First kiln build

[Crookedkut]

I am new to this forum and have some questions about building a kiln.  Any advice would be greatly appreciated.

I live in South Texas (close to South Padre Island).  It's really never that cold here but it is somewhat humid.  

1. If I build a kiln, could I get away without insulating it?
2. I have lots of brick and was thinking of making the outside walls with brick and concrete floor. 
3. I was planning on following the Virginia Tech kiln plans with the modifications above.   

I understand that it would be best to insulate it but due to our warm weather for most of the year (maybe 40 degrees for about two or three weeks) I figured maybe I could get away with some modifications.

Thanks in advance. 

[Crookedkut]

The kiln will be 10 feet long by 4 feet wide. 

[firefighter ontheside]

I need to build a kiln too.  I would think for the hottest times of the year, no insulation would be fine, but for the cooler times, no insulation is gonna hurt ya.

[Crookedkut]

I am gonna try it without insulation.  I will keep on eye on it the first winter.  If I see it needs insulation I will add it.  

[YellowHammer]

 Since large uninsulated masses will act as a thermal sink and thermal ballast, and are generally used as thermal regulators to damp out temperature oscillations which is how a solar kiln works.  50% duty cycle, with only a limited time to heat and limited time to cool, the use of large thermal masses would dampen its cyclic usefulness.  If brick is used, I would use air gaps between layers, which acts as a dead air space insulator.

Certainly, using the proper collector size, which may need to be increased over the current value, the solar kiln will still heat up during the day, and just as importantly, cool down at night, my guess is that it's peak effectiveness would be decreased and drying time would be increased.    
   
I'm interested to hear what Gene says about this.  

[Crookedkut]

Since large uninsulated masses will act as a thermal sink and thermal ballast, and are generally used as thermal regulators to damp out temperature oscillations which is how a solar kiln works.  50% duty cycle, with only a limited time to heat and limited time to cool, the use of large thermal masses would dampen its cyclic usefulness.  If brick is used, I would use air gaps between layers, which acts as a dead air space insulator.

Certainly, using the proper collector size, which may need to be increased over the current value, the solar kiln will still heat up during the day, and just as importantly, cool down at night, my guess is that it's peak effectiveness would be decreased and drying time would be increased.    
 
I'm interested to hear what Gene says about this.  

How would leaving air gaps between the layers help me.  This would contradict the insulation theory would it not?  I am not questioning you in a negative way, I just want to know.   Could you elaborate on this a bit more please?  

And who's Gene?   

[PA_Walnut]

How would leaving air gaps between the layers help me.  This would contradict the insulation theory would it not?  I am not questioning you in a negative way, I just want to know.   Could you elaborate on this a bit more please?   And who's Gene?   

Air is a decent insulator--is what Yellow is deferring to. What you are intending to use as your heat source, which may dictate what/how-much insulation you use. In most scenarios, NOT using insulation is false economy, but not knowing what you are drying, your timeline, etc. it's difficult to determine.

Also, depending upon how wide your charges (stacks) are, 4' may not be enough. Have you considered how you're going to move air? Do you have plans to install fans? A solar kiln may be a good plan for you, and there's LOADS of information (including plans on building) and Gene may further guide you.

Gene, is "Dr. Gene Wengert" who is know in the community as "The Wood Doctor"...he's an authority on wood and drying issues, including having written books on the topic, etc. I'll take a liberty here in saying that he's "old school", just as drying lumber is--nothing new to be invented here and the science has been well established.

Welcome and enjoy the collective of MUCH wisdom here, well beyond my own!

[Crookedkut]

How would leaving air gaps between the layers help me.  This would contradict the insulation theory would it not?  I am not questioning you in a negative way, I just want to know.   Could you elaborate on this a bit more please?   And who's Gene?  

Air is a decent insulator--is what Yellow is deferring to. What you are intending to use as your heat source, which may dictate what/how-much insulation you use. In most scenarios, NOT using insulation is false economy, but not knowing what you are drying, your timeline, etc. it's difficult to determine.

Also, depending upon how wide your charges (stacks) are, 4' may not be enough. Have you considered how you're going to move air? Do you have plans to install fans? A solar kiln may be a good plan for you, and there's LOADS of information (including plans on building) and Gene may further guide you.

Gene, is "Dr. Gene Wengert" who is know in the community as "The Wood Doctor"...he's an authority on wood and drying issues, including having written books on the topic, etc. I'll take a liberty here in saying that he's "old school", just as drying lumber is--nothing new to be invented here and the science has been well established.

Welcome and enjoy the collective of MUCH wisdom here, well beyond my own!

Being that it is pretty warm year round down here in South Texas I was thinking about not using a heat source.   In South Texas we still have to mow our grass in December.  I don't see myself getting stacks wider than 3', but I could be wrong.  I plan on having fans powered by a battery that I will charge with a separate solar panel.  I want to have it activated with a thermal switch.  As far as what I am going to dry, well I would say mesquite, oak, some cedar and some ash trees.   Down here we don't have access to maple or other trees that grow up north.     


I want to make the outer walls from brick.  I have a lot of it.  I was just going to seal it on the outside with a waterproof sealer (thompsons or something like that).  I want to paint the inside black and use a sheet of treated plywood for the access door(s). 

[YellowHammer]

Yes, dead air spaces are what gives expanded foam and fiberglass batt insulation much of its R value.

Concrete, brick, rock, etc are poor insulators and conduct heat readily, to the point that in a conventional kiln build, foam isolation is sandwiched between the concrete and the ground to prevent conduction.

Dr. Gene Wengert, Professor Emeritus, member of this Forum as Wood Doc, is credited with the development and usage of the Va Tech Solar Kiln, and may have some suggestions for using brick and concrete as construction material.  

