Office Trailer Kiln

[jemmy]

I am in need of a kiln. When I met with my biggest potential client he told me I should get a shipping container and outfit it to be a kiln. I thought this was a grand idea, but I thought of something that I believe to be a better idea. There are many office trailers around my area that are very inexpensive, generally about 500$ for a 8x28ft trailer. These trailers are outfitted with electrical and insulation. My thought is that these things are practically perfect for a DIY kiln, all I have to do is secure the roof, and seal any holes. I have bought a 50x10 for an instant shop, and I wonder with a few heaters, fans, and dehumidifiers I could have my kiln. Thoughts?  

[doc henderson]

A great idea.  A few thoughts.  You will need to seal the inside so the insulation does not get infiltrated with water and decrease insulative values and rot the frame and grow mold.  The other issue is how to load and unload.  Not sure how large the entrance is, but may have to load and unload manually, vs with carts or forks.

[Southside]

I respectfully disagree with Doc. An office trailer will fall apart if used as a kiln. Water will get behind the walls, the floor is not strong enough, insulation value is too low and if it's fiberglass matt will be useless once it's wet. 

Kiln chambers experience high humidity, corrosive air, lots of weight, and up to 160 degree temperature.  Every non needed wall opening such as a door or window will be an opportunity for heat loss and moisture infusion. 

A refigerated shipping container makes the best chamber, but you could build a better chamber from scratch than an office trailer will create.

[GeneWengert-WoodDoc]

I also think that the heat and moisture, and even acidic components emitted from the drying wood, will deteriorate the building.  For reference 1000 bf of fresh oak weighs about 6000 pounds.

A reefer trailer is a wonderful idea, so long as the interior is still sealed and the insulation can withstand 150 F or so. NYLE does have plans for this type of,kiln.

My favorite small kiln building, which from a tax viewpoint is a depreciable piece of business equipment, is a wood frame, 2x8 or 2x10, well insulated, vapor proof, building with a concrete floor (insulated).  Again, NYLE has plans. It will last for,30 years with minimal maintenance unless the brakes on your lift truck fail.  If you can sling a hammer, or nail gun, this can be a financially positive option that should be considered.

[doc henderson]

Well, I agree it is a great idea, but noted are some of the "major" problems.   :laugh:  It sounds economical but may not work well long term and not be convenient to use.  Thanks southside and Doc Wengert.  Jemmy, Doc Wengert has been involved in years of research and published many articles and books, and is the expert that I look to.

[K-Guy]

The trailer wall insulation may not be rated for the temperatures a kiln has and will break down over time on top everything else the others mentioned. Remember a kiln is a severe environment.

[GeneWengert-WoodDoc]

The cost of kiln drying.
In DRYING HARDWOOD LUMBER I provided more detail on the cost of drying.  Here is an example...
We have two types of costs- -

1) FIXED are those costs related to the kiln and equipment.  Fixed costs occur every day, even when the kiln is,not running.  (The best example is the kiln and equipment cost, called amortization.). It is this cost that directs us to use the kiln as much as possible so these costs are spread out over a lot of BF of lumber, which means these costs will be low.

2) VARIABLE are those related to the cost of RUNNING the kiln.  The best example is electrical costs.  They only occur when you are actively drying.  To keep these costs low, we might use lots of insulation to save energy.

So when we want to consider drying costs, we need to look at both.  A rough estimate for a 10 day kiln cycle with DH might be $35 variable costs (mostly energy) and $50 fixed costs (building, DH compressor and labor).   Now assume a kiln building and the compressor have a total cost of $30,000.  With a 20 year life (compressor less and building more), that means $1500 per year.  If you dry 10 loads a year and 3000 bf in each load, that means the building cost and DH cost are $50 per MBF.  With air drying, you could dry 20 loads a year or more dropping this cost to $25 per MBF.  The overall point is that you can afford an expensive building if you use it a lot and then with all the lumber, the building is cheap

[jemmy]

Is it really that harsh of an environment? I couldn't take the moister out the air at a fast enough rate to avoid ruining the insulation? I have a feeling I am going to need to build, but I am baffled that kiln only lasts 20 years, especially if I were to build it myself. Seems like a big headache. My other thought is to air dry the lumber and then finish it off in the office trailer so I avoid the vast majority of the moister removal, and thus creating a far less harsh environment in theory. 

