Small kiln...anyone built one?

[Daniel McCurdy]

My father was wondering if it would make sense to build a small kiln to help finish up drying some lumber and speed up the stage between being stacked outside and being ready to work. From 14% down to maybe 9%-8%.

Just something sized to fit boards for one or two projects is what he was thinking.

I've seen a couple of simple plans out there, just thought I'd ask around here for any experiences you've had with this.

Thanks

[Stephen Edwards]

I don't know anything at all about the mechanics of kiln but there was a guy around here, passed away now, who built a small one in his back yard that he somehow rigged to work with the compressors from old air conditioners. If I understand it correctly it didn't work with heat, rather, it was as if it "dehydrated" the lumber. I do know that it worked and that he would dry lumber for other folks, too. Sorry, I can't be of more help.

[Daniel McCurdy]

Interesting.

I failed to mention that we were just thinking of something that would have a window and basically just be a solar kiln. Realizing now that I should have put solar kiln in the title :o

[Neal Clayton]

an airtight box with a dehumidifier from the borg pumping out through a garden hose works well. my stepbrother has a used shipping container (like an 18 wheel truck container) that we dry ours in with a dehumidifier and two fans, but any smaller box should work just as well.

[John F. Snyder]

Plans to build a solar kiln are availble from Virginia Tech (I believe). Information is available at www.woodweb.com (http://www.woodweb.com).
John

[Scott T Smith]

If your fathers lumber is already at 14%, simply have him place his boards in an attic for a couple of weeks.

[Mark Bolton]

For a small run Neal probably has the easiest solution. We have a small solar kiln (1 - 1.5 Mbf). Works great but it will involve building it permanent on your site.

You can KD small runs quickly many ways using the attic as one post mentioned, building a simple air tight tent around the lumber with 6 mil poly sheeting and using a small heater and fan, or the dehumidifier.

The tent option, or an option like it that you could setup and take down as needed would be a great option if you dont want a dedicated building on your property somewhere. It would also make loading the kiln a breeze as you could just stack your lumber and assemble around it. One of the chores of a kiln that doesnt have a car, is loading it.

Mark

[Jamie Buxton]

Here's a new book about vacuum kiln drying with a shop-built kiln. http://vacuumkilndrying.com/ He says he dries lumber in days to weeks.

[Bernhard Lampert]

Here is the link to the VA Tech solar kiln. http://www.ext.vt.edu/pubs/forestry/420-030/420-030.html

The plans are a free download. VA Tech also offers a 3 day course on the building and operation of the kiln.

Eventually, I plan to build one for my personal use.....eventually.
Cheers,
Bernhard

[Mark Bolton]

Here is the link to the VA Tech solar kiln. http://www.ext.vt.edu/pubs/forestry/420-030/420-030.html


Almost identical to the kiln we built. Only difference is we made ours end load as I plan to build some angle iron rails and a car with steel V groove wheels to make loading and unloading a breeze. This way we can fork a lift of stickered lumber onto the car, roll it in, and fork it off.

Climbing into the kiln to sticker/stack is a real PITA even with two people. Its exhausting with one. The design you posted allowing the entire back to open would be a bit easier but still a lot of work.

For anyone interested, I think you can build a car for about 300.00 with the wheels being the most expensive part. It would of course cost you 2-3 courses of board volume but the ease of loading/unloading would be huge.

Mark

[Bernhard Lampert]

Almost identical to the kiln we built. Only difference is we made ours end load as I plan to build some angle iron rails and a car with steel V groove wheels to make loading and unloading a breeze. This way we can fork a lift of stickered lumber onto the car, roll it in, and fork it off.

Climbing into the kiln to sticker/stack is a real PITA even with two people. Its exhausting with one. The design you posted allowing the entire back to open would be a bit easier but still a lot of work.

For anyone interested, I think you can build a car for about 300.00 with the wheels being the most expensive part. It would of course cost you 2-3 courses of board volume but the ease of loading/unloading would be huge.

Mark

...not intending to hihack this thread, but I am curious about your experience with your kiln. Can you share some of your experiences/success? What kind of wood/thickness have dried?

BTW. I plan to build the kiln with open access on the back side so I can load and unload with my loader.

