Solar kiln

Jon1270 said:

On reflection, it could be that kilns meant for drying long pieces of lumber down to 6-8% MC without creating defects like case hardening and checking need to maintain some combination of higher / more consistent / more controllable temperatures and humidity levels, thus the electric fans and insulation that go into those arrangements. Firewood doesn't need to meet the same specs, so something simpler might very well suffice.

If only such a kiln worked in the shade...

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They most definately DO need balanced moisture to dry lumber. The point of a kiln when drying wood for lumber is to remove the INNER moisture with heat, but keeping the air very humid so the OUTER wood doesn't dry out too fast. Most solar kilns I've seen that were designed for lumber had a big pan of water on the floor of the kiln to help keep the humidity high. You wouldn't want that in a firewood kiln.

I like the idea of drawing the vapor up and letting it 'run' off of the inside of the ceiling to the outer wall, where it could drip away......I'm definately going to do this to my shed in some form or another, when I get around to building it.

Scotty Overkill said:

"shiln" (kiln/shed)

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Nice...you need to trademark that Scotty!

Scotty Overkill said:

...Don't worry, I'll take plenty of pics and document the whole project.

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Gotta uphold the namesake...Overkill!

What happened with the solar kilns? Did anybody have success with that method? Would it help to have a condenser in the kiln to take the moisture out of the air during the day?

area_man said:

Would it help to have a condenser in the kiln to take the moisture out of the air during the day?

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If you've got some type of passive ventilation, that should be good enough. I guess the question is, how much? Trial and error would answer that.

Such a condenser would otherwise be called a dehumidifier, and yes, it could help, but dehumidifiers are expensive to run, and the liquid condensed in a lumber kiln tends to be rather corrosive so you need a specialty dehumidifier designed for lumber kilns, which is also expensive.

Is there a 'Whatever happened to..?' thread on the site anywhere?

Like, in this case, Scotty Overkill? Used to be a solid poster - I see other names in other posts that get bumped up too that I kind of had forgotten about until seeing the name again.

EDIT: Guess the forum software edited out the name I typed...

area_man said:

What happened with the solar kilns? Did anybody have success with that method? Would it help to have a condenser in the kiln to take the moisture out of the air during the day?

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They have always worked since they first designed.
If you are uncertain, research solar lumber kiln. The design is simple enough.
An even simpler temporary (and inexpensive) fire wood kiln can be constructed to reduce seasoning time by 60% or so.
If you can't find reference to it, I will detail it out here (again).

Augie said:

Here is a link to an article from Cornell summarizing a study of this very fact. They say that in 3 months 8inch splits and rounds are below 20% moisture content. I will probably tent up 4 full cords this summer in an attempt to speed the process. As Im a new burner I am trying to build up my supply of seasoned wood. By tenting 4 cords I should have enough seasoned for the following winter. Of the 4 I was thinking of tenting some oak in an attempt to shorten the seasoning from 3 years to 2 maybe and then Ill be set for the future.

Looks pretty easy Air in from the bottom and a small vent at the top. priced it out based on my situation looks like it will cost $40 for the four cords for cheap plastic and I have enough scrap lumber to fab up the frame. $40 for 4 seasoned full cord is pretty cheap IMHO.

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Vent at the top is counter productive; you will be venting heat. Moisture condenses and exits as water.
Important factors of construction;

1. Plastic must not touch the wood at any point.
2. Plastic must not touch the earth.

I have been playing with a small scale one this year. One row on a half width pallet. Minimal ventilation and maximum heat gain seems to be the key as others pointed out above. I started out with an open pallet bottom. Not till I put plastic on the pallet was I able to achieve elevated temperatures in the lower reaches of my kiln. My top and sides are fully enclosed with no purposeful venting other than it isn't sealed tight. You certainly do not need active ventilation. If you gap your lid like the Cornell design you will make little more than a solar powered convection current pulling cooler air up through. I do note that the Cornell study completely lacks any measurement of its effectiveness. It just says after 3 months the sample elm was bone dry and burnt freely which is rather short on facts. The Alaska/Fairbanks kiln is also flawed in that they allowed a large area for ventilation and did not try to maximize heat gain.

i dropped a white oak in april this year, split and stacked on skids by may 1st. i wrapped it in 6 mil clear plastic and only had the bottom foot exposed, on aug. 1st i lifted the plastic to only cover the top. today i pulled 5 pieces from different parts and have between 19%-24% moister. this is only my first full summer to mess around with the solar drying, by next summer i will build a structure.