Cheap kiln

[marshall]

I got sick of waiting for slabs to dry out in my basement so I built a really simple kiln.

The floor is green treated lumber 16" on center using a 3/4" subfloor plywood. The sides and the top are framed using 2x4s ripped in half as well as 1" thick foam board. Sides and back are just screwed together since I am lazy.

Overall, it is 4 feet by 8 feet at the base and 4 feet tall since that is really easy to make with standard plywood and foam boards. Most of my wood is for woodworking and is under 8', but you can easily expand this to a 12' or even 16' length.

Inside there is a household dehumidifier and a small fan. Not sure how well this will work, but figure the it was worth a shot. This breaks down into the base, sides and top for easy storage if I don't need to use it for a while.

 

[marshall]

2nd try at photos...

 

[qbilder]

It will surprise you how well it works.

 

[IyaMan]

Simple and nice. Curious to know the results over time.

 

[Gixxerjoe04]

I want to build a solar kiln next year hopefully, thought about buying a crappy little trailer and moving it into the sun when I'm using it and put it away when not, figured the wife wouldn't want a permanent one in the yard haha. One thought on yours, wonder if you hook up a light bulb inside to create some heat to speed up the process would be beneficial, of course I don't have any experience in kilns, was just a thought.

 

[marshall]

I want to build a solar kiln next year hopefully, thought about buying a crappy little trailer and moving it into the sun when I'm using it and put it away when not, figured the wife wouldn't want a permanent one in the yard haha. One thought on yours, wonder if you hook up a light bulb inside to create some heat to speed up the process would be beneficial, of course I don't have any experience in kilns, was just a thought.

Good question. I have a household dehumidifer in there and a small fan. The dehumidifer provides a bit of heat an in that small space it really makes a diference. I don't have exact measurements, but when it was in the mid 70s in the garage the inside of the kiln was over a hundred degrees.
I am pretty much a hack at these things, but have heard you need to get it pretty hot (above 140 degrees?) to sterilize the wood or set the pitch on pine. Since I don't need to do either of these, I will probably just let it dry out as is.
I am in Minnesota, so later in the year I might need to add a space heater. If I do that I might need to seal and insulate it a bit better.

I like the trailer idea too and thought about it before I built this. I really wanted to build a solar kiln, but didn't think there was any chance of getting that by the wife. This was sort of a compromise that she could live with.

Now the painful part is waiting patiently - I have to resist the urge to open it up everyday to see how the wood is doing!

 

[rarefish383]

I don't call using screws lazy, it's smart. Most anything I build now I use deck screws with the star bits. They don't strip out like phillips, and you can take it apart. We have a whelping/birthing box for our Burnese Mountain Dogs. In two hours we can turn the kids weight room in the basement into a hospital ward for Burner puppies. When the puppies are gone, two hours later, it's a weight room again, Joe.

 

[rarefish383]

I forgot to say I like your kiln. I was going to ask how you empty the dehumidifier, then I saw the hose and 5 gallon bucket, good work, Joe.

 

[Gixxerjoe04]

Good question. I have a household dehumidifer in there and a small fan. The dehumidifer provides a bit of heat an in that small space it really makes a diference. I don't have exact measurements, but when it was in the mid 70s in the garage the inside of the kiln was over a hundred degrees.
I am pretty much a hack at these things, but have heard you need to get it pretty hot (above 140 degrees?) to sterilize the wood or set the pitch on pine. Since I don't need to do either of these, I will probably just let it dry out as is.
I am in Minnesota, so later in the year I might need to add a space heater. If I do that I might need to seal and insulate it a bit better.

I like the trailer idea too and thought about it before I built this. I really wanted to build a solar kiln, but didn't think there was any chance of getting that by the wife. This was sort of a compromise that she could live with.

Now the painful part is waiting patiently - I have to resist the urge to open it up everyday to see how the wood is doing!

I'd be leery of using a space heater for it later in the year, they do generate a lot of heat but I always see stories of people's houses burning down because of space heaters. Don't know if it's caused by them catching stuff around them on fire, like paper or something, or if they short out and catch fire. I've used a space heater in my room before, but never leave it running if I'm not in the room.

 

[IyaMan]

I am in Minnesota, so later in the year I might need to add a space heater.

The most important factor is humidity. Yes, warmer air can hold more moisture (which is why evaporation happens more in hot weather), but if the humidity level is very low, then the evaporation rate is fairly similar at any temperature. As long as it stays above freezing and the humidifier is running, you'll be fine without the heater. @Gixxerjoe04 makes a good point about the dangers of an unattended space heater, not to mention all the additional electric it will suck up.

 

[Richard 1353]

Good question. I have a household dehumidifer in there and a small fan. The dehumidifer provides a bit of heat an in that small space it really makes a diference. I don't have exact measurements, but when it was in the mid 70s in the garage the inside of the kiln was over a hundred degrees.
I am pretty much a hack at these things, but have heard you need to get it pretty hot (above 140 degrees?) to sterilize the wood or set the pitch on pine. Since I don't need to do either of these, I will probably just let it dry out as is.
I am in Minnesota, so later in the year I might need to add a space heater. If I do that I might need to seal and insulate it a bit better.

