Solar kiln for hardwoods

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
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
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20170708_120414.jpg
 

Jan Pijpelink

Minister of Fire
Jan 2, 2015
1,574
Lindenwold, South Jersey
Great stuff! Thanks for posting.
 
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Akon

Member
Dec 1, 2016
17
Maine
I put together a temporary solar kiln in mid September when I was moving wood and saw I had 1.5 cords of ash that was still low 30s. Used scrap wood and 6 mil plastic 12x6', 7' tall. 3 rows on pallets inside. Hoping it's good to go by Feb. Part sits under the deck so access point isn't in snow. I wasn't sure how big to make vent on top in balance of trying to keep it warm vs letting moisture out. I just used 1" pvc in front and back. I get consistent wind off the water; so, hopefully that's enough.

image.jpegimage.jpeg
 

showrguy

Feeling the Heat
Aug 2, 2015
370
Marysville, Pa.
Thanks for starting this Woodsplitter, my problem is I live in the woods and there's no way I can get full sun all day..
 

chemie

Feeling the Heat
Aug 11, 2018
257
New York City
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
Thanks for sharing your experience. I am very interested. I have four 4x8 and two 4X4 Landmann brand wood racks. We don’t have much space in our backyard so I just gathered about 2.5 cords of seasoned firewood from Craigslist to use in our newly installed BK AF25 insert. We live close by to a city forest filled with fallen dead oak trees from previous storms. I recently cut and split about 10 logs. The moisture of splits range %23 to %30. I’m hoping they could go below %20 so that we can use them in March-April. For next year though, if I could make sun kiln work , I can use it on the oak woods from the fallen dead trees in coming May.
So if I could make it work, they could be even dry in 2 months ( May- June)?
Do you have more pics of your set up that you can share?
Thanks!
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
Thanks for starting this Woodsplitter, my problem is I live in the woods and there's no way I can get full sun all day..
So with out a large solar gain your drying time will increase, but thats not to say you cant get quality results. In full sun i can easy make 2 runs and get sub 20% on both runs. So in your case eather a larger kiln, 2 kilns or just 1 kiln and 1 run. I would say try a 1 rack kiln run and post results which will help people similar to your situation. I believe my first run cost me less than 50 bucks to do and I'm still sitting on some of the material to put together another kiln
 
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Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
Thanks for sharing your experience. I am very interested. I have four 4x8 and two 4X4 Landmann brand wood racks. We don’t have much space in our backyard so I just gathered about 2.5 cords of seasoned firewood from Craigslist to use in our newly installed BK AF25 insert. We live close by to a city forest filled with fallen dead oak trees from previous storms. I recently cut and split about 10 logs. The moisture of splits range %23 to %30. I’m hoping they could go below %20 so that we can use them in March-April. For next year though, if I could make sun kiln work , I can use it on the oak woods from the fallen dead trees in coming May.
So if I could make it work, they could be even dry in 2 months ( May- June)?
Do you have more pics of your set up that you can share?
Thanks!
So the biggest asset to the kiln is the sun and solar gain.. even though i have not proformed a run in the spring and winter. I did a run untill the latter part of october and the temps along with the diration of sun was not what i would consider ideal for seasoning

Also. The wood needs to season on its own some for the process to work. Cutting wood and putting it in the kiln will only hinder the results. The center of the split will have alot of moisture in it and the ends will have shrunk down making it harder for the MC of the wood to drop..
 
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chemie

Feeling the Heat
Aug 11, 2018
257
New York City
Also. The wood needs to season on its own some for the process to work. Cutting wood and putting it in the kiln will only hinder the results. The center of the split will have alot of moisture in it and the ends will have shrunk down making it harder for the MC of the wood to drop..
Do you consider wood obtained from fallen dead trees as pre-seasoned and can directlygo into kiln? I can talk about only one experience that I recently cut 10 logs from a dead tree and after the split , MC was about or below 30. I’m posting some pics so that you can have visual of the conditions of the wood.
d9dd769f81752551d392cc2f5e1d42b8.jpg
06e85129a83f4e03dd80c125c339b01b.jpg
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
Do you consider wood obtained from fallen dead trees as pre-seasoned and can directlygo into kiln? I can talk about only one experience that I recently cut 10 logs from a dead tree and after the split , MC was about or below 30. I’m posting some pics so that you can have visual of the conditions of the wood.View attachment 231178View attachment 231179
If your sub 30 i thinks your going to be ok its going to be hard ro tell from the pics but the wood dose not look green or wet. ..i can tell when the wood is ready by when the stacks start to shift, then you know you have achieved shrinkage..
 
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showrguy

Feeling the Heat
Aug 2, 2015
370
Marysville, Pa.
So with out a large solar gain your drying time will increase, but thats not to say you cant get quality results. In full sun i can easy make 2 runs and get sub 20% on both runs. So in your case eather a larger kiln, 2 kilns or just 1 kiln and 1 run. I would say try a 1 rack kiln run and post results which will help people similar to your situation. I believe my first run cost me less than 50 bucks to do and I'm still sitting on some of the material to put together another kiln
Well, I'm pretty good at keeping a few years ahead, but this solar kiln stuff has my attention..

I sort of tried it this summer with a load of hickory slab wood on my dump trailer, I wrapped the 4 sides and top with a piece of plastic from my sisters green house, left it on for about 6 weeks, some days temps would hit 135 deg.

Since then, they replaced the plastic on the g-house, I got the old stuff, so I have plenty to play with..
 

chemie

Feeling the Heat
Aug 11, 2018
257
New York City
Well, I'm pretty good at keeping a few years ahead, but this solar kiln stuff has my attention..