[doc henderson]

Jemmy, we have all been there.  It might last a good long time and you can then make a better one.  If it is a hobby thing no biggie.  Not sure what your investment will be in time and money and I guess you have to decide if you want to try it.  Not the end of the world if it is not perfect or only lasts for a few years.  But before someone jumps in, we are trying to help you not potentially waste your time and money on something that may not last.  If you are content to use it knowing that, go for it.  We are just trying to help you foresee the potential problems.  Again it will have to be hand loaded.  It may not be designed for that kind of wt.  You might surprise us all.  good luck.

[Southside]

I just re-read your first post.  Like Doc said - if this is a hobby then that is one thing, but it appears to me you are trying to make money doing this.  A couple problems you will encounter with what you initially described in addition to the building are that most electrical devices have a 40C or 104F degree safety cut out in them, so your fans and dehumidifiers won't operate above that temperature, you could run into issues with getting moisture out of certain species or below certain MC.  Heat treating / pitch setting to an acceptable level will also be a problem with a 104F limit.  

Nobody is trying to discourage you, the folks who have responded here with replys that were opposite of what you were hoping to hear have quite a lot of experience with drying lumber so they are giving you real world advice.  If you are anywhere near someone who has a kiln then I would suggest contacting them and visiting one day when the kiln is running, this way you can see for yourself how things operate, how much water vapor is suspended in the air, how much circulation velocity is necessary, what is involved with door seals, loading, etc.  Then you can make an educated decision about how effective your idea would be.  Perhaps it would work very well for you, but better to know what you are up against before hand rather than once you have invested time and money into it.  

[GeneWengert-WoodDoc]

If you have a car that is 20 years old, it has a lower quality radio system without Sirius radio, it has no air bags for passengers, it probably needs an engine rebuild or at least new brakes and cooling system, maybe a few dents or rust spots, etc.  it is the same for a kiln...after perhaps 20 years you will have major maintenance...new doors, new roof, new duct work, new concrete floor, modern controls with safety features, etc.  But, if you dried 1,200,000 bf in 20 years, the $36,000 for the initial kiln investment is 0.3 cents per BF.

[jemmy]

Dropping 36k on a kiln is currently not an option unfortunately. Maybe in a few years.... I need to get my circle mill running first. haha, I'm 24, in school full time, and I have many (some will argue too many) irons in the fire. And this is one that seemed like an "easy" fire to put out, but with wood working (especially drying) nothing is THAT simple. I will continue to do my research. Any good threads I can refer to for building a kiln? 

[doc henderson]

Jemmy, when you get your saw up and running, I know where you can get good framing lumber and siding ...from trees. lol.  Dr. Wengert has written books and articles.  google Virginia tech solar kiln.  also lots of pages on woodweb as well. Nyle has the construction plans as part of the manual to their dehumidifier kilns.  see link at the left, they are a sponsor, go to resources, click manuals,then choose a manual such as the l200 or the 53,  first 20 pages are all about the build.  also google timber green farms and see a video how to do small amounts on a pallet with plastic.  We all start somewhere, I am 58 and do not have a formal kiln.  but I am a hobbyist.

[Southside]

For what it's worth I don't have half that in my kiln, lot of labor, but with leg work it is possible. 

[jemmy]

Well, I imagine I could do a kiln for a lot cheaper than most believe is possible. I still know it will cost a decent bit of $. Just thought this would be a cheap first kiln to get me going, and I can re purpose the trailer so long as it is not a moldy mess afterwards. I overbuilding things habitually, and I like guaranteed results. Kilns seem to be finicky by nature, that's why I like consulting the experts. I have seen some crazy simple designs for kilns, that seem like they get decent results. This seems to be on the riskier side of a kiln design, and maybe I will go for it. But I am also contemplating a legit build for massive production, just know the $$$ are gonna be coming. This kiln could potentially pay for a big nice kiln. I have to weigh the options. This will not be a permanent solution, I know that. I am in launch mode. Every dollar I make goes back towards my ventures, which I have many different things that need $, time etc.

[jemmy]

For a large build in a concrete pour alone I know I will have a few thousand. Stone, rebar, concrete etc aren't free and thats one aspect, I know structures start racking up quick, and that's not even the highly specialized equipment that is needed for something like this. 

[doc henderson]

Jemmy, I bought the book by timber green.  If you get your mill working you can use some inexpensive things to get started, if nothing else to provide you own materials for the build.  The insulation that can withstand the temp and humidity is a big expense.  They show you now to make a solar kiln on a pallet using plastic.  Is it going to wow people?  Some.  look at that video.  read about the VT kiln that Doc Gene helped design and study.  You may have all the materials you need for that,  and then get your mill sorted out.  Best Wishes

[doc henderson]

what are you studying in school?