Solar kiln build in the near future

[Gavin Wellman]

Just scored a great deal on about 4000bf of green lumber (red oak, ash, & some maple, cherry,hackberry, poplar). I hope to finish stickering today. With this much wood I think that I can justify a solar kiln to completely dry it down after it has air dried for about a year. Currently I'm looki at the VA tech plans as my guide. Can you guys give me any tips on do's and don't as I approach this project?

[Bert Kemp]

I thought a solar Kiln was air dried

[Cody Colston]

The VA Tech solar kiln is well thought out and there is actual science behind the design. You can modify the size to suit your needs but adhere to the ratio of solar collector to bf capacity. No need to try and re-invent the wheel. The best tip I can give is to plan the kiln location considering future growth of any nearby trees, etc. I'm faced with moving my solar kiln because over the years, the trees have grown and what was once a full-sun location is now partially shaded.

The Maple lumber will likely stain while air drying. It really needs to go in a kiln asap after sawing if you want to preserve the bright color. The Red Oak will benefit from air drying first. Just be sure to seal the ends or it will check.

I will be interested in seeing pics of your kiln when you get it built...the lumber, too.

[Scott T Smith]

Ditto the positive comments on the Va Tech model. They have both an 800 bd ft and a 2000 bd ft model. I have a 2k bd ft one that has the floor dimensions of the 2k model but the door style of the 800 bd ft model and I use it a lot.

Normally I agree with Cody 100% but in this instance I would suggest going into the kiln green and not air drying got a year with the red oak (presuming that it is 4/4 or 5/4).

Bert, technically all kilns except for vacuum kilns use air flow to dry lumber, so I guess that all KD lumber could be considered AD - LOL! Although I also have Nyle kilns, the solar kiln is a legitimate kiln because it provides greater heat and a system for accelerating and controlling the drying rate over just AD lumber. Mine works do well that I'm building additional ones to augment my DH kilns.

[Cody Colston]

Normally I agree with Cody 100% but in this instance I would suggest going into the kiln green and not air drying got a year with the red oak (presuming that it is 4/4 or 5/4).

I humbly defer to your superior knowledge.

Actually, I ruined some 2" Post Oak by letting it air dry first. It was hot summertime in Texas with a frequent dry, southerly wind. The Oak was full of honeycomb when I began working it.

So, I go directly to the solar kiln with Oak now because I can control the drying rate there. My advice contraicted my own pratices. My bad.

[Scott T Smith]

I humbly defer to your superior knowledge.

Actually, I ruined some 2" Post Oak by letting it air dry first. It was hot summertime in Texas with a frequent dry, southerly wind. The Oak was full of honeycomb when I began working it.

So, I go directly to the solar kiln with Oak now because I can control the drying rate there. My advice contraicted my own pratices. My bad.

Lol. Sometimes if it is in the middle of a hot summer I might AD oak under cover for a few months before going into the kiln, but the rest of the year it is ok to go in green as long as the load is properly sized to the solar collector.

[Tom Hyde]

Just finished and loaded my new kiln based on va tech design with a number of modifications. Since I'm drying mostly softwoods, including western red cedar, I made my collector to board foot ratio a little larger. I currently have about 1100bf in a 8'x18' solar kiln with about 160 sq. ft. of collector.

I used triple wall (double cell) polycarbonate greenhouse panels for better heat retention. They weren't cheap but by purchasing from an agricultural supply warehouse I paid roughly the same as I would have for the wavy single wall polycarbonate at big box. I also put black metal roofing under my 2x6 rafters with the fans blowing air out of a plenum above my height (easier loading and unloading), down over the metal, with air coming out at the bottom through a gap at the front of the kiln and flowing back through the lumber pile. Likely an unnecessary added expense but a bit cleaner design.

The loading doors in the back are unique, as far as I know. They are bi-fold and span a 16' opening (4 doors in two sections) built in the shop using 2x4 construction, fiberglass insulation and sandwiched with 1/2" cdx. Strong, no sag, and at over 100lb a piece, heavy. They are supported in the very center with sliding barn door hardware. I can open them with one finger and there is absolutely no sag. Installed with only a 1/4" gap, or less. After doors were hung, the siding was screwed on slightly oversized to cover the gaps.