Cheers,
Bernhard

[David Freed]

I have dried lumber in solar, dehumidification, and vent type kilns, usually air dying first. As Mark said, there are many different kiln designs and temperatures to run them at, but they all dry lumber the same way; by lowering the humidity inside the kiln. The drying lumber is constantly raising the humidity, but the kiln gets rid of the moisture one way or another. The faster you are trying to dry the lumber, the more you have to pay attention to conditions inside the kiln. Companies that have large commercial kilns have someone constantly watching temperature, humidity and air flow speed day and night. A solar kiln is one of the slowest kilns, so checking it once or twice a day is fine. Drying in an attic is slower yet and checking it every few days is good enough. If you don't have a hot attic or barn loft to stack it in, you can make an "imitation" attic by simply making a box out of plywood or osb and paint it black. A small crack (1/4" to 1" depending on how many bf are inside) on the top on one side and the bottom on the other side acting as vents will let the moisture escape. A solar kiln is much more complicated in comparison.
This link will give you enormous amounts of info about drying - http://www.woodweb.com/cgi-bin/search/search.cgi?Realm=All&Terms=solar+kilns&submit.x=11&submit.y=9#reference

Bernhard,
What species and how thick are you wanting to dry?

[Mark Bolton]

...not intending to hihack this thread, but I am curious about your experience with your kiln. Can you share some of your experiences/success? What kind of wood/thickness have dried?

BTW. I plan to build the kiln with open access on the back side so I can load and unload with my loader.

Cheers,
Bernhard

The spot where we built our kiln loading from the back was not the best so we went the end route. Using the loader is by far the best way as, like I said, hand loading is a real chore and hard on the back.

With regards to use and operation it has been simple and straight forward. Thickest material we have dried so far has been 8/4 (we sawed at about 2 1/2"). Mostly 4/4 and 5/4 though. We have only run perhaps 10-15Mbf through total. Mostly chestnut oak and hickory with a little maple and poplar. Our work has been so busy that we havent been able to saw and dry as much as we planned. That said, the nice thing with the solar kiln is that it doesnt need much babysitting once you get the initial drying out of the way. If you are going to be tied up for a few days just close it up a bit, the kiln saturates and drying slows.

We have followed Gene Wengert's advice on woodweb and havent had any surprises so far but they will surely come. Most of our drying is not pressed for time so we tend to take it slow. If you follow the species guides with regards to rates it goes pretty smoothly. We tend to run a bit slower than the recommended rates partly due to location and partly due to the fact that we often dont saw a lot in the dead of summer. This puts us drying in the fall/winter when the kiln simply operates slower.

If you have access to green lumber reasonably its a very worthwhile investment in my opinion. Having our own small band mill and about 80 acres of timber on our land its great for us if we could only free up the time to saw more.

Mark

[David Freed]

I have dried approximately 250,000 bf in batches of 500 to 4000 bf per load. If you are going to get into kiln drying full time, I would suggest that you read as much as you can about kiln drying. As John said, http://www.woodweb.com/ is an excellent place to start. I have spent 100 to 200 hours reading as well as the experience I have, and I don't know nearly everthing there is to know about drying lumber.

The last kiln I built is 9 1/2' x 22 1/2' (inside dimensions) and 10' tall. I built it with large vents and put an 80,000 btu lp gas heater and a Nyle L200 in it so I could use it as a vent style, dehumidification, or a combination of both. One entire wall is a 10'x24' door that rolls on an overhead track to load and unload through. I have had it up to 180* (that is HOT) when I was setting the pitch in a load of pine.

Venting moisture while running the Nyle defeats the idea of having a sealed dehumidification kiln, but it allowed me to dry more bf per load when drying poplar. You need to remove at least 10% moisture per day when drying poplar, which is 50+ gallons per day in a 3,000 bf load. It required the Nyle and the vents to keep up.

[Ed Peters]

plans from Virginia Tech and massaged the sizes a bit. It is currently being built and you can see pictures of the process at www.crookedlittletree.com (http://www.crookedlittletree.com)
Click on the BTSACLT button (Behind The Scenes At Crooked Little Tree) on the opening page. The overall size of my unit is 10' tall on the north wall. 8' front to back(north wall) and 18' let to right. The front wall (south wall) and the roof will be opened and closed with a cable and winch arrangement. More pictures will be added as the work progresses. Unfortunately the rains have slowed our progress.

