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rdecker
rdecker's picture
Solar Kiln operation
I've had my HD36 for about 4 years now and love it, but I no longer have the patience for air drying. I am looking to build a variation of the Virginia Tech solar kiln but I can't find any guidelines on the operation of the kiln. When should the vents be open and closed, is there a rule of thumb based on the humidity of the boards compared to the air etc.? I am a retired engineer so I have been know to "over think sometimes, maybe it's as simple as vents closed for the first 3 weeks and wide open the next 3 weeks... anybody have and input on "Vent operations"? Thanks RD
eddiemac
eddiemac's picture
The best source for wood drying information is the Woodweb Sawing and Drying Forum: woodweb.com/cgi-bin/forums/sawdry.pl
rdecker
rdecker's picture
Thanks, I'll check it out
eddiemac
eddiemac's picture
How much to open the vents baffled me at first too. I dry hardwoods such as oak and walnut, and always air dry them first. I've never found a need to open the vents more than 1" (at the start); and as the moisture approaches 6-8%, the vents are almost closed (about 1/8") - intake and exit. If you begin with green wood, you will need to start with the vents almost closed and gradually open up as the moisture leaves the lumber (to prevent drying too fast and damaging the lumber). Much depends on the species of lumber you are drying.
rdecker
rdecker's picture
So generally speaking: Closed until 12-14%, 1" open until 6-8% gradually closing until 6%. How long do you leave them in the kiln once it hits 6%?
eddiemac
eddiemac's picture
I assume you could open the vents in a gradual fashion as the lumber moisture goes down from green. You just have to make sure the lumber is not drying too fast; and there are techniques to measure that (check Woodweb). If you get to 6 or 7%, the lumber should be removed to prevent over-drying (which encourages cupping and brittleness). And the 1" vent opening only applies to hardwoods - many softwoods can be safely dried at a faster rate. Drying technique is somewhat species specific, so don't take what I have said as universal.
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