I like the trailer idea too and thought about it before I built this. I really wanted to build a solar kiln, but didn't think there was any chance of getting that by the wife. This was sort of a compromise that she could live with.

Now the painful part is waiting patiently - I have to resist the urge to open it up everyday to see how the wood is doing!

The most important factor is humidity. Yes, warmer air can hold more moisture (which is why evaporation happens more in hot weather), but if the humidity level is very low, then the evaporation rate is fairly similar at any temperature. As long as it stays above freezing and the humidifier is running, you'll be fine without the heater. @Gixxerjoe04 makes a good point about the dangers of an unattended space heater, not to mention all the additional electric it will suck up.

hey how are you my name is Richard I have ask this to a few sawmills how to cry my logs and lumber fast no one to me so. Some idiot told me a inch per year on a log I'm thinking no I would die if I had to wait to cut my first log ha ha. Really I don't think that is true

 

[Philbert]

Marshall,

How has it worked so far?

You might look through stuff like these for more technical info:

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf

Or try contacting the guys at the research center in Madison (I am much farther east of you, so things may be different over my way).

Philbert
Saint Paul, MN

 

[IyaMan]

hey how are you my name is Richard I have ask this to a few sawmills how to cry my logs and lumber fast no one to me so. Some idiot told me a inch per year on a log I'm thinking no I would die if I had to wait to cut my first log ha ha. Really I don't think that is true

Welcome to the site. Inch per year is the general rule, but varies widely depending on drying conditions, wood type, and wood thickness.

Using a kiln is good to dry fast, but even using a fan in a dry place inside would be a big help. Just be sure to have enough space between your boards.

 

[marshall]

It worked out great. We had a fairly warm and damp summer, but the little kiln was dry as a bone. Two small fans were the key to keeping the air circulating and the wood drying out quickly.

I didn't take exact moisture measurements, but just from the sound of knocking the wood together as well as the change in weight, the boards were dry enough. I am letting them sit in a dry basement over the winter to sort of even out and level off to inside humidity.

I have heard the inch a year guide, but I agree with IyaMan - fans are the way to go. One other suggestion - clean the saw dust off the boards. I don't know why, but saw dust on the boards really seems to slow down the drying. I have no scientific guess why that would be the case, so it might just be my perception. Either way, doesn't hurt.

 

[Picaso]

if you cut any blanks at the same time then you can use that damp sawdust in a paper bag to help keep them from drying too fast.


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[marshall]

I was asked to provide an update -
I have only dried a couple of loads with this kiln, but both worked pretty well. It was cheap and really easy. I didn't need to touch it while it was running.
The dehumidifier I was running inside of it has a setting for target humidity. At 25%, the dehumidifier just runs nonstop and the air temp inside gets to over 110 degrees. I thought that was overkill and probably a waste of energy, so I set the dehumidifier to 30% and it rarely turned on, but the inside stayed plenty dry.
The key to the system is the fans. They really do the work.

The other lesson learned is also old news to most of you, but it is about strapping the boards together and putting weights on top to keep the slabs straight. I use simple tie down straps that you would use to secure loads on a trailer to keep the boards in a bundle. I also throw big patio pavers on top. Most of the wood I dried turn out great, but I had a few maple boards that I didn't secure enough and they warped pretty bad on me.

I have a few loads of oak to run this summer, but I don't see any real changes I'd make to the base set up. I wish it was bigger, but that is more about garage space.

 

[ChoppyChoppy]

We have a small Nyle kiln and it's basically the same as your setup. Room is about 20x20x12ft tall.
It uses a combo of a dehumidifer, heater and a couple fans. Takes about a month to dry a full load.

 

[Old Blue]

Thanks for the update marshall !

Old Blue

 

[rarefish383]

How thick are the boards you milled? I usually mill mine 12/4 for benches and table tops, so they are pretty thick. Does milling them thinner make then more prone to movement? I would think it would, Joe.

 

[marshall]

How thick are the boards you milled? I usually mill mine 12/4 for benches and table tops, so they are pretty thick. Does milling them thinner make then more prone to movement? I would think it would, Joe.

I milled boards between 4/4 and 12/4. I am not sure if the warping on the thinner boards is worse, but it is a much bigger problem. If I had a thick slab and i warpped badly, I can plane off a half inch for eah side and still have something usable. Not so with the thinner boards.
I had some nice maple that I cut thin and it warpped quite a bit. When I cut those, I left them as rough edge slabs. If I could do it again, I'd trim the edge down to final dimensions and immediately strap the budle together super tightly.
As a diy hack, maybe just cut the boards a bit thicker and plan or resaw them to final thickness.

From now on, I am not going to be cutting anything thin. Save my milling for the big slabs that are unique and that you can't just go to the store and buy.