Ed

[paul dyar]

I agree with Mark, mine opens from the back, and it is still a lot of work to load and unload. I can imagine it would be much harder to load from the side. I have dried 2 loads of 1” red oak, and now have pine in it. Some is 1” and some is 2”. I was fortunate to have some doors and windows left over from remodeling jobs, so mine has double panes of glass. I use thermal controlled attic fans, so they only run when it is hot enough. Didn’t keep up with the cost to build it. The inside dimension is 9’4”x 8’
paul

[Mark Bolton]

Drying in an attic is slower yet and checking it every few days is good enough.

Actually, attic drying can be way too fast especially in the early stages when you have to take moisture off slowly. There is no means of control in an attic so if you really want to get any quality lumber out it has to be pre-dried (air) quite a bit.

If anyone loads pretty green lumber to an attic they are likely going to have surface checking to an extent that is unrecoverable.

Kiln drying lumber is like anything, the faster you want to do it, the more difficult it becomes. I dont think anyone considering a solar kiln is looking for "fast".

Mark

[Mark Bolton]

I agree with Mark, mine opens from the back, and it is still a lot of work to load and unload. I can imagine it would be much harder to load from the side. I have dried 2 loads of 1” red oak, and now have pine in it. Some is 1” and some is 2”. I was fortunate to have some doors and windows left over from remodeling jobs, so mine has double panes of glass. I use thermal controlled attic fans, so they only run when it is hot enough. Didn’t keep up with the cost to build it. The inside dimension is 9’4”x 8’
paul

Paul,
How are you setting the pitch in pine in a solar kiln? We dont saw much pine but I have always wondered about sources of auxiliary heat for setting pitch. the heat loss of the glazing in a solar kiln would seem to make sustaining setting temps a real chore. After that, equalizing the lumber would again be a pain.

For these reasons we have stuck with hardwoods but we really like pine. We have found some decent sources for rough pine (tough to do in WV) so the pressure is off.

Mark

[Scott T Smith]

Actually, attic drying can be way too fast especially in the early stages when you have to take moisture off slowly. There is no means of control in an attic so if you really want to get any quality lumber out it has to be pre-dried (air) quite a bit.

If anyone loads pretty green lumber to an attic they are likely going to have surface checking to an extent that is unrecoverable.

Kiln drying lumber is like anything, the faster you want to do it, the more difficult it becomes. I dont think anyone considering a solar kiln is looking for "fast".

Mark

Mark is correct regarding attic drying of "green" lumber in the summer time. During the winter though, depending upon where your attic is the environment would probably be similar to a solar kiln in the spring or early summer - warm during the day and cool at night.

My original recommendation was caveated on the fact that the lumber in question was already at 14%. There is no drying related danger from placing 14% MC lumber in an attic.

Lumber drying rates vary depending upon species and thickness. Certain species, such as pine and cypress, are very difficult to damage in a kiln because they dry so quickly. Other species, such as oak and sycamore, can be extremely challenging due to the relatively slow rates required (3% daily target for 4/4 oak).

The most critical time of the drying process is taking your lumber from green down to 35% MC. Most of the degrade occurs during this time, but it does not usually reveal itself until the lumber has dried below 25%.

I too operate a DH kiln and concur with David's comments.

Much time is spent in loading, and then baffling a kiln. If you have a forklift or something similar, side loading is much more expeditious than end loading. If your only option is to load from the end, then a rolling cart on a track allows for faster loading because you can stack and sticker outside.

[Alan Schaffter]

Before anyone dives into making and using a solar kiln, I strongly suggest they read the stuff published by the USDA US Forest Service, Forest Products Laboratory, VA Tech and U. Wisc. All are available online directly or through WoodWeb. Look especially for stuff written by Dr. Eugene Wengert or Dr. Brian Bond. Here is are some of them:

Air Drying Lumber (http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr117.pdf)

Kiln Operators Manual (http://www.woodweb.com/knowledge_base/fpl_pdfs/intro_gloss_index.pdf)

Wood Industry Fact Sheet; Solar Drying Basics (http://www.wvu.edu/~agexten/forestry/wooddr1.pdf)

I would be very skeptical of something like the vacuum kiln mentioned in an earlier post- not that it doesn't work, but the info and the claims at the link that you can dry wood in a few days are misleading or a real stretch of the truth. Each species has an optimum drying rate- exceed that and you can end up with a pile of checked and warped fire wood- see the third link. A solar kiln is not a Ron Popeil "Set it and forget it" proposition.

