Solar Kiln Basics

The next thing that we want to do is talk about kiln drying and the advantages that kiln drying brings to lumber. We looked at that air dried stack, and one thing we know is that it's only going to dry it down to about 12 or 14%, and it's going to take a long time. Well, my friend Dave Munkittrick is here. He's been working wood for about 30 years as a professional and amateur woodworker. He's also got some experience with finding opportunity wood, just some unusual stuff that's come off of woodlots and had some experience working with, and drying that material.

So Dave is going to help us out on kiln drying. So go ahead, Dave, and tell us, give us some of the advantages that kiln drying brings to the woodworking table. Well, kiln drying over air drying, of course, the biggest advantage, to my mind is the controllability. You can control the rate of drying, and by doing that you can not only speed it up over air drying, but you also reduce the number of defects that you might get in, while you dry the wood. So I'm going to get, from a kiln drying process of any kind, I'm going to get a better quality product.

You'll get a better quality product in less amount of time compared to air drying. And final moisture content out of the kiln? You should be able to get it down right where you need it around 6% to 8%. So for our cabinet and furniture work, we want to bring that moisture content down. Really the 12% to 14% out of air dried isn't low enough.

We want to get that down to a lower moisture content, which then, what's the big advantage to that for us? Well, the reason you want the low moisture content is it allows you to put your furniture that you've made in a house that has climate control. So the big thing is in the winter time, when you're heating that dry air, the air in your house dries out. And if your wood is too wet, it will keep drying and shrinking and your furniture falls apart. So with the air dried stuff, as stable as it gets in that pile, it's still very prone to expansion and contraction in a house environment.

Yeah, well it'll continue to contract is the big thing. Yep. Cause it'll, it'll want to dry out to about 8%. That's where the wood will reach what they call equilibrium moisture content, and in a heated home that's right about at 8%. Okay.

So our big bullet points with kiln drying are, lower moisture content and speed of drying. Now in a kiln, we know that with that air dried stuff it's going to take what seems like forever. It's maybe going to take a year. What can we expect out of a kiln? Well, depending on the species, anywhere from two to six weeks.

So months to weeks. When I, when I cut that stuff on the saw mill and I'm all excited about working with it, it's going to significantly reduce the wait time for me to get that stuff in my shop, and start playing. Now I know that you've air dried wood. You also home built a dehumidification kiln. Yep And the latest version, Dave 03 here, is the solar kiln that's behind us.

And this is pretty cool. Simple technology, right? It's as simple as it gets. It's a, as close to set it and forget it as you can get. All right.

Well, next thing we're going to do is Dave's going to give us the tour of the greenhouse back here, the solar kiln, and talk about how that works. Well, Dave, I think the solar kiln is really neat. It's very low tech. Why don't you just walk us through a little bit, tell us kind of the 30,000 foot view of how the kiln works and what it does? Well, as you can see, I mean the construction is very simple.

I mean, the only thing you really have to be concerned about is your roof angle. And here in Wisconsin, 45 degrees is just about right. So that makes it even easier to build. Other than that, you just want to be able to keep the elements out. You don't want it raining in there, or snow piling up or anything like that.

So, beyond that, there's not a whole lot more to it. Parts are removable, the roof comes off and the front comes off, so it's easy to load. So really what you've got here is a, it's a greenhouse. Basically a greenhouse. And we're letting the sunshine in there, trapping the heat as best we can.

Yep And just the heat of the sun is gonna heat the wood, drive the moisture out of it. Yep Now, what about air temperature inside here? Well, I like to put a remote thermometer in here. You can just buy them at Radio Shack. They're fairly inexpensive.

And I put the receiver over in my shop. So even on a cold winter day, I can just take a look at the receiver and just see what the kiln's doing. And that helps me set when the fan runs. There is a fan inside to circulate the air through the stack. That's fairly important.

So today it's about 65 degrees outside. What's your temperature inside here? I had a reading of 135 degrees. That's pretty impressive. That's warm, yep.

That's pretty impressive. All right, well next step, let's have a look at the inside of this and see what makes it go. Okay. Well Dave, you're, you're right about simplicity. This looks like a very simple garden shed.

Give us, give us the lowdown on the mechanics of how this thing goes. Well, like you said it is a very simple design. Starting at the back, you can see we have vents at the top and at the bottom, and that's just help with the air circulation. Sometimes you want to get rid of moisture and bring in that fresh, dry air. This is the fan plenum, which just, it's suspended between the two walls and there's a gap in behind it.

And it's designed to push the air, the hot air down off the roof, and down in front of the pile, through the pile, and back up underneath. And just to circulate air through the pile, which is very important to dry the wood. And then the pile starts on these blocks of wood. Again, keeps the stack up off the floor and aids in circulation going through. So it's all about air flow.

Yep. Keep the air moving. You do have to have air flow. It can't just sit there stagnant. So, and this provides enough air flow for this size kiln.

You want to have a certain amount of air flow going through each layer of the stacks. And what separates the layers are these stickers. You see these are well used and you just lay 'em on there. A layer of boards, and then a layer of stickers and build it right up to about here. And then usually, in fact always, we weight down the stack with these blocks and that helps hold the pile tight so it doesn't warp.

None of the boards warp as they dry. And we paint everything black cause that really helps build the heat in the, inside the kiln. So once you've got this loaded, we know that you can you can watch the temperature from the comfort of your shop. Yep. And that gives you some indication about maybe opening and closing your vents, top and bottom, to maintain the right temperature inside here.

And it also let's me know when to have a fan turned on. Now, the fans on a timer. You don't want the fan running all day long. There's no need for that. It really only needs to run when the temperature gets up there.

So I have it set right now for about two hours after sunrise, and it shuts down about an hour before sunset. Well, Dave, about how many board feet you think you can load into this kiln? Oh, this kiln can easily do a couple of hundred board feet. Wow, this is pretty cool. So this really is something that, you build this little shed looking thing in your backyard, and as long as you have a good Southern exposure, the average woodworker can load this with lumber and very successfully dry their own lumber.

Yep. I did some poking around on the internet before we talked. There are plans everywhere for these solar kilns. In fact, I saw one very similar to this, just a little bit bigger scale. And the guy is loading 2000 board feet of wood into that kiln, very effectively drying it.

So, really cool. I love the low tech aspect of this. I love the way that we're making the sun do the work. So, thanks for taking the time to share this with us today. You bet.