# Solar kilns



## StihlHead (Sep 19, 2013)

Anyone build/use a solar firewood drying kiln?

http://www.builditsolar.com/Projects/WoodDrying/wood_kiln.htm


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## PapaDave (Sep 19, 2013)

No, but I've thought about building one for several years. 
I've got plans saved.


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## Augie (Sep 19, 2013)

Yes, I have mentioned it a few times and usually I am ignored or branded a heretic! 

I have used one successfully to season Oak from the mid 50's to just under 20 percent in 4 months. 

Mine is much simpler, I use clear plastic and scrap wood to make a frame that is attached to the wood I am looking to season. Cost is about $20 for 2 cord(plastic cost) but I can use the plastic a few times I think. I am getting ready to cover the second two cords for next year. I think with this method I will not have to keep more than one year ahead at any time.


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## StihlHead (Sep 19, 2013)

Augie said:


> Yes, I have mentioned it a few times and usually I am ignored or branded a heretic!


 
A heretic? I dunno about that. Maybe a wood tic... 

What you are doing is what I am thinking of doing here. Cover up racks that I already have stacked with a frame and greenhouse plastic and fast dry them. Wood already takes up a lot of space here, and we cannot all be like Scotty the Overkiller. I have room for 5 cords and I burn about 3 cords a year. I am also above the 45th parallel and it rains a lot here (about 100 inches on average) . I have a hard time drying wood in the short (somewhat dry) PNW summers. Covering them with plastic and venting them properly seems to be the trick, to get them nice a toasty and deal with the condensation that forms ~inside~ the plastic. 

How do you attach the frame to the seasoning wood? I have wood drying in double rows 12' long, and raised up on pallets and staked with t-posts at the ends. I cover then with tarps, flat on top in the summer, and fully wrapped in the winter.


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## MrWhoopee (Sep 19, 2013)

Forest Service Study:

http://www.fs.fed.us/pnw/pubs/pnw_rn450.pdf

"I don't make this stuff up, I just report it."
Gallagher


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## NW Walker (Sep 19, 2013)

I have a clear, double wall roof on my wood shed, since it's connected to my greenhouse.  I'm really interested in finishing out the sides to make it into a kiln.  It's just so moist out here in the winter, I think it would make a big difference.


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## StihlHead (Sep 19, 2013)

MrWhoopee said:


> Forest Service Study:
> 
> http://www.fs.fed.us/pnw/pubs/pnw_rn450.pdf
> 
> ...


 
Two issues... one, they are 'drying' impossible to dry unsplit birch, and two they were testing in very high latitude Alaska. I realize that birch is one of the few firewoods available in Alaska, but if I leave birch here unsplit, it will rot before it dries out, regardless. So I do not think that is a good test for this type of solar kiln.

I would like to see results from lower latitudes using a different species and of properly ~split~ hardwood. Oak, Alder, Maple, something else. Then I would believe it, but until then my engineering background tells me that a warmer solar kiln will effectively dry wood faster than without one.

I also saw Gallagher film one of his movies in Sand City, CA... from under a plastic tarp, of course, and the smashed watermelons flew by.


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## MrWhoopee (Sep 19, 2013)

StihlHead said:


> Two issues... one, they are 'drying' impossible to dry unsplit birch, and two they were testing in very high latitude Alaska. I realize that birch is one of the few firewoods available in Alaska, but if I leave birch here unsplit, it will rot before it dries out, regardless. So I do not think that is a good test for this type of solar kiln.
> 
> I would like to see results from lower latitudes using a different species and of properly ~split~ hardwood. Oak, Alder, Maple, something else. Then I would believe it, but until then my engineering background tells me that a warmer solar kiln will effectively dry wood faster than without one.
> 
> I also saw Gallagher film one of his movies in Sand City, CA... under a tarp, of course.


 
Agreed. It is, so far, the only relevant study I've been able to find. My only thought on the subject is that the kiln must be somehow ventilated to remove the moisture while still holding the heat. One of the east coast, lots of oak people should do something similar. Anyone? Anyone?


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## barnuba (Sep 19, 2013)

Here is the kiln that  I just built:

https://www.hearth.com/talk/threads/labor-day-wood.113026/#post-1507473


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## Augie (Sep 19, 2013)

I have posted a white paper from Cornell a few times that contradicts the Forest Survey. It is what I used to base mine off of.   studyhttps://www.google.com/url?ttp://ww...ting/CC Accelerated Seasoning of Firewood.pdf


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## oldspark (Sep 19, 2013)

MrWhoopee said:


> Agreed. It is, so far, the only relevant study I've been able to find. My only thought on the subject is that the kiln must be somehow ventilated to remove the moisture while still holding the heat. One of the east coast, lots of oak people should do something similar. Anyone? Anyone?