The second link above states:

"A kiln schedule is a carefully worked-out compromise
between the need to dry lumber as fast as possible and,
at the same time, to avoid severe drying conditions that
will cause drying defects (ch. 8). It is a series of dry and
wet-bulb temperatures that establish the temperature
and relative humidity in the kiln and are applied
at various stages of the drying process. Temperatures
are chosen to strike this compromise of a satisfactory
drying rate and avoidance of objectionable drying defects.
The stresses that develop during drying (ch. 1)
constitute the limiting factor that determines the kiln
schedule. The schedules must be developed so that
the drying stresses do not exceed the strength of the
wood at any given temperature and moisture content.
Otherwise, the wood will crack either on the surface
or internally, or be crushed by forces that collapse the
wood cells."

[David Freed]

Actually, attic drying can be way too fast especially in the early stages when you have to take moisture off slowly. There is no means of control in an attic so if you really want to get any quality lumber out it has to be pre-dried (air) quite a bit.

If anyone loads pretty green lumber to an attic they are likely going to have surface checking to an extent that is unrecoverable.


Up to this point we were talking about air dried lumber. Daniel stated that his lumber was 14%, and in my original post I stated that I air dried most of my lumber before putting it in a kiln. I still stand by my statment that a solar kiln would finish drying his lumber faster than putting it in an attic.

If you want to talk about drying lumber without air drying first, I have dried 8 or 10 loads that way and it does require much more monitoring for the first 1 or 2 weeks while the moisture is high. You can't put green lumber in any kiln and just turn it on full speed.


Kiln drying lumber is like anything, the faster you want to do it, the more difficult it becomes. I dont think anyone considering a solar kiln is looking for "fast".

That was my point exactly. Daniel is just wanting to finish drying a few boards, which is why I suggested a simple box painted black. It would be slow, but I wouldn't recomend that they go to the time and expense of building a complete solar kiln for a few boards.

When I first read through the posts in this thread, I missed your suggestion of a plastic tent. I will agree that idea would also work with the exception of it being airtight. The moisture has to get out somehow. I am pretty sure you know that and just misspoke. The tent would also be a lot cheaper and quicker than a permanent kiln.


My second post was in response to Bernhard, who seems interested in an ongoing drying situation.

[Randy Smith]

If this is just for an occasional load of 100 bd ft or less, there have been articles written on simple insulated boxes built inside with some heat source (light bulb) and ventilation, or a standard dehumidifier. I think that would work well.

If you're set on solar and don't want to go all out with a full sized kiln then I think some sort of plywood box with a plastic film collector along with some black painted surface would be an easy build. I run a 500 bdft VT kiln and it works nicely (albeit a tad slow). I've tried to collect lots of info on my kiln construction as well as solar kilns in general and consolidate them in one place (www.solarkilninfo.com) so check it out if you get a chance.

[paul dyar]

Mark,
I am new to the solar kiln process, what I don’t know for exceeds what I do know. My plan is; after the pine is down to 7 or 8% to shut the fans off. As I stated I have double glass on it, and hope this will hold enough heat. I know it will get to 125 degrees in the summer with the fans running. I have read where they will get to 200 degrees without the fans. If it doesn't get hot enough, I will put heat in the kiln. Will let you know how it works out.
paul

[Daniel McCurdy]

Thanks everyone for all the info. Also, thanks for keeping in mind that I'm only looking for a finish up solution. A couple of points I wanted to add here...

This will be an occasional use situation, but we're looking to have something set up that's always available when needed. Not sold on solar, but looking to keep from having to use the level of electricity something like a dehumidifier would require.

Attic isn't the way we want to go.

Will check out some of the links provided and also keep updating on some of our ideas.