I sort of tried it this summer with a load of hickory slab wood on my dump trailer, I wrapped the 4 sides and top with a piece of plastic from my sisters green house, left it on for about 6 weeks, some days temps would hit 135 deg.

Since then, they replaced the plastic on the g-house, I got the old stuff, so I have plenty to play with..
What was the before and after MC reading of 6 weeks trial?
 

showrguy

Feeling the Heat
Aug 2, 2015
370
Marysville, Pa.
What was the before and after MC reading of 6 weeks trial?
I did'nt check it after, before though most was under 20%, but a few were 30 +%, I also had a box fan in there blowin the air around..
 

Poindexter

Minister of Fire
Jun 28, 2014
2,049
Fairbanks, Alaska
Awesome, thank you. This build is more or less the prototype I should have done before I built mine.
 

shortys7777

Member
Nov 15, 2017
119
RI
Is the plastic touching the ends of the wood? By the pic it looks like it's wrapped pretty tight. Clearly your still getting good results. I'm going to try this in the spring. Thanks
 

Poindexter

Minister of Fire
Jun 28, 2014
2,049
Fairbanks, Alaska
So basically you got a couple of these from Home Depot:

landmann-firewood-racks-82433-64_1000.jpg

Placed them end to end. The vertical 2x4s at each end. Some rope for a ridgepole, scrap plastic, and you can season two loads (of hardwood) each summer at your location?

Nice job.
 

Poindexter

Minister of Fire
Jun 28, 2014
2,049
Fairbanks, Alaska
The thing I love about this build is @Woodsplitter67 didn't really have to buy anything or use much in the way of tools.

Those H-D racks are everywhere, inexpensive, lots of folks have them already.

The 2x4s he used were plain old 8 footers. No cutting.

For proof of concept you could get the cheapest plastic available. I am using 6mil clear and getting about 18 months per kiln cover, but if you want to just try this you could get the clear plastic drop cloth in the paint aisle for a lot less money.

He did use some paracord, or similar, but what 50, 55 feet? Under ten bucks even up here, more like $3 or 4, even after shipping to Alaska.

Starting from scratch and paying Fairbanks prices I could duplicate this build under $100.

I am willing to bet most of you have most of the parts required laying around already.

IIRC his has an open bottom and three grapefruit sized holes at the top per cord, he is seeing 110s dF, and it works. I am running one cantaloupe sized opening at the top for two cords with a vapor impermeable floor but the bottom edge of the roofing loose and free. I do see 140s dF in the summer, partly because I get 18+ hours of direct sunlight daily on mine at 64 degrees north.

I do agree solar gain is key. Keeping the rain off is nice, but solar gain, high internal kiln temperature, lowers the target EMC (equilibrium moisture content) and increases the diffusion gradient between where the wood is and how dry it is trying to be to reach equilibrium. Solar gain, a hot kiln, makes the wood dry faster.
 

Poindexter

Minister of Fire
Jun 28, 2014
2,049
Fairbanks, Alaska
@shortys7777

As far as plastic touching the ends of the splits, what I see is when ambient is below freezing the moisture coming out of the wood condenses on the plastic and runs down. With ambients above freezing I don't see condensation on the inside of the plastic, i think then the water is mostly going out the top as vapor.
 

shortys7777

Member
Nov 15, 2017
119
RI
Thanks for the clarification. I have everything needed laying around except plastic. That'll be a purchase this winter.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
Thanks for the clarification. I have everything needed laying around except plastic. That'll be a purchase this winter.
The plastic is touching the ends of the splits, the bottom end of the plastic goes all the way down to the 2x4 rail that the splits sit on. There is nothing under the first row of splits to allow the air to work its way through the stacked wood and out the top vents.
 
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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,472
SEPA
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
Good stuff, WS67. Thanks for doing the work and reporting back to The Community.

And to top it all off, you got Poindexter's adulation. That's something.
 

rygar

Burning Hunk
Sep 23, 2013
165
so with a solar kiln, how do you prevent the grain ends from clogging from drying too quickly?
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
Good stuff, WS67. Thanks for doing the work and reporting back to The Community.

And to top it all off, you got Poindexter's adulation. That's something.
Thanks ED i really never planned to post this in its owne thread. I didnt take alot of photos of what i have been doing and i have yet to take more data like how much the splits actually dropped in MC. My next run which will be this spring i will take the time to get more information to share. Im going to be doing a run on white oak this spring.
 
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Woodsplitter67

Minister of Fire
Jan 19, 2017
1,051
Woolwich nj
so with a solar kiln, how do you prevent the grain ends from clogging from drying too quickly?
Best bet is to let the wood season for 2 months prior to the kiln run. That should be good enough to let the rest of the MC run out...
 
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rygar

Burning Hunk
Sep 23, 2013
165
Best bet is to let the wood season for 2 months prior to the kiln run. That should be good enough to let the rest of the MC run out...
excellent. all my wood has been C/S/S for a minimum of 6 months. so its all eligible for proper solar kiln.
 

rygar

Burning Hunk
Sep 23, 2013
165
So with out a large solar gain your drying time will increase, but thats not to say you cant get quality results. In full sun i can easy make 2 runs and get sub 20% on both runs. So in your case eather a larger kiln, 2 kilns or just 1 kiln and 1 run. I would say try a 1 rack kiln run and post results which will help people similar to your situation. I believe my first run cost me less than 50 bucks to do and I'm still sitting on some of the material to put together another kiln
how long is a run?