[PA_Walnut]

Yes indeed...many fall short on insulation where it counts...like concrete. I just dug a foundation for a monolithic pour and have done through GREAT extents to insulate the slab. I will post some pix later today. Concrete on grade can deplete a kiln of LOTS of heat. :-\

[Crookedkut]

Okay, I gotcha, no concrete then.  

[Bruno of NH]

What about a radiant hot water heat system in the slab ?

[Ljohnsaw]

How would leaving air gaps between the layers help me.

I don't think your question was answered.  I think what PA_Walnut is saying is you need a thermal break between the inside (hot) of the kiln and the outside air.  If you built a double wall of brick with an air gap between, then the heat would not travel quite so quickly to the outside air.

I think you may have interpreted his suggestion to have gaps/breaks in your mortar joints.  Now that would be a lot of heat transfer... :D

[GeneWengert-WoodDoc]

Although the hot outside in the summer will help solar drying, the walls will conduct some of the heat out of the kiln before it can evaporate moisture.  Generally, we want to use as much of the heat we collect for drying lumber.  With pine especially, hotter is better.  With green oak, not so.  With air dried of any species, hotter is better for 1" and 2".  I would estimate that an uninsulated kiln will increase drying time by 50%.  Although we have many steam heated masonry brick kilns, they work because the heating system has extra heat, which we do not have in the VT solar kiln.  At the least, try some rigid foam boards fastened to the inside of the brick walls.  Tape the joints or use a compatible caulk.  Some boards are sensitive to heat...they will shrink and disappear when heated, so check the temperature rating.

I do agree with the heat sink comments for the floor...avoid concrete.

[Crookedkut]

Although the hot outside in the summer will help solar drying, the walls will conduct some of the heat out of the kiln before it can evaporate moisture.  Generally, we want to use as much of the heat we collect for drying lumber.  With pine especially, hotter is better.  With green oak, not so.  With air dried of any species, hotter is better for 1" and 2".  I would estimate that an uninsulated kiln will increase drying time by 50%.  Although we have many steam heated masonry brick kilns, they work because the heating system has extra heat, which we do not have in the VT solar kiln.  At the least, try some rigid foam boards fastened to the inside of the brick walls.  Tape the joints or use a compatible caulk.  Some boards are sensitive to heat...they will shrink and disappear when heated, so check the temperature rating.

I do agree with the heat sink comments for the floor...avoid concrete.

Thank you for the reply.  Please tell me if I am beating a dead horse here but what if I just make the outside walls with brick and only use a concrete base but use wood flooring with insulation in it. Then I insulate the inside like you mentioned.   I may not understand the heat theory but I keep hearing that heat is needed but it is so hot down here for most of the year I am more worried about the humidity in the atmosphere.   It is not uncommon for a day to be 95 degrees with 100% humidity outside.  Heck it is 2 am right now and the temperature outside is 69 degrees with 83% humidity. 

[Ianab]

If you have high heat AND humidity, then you still need to raise the temp in the kiln. This reduces the relative humidity. So if you heat 95 deg / 100% humid air to 120 deg with the solar collector, then the relative humidity will drop. You can look up how much, but say it's now 70%. Blow that warmed air through your wood stack, and it can pick up some moisture. Then you vent that air, and the water is gone from the kiln. Heat some more air, remove some more water, repeat every day, and eventually the wood will be dry. 

So to get that drying, you want the air in the kiln up to temp as quick as possible once the sun starts shining. Hence insulating the the kiln from a large thermal mass of concrete. By the time you get that up to temp, the day might be nearly over. Then the sun drops, and the kiln starts cooling off for the night time recondition cycle. Humidity goes up again, and the drying basically stops. 

Now a brick or concrete structure could work as the structural part, but I'd work out a way to air gap / insulate the chamber inside. That could be some battens / fibreglass or foam / light plywood depending on what you have available. It's only an insulating layer inside your sturdy masonry chamber.

Now it may be possible to design a kiln that makes use of the thermal mass, maybe for a steadier drying process? But one of the advantages of the solar kiln design is that night time cool off and recondition, which makes the exact control less important. 8 hours of hot/dry shouldn't harm the wood, if it then gets 16 hours of cool and humid to "relax" again. It's the cyclic nature of the drying that makes the simple solar kiln practical, without the fancy control system of a normal kiln. 

[PA_Walnut]

Concrete IS an option for the floor so long as you insulate it. I'm about to do a pour for a fairly large kiln, but have paid significant attention to insulating (isolating) the slab from the ground, so that it doesn't conduct my slab heat out of the building.

This includes insulating the sides and bottom of the slab. I'll get pix posted asap.

[Crookedkut]

Concrete IS an option for the floor so long as you insulate it. I'm about to do a pour for a fairly large kiln, but have paid significant attention to insulating (isolating) the slab from the ground, so that it doesn't conduct my slab heat out of the building.

This includes insulating the sides and bottom of the slab. I'll get pix posted asap.

Thanks, I will be looking forward to the pix. 

[GeneWengert-WoodDoc]

Ina solar kiln, in 24 hours we will get a certain amount of energy input.  If we use a heat sink to store energy, on purpose or not, during the afternoon, we still get the same amount of heat input in a 24 hour time.  So, storing heat is not really a great idea.  So, no concrete floor in the kiln unless insulated.  No masonry walls unless insulated.  In fact, I suggest 6" minimum wall insulation.  The key, as mentioned, is that the hotter we can get the kiln, the more water we evaporate in a short time.  It lowers the humidity and makes water move faster within the wood.  So, this peak heat is better than storing heat and running lower peak heat.