Kiln Drying in a Heat Wave

      When conditions are wrong, a solar kiln can easily be too hot for good results. Here are tips on controlling drying conditions during hot weather. May 15, 2012

Before I had my motorcycle wreck, I put about 400 bd ft of pecan in my VT designed solar kiln. That was the 1st of May. A couple of weeks ago I checked the moisture content and it was 6%. So broken neck and all, myself, my girlfriend and a woodworking friend cut one log a morning and I now have 1,000 bd ft of lumber to go in the kiln.

We have had record breaking heat here in Oklahoma. My thermometer only goes up to 158 degrees and my kiln exceeds that every day. Should I wait until the heat breaks to put in the 1,000 bd ft of green red oak? Can it get too hot in the solar kiln? The green lumber is stickered and under barn metal waiting for your answers.

Forum Responses
From Professor Gene Wengert, forum technical advisor:
If your capacity is 1500 and you have 1000 bf, then cover up 1/3 of the collector. Avoid having green oak over 110 F. So the kiln can easily be too hot. Control the drying rate so that you do not dry too fast. We do that by keeping a high humidity, especially in the afternoon.

In your present heat wave, even air drying can be too severe, as the humidity can be under 30% when it is over 100 F, even when our body says it is hot and humid. Check the Weather Channel or and see how dry it really is. Cover air piles with burlap to prevent excessive drying. The steam kiln conditions for green oak are 110 F and 87% RH.

From contributor T:
I agree with Gene - this extreme heat wave has caused havoc on my log pile and may have already caused some loss of lumber to be sawed. Your cut lumber would react even worse and quicker due to the speed it would change the MC rate.

The Anchorseal company also sells a fabric netting for sun protection of log piles. I thought this wouldn't apply to me, but the gotcha bug bit me hard. Part of mine were in a dry shady area (not much damage), but the others were straight out in the sun (ouch!).

From the original questioner:
Correct me if I'm wrong here. I could put it in the kiln and cover the entire collector, keep the vents closed, and run the fan on low. My kiln holds 1,000 bd ft, not 1,500. The way I see it, that would be my best way to keep humidity up and temp as low as possible. What do you think?

From Professor Gene Wengert, forum technical advisor:
Possibly it will work, but if the RH is too high, you will get mold and staining. The best is not to saw oak lumber when the outside conditions are so extreme.

From the original questioner:
Lesson learned! Just part of the learning curve I guess. I hope I don't lose it all. I'll just let it air dry in the outside for a while longer until things mellow out and the MC drops.

From contributor K:
When I've got oak sawn in hot dry weather, I sticker and cover with fabric to limit air movement. This might be the best way to store it till the weather cools. I've got some ground cover weed barrier I'm using. Lets water through, so it's about right for protecting my QSWO when it's too windy/hot/dry.

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