Just built a little lumber kiln

[DaltonPaull]

I've been getting tired of buying wood while I wait for nicer wood that I milled myself to dry out so I decided to build a little lumber kiln. My objectives where to build something that would be easy to load, compact and efficient, use minimal materials and be usable year round. I settled on a 4'x4'x10' large "coffin" design and think I'm on the right track. Of course I have no experience with lumber kilns so I'm expecting a steep learning curve and some trial and error.

The kiln is based around a Frigidaire FDL70S1 70 pint consumer dehumidifier and also includes a fan to provide constant air flow (the dryer hose the fan blows into can be seen in the pictures but the fan is hidden by the wood.) At first I thought I could just lift the lid by hand but it's a little heaver than I thought so I decided to use a boat winch I had laying around to raise the lid. The project ended up costing a bit more than I wanted - $500-600 including $260 for the dehumidifier. I tried to find a good used dehumidifier but decided that it was worth paying a little more to get a warranty. Little stuff like roofing, screws and paint really started to add up.

I've had some 9/4 walnut slabs that had been air drying for a while in the kiln for two weeks now and I think I'm seeing a lot of progress with only the type of checking that I would expect (like around the knot in the visible top slab.) I'm shopping for a moisture meter to help to monitor the drying process.

It has been hot in the kiln but not scorching - I keep forgetting to pick up a thermometer when I'm at the store but that will be the next thing I add. Once I know the temp I'll decide if I want to add a layer of Reflectix. I'd rather add insulation and add an additional heat source.

If I want to get really fancy I might use my electrical engineering background to design a embed control system to monitor and control the temp and humidity - but I've got some other stuff on my to do list.

Anyway I just thought I would share my design and see if anyone might have some input that might save me some headache.

 

[mtngun]

That should work fine. Only issue I see is the power required to run the dehumidifier. But, considering your climate, a dehumidifier is probably justified.

Good job.

 

[crashagn]

The fan with the dryer hose is that putting fresh air into the box or you using it for a exhaust? Also the dehumidifier - do you have a hose on the water tank so you dont have to keep dumping the tank? If this works out for then let us know how it goes. I already got a stack of roofing steel, screws and framing lumber from salvaging a hay shed, old dehumidifier down in the basement running and a fan i can get ahold of easily. Got some maple i slabbed out 3 months ago that is out in the old storage shed that i would like to use soon. If it works ill build 1 but something i can move around with the tractor forks and also the front would open up so i can get forks into it as well to make stackin easier on me

 

[DaltonPaull]

The fan is to recirculate air - there is no exhaust. As far as I can figure, the dehumidifier takes care of the moisture and introducing outside air would only make the dehumidifier work harder. Kilns without dehumidifiers (like solar kilns) do need to be vented.

I do have a hose to drain the dehumidifier, although at first I had it kinked and the dehumidifier tank filled up anyway.

I'll let you know how pleased I am with the results.

 

[bytehoven]

How about using Tyvek as a venting membrane?

Based on GoreTex, Tyvek allows moisture vapor to escape but will not permit water droplets to get back into the kiln.

I thought as air pressure builds in the kiln from increased heat, rising moisture could work thru a Tyvek membrane around some portion of the kiln top.

I have thought about building a smaller kiln, just small enough to dry freshly cut oak, a little at a time.

 

[Daninvan]

DaltonPaul,

Nice piece of work! I built a kiln using ply and insulation that does not look near as well done as yours. I think it'll work well, the only things I'd suggest to look out for are based on the fact that it is located outside. Mine was outside as well (Vancouver BC) and I found a couple things about that which caused me to eventually move it inside.

First, it was difficult to bring it up to "operating temperature" when it was cold outside. Like close to freezing or below. I wound up putting in a couple lightbulbs in which proved inadequate, eventually put in a 1000w ceramic heater.

Second was the temperature stability was not that good. The kiln tended to get colder when it was cold outside.

Anyways, I'd be interested to see what kind of results you get over the winter. Like I said, yours looks a lot more skookum and better insulated than mine.

Dan

 

[WoodChuck'r]

That's really cool. It's small, but a damn solid setup!!

Rep'd.

 

[Brmorgan]

I'll say it looks solid! It has some similarities to the one that I built a couple years ago. I used a couple heat lamps as an additional heat source since my dehumidifier won't kick on by itself at room temperature in my house - the ambient humidity is usually 20-35% at most unless it's a hot, rainy summer day. I posted a thread with some pics of my kiln box a few months ago HERE[/COLOR][/B]. It might give you an idea or two.