Turning my shop attic into a dehumidification kiln?

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Forum topic by bigblockyeti posted 06-10-2017 04:44 AM 1240 views 0 times favorited 11 replies Add to Favorites Watch
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5134 posts in 1743 days

06-10-2017 04:44 AM

Topic tags/keywords: question tip

I’ve toyed with the idea of building a solar or dehumidification kiln for a some time now and while in my shop attic where I have quite a bit of wood stored and I realized I’ve already got most of the kiln right there. It only has gable and soffit vents that would be easy enough to block off, beyond that I would just put a dehumidifier up there with a drain line for uninterrupted extraction, crank the humidistat and let the sun do the rest of the work. I’m thinking I might also need a fan for circulation for equalized humidity and temperature throughout the attic. Any glaring reasons why this wouldn’t work? The only obstacle immediately apparent to me would be trying to get heavier slabs up there which I’m already well on my way to resolving.

11 replies so far

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1747 posts in 2498 days

#1 posted 06-10-2017 11:22 AM

There is a lot of water in wood. Putting all that moisture in an attic, even with a dehumidifier, does not sound like a good idea. Plus, there would be no way to control the drying conditions which can lead to more drying defect like cupping, checking, warping, etc.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln.

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8 posts in 373 days

#2 posted 06-10-2017 11:31 AM


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5134 posts in 1743 days

#3 posted 06-10-2017 12:49 PM

Danny, I was hoping you’d chime in. The moisture was one of my concerns, but the lack of control with the dehumidifier running pretty much constantly and the big variable being the temperature entirely dependant on what the sun and weather are doing on any given day is making me reconsider this. I know the moisture can be incredible, especially when moving a big timber at 50% MC then moving it again when under 10%, its amazing how much water can be in there.

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1319 posts in 3568 days

#4 posted 06-10-2017 12:59 PM

along with the dehumidifier, how about a thermostat controlled exhaust fan on one end, with a vent on the opposite end.

-- Smitty!!!

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2958 posts in 1503 days

#5 posted 06-10-2017 01:21 PM

How do you get the wood up there? Is the gable end open?

What about all that weight? I don’t think trusses are designed to do that, are they?

I don’t think moisture will be a big problem if the attic is roomy a fan will give ventilation.

Overall IMO: Bad idea.

If you want a kiln, I would build a solar kiln.

-- Everything is a prototype thats why its one of a kind!!

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5134 posts in 1743 days

#6 posted 06-10-2017 01:49 PM

I wanted to avoid venting the air out as it would have to be replaced with air of higher humidity than that which had already been dehumidified, it would also be potentially cooler air if the sun had been beating down on the roof all day. I’m not worried about the weight at all, it’s a 13.5’ span with 2×12’s 16” OC and I’m not planning on putting 1000’s of bdft. up there, a couple hundred at the most at a time. I have a pull down ladder in the middle of the shop to get up and down, I’m considering adding a block to the ridge board so I don’t have to push the entire weight of every plank or slab I need up there. An open ended gable like some barns have for their hay loft would be nice but I’m far more interested in moving than dumping any money into where I’m currently at.

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1025 posts in 1583 days

#7 posted 06-10-2017 03:30 PM

Do you have an asphalt shingled roof? Those vents you are thinking about closing off serve a purpose to help reduce heat in the attic to help the life of the shingles and roof sheathing.

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790 posts in 1241 days

#8 posted 06-10-2017 10:54 PM

hope it gets hot enough to kill bugs that could be in the wood.

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435 posts in 1159 days

#9 posted 06-10-2017 11:01 PM

I would air dry the wood first to 15% or less, then finish it off in the attic. Some of my wood is stored on my parent’s farm. I have a few stacks on the top of the barn and a few stacks in the attic of one of the other buildings which has top access through the side. Both get very hot but you can open the doors to adjust for the humidity and get a nice cross breeze.

Before I bring any wood into the shop, I cook it off using my cargo trailer as a solar kiln. A milk heater keeps it warm at night, about 115F. During the day, it gets about 130-140F in the traile when it’s sunny & 85-90.

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1747 posts in 2498 days

#10 posted 06-11-2017 11:51 AM

Yes, if you air dry first, that is a different story. Then, most of the moisture has already been removed, and putting the air dried wood in the attic will not be an issue in relatively small quantities. Since the wood is air dry, no need for precise drying controls and the higher temps will not hurt the air dried wood.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln.

View bigblockyeti's profile


5134 posts in 1743 days

#11 posted 06-11-2017 03:28 PM

That’s another thing that I was curious about, I realize air drying is pretty safe if everything is stacked and stickered properly but the accelerated drying time of significantly higher temperatures coupled with low humidity is something I have no experience with. When you state it needs to be already air dried, is there a specific MC that I should see before hot & largely unregulated drying? I just cut some cottonwood and the MC was registering at 50% (the max reading for my cheap pin meter) so it was likely much higher than that. I wouldn’t dare dump something that wet into a hot uncontrolled kiln as it would do little more than rapidly make for some dry firewood.

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