Dehumidifier Kiln: Part Deux

**Full Disclosure**–I have recently heard from Daren Nelson, the original designer of this kiln.  He was not happy with my “ample deference and credit” to him for the design of this kiln.  I contacted him and had a nice 42+ minute conversation about copyright law and the general nefarious nature of stealing someone else’s intellectual property.  Though  I do not agree with his assessment of my well-meaning description of the construction of his kiln, I am happy to make the changes in this post that he requested.  Please note that I am providing only general advice as to the construction of his kiln, and can comment only on the successes/failures that I, myself, have encountered.  Daren offered, and delivered on,  his promise to provide any technical support needed during the construction of his kiln, and I cannot stress enough the instrumental part he played in the successful operation of my version of his kiln.  Please, if you are considering building your own kiln, visit Daren’s site.  He is the originator of this kiln, and, as such, is the best authority on its operation.

Well, hello everyone (all two or three of you), I’m back from the job from Hell.  The 10 hours/day, 7 days/week work schedule is finally over.  63 or 64 days straight, I don’t know, I actually lost count.  Anyway, I’m back in the shop for some much-needed cussing and swearing at cantankerous tool set-ups, finicky handplanes and the resultant tear-out, and lets not forget that now I have to start a fire every time I spend time in my little slice of Heaven, The Bronze Oak Leaf Shop.  That’s right, that old construction adage that “the heat’s in the tools” just doesn’t flush when you can’t get the shop above 50 degrees.

I’ve noticed a lot of hits on my Dehumidifier Kiln post, and, since I’m almost done drying another glorious load of cherry, I thought it may be a good time to add a little more explanation to the construction and operation of the kiln.  I avoided going into too much detail in the first post so as not to trample all over Daren Nelson’s feelings, being he’s the original designer, but with ample deference and credit given to him, I see no problem in detailing how I built my version of his kiln.

As I said in the first post, it’s almost so simple that it’s silly.  You start out with an air-tight, insulated box, add a small heat source and a fan, (and, of course, a dehumidifier) and you have a d/h kiln.  There is a lot of room for personalizing this box, and I built mine to suit its location, the amount of lumber I thought I wanted to dry per load, and my goal (in the tradition of all novice woodworkers), of minimum cost.  All things considered, it worked out pretty much how I intended.

Location, location, location

I originally was going to build the kiln outside behind the shop.  I thought seriously about where to locate the door to make loading easier, how to weatherproof it, and how well insulated it would have to be.  Thank goodness I came to my senses.  If this is the only place you have to put your kiln, think twice about building one.  Now that I have put three separate loads through, I can’t imagine how much more difficult it would be to have it outside. Weatherproofing, insulating, heating, oh my.

I wound up putting it in the nice large shed I built a few years ago.  It is a pretty big shed, but the kids do have a lot of toys, so I had to move some things around a little.  It was worth it.  Having it indoors is a plus.

Size doesn’t matter

Yeah, right.  As much as we’d all like to believe that one, you need to carefully consider the size of lumber you’ll be drying.  If you’re selling lumber, they like it cut as long as possible.  If you’re using the lumber, you need to adopt some unorthodox ways of thinking about length.  For instance; how often do you really need 10′ lumber? 8′ lumber?  This thought occurred to me the other day when I was cutting the 13’6″ cherry down to 10′ to fit in the kiln.  I thought I was doing the right thing when I cut the bole of the tree at its longest possible length.  I never stopped to consider that I would never need 13’6″ lumber.  I would have saved myself some time and aggravation if I had just cut the log into 2 lengths of 6′ each; a very useable size.

Anyway, the length of your kiln is a consideration, and remember that you have to add a dehumidifier and some fans, too.  My kiln is 41″ high (it had to fit under some shelves), 44″ deep, and 12′ long.  With these measurements, I can dry almost 300 bdft. if it’s stacked right (and if my math is right).  I can fit 123″ boards max, and have a separate chamber for the dehumidifier and fans.

Construction

I kept the construction as simple as possible, and it’s not pretty.  OSB and 2×4′s for the whole thing.  My door is on the front and hinged on top so it lifts up and out of the way for loading.  The inside is painted and all inside corners are caulked with silicone.  I used some weatherstripping around the door opening to seal the door, and screw it shut when in use.   **TIP** If you insulate the outside of your kiln instead of the inside, you can remove it for temperature control.  I used a cheap indoor/outdoor thermometer with a sensor that I mounted on the inside wall opposite the dehumidifier.  Just drill a hole, stick the sensor to the inside wall, and silicone the hole shut.

I walled-off a section of the kiln to house the dehumidifier, and I cut the dual window fans into that wall.  I was trying to solve the problem of air circulation through the lumber pile, and I think I’m on the right track.  The wall that separates the dehumidifier from the rest of the chamber is tight to the back wall and the roof, but I left an 8″ gap between the wall and the door.  The fans blow behind the stack of lumber, through the lumber, and back past the dehumidifier.   I also built some louvers to direct the air through the pile.  Click on the picture below to see how I installed the louvers.  They start at the fans and then angle to the back wall, creating a sort of funnel to help with circulation.  It seems to work, but I still have some tweaking to do.

The 2×4′s are removable for loading, then replaced before closing

Operation

Load the kiln, seal it up, then turn everything on.  It took me a day or two to reach 90 degrees, depending on the ambient temps.  The heat source (three 100W light bulbs) is run out separately so I can unplug it when the kiln is up to temp., as per Daren Nelson’s instructions. The fans and the dehumidifier make their own heat, keeping the kiln within the temperature range you want (Reference Daren Nelson’s site for the proper range).  Watch it for a couple days, adjusting the insulation as needed.  I ran a hose out through the wall from the dehumidifier, and I put it into a gallon jug to keep track of how much water is being removed.  No rocket science here, just making mental notes on the amount of water I dump out each day.  I have only dried lumber that has been stacked and air-dried for at least a year, and I usually dump out the gallon jug twice a day for the first couple days.  Then it slows down, and in about a week to ten days it seems to stop.  I let it run for a full two weeks, as per Daren Nelson’s instructions, and only then do I open ‘er up to check on things.  So far, two weeks has been plenty.  I open the door and let everything cool for a day or two, then check moisture content.  If you don’t have a meter, you can safely bet that air-dried lumber is between 6 and 9 percent; ready to move into the shop.

There is a lot more I wanted to say about this, but it’s already been too long since my last post, and frankly, I’m working on something much more witty and thought-provoking than the boring nuts-and-bolts of drying lumber.  However, I will be adding to this post as I run across anything important that I think may help you start drying your own.  I’m adding an email address to this already convoluted mess of a blog in the hopes that any questions, advice, or just plain B.S. about all things wood can find their way to me.  I love talking shop, so don’t be afraid to shout out.  Until I figure out how to put the email link on the home page, I’ll put it here: bronzeoakleaf@gmail.com

Also, I’ve almost completed the Enfield Shaker cabinet, and hope to post pics soon, along with any witty or insightful revelations inadvertently found along the way.  Boy, wait ’till you hear about some of the stupid mistakes I’m capable of. Sheesh.