Over the years I have run across a few articles talking about speeding up the drying process with a kiln, plus Augie posted his before, what exactly are you looking for?


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## BrotherBart (Sep 19, 2013)

I am doing a test this season. I moved my stacking area two years ago with my usual top covering. Seems the ground under the new area stays wet. When I moved the stuff into the shed in April like I always do a lot of that oak was wet. 

I had just put a solar powered gable fan in the attic replacing the AC powered one that crapped out. In June I had the roof replaced and ridge vent installed so I took the solar attic fan out of the attic and installed it in the front of the woodshed and when the sun is out it blows into the shed. Been doing it all summer.

Hope that does drying stuff.


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## HDRock (Sep 20, 2013)

Augie said:


> Yes, I have mentioned it a few times and usually I am ignored or branded a heretic!
> 
> I have used one successfully to season Oak from the mid 50's to just under 20 percent in 4 months.
> 
> Mine is much simpler, I use clear plastic and scrap wood to make a frame that is attached to the wood I am looking to season. Cost is about $20 for 2 cord(plastic cost) but I can use the plastic a few times I think. I am getting ready to cover the second two cords for next year. I think with this method I will not have to keep more than one year ahead at any time.


 I'm with ya man ,going to try it next summer


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## bmblank (Sep 20, 2013)

My shed is similar. I installed a 1200 cfm roof fan. I drilled holes in the side of the shed just below the eaves into each stud bay. Then i put up walls in the shed leaving a gap at the bottom, so the fab draws air in the holes, down the stud bay, through the wood from the bottom up and out the fan. I'm hoping in winter it'll dry even better with the lower humidity.
I don't have a moisture meter, but its definitely drying some wood.


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## HDRock (Sep 20, 2013)

BrotherBart said:


> I am doing a test this season. I moved my stacking area two years ago with my usual top covering. Seems the ground under the new area stays wet. When I moved the stuff into the shed in April like I always do a lot of that oak was wet.
> 
> I had just put a solar powered gable fan in the attic replacing the AC powered one that crapped out. In June I had the roof replaced and ridge vent installed so I took the solar attic fan out of the attic and installed it in the front of the woodshed and when the sun is out it blows into the shed. Been doing it all summer.
> 
> Hope that does drying stuff.


 Sounds like a good idea there


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## MrWhoopee (Sep 20, 2013)

Augie said:


> I have posted a white paper from Cornell a few times that contradicts the Forest Survey. It is what I used to base mine off of.   studyhttps://www.google.com/url?ttp://www2.dnr.cornell.edu/ext/info/pubs/Harvesting/CC Accelerated Seasoning of Firewood.pdf


 
There was a problem with that link, but I found it.
http://www2.dnr.cornell.edu/ext/info/pubs/Harvesting/CC Accelerated Seasoning of Firewood.pdf

 Good info, and pertinent to the parts of the country where humidity is high(er) and hardwoods season slowly.
I wouldn't say that it contradicts the other study, since the wood was a different species and was split. These kind of details can result in large differences.
It is somewhat limited in scope, did not have a control group and provded no actual data, but is still very encouraging. Much more promising than the Alaska study. I would like to see someone take a batch of green oak (both split and small diameter unsplit rounds), divide it into 2 stacks side by side and construct a solar kiln over one. Then take moisture measurements over the course of a summer. Based on this white paper, I suspect it would be beneficial for people with limited storage space to build solar kilns.


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## Mr A (Sep 20, 2013)

MrWhoopee said:


> There was a problem with that link, but I found it.
> http://www2.dnr.cornell.edu/ext/info/pubs/Harvesting/CC Accelerated Seasoning of Firewood.pdf
> 
> Good info, and pertinent to the parts of the country where humidity is high(er) and hardwoods season slowly.
> ...


 For the East Coast , I am thinking your freezing temperatures over multiple days and weeks may hinder the progress of your wood drying. I may have mentioned before, I oak rounds up to 2 ft. across that are seasoned in 1 year. I collected them sometime earlier this year. If I remember right, this stack of oak was cut last September '12. I just split it yesterday, Harbor Freight Moisture Meter says 10%-15% in the center. It is Blue Oak. As long as we're looking for experiment ideas, I would try digging a compost pit to generate heat, build the greenhouse to include the wood stack and compost pit, the wood will not freeze and maybe it will season a lot faster.


