Solar kiln for hardwoods part deux

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
My first thread that was put together for the solar Kiln was not actually intended to be posted, so this time I took the time to try to put together more information.

The wood was split March 30th and the racks were set up on April 6th the wood that was split was all Oak and the moisture readings were between 34 and 37%. All of the wood that was split was Oak and over the course of the next couple of months some additional Beach was added to the top. The total amount of wood is over 2 cords

The racks are from the big box stores just regular 4 foot high wood racks raised slightly above the ground on blocks. The wood was stacked on the racks on April 6th and just top covered until July 4th. As you can see in the pictures below all that we did was add some wood bracing across the top to make a roof the wood was basically zip tied and screwed to the center wood rack and a beam placed to the top so the plastic can be pulled over. We took the staple gun and stapled the plastic around the bottom row then we took contractors stretch wrap and wrapped the bottom of the plastic all the way around the racks of wood to hold the plastic tight. The vents were cut in in a u shape or like a flap so that way they can be adjusted if needed.
The plastic was over the Kiln for approximately a half-hour, the wood really has not had a chance to heat up, the outside temperature was 85 and the inside of the Kiln was already at 126 degrees. I let the air probe sit in the vent for a little while the outside temperature was checked at 90 degrees and the inside of the kiln was at 135 degrees. This temperature was not at the vent, I put the probe through the vent the probe was all the way down to the top row of wood.

Over the course of time I have seen a lot of questions regarding the solar Kilns if you think about it basically you were building a mini Greenhouse or Greenhouse type structure over the wood all greenhouses that I'm sure you have seen are all made with clear plastic black plastic does not make the greenhouse any warmer it makes it cooler by shading you're not heating the greenhouse with plastic the object of the plastic is to trap the air you do not need to add any black fabric to help heat the kiln as you can see 135 degrees will be plenty to dry the wood I will run this Kiln for no more than 60 days after that I will take the Kiln apart and tarp the wood. Trust me all of this wood will be dry within 60 days
Your Kiln does not need to be pretty actually this is the ugliest one I put together it just needs to work. In my area our summertime temperature is in the mid 80s to low 90s so I try to set the kiln somewhere around 114 degrees when it's 80 degrees out. When we have our average temperature it will run plenty hot. The last picture is of the temp and plastic, notice there is no moisture on the inside of the plastic.. a sure sign its running well

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MissMac

Feeling the Heat
Dec 4, 2017
449
NW Ontario
can you post a few pics of the vents that you punched into the wrap, and explain a bit more how you adjust the venting?
 

KJamesJR

Feeling the Heat
Jan 8, 2018
345
New Hampshire
I’m getting some temp differences in mine. I did a top cover using mil plastic and wrapped the bottom half with pallet wrap. The top portion hit 135 today but the bottom portion was only 95. I may have to do a full cover with mil plastic.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
can you post a few pics of the vents that you punched into the wrap, and explain a bit more how you adjust the venting?
The vents are cut in a u shape and are about the size of a grapefruit on both gable ends. Once cut they are like a flap. The larger the cooler the kiln, the smaller the hotter. What you need to do id make a cut, put the probe in and let it sit for a bit. If it gets to warm open it up more
Example.. if the outside tem is 75 and the temp inside is 120 you should open it up more. If its 75 out and the kiln is at 90 you need to close the vent some to build more heat. You need to base your temp on your average summer temp. I set the kiln for aprox 5 degrees lower than the average temperature.. here at my house the summer temps are 85 to 92.. so if i set the kiln up at 80 on the normal temp days it runs hot. Its dosent take long for wood to dry at 135 degrees ...
Once you have the kiln vent set... dont change it. Leave it alone.
You adjust it by its size.. if you cut it to big.. Gorilla Tape works great to seal the cut and make it smaller..you can tape it open to keep it at the desired opening
 
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Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
I’m getting some temp differences in mine. I did a top cover using mil plastic and wrapped the bottom half with pallet wrap. The top portion hit 135 today but the bottom portion was only 95. I may have to do a full cover with mil plastic.
Yes.. you need a full cover from top to bottom
 
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Jan Pijpelink

Minister of Fire
Jan 2, 2015
1,659
South Jersey
For all who still have doubts; I have tried @Woodsplitter67 method, and it works!
 
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Jan Pijpelink

Minister of Fire
Jan 2, 2015
1,659
South Jersey
I tried it last year for the first time. Stack is facing SE. Put kiln up in mid June. Wood was 38%+. Took plastic off mid October. Wood was 16-17%.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
At 60 days time in kiln what is your target moisture level on the wood inside. Thanks for the informative post
Im thinking its going to be about 14 to 18%.
I did a kiln 2 years ago and left it in there to long.. i started in at this time and opened the kiln in october my oak was like 8% and the cherry was at 2%.... wayyyyyy to dry.. 60 days will be plenty...
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
I tried it last year for the first time. Stack is facing SE. Put kiln up in mid June. Wood was 38%+. Took plastic off mid October. Wood was 16-17%.
This year i oriented the stacks going east west. I am 3 rows deep this time. With the sun angle this time of year the sun will hit the kiln north, south, east and west..
 

