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Thread: Drying in the attic?
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19th November 2016, 08:56 PM #1
Drying in the attic?
Watching the Ventis measure ceiling cavity temp rise above 50° today and humidity drop to almost zero ... I wonder if anyone has tried basically using their attic for kiln-drying timber?
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19th November 2016, 09:04 PM #2
No, but I was almost kiln dried in my studio today!
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19th November 2016, 09:25 PM #3.
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If you put a few pieces of green wood (especially boards) up there in mid-summer the external faces may dry out too fast and you may end up with cooked wood i.e. cracked pretzels.
In other seasons you should be OK
If you put a stack of timber up there, as well as the weight problem there are a couple of other things to consider.
Temperature is one thing but if the air is not moved though the stack i.e. recirculate the air; and some of the humid air is vented you will get bugs growing in/on the wood.
If you want optimum drying speed typically you need considerable air movement.
CSIRO have determined the optimum power to be 4-5 W of recirculation fan power per cubic ft of drying space (not timber volume )and 1-2 W of venting fan power.
The power requirements can be scaled back considerably and still keep bugs at bay but of course drying will take longer.
A whirly bird or two will suffice for venting but remember it only works when the wind is blowing and they also drag a lot of cooler damper air in a night
Some of this cooler air is OK and actually helps the wood relax but ideally the vent fan should sense the humidity and only vent above a set level. This level will change as the wood gets drier.
It works out that the cost of electricity for the fan power becomes a major cost so the timber must be of considerable value to justify the fan power requirements.
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19th November 2016, 11:04 PM #4GOLD MEMBER
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Far be it for a fool like me to argue with CSIRO... but their numbers are...*sighs*... misleading.
Actually their numbers are exceptionally accurate but only in a certain type of kiln operating on a certain species with intake moisture level of x, safe drying rate of y, when thickness is z.Their numbers are perfect for that, but after that you better vary it or you'll turn the charge to cracked pretzels or a mouldy black mess. Actual fan speed will depend on chamber design, kiln type, size/depth/ thickness/species of charge etc etc. You cant dry 75mm boards like 25mm ones, you can't dry a refractory hardwood like you would a softwood, you can't treat a high temp conventional like a low temp conventional, or a DH kiln, or a VacKiln, or an RF kiln... and fan power requirement is directly proportional to air speed requirement, air speed requirement is determined by the depth of charge in the kiln, with a bit of fudge factor relating to plenum design. Well thats if you need air speed at all which neither RF or Vackilns do! So while I dont disagree with CSIRO... I just know that their numbers would blow the doors clean off my kiln, which might be the only way it'll save the wood inside it because if the door dont blow off the load will be toast.
But I agree with Bob, and would also add that you need to think about what a PITA its going to be to get timber in and out of the attic in the first place.
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20th November 2016, 11:02 AM #5.
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Yeah I agree John those CSIRO numbers were for a very specific solar kiln scenario and for optimum speed drying.
What I was trying to say is you can't just stick green wood in a hot air tight box without considering lots of other factors such as those you have mentioned.
I have some slabs under the house, it's cool and dry but its actually a reasonable environment for drying wood. However I stopped doing that simply because the entry way - a 3 x 3ft opening makes it a right PITA to get anything in and out.
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7th December 2016, 07:33 PM #6
I live in Canberra and use my roof space to dry pen blanks I use a normal fan to blow through the stacks proof here never lost a one.
Peter.Nil Desperandum
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7th December 2016, 07:42 PM #7.
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Small dimensioned timber can be dried just about anywhere but there is a bit of a difference between drying pen blanks and drying larger pieces of lumber.
Pen blanks are typically small and even in cross section so will dry more quickly and evenly, any twist developed is small and irrelevant, and being so small the blank is unlikely to crack, and if it does crack there's no great loss involved.
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7th December 2016, 07:56 PM #8
My wisdom here will be worthless, but for pen blanks I just put them into the black cardboard stackable fruit boxes from woolworths and put them on the shelf. They dry out in absolutely no time flat.
MapleMan, DustEater and TasTimbers send me several hundred at a time.
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8th December 2016, 09:49 PM #9
Picture of
some blanks drying in my roof space. I built a quick access ladder into the ceiling in the hallway, can be in the roof in one minute.Blanks drying in the roof.JPG
Peter.Nil Desperandum
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