Solar Kiln Q&A

A few basic questions about solar drying kilns, answered. December 8, 2012

I am considering building a solar kiln using the Virginia Tech design. I am hoping to build the larger capacity model and wondering if anyone has experience with this. How forgiving are these models for the novice? Can dried lumber be left in the kiln for storage? I have read that the dried lumber can be wrapped in heavy plastic and stored and the moisture content will stay nearly as is.

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
What species will you be drying? The key for oak is 1 sq ft of roof to 10 bf of lumber. This is true even if the kiln is half full, so then cover part of the roof. The ratio changes for wood that needs faster drying for color or other reasons. You can store lumber in the kiln after drying, but the heat may melt the plastic in a fan. It is better to build two kilns when going much over 1200 bf capacity. The kilns are pretty much foolproof if following the directions for building and operating. That was a key item when I designed them.

From the original questioner:
Thanks. I will first be drying walnut 4/4, 5/4, 8/4 in different loads. Is it okay to air dry for a few months first? It may take that long to get it built. Or should it go into the kiln ASAP? I could speed up my schedule for building it. The ends of the boards will all be sealed and properly stickered and weighted under cover in an outbuilding. I will also be drying some cherry, oak, poplar and probably cedar.

I guess I was not clear in my storage questions:
1) Can you just leave wood in the kiln as is, uncovered, to store?
2) Can dried lumber be stored wrapped in heavy plastic, off the ground a foot or so, in an outside unheated building, without regaining moisture?

So you would suggest two smaller kilns, which is fine for this 8 foot lumber, but I would like to dry longer material at a later date (up to 16').

From Professor Gene Wengert, forum technical advisor:
Air drying for walnut and the other species you mention is okay, if it is done correctly. In answer to your questions, yes to both. Smaller kilns are generally better, but length is important.

From the original questioner:
Thanks. How about this idea? Build two smaller kilns (Virginia Tech) joined together with an adjustable, insulated, removable center wall. It could be run as 1 or 2 units as needed, or remove or adjust the center wall to fit the desired length lumber.

From Professor Gene Wengert, forum technical advisor: