Solar kiln for hardwoods

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Woodsplitter67

Minister of Fire
Jan 19, 2017
2,471
Woolwich nj
Wouldn't the low OA dewpoint in the winter play to your advantage? You need less of a temperature lift when it's really cold, to a have really low %rh.
The low angle and shorter daylight hours would be a downer though.

This is a nice simple dewpoint/humidity/temp converter to play with http://www.dpcalc.org/

Im not sure why, but our wood seasons better with heat. Wood seasoning slows in winter late fall and spring. Speeds back up when the temps climb. I'v checked my wood in fall and then spring and its barely moved. Let the summer sun and heat get to it and progress is made alot quicker. I really think its a combination of the temp and difference in RH. I just know this.. it works dam good doing it this way.
 

Dmitry

Minister of Fire
Oct 4, 2014
1,101
CT
My solar kiln, was made from the big box store wood racks as an experiment to see if i could season hardwoods like @Poindexter has done with softwoods.
Materials used were wood racks, 2x4 pressure treated, 6 mil clear plastic, a small roap, contractors stretch wrap and a staple gun
My wood racks were 5 inches above ground and sitting on 2x4 for a total of aprox 8 inches. I secured some two-by-fours on the ends and tied a rope between them making a roof over the top I put plastic around the racks and secured the bottom of the plastic to the first row of firewood with contractors stretch wrap and some Staples I cut in 3 vents to on either end approximately the size of a grapefruit and one smaller one in the middle this would was split in May and sat on the racks until the week of July 8th in which I started the kilm all of my splits were large 6 to7 in thick and 18 in Long and those splits at in the kiln until October when I open the Kiln the Cherry splits were down to approximately 2% and all of the oak was down to 9% so given that you could easily do two runs with in a rack
The way that the kiln needs to be set up for Hardwoods is you need it in a full sun area you do not want the venting to be too much as you want the temperatures to get extremely warm within the kiln it does need to vent the moisture out so typically my kiln Ran from anywhere from 110 degrees and I've gotten it as high as 121 degrees
The first day I ran my kiln it was a cooler day no more than 76 degrees and within a couple of hours of setting up the kiln it was over a 110. I used an air probe for my smoker to measure the internal temperature of the Kiln at various points.
I did all of this to see if I ever get jammed up that I could actually season a Year's worth of firewood over the course of the summer I also did another experiment with nothing but Oak and even larger splits those splits started in the upper 30s to low 40s and I got them down to sub 20% moisture content in 2 months
View attachment 231154 View attachment 231155
We had very wet summer here and some of my wood got touched by fungus . I scraped as much as I can. Do you think it’s still Ok to to kiln with wood like this? I think I might kill 2 birds with one stone here. Not let any more autumn moisture to wood and and bring eventually moisture down to stop fungus inside the pile.
 

Dtunes

Member
Mar 7, 2012
78
Southern NH
The visible portion of fungi is usually just the fruiting bodies(like flower/seeds in plants) and the majority of the organism is already distributed throughout the substrate. So if you see a mushroom on your lawn, the actual bulk of the organism is far larger in the soil. The same is probably true with the wood, so scraping it off might reduce its ability to spread but won't remove the fungus from the wood.

That being said, I have no experience with solar kilns so I don't know if it will get hot enough to kill or slow the fungus. It might in that summer, I'd guess not during the colder months.

Fungi also need fairly high moisture levels to grow. If the kiln dries quickly you might reduce the moisture faster than the fungus can grow.

Personally, I wouldn't risk good wood by placing it in the kiln with fungus infested wood, but if the wood is all similarly touched by fungus it might be worth a shot during the summer. I wouldn't try it in the fall unless you have excellent southern exposure and fairly high temps.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,471
Woolwich nj
We had very wet summer here and some of my wood got touched by fungus . I scraped as much as I can. Do you think it’s still Ok to to kiln with wood like this? I think I might kill 2 birds with one stone here. Not let any more autumn moisture to wood and and bring eventually moisture down to stop fungus inside the pile.

You have fungi because your wood is wet and stayed that way. I havent had your issue. That being said this fungi will not be able to live and prosper if you drive the moisture out. You could kill off the fungi by putting it in a kiln. I think you would be ok. I wouldn't store the wood in the house.. i would kiln the wood, once the fungi is gone put it directly into the stove..hope this helps
 

wooduser

Minister of Fire
Nov 12, 2018
679
seattle, wa
. I wasn't sure how big to make vent on top in balance of trying to keep it warm vs letting moisture out.


Amazon or Ebay both have wide selections of hygrometers that measure humidity. They are available in both mechanical and electronic versions.

You might want to consider using a hygrometer along with your thermometer to measure the humidity being generated inside your kiln. You could also rig up an air velocity telltale made from paper to measure the amount of humidified air that is exiting the kiln. The paper telltale could be arbitrarily calibrated with a series of marks to measure the velocity.

Day X Temp 120 Humidity 60% Air velocity Mark 3

Day Z Temp 80 Humidity 30% Air velocity Mark 1

Or whatever.
 
