setup?

Here is my setup.  A LP torpedo heater is installed on a covered shelf added onto the side of the kiln so that it's discharge is directed behind the circulation fans.  There is a metal baffle on the inside of the kiln to protect the first few feet of air baffle.
We used a double wall stove pipe through the kiln wall to protect it from heat, and the heater outlet is inside of the double wall pipe.
Placing the heater near the top of the kiln helps keep the hot discharge air from blowing directly onto the lumber, and allows for the most consistent circulation through the kiln.

We are seeing around a 5 degree delta in temperature across the top of the kiln when the heater is running.  Typically we're averaging 150 on low and 172 on high - measured behind the fans, during the early spring.  
We typically run the heater on its lowest setting to keep from overheating the kiln (and melting the solar collector), although during a cold winter day we may have to run it on medium.

Thank you for the details. I'll definitely look into setting this up. 
This might be a "how long is a piece of string" question but roughly how long does that propane last say in the winter when set on medium? 

[Ianab]

The specs for the heater should indicate the fuel use. 

Looking up a local supplier they say a 15kw heater will use ~1 kg of propane per hour at full power.  Running it at 1/2 power, approx 0.5 kg I guess. And 28w of electricity for the fan, but that's negligible. 

This would be the reason that solar kilns are popular  ;). You just have to calculate in the cost of that extra day of heating to complete a "100% dead bug" cycle, and don't have to heat the kiln for a whole cycle. 

[scsmith42]

I added a propane torpedo heater to one of my solar kilns just so that I could run a 24 hour sterilization cycle.  It works great and will easily maintain 150F.

Interesting! Do you have the heater outside and run a dryer hose into the kiln? Do you have any pictures of the setup?

Here is my setup.  A LP torpedo heater is installed on a covered shelf added onto the side of the kiln so that it's discharge is directed behind the circulation fans.  There is a metal baffle on the inside of the kiln to protect the first few feet of air baffle.
We used a double wall stove pipe through the kiln wall to protect it from heat, and the heater outlet is inside of the double wall pipe.
Placing the heater near the top of the kiln helps keep the hot discharge air from blowing directly onto the lumber, and allows for the most consistent circulation through the kiln.

We are seeing around a 5 degree delta in temperature across the top of the kiln when the heater is running.  Typically we're averaging 150 on low and 172 on high - measured behind the fans, during the early spring.  
We typically run the heater on its lowest setting to keep from overheating the kiln (and melting the solar collector), although during a cold winter day we may have to run it on medium.

Thank you for the details. I'll definitely look into setting this up.
This might be a "how long is a piece of string" question but roughly how long does that propane last say in the winter when set on medium?

Basically we are going through a 100 lb tank per sterilization cycle (24 hours), which is around 20 gallons of propane.  My kiln is 2K bd ft kiln, so the cost amortized across a lot of bd ft is acceptable.

[Kit B]

Thank you so much for posting this.  Super helpful, especially with the pictures.  I've struggled with getting my solar kiln consistently hot enough to sterilize wood.  I can't wait to duplicate your set up on my kiln.

[Brad_bb]

And you've got to make sure you don't get it too hot that you melt your windows.  What did you make your  windows from? How much can they take?

[Sod saw]

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Brad has a very valid concern.  At 150 degrees (F) things are at a low enough temperature to probably be ok and still be hot enough for the heat to work its way into the wood.

But as the temperature rises, more of the kiln parts might become damaged.

My question:   I assume that the heater has an electric fan built into it.   Is there any way that a thermostat located near the bottom of the kiln can control the power to that heater and turn the whole heater off at, say 153 degrees and turn that heater back on at some what near 148 degrees?

The internal kiln fans must be operating full time, independently, and not controlled by the thermostat.  The temperature at the top of the kiln chamber should be near the same temperature as the bottom layers of wood.

My thermostat is used only for sterilizing the wood and the kiln fans operate 24 hours during that sterilizing time.  During normal drying days the kiln fans are on during daylight but off when the sun sets.  The 12 volt kiln fans run directly on solar panels except during sterilizing cycles.

have fun and be safe with that gas supply.


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[scsmith42]

And you've got to make sure you don't get it too hot that you melt your windows.  What did you make your  windows from? How much can they take?

Brad, I don't know if you're directing that question at me or the OP.
In my case, I used Palram Thermaglas 8mm double wall polycarbonate greenhouse panels sourced from Greenhouse Megastore.  They have a maximum temperature rating of 270F.
They were not inexpensive, but I've had zero problems with them in 7 years.  They carry a 10 year manufacturers warranty.

[scsmith42]

Brad has a very valid concern.  At 150 degrees (F) things are at a low enough temperature to probably be ok and still be hot enough for the heat to work its way into the wood.

But as the temperature rises, more of the kiln parts might become damaged.

My question:   I assume that the heater has an electric fan built into it.   Is there any way that a thermostat located near the bottom of the kiln can control the power to that heater and turn the whole heater off at, say 153 degrees and turn that heater back on at some what near 148 degrees?

Yes re the electric fan.  I had to bypass the thermal cutout in order to get the temps high enough inside the kiln.  We did several test runs and the temps have not exceeded 180F anywhere inside with the heater running on it's "low" setting.
I can't use a thermostat with it because you have to physically hold a button in to ignite the burner.  As configured from the factory, if the thermal cutout shuts it down you have to power down, let it cool down and then manually restart it.  
It's pretty much a non-issue since it does a pretty good job of maintaining the temp based upon it's own setting (low, medium or high). 

[burdman_22]

I've been looking at electric bed bud heaters for this. Most of them are made to maintain a temperature of around 140-150 degrees by default and are usually designed for heating spaces of around 200 sq ft.

[Sod saw]

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In your other post about finishing the kiln, I asked questions about your proposed heater.

please answer here or there.

thanks


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