The bifolds do limit my loading width to 13+ feet but that's fine for purposes. I just loaded mostly 12' and 13' 12/4 cedar with no problems. Doors open just above height of my trailer. Also, the narrow 24" side access door (also insulated) is handy for quick checks of the charge.

Do build a strong floor, paint everything inside and out, insulate heavily and use a vapor barrier on the inside to prevent moisture inside the kiln making it inside the walls. I also caulked and sealed everything and painted the inside with two coats of aluminum paint (4 on the floor).


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[Cody Colston]

That is an awesome kiln. You obviously took care to build it right. It should serve you well for many years.

[Todd Burch]

Would Red Guard work on the interior for keeping the moisture inside? Seems like a better solution than stapling up some plastic. I just re-did my shower in the master bathroom and used two coats of Red Guard everywhere in the shower. It seems to be a pretty good product.

[Tom Hyde]

Would Red Guard work on the interior for keeping the moisture inside? Seems like a better solution than stapling up some plastic. I just re-did my shower in the master bathroom and used two coats of Red Guard everywhere in the shower. It seems to be a pretty good product.

Not sure about that but to be clear on my kiln I put in the insulation, then stapled the plastic to the studs, then put up 1/2" cdx ply, caulked all seems, then painted over with two coats of aluminum paint. Whatever will help keep moisture from migrating into the walls.

[James White]

Not sure about that but to be clear on my kiln I put in the insulation, then stapled the plastic to the studs, then put up 1/2" cdx ply, caulked all seems, then painted over with two coats of aluminum paint. Whatever will help keep moisture from migrating into the walls.

That is what I did with mine. It has served me well.
I don't see it in the photos. But is there some sort of gaskets to seal the doors? That was one of the biggest challenges for me. Not allowing any moisture to escape so that you can keep control of the RH. I had to resort to some metal brackets and some tapered wedges to put pressure on the doors. That is what finally got me a good seal.

[Tom Hyde]

That is what I did with mine. It has served me well.
I don't see it in the photos. But is there some sort of gaskets to seal the doors? That was one of the biggest challenges for me. Not allowing any moisture to escape so that you can keep control of the RH. I had to resort to some metal brackets and some tapered wedges to put pressure on the doors. That is what finally got me a good seal.

The gap around the doors is only 1/8" to 1/4" and the slightly oversized T111 screwed to the outside of the doors covers most of the gaps. I use cane bolts on the inside to cinch the doors up tight against the jamb and secure them closed. That's another reason to have the side access door - I can lock the kiln with one lock on the side door and with the cane bolts on the inside, it's impossible to get locked inside.

The door fit is so tight, and the doors can't sag with the sliding overhead barn door hardware, that I don't seem to need additional weatherstripping. I might put a bit on the outside hinge sides but I get more air leakage through those vents I have. I used some of the truck canopy stick on weatherstripping under the edges of the polycarbonate panels - worked well and really cheap compared to other options.

Having a short roof overhang on the back also keeps weather off the doors.

Doors partially open:

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[Kevin Beitz]

I followed no one rules but my own... works great.
One fan at the top pulling air in and two at the bottom sides
pushing air out. Thermostat controlled. Cost me nothing to
build it. Inside is painted with Tar and diesel 50/50.

Tar and diesel.jpgTar and diesel.jpgTar and diesel.jpg

[Scott T Smith]

I followed no one rules but my own... works great.
One fan at the top pulling air in and two at the bottom sides
pushing air out. Thermostat controlled. Cost me nothing to
build it. Inside is painted with Tar and diesel 50/50.

Tar and diesel.jpgTar and diesel.jpgTar and diesel.jpg

Hi Kevin. That really came out well. On my solar's I mainly dry oak, so instead of continually exchanging the air I only crack the vents slightly. This helps keep the RH% higher in the kiln and reduce drying related defects.

Best,

Scott