Home-Built Wood Drying Kiln Questions

[internet.user.human]

Hi there,

I've built my own 4' x 4' x 12' wood drying kiln with fire resistant plywood, rockwool, and plastic wrap around the outside of the kiln. I use a small 70pint dehumidifier paired with a box fan when I put freshly milled wood in to draw out as much moisture as I can for about a week. My normal loads are >100 BF of red maple, red oak, white ash etc.

Once I've reached a general 6-8% M.C. (checked with a prong moisture meter - I know, not the most accurate but I'm learning and starting out small) I take out the dehumidifier and box fan. I then fire up two 500W halogen work lights inside the kiln and get the kiln up to ~170 degrees F. I leave it there for 24 hours for sterilization of all the buggies.

My concern/question is, I never see the dehumidifier pulling any water out. The basin/container is bone dry, and the hose I have hooked up never empties any water into my bucket outside of the kiln. With just the box fan and the dehumidifier running, the kiln reaches about 120 degrees F and 25% R.H. I monitor this with an Inkbird temp and humidity controller (linked for reference). My question is, am I seeing this because my wood loads are so small? Or is the dehumidifier not working? I've tried two dehumidifiers and get the same result. By the time I'm all done with the process the wood seems to be pretty stable and I haven't seen any indication that the moisture content ramps back up, in my basement the wood usually stays around 8%. So I guess I shouldn't complain but I expected to see more water being pulled out of the loads. The picture showing the wood inside the kiln right now is very small even for my normal. I usually have 3 or 4 more rows of planks stacked and stickered.

See photos of my setup, attached. Any suggestions or thoughts would be helpful. Thanks!

 

[Assembler]

Great thread and thanks for posting.
My tip would be:
Desiccant dehumidifiers tend to be smaller, lighter and can be quieter than compressor units. Whilst compressor dehumidifiers only work well in warmer temperatures (over 20°C), desiccant units extract the same amount of moisture in any temperature between 1-20°C.

My second tip would be to add a generator for the 2 lights and use the head off of the generator to speed things up as far as getting the temperature up to near 200 degrees.

 

[internet.user.human]

Thanks for your reply. Any idea about why I’m not seeing any water being gathered? I’m not too concerned with noise as when I shut my doors on the kiln I can barely hear anything the compressor when it’s running.

I’m only running those two lamps on a 120V circuit so I don’t think I can justify adding a generator and putting it in my basement at this time.

 

[Assembler]

Thanks for your reply. Any idea about why I’m not seeing any water being gathered? I’m not too concerned with noise as when I shut my doors on the kiln I can barely hear anything the compressor when it’s running.

I’m only running those two lamps on a 120V circuit so I don’t think I can justify adding a generator and putting it in my basement at this time.

I forgot that you had this dryer indoors.
My guess is that the compressor has to be vented to the outside in order to work the best.
Go look at the specs on the compressors to see what the working factors are for best water removal to start with.
The compressors likely have an ideal temperature range to work in.

 

[Up A Creek]

The two dehumidifiers I have only register down to I believe 30% humidity. It's possible they can't dry the air anymore than that? Both of mine are just basic Box Store dehumidifiers. You may need something more specialized?
I built a small Kiln in my basement with 2 in insulation panels. I didn't get any water in my dehumidifier either. I got plenty leaking out onto the floor though. I used a space heater with the thermostat removed and an external thermostat with a box fan. I did it the first time without the dehumidifier and the second time with it.

 

[internet.user.human]

The two dehumidifiers I have only register down to I believe 30% humidity. It's possible they can't dry the air anymore than that? Both of mine are just basic Box Store dehumidifiers. You may need something more specialized?
I built a small Kiln in my basement with 2 in insulation panels. I didn't get any water in my dehumidifier either. I got plenty leaking out onto the floor though. I used a space heater with the thermostat removed and an external thermostat with a box fan. I did it the first time without the dehumidifier and the second time with it.

Well, what confuses me is that if I take either one of the dehumidifiers I’m using out of the kiln and just run it in my basement, I get a full tank of water in them in about an hour and a half. Surely the air in the kiln with all that wood should have plenty of moisture to pull out right?

I haven’t noticed any moisture on the floor of the basement or inside the kiln when I’ve used it. Just some condensation on the plastic wrap in the summer time. I’ve been trying to only dry in the winter if I can help it because it gets muggy in the basement and I started to see mildew behind the rockwool in the large door of the kiln. Which makes me still think the compressor is having a hard time actually doing it’s job….maybe I should leave the small door of the kiln cracked open a bit?

 

[internet.user.human]

The two dehumidifiers I have only register down to I believe 30% humidity. It's possible they can't dry the air anymore than that? Both of mine are just basic Box Store dehumidifiers. You may need something more specialized?
I built a small Kiln in my basement with 2 in insulation panels. I didn't get any water in my dehumidifier either. I got plenty leaking out onto the floor though. I used a space heater with the thermostat removed and an external thermostat with a box fan. I did it the first time without the dehumidifier and the second time with it.

Oh, also wanted to ask if your efforts were successful and the wood became useable? So far I’ve been fairly happy with my results; haven’t had any major shifting of the wood after I’ve taken it out of the kiln. Most of my boards were air dried for a few months under my deck before bringing them in to the kiln.

 

[Up A Creek]

I've only ran it twice so far. It's a pain to put up and take down, takes up a bunch of space in my basement, and I can only use so much wood at once.

I was mainly trying to kill bugs. The wood had already been outside for several years under a tarp. I actually didn't expect water the first time I did it. I just had the heater and a box fan. I didn't get large puddles, but water leaked out all around the edges. That's why I put the dehumidifier in there the second time. Still got water, but the dehumidfier was empty. I'm honestly not sure why. Haven't put a lot of thought into it. I may have to soon though, I'm cutting a LOT of wood right now. Considerably more than I had before.
My basement is dry. It's 120 year old unsealed concrete. I don't ever get water in it and it never smells musty. But the dehumidifier will still fill up in a day or so, unless it's been really cold and the outside air is bone dry.

The wood was already split from sitting outside but it didn't get noticeably worse. Hickory with some small pieces of cherry. I didn't check with a moisture meter. It sat for another year in my basement and I'm just now getting around to using it in the next few months (I hope).

 

[Automender]

I can say I used a similar concept in my basement when a blocked drain got an isolated spot in my carpet wet. I also had used the idea when my portable AC unit in my bedroom leaked condensate into my carpet. I put a dehumidifier under a tent of 6 mil plastic and let it run. Both times the tank got filled in 24 hours and the carpet was crispy dry.
A 70 pint unit should draw 500 to 700 watts so it should heats thing up. I think your issue is the rate in which the water can leave the woods surface. It seems like it is really slow. Does the humidifier cycle very much. It can be running the fan but there is no humidity in the inside air so the compressor shuts off. My humidifier had a constant on function.
If you sticker the wood you need to have the fan blow parallel to the stickers to get good air flow over the wood surface.
A test would be to place a few wet towels into your kiln and see how long it takes to collect the water in the bucket.

https://www.rockler.com/learn/using... temperature of,Kiln Operators Manual, 1991).

 

[sonny580]

could the water be just evaporating since its a low temp, small unit? PLUS the wood gives up water slower than outside air so it could be just evaporating and going out in the fan air.
If the wood is actually drying down, then it gotta be evaporating!