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## StihlHead (Sep 20, 2013)

Augie said:


> I have posted a white paper from Cornell a few times that contradicts the Forest Survey. It is what I used to base mine off of.


 
I think that Cornell trumps the Forest Service. My parents met at Cornell... 

Also the Forest Service 'study' says that birch bark is virtually waterproof, so I do not see how they can come to any conclusion like the ones they do. Its a poorly designed test, with an even worse conclusion. All they prove is that birch does not dry if it is left unsplit, which a lot of us have independently verified. I see little if any value in that, really. Its typical of the government though, like the EPA testing wood stoves in a way that no one uses them. And I mean no one burns wood that way, save for the testing places, 3 of which are here in the city nearest me.


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## HDRock (Sep 20, 2013)

PapaDave said:


> No, but I've thought about building one for several years.
> I've got plans saved.


 Break out the plans man


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## StihlHead (Sep 20, 2013)

Mr A said:


> For the East Coast , I am thinking your freezing temperatures over multiple days and weeks may hinder the progress of your wood drying. I may have mentioned before, I oak rounds up to 2 ft. across that are seasoned in 1 year. I collected them sometime earlier this year. If I remember right, this stack of oak was cut last September '12. I just split it yesterday, Harbor Freight Moisture Meter says 10%-15% in the center. It is Blue Oak. As long as we're looking for experiment ideas, I would try digging a compost pit to generate heat, build the greenhouse to include the wood stack and compost pit, the wood will not freeze and maybe it will season a lot faster.


 
Wood will dry even in freezing temps. I have studied all kinds of effects of snow and ice melt in avalanche training for the ski patrol. Evisceration Sublimation happens (water vapor forming directly from ice and snow) below freezing, similar to evaporation happening (water vapor forming from water) above freezing. Also in colder areas in winter, the solar snow reflection is intense on clear days. I get the highest readings on my solar watt meter here when there is snow on the ground in winter months, higher even than in summer. You also get the most snow and ice melt on semi-clear days with high thin cloud cover, when the solar intensity is the greatest. So I do not think that you even need a heat source in winter to dry wood faster.

I like the intro to the Cornell paper, they spell it out, to paraphrase:  You can speed up wood drying time by cutting pieces shorter, splitting them smaller, stacking for maximum solar and wind exposure, keeping the rain off and keeping the wood off the ground. Also they mention that plastic does not last very long in full sunlight.

High quality UV-resistant plastic can be bought around here, as there are many professional greenhouses in this area. I like their simple but open design, and large area for air circulation. In places that get a lot of snow (like here) they would need more 'roof' support though.


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## maple1 (Sep 20, 2013)

Augie said:


> Yes, I have mentioned it a few times and usually I am ignored or branded a heretic!
> 
> I have used one successfully to season Oak from the mid 50's to just under 20 percent in 4 months.
> 
> Mine is much simpler, I use clear plastic and scrap wood to make a frame that is attached to the wood I am looking to season. Cost is about $20 for 2 cord(plastic cost) but I can use the plastic a few times I think. I am getting ready to cover the second two cords for next year. I think with this method I will not have to keep more than one year ahead at any time.


 
Pictures might end the ignoring.


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## oldspark (Sep 20, 2013)

"Wood will dry even in freezing temps"
Yes it will but it is much slower then warmer temps, two kinds of water in wood, bound and free and one of them (have to look it up) doesn't do anything below 32 degrees, a kiln works quicker because the high temps drive the moisture out of the wood and the air movement takes the moisture away from the surface of the wood.


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## NortheastAl (Sep 20, 2013)

Augie said:


> Yes, I have mentioned it a few times and usually I am ignored or branded a heretic!
> 
> I have used one successfully to season Oak from the mid 50's to just under 20 percent in 4 months.
> 
> Mine is much simpler, I use clear plastic and scrap wood to make a frame that is attached to the wood I am looking to season. Cost is about $20 for 2 cord(plastic cost) but I can use the plastic a few times I think. I am getting ready to cover the second two cords for next year. I think with this method I will not have to keep more than one year ahead at any time.


Augie, I think you are difinitely on to something that works. Try it one more time, but leave one stack outside the kiln as a comparison to the kiln enclosed stack. Then report the results. I too want to dry my wood without having to keep three years around, if possible. The 5+ cord that I have now are topping out much of my usable space. I need about 9 cord to make the three year goal, and if I could cute that number back by using a kiln, then I would be happy.


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## Craig S. (Sep 20, 2013)

Could even take this one step further, and build a DIY heliostat to keep the sunlight on the kiln for longer periods of time.