MissMac

Feeling the Heat
Dec 4, 2017
449
NW Ontario
I set the kiln for aprox 5 degrees lower than the average temperature.. here at my house the summer temps are 85 to 92.. so if i set the kiln up at 80 on the normal temp days it runs hot. Its dosent take long for wood to dry at 135 degrees ...
Hey thanks for the reply! What do you mean by this part of your response? I don't follow you here, but i feel like it's a critical piece of info.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
Hey thanks for the reply! What do you mean by this part of your response? I don't follow you here, but i feel like it's a critical piece of info.
What is the average summer temperature where you live
For me our temps are 85 to 90 degrees
 

MissMac

Feeling the Heat
Dec 4, 2017
449
NW Ontario
let's say about 25 degrees Celsius
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
let's say about 25 degrees Celsius
Ok.. so your average summer temp is like 77 degrees. .
Hopefully your in full sun
Your kiln will not run as warm as mine and your drying time will be a bit longer.. just curious are you doing hardwoods...
On a sunny day thats about 77 i would vent it just enough to het the temp inside to like 114..118 degrees
 

MissMac

Feeling the Heat
Dec 4, 2017
449
NW Ontario
Ok.. so your average summer temp is like 77 degrees. .
Hopefully your in full sun
Your kiln will not run as warm as mine and your drying time will be a bit longer.. just curious are you doing hardwoods...
On a sunny day thats about 77 i would vent it just enough to het the temp inside to like 114..118 degrees
Okay, thanks for the advice - why this particular temperature spread? And i am doing mostly softwoods - jack pine, black spruce, and then also a bit of poplar and white birch
 

Jan Pijpelink

Minister of Fire
Jan 2, 2015
1,659
South Jersey
Just checked the temperature inside my kiln.
Outdoor temp is 85F, inside kiln (which is facing East) 125F measured at 3 different spots.
I love this system; easy, cheap, fast.
 
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Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
Just checked the temperature inside my kiln.
Outdoor temp is 85F, inside kiln (which is facing East) 125F measured at 3 different spots.
I love this system; easy, cheap, fast.
Your right on the money...
I guess i should check mine, i havent really looked at it.. i set it up and then leave it alone
 
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Jan Pijpelink

Minister of Fire
Jan 2, 2015
1,659
South Jersey
just an update.. took some pics at 5pm today.. temp inside was 134. I allso tooka pic of the inside of the kilnView attachment 245829 View attachment 245830
I did a measurement around 2 PM today. It was 102 F in our back yard, in the sun. Inside the kiln it was 135 F. I also stapled plastic to the front of my shed. The two sides and back are open. The shed faces South. It was 125 F inside.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,113
Woolwich nj
I did a measurement around 2 PM today. It was 102 F in our back yard, in the sun. Inside the kiln it was 135 F. I also stapled plastic to the front of my shed. The two sides and back are open. The shed faces South. It was 125 F inside.
I looked inside the kiln and it looks like the splits are drying well already
 

Jan Pijpelink

Minister of Fire
Jan 2, 2015
1,659
South Jersey

Coalescent

Member
Jul 13, 2015
94
New Hampshire
Thank you for this awesome thread, @Woodsplitter67 . I have some questions for you that I hope you don't mind answering.

Questions:
  • Are you using 6 mil plastic? If so...is it "greenhouse grade" or the cheaper 6 mil stuff sold at Home Depot/Lowes?
  • How much space are you leaving between the bottom of the plastic and the ground? Looks like maybe 4 inches or so?
  • Does the plastic wrap underneath, or does it just terminate a certain distance from the ground?
  • Is the top of the framing supporting the plastic 8' from the ground?
  • Can you share the make/model of that thermometer you picture to test air temperature in the solar kiln?
Background: I live in New Hampshire and heat 100% with wood. I moved an hour further north early last November and used wood left by the previous owner, and this spring I finished bucking, splitting, and stacking the rest of the grapple load he left me. I have only perhaps two cords out of that, and I know I need more. I have about 18 acres now and have been felling some red oak, beech, birch, and pine, but I need to speed-dry it... so I am very interested in copying your exact design here.

I have the wood on pallets, with pallets fastened to each end (with bracing). The wood is in two long rows exactly 4' high, each row is 1.10 cord.

Thank you!