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ispinwool

Feeling the Heat
Feb 5, 2010
327
Butler County, Pa.
I'm sorry to dig up an old discussion (but I'm so glad I found it!
I had NO idea we could build a homemade/backyard kiln)
but I'm wondering if using the thick black
plastic would work as well? I've always been told that black clothing/cars/etc
get hotter faster...? I guess it's "whatever works best for your circumstance"...
would there be any reason NOT to?
I'm intrigued!
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,471
Woolwich nj
I'm sorry to dig up an old discussion (but I'm so glad I found it!
I had NO idea we could build a homemade/backyard kiln)
but I'm wondering if using the thick black
plastic would work as well? I've always been told that black clothing/cars/etc
get hotter faster...? I guess it's "whatever works best for your circumstance"...
would there be any reason NOT to?
I'm intrigued!
your building a green house over your wood stacks.. ever see a greenhouse with black plastic... never... thinted windows keep a cars interior cooler... the pladtic does not heat the kiln.. the pladtic traps the heat in.. you need sun to get into the kiln to work it.. look in my signature to see how to make one
 
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ispinwool

Feeling the Heat
Feb 5, 2010
327
Butler County, Pa.
I hadn't even thought of 'tinted windows'! ;emgood point!

Thank you for the info you compiled/shared. I had no idea that there was a way
to hurry along the drying process for backyard use. Clever!
 

FreddieFire

New Member
Feb 6, 2022
3
Cumberland Plateau
I've been struggling with the 6-mil plastic in my mind because I know it's not very UV resistant. If that stuff sits out in my area very long you can easily tear it apart due to the UV degradation.
Now house wrap on the other hand can weather the sun, wind, rain all season long and it still looks just like it did when it came off the roll. Your design probably needs to be devised around the 9' width, but that would be a small price to pay for having a material that would last years and not be a throw away after each kiln build.
Any thoughts on house wrap given that it's not clear? Home Depot currently sells a 9x150 roll for $105. The 12x100 roll of throw away 6-mil is $70.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,455
South Puget Sound, WA
They make UV-treated plastic film for greenhouses. That will last much longer.
 

FreddieFire

New Member
Feb 6, 2022
3
Cumberland Plateau
Good point! I'll snoop around at pricing. Plus the added advantage of NOT having to advertise with your woodpile 😁.

Still intrigued by house wrap for some reason ... interested in thoughts.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,471
Woolwich nj
As be green said.. greenhouse plastic. You will get years out of it. using material that blocks the sun slows the process. The sun is what drives the kiln. Your building a mini greenhouse around the wood.. using house wrap around the wood is putting it in constant shade..
 

Dfw245

Member
Jan 28, 2022
161
Dallas
Looks like I'll be joining this trend also. I'm in Texas so I'm sure the heat will be even more of an asset. Also have a bug problem. I'll see if the kiln remedies that
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,471
Woolwich nj
Looks like I'll be joining this trend also. I'm in Texas so I'm sure the heat will be even more of an asset. Also have a bug problem. I'll see if the kiln remedies that
I just responded to the other thread.. you should be ok doing a kiln
 
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DonTee

Minister of Fire
Dec 1, 2021
672
Upstate NY
Question for you guys, and excuse me if it’s already been mentioned. Has anyone ever used their existing woodshed to make a kiln? For example, I have a woodshed with a flat metal roof. It’s green steel that gets pretty hot. How about wrapping the four walls with plastic, and leave some vents on the tallest part but the rafter ends?

Maybe it wouldn’t trap as much heat in because the roof is solid, but it might do something. Just wondering if it’s been tried before.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,573
SE North Carolina
Question for you guys, and excuse me if it’s already been mentioned. Has anyone ever used their existing woodshed to make a kiln? For example, I have a woodshed with a flat metal roof. It’s green steel that gets pretty hot. How about wrapping the four walls with plastic, and leave some vents on the tallest part but the rafter ends?

Maybe it wouldn’t trap as much heat in because the roof is solid, but it might do something. Just wondering if it’s been tried before.
There is a member here that has a complete 4 sided board and batton shed. Pretty sure it is in NC. Can’t recall who it is.
Found it.
Post in thread 'Show Us Your Wood Shed'
https://www.hearth.com/talk/threads/show-us-your-wood-shed.181210/post-2525713

It’s gotta be in nearly full sun and well enough sealed to trap the heat but allows moisture out. And really might not have enough time this year.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,471
Woolwich nj
Question for you guys, and excuse me if it’s already been mentioned. Has anyone ever used their existing woodshed to make a kiln? For example, I have a woodshed with a flat metal roof. It’s green steel that gets pretty hot. How about wrapping the four walls with plastic, and leave some vents on the tallest part but the rafter ends?

Maybe it wouldn’t trap as much heat in because the roof is solid, but it might do something. Just wondering if it’s been tried before.

I would just do the kiln and not take a chance of the wood not being ready. You can put the wood on racks, wrap it and still fill the wood shed with next years wood to try to get ahead. Your in upstate NY so it gets cooler faster You will.dry faster and longer with the plastic. I did a test this fall/early winter with a mini kiln and it culd be 50 degrees outside but in the kiln its 85.. your not going to get that with just warmth from a roof in a low sun angle condition.