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## MrWhoopee (Sep 20, 2013)

StihlHead said:


> Wood will dry even in freezing temps. I have studied all kinds of effects of snow and ice melt in avalanche training for the ski patrol.* Evisceration* happens (water vapor forming directly from ice and snow) below freezing, similar to evaporation happening (water vapor forming from water) above freezing.


 
I think the word you're looking for is sublimation:
"Sublimation is the transition of a substance directly from the solid to the gas phase without passing through an intermediate liquid phase"

Evisceration is an entirely unrelated process:
"To remove the entrails of; disembowel".

Sublimation is more popularly known as freeze-drying or freezer burn, depending on whether it was intentional or not.
It is possible for laundry to dry on the line even though temperatures are below freezing. However, it is a slow process and, as the object becomes thicker, the movement of moisture slows even more. While winter camping at temps well below freezing, I found that thin nylon items will dry very nicely overnight, leather and wool items will not.  I doubt firewood will dry very much at temps below freezing, at least within a period of time that would be helpful.


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## StihlHead (Sep 20, 2013)

Ah yes, deer hunting season is leaking into my brain ahead of ski patrol season. Sublimation... not evisceration.

Of course, maybe I suffer from the sublimation as used in psychology, where it is defined by a mature type of defense mechanism where socially unacceptable impulses or idealizations are consciously transformed into socially acceptable actions or behavior, possibly resulting in a long-term conversion of the initial impulse. Whatever that means...

I have found that ice covered firewood will dry below freezing here if I move it to a dry location. That is re-wetted firewood though, and not green. And it takes exposure to air to do it so it has to be stacked really loose.


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## StihlHead (Sep 20, 2013)

Craig S. said:


> Could even take this one step further, and build a DIY heliostat to keep the sunlight on the kiln for longer periods of time.


 
Snow works great for that here when it is on the ground. Building a solar concentrator (or wood cooker) would have to be rather large, and for many the issue is reducing space. It would also have to put up who a lot of wind here in the Cascades, as well as snow loading.


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## Augie (Sep 20, 2013)

MrWhoopee said:


> It is somewhat limited in scope, did not have a control group and provided no actual data, but is still very encouraging. Much more promising than the Alaska study. I would like to see someone take a batch of green oak (both split and small diameter unsplit rounds), divide it into 2 stacks side by side and construct a solar kiln over one. Then take moisture measurements over the course of a summer. Based on this white paper, I suspect it would be beneficial for people with limited storage space to build solar kilns.



So I did have some Oak out of the kiln from the same tree. It was still reading 35+ percent MC when the Kiln oak was dry. I didn't take measurements every month, because I am out doing other things besides watching my wood dry. 

I know that it works now, so I don't feel like preforming another experiment to determine exactly how well it works. LOL 

I put the wood in, and it comes out in 4 months ready to burn. I have posted my sources and described my process. This isn't academic research, I do know how to write a white paper, but  I dont think I should need a control group to prove my results.  The internet is pessimistic by nature, no matter how much proof I provide someone will say I faked it or it isn't true.  
*
I put exactly as much effort into "testing" as I feel was necessary to determine if it worked for me*. 

I have let the forum know what works for me, and Ill post whenever someone brings it up, but I don't feel it necessary to prove to the internet in general what I have found works for me. 

Take it for what you believe it is worth. 

*C/N:Homemade Solar Kilns work for drying Oak, in Michigan, in four months, I'm too crotchety to put more effort into proving how well it works. *


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## MrWhoopee (Sep 20, 2013)

Augie said:


> So I did have some Oak out of the kiln from the same tree. It was still reading 35+ percent MC when the Kiln oak was dry. I didn't take measurements every month, because I am out doing other things besides watching my wood dry.
> 
> I know that it works now, so I don't feel like preforming another experiment to determine exactly how well it works. LOL
> 
> ...


 
So you did have a control group. That's good enough for me. It's the final result that counts, anything in between is just to confirm the trend and validate the final result.


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## StihlHead (Sep 20, 2013)

Augie said:


> Take it for what you believe it is worth.


 
Yes, we are saturated with double blind studies and endless debates about what exactly is inside of a ping pong ball (or as in this case, a passive solar wood kiln). And whatever the results, they will be refuted by some non-believers or religious faction that does not believe in some particular scientific finding or phenomena, no matter how high the mountain of proof (I submit _evolution_ as but one example). Then it has to be ground up and regulated by some authoritative government entity and looked over for any potential for taxation, licensing, further legislation, or outlawing if it is too controversial or conflicts with a majority (or in some cases, a minority) opinion, or impedes on some business monopoly or registered patents. If it is then challenged, it will spend an eternity in the court system to be dissected and analyzed, and some eventual ruling will result that will likely start the entire process all over again.

Go split your rounds... or better yet, put your chainsaw in a new movie as we are simply dying of boredom out here in the real world.


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## NortheastAl (Sep 20, 2013)

Augie, I'm sure you don't want to redo something you are quite sure works well. I have confidence in your use of the kiln, and that it worked. I also happen to trust Cornell, seeing they are in NY, and must have done the test in NY. Going to give it a try in the spring because of the need for space. Adding almost 4 more cord of wood is going to be a problem. Too many steep places on the property, and I don't want to waste what precious little flatland we have. 

Thanks for keeping this in the forefront. For those of us with smaller lots this may be the only answer to having truly dry firewood.


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## Augie (Sep 20, 2013)

So I am guessing that if I tent up a cord or two this fall once the leaves drop I will have enough sunlight to heat and season a cord by the time the leaves begin to grow next spring, Likely 6  months away, we shall see


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## PapaDave (Sep 20, 2013)




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## jebatty (Nov 26, 2013)

Solar kilns, any device in fact, that provides heat and air movement will dry wood at least to the equilibrium moisture level of the surrounding air. All involve time, and the thicker the splits, the longer it will take. And most involve energy input with fans, heaters, dehumidifiers, etc., which are costly. 

I have a simple solar dry kiln which I built to dry lumber, mostly pine but also some birch, oak and ash. All of my lumber was 1 - 2" rough cut. It's not easy to achieve even drying through the board, and I would think it would be much harder to obtain even drying through a firewood split. There needs to be lots of air space between the boards or splits to carry away the moisture. A 2" x ___ might end up with 6% MC near the ends and pockets of +30% at different points in the board. For lumber purposes it worked best to sticker and air dry in a covered space with air circulation after the kiln drying to achieve an evenly dried board suitable for finish lumber purposes.

During a hot, windy and dry period during the summer stickered kiln lumber dried no faster than stickered air dried, and the stickered air dried was more evenly dry. But in a wet, cool, and calm environment, the kiln out-performed the air drying. Both, with sufficient time, produced equivalent quality of drying.

Since I burn splits generally up to about 8" in thickness, and of course thinner splits, I really can't imagine trying to sticker and kiln dry splits of varying thickness. The thin splits will be more dry, the thick splits will be less dry. I think it can work and can speed drying, but for me the handling, cost of fans, cost of building and maintaining the kiln, etc., all are outweighed by air drying and letting nature do the work without the additional cost.


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## Craig S. (Jan 2, 2014)

Craig S. said:


> Could even take this one step further, and build a DIY heliostat to keep the sunlight on the kiln for longer periods of time.



Here's one ... watch the videos, for $299 it could certainly be used to concentrate sunlight on a woodpile, or woodshed.
http://wikoda.com/the-sunflower/


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## Augie (Apr 8, 2014)

If you want to season oak in 3months try this. It has been working for me


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## bodhran (Aug 14, 2015)

Augie said:


> If you want to season oak in 3months try this. It has been working for me



How long do you think it would take to dry balsam fir and spruce?


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## jaoneill (Aug 15, 2015)

One of my brothers built a fairly large (20'x40'x12'H) woodshed that also houses his outdoor boiler. It is sided and roofed with metal but a substantial part of it is clear polycarbonate. It has a foot or so of intake at the base of the perimeter and plenty of roof ventilation. Average daytime temps inside through the summer are well in excess of 100 degrees. His wood goes in green in April/May and is down to 15% by September.
I try to get my woodshed filled by early July with wood that has been partially seasoned (25% or so). Although I don't have the advantage of solar, I have an old 1/4 hp, slow speed furnace blower that uses a negligible amount of electricity but creates a constant strong breeze (of warm summer air) through the wood during the daylight hours. I resplit a few pieces of hard maple yesterday and found the moisture at 15%-18%, cherry was all below 15%. I generally put the blower away when the weather cools off in late September. Should be in good shape by heating season this year.


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## Babaganoosh (Aug 15, 2015)

I'm not sure how that first report by the forestry place got that it peaked at 9 degrees hotter because I have wood in just shrink wrap and I've gotten temperature readings as high as 160.


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## turn_n_burn (Aug 19, 2015)

I'm a firm believer in dark colored surfaces to absorb radiant heat. A black car gets hotter inside than a white one.


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