Vacuum drying

[2feathers Creative Making]

I run two 4500sf dehumidifiers in my basement at all times. They aren't quite as efficient as they used to be, but they keep it reasonably dry considering how humid it gets outside here in PA. It's been about 43%RH over the last 3 days according to one of my sensors. I suppose i could run another small one in the kiln, but i figured that might be overkill.

This is also verified by the wood one had in my shop a while. It all sits around 7-8% per my lignomat.

View attachment 278044

If you are planning to kiln inside the basement and open vent the air to the basement to be dried back out, that should work

 

[Big Ry]

I was just going off what i saw online for a DIY kiln, and it didn't include a dehumidifier. I assumed the water vapor would leak out cause it's really not truly air tight no matter what. But if that's not the case, then I'll do whatever. It's just gonna be a really really tiny kiln, so space is limited.

 

[Mike1950]

If you are planning to kiln inside the basement and open vent the air to the basement to be dried back out, that should work

Maybe

 

[2feathers Creative Making]

I defer to the guy who owns a kiln on this comment

 

[Mike1950]

I was just going off what i saw online for a DIY kiln, and it didn't include a dehumidifier. I assumed the water vapor would leak out cause it's really not truly air tight no matter what. But if that's not the case, then I'll do whatever. It's just gonna be a really really tiny kiln, so space is limited.

I buy a cheap indoor outdoor humidity thermometer. Do not get the wireless unit. It is self destructive in the hot humid environment.
You might vent into basement. Getting the moisture out of box is needed. As I said before there is a lot of moisture. I know you are talking small but basics are the same.
100 lbs of green maple 25 bd ft weighs Dry is 75 lbs. 3 gallons of water. I am always amazed how long 1500-2000 lbs of produces drip a minute. 2000 lbs of maple = 500 lbs water. 60 gallons.
You have to have plan for water.
I run a little hose outside of kiln. When it gets too cold I have to pay attention. Hose end freezes and it becomes a closed system. Dehumidifier overflows and it just circulates the water inside kiln.
Add a couple small fans to circulate.
Good luck.

 

[Mike1950]

I was skeptical at first. There was a member here that sold plans on ebay. I had looked at inside of giant steam kiln and did not think it could be that easy. It is. Dehumidifier. 2 cheap 20" box fans and I was impressed.
IDry , + fast and little degradation. - because a vacuum is not heatable, it uses thin metal panels that you place between the boards. This heats the wood. Also adds a bunch of work and time.
I was at Bohlkes in Cincinnati. They had a vacuum kiln that had just been delivered. Looked like a mini sub. I do not know how it worked.
The metal panels - me- and my tractor are definitely not compatible...

 

[Big Ry]

Well i suppose i can just add a dehumidifier, though how does steam drying work then since that obviously requires moisture. That has me confused now.

As for a vacuum, i figured i might try that if it was substantially faster. But it doesn't sound like it would be unless i invested in much nicer equipment.

 

[rob3232]

@Mike1950 is there a chance that it was a steam powered boiler that produced heat for the kiln and not a “steam kiln “?

 

[vegas urban lumber]

How much faster would you estimate it is to dry this way vs air drying in a controlled environment like a house?

I wonder if its possible to reduce/eliminate the risk of water vapor getting into he pump by using extra long hose or some sort of secondary chamber that exceeds the volume of the vacuum chamber. The logic being that the entire volume of the vacuum chamber would fit inside the hose/secondary chamber, so you would reach full vacuum before any water vapor can reach the pump. You could even run it through a filter of silica pellets to capture any moisture that makes it to the end. Though that filter idea might not be worth the expense. Or perhaps an even better idea would be to setup a makeshift condenser. Put a large volume of the hose in an ice water bath to cool it down enough to turn back to liquid and be drained.

yes at the dentist the vac in your mouth runs through a secondary jar to drop moisture out of air on it's way to the vac pump

 

[Mike1950]

@Mike1950 is there a chance that it was a steam powered boiler that produced heat for the kiln and not a “steam kiln “?

Oh it was definitely powered by steam. Mill created own electricity with scrap. I really do not know. I worked nights at planers. I do know there was steam? Rising from 2 kilns in winter. Looked like it was on fire.

 

[Big Ry]

@Mike1950 is there a chance that it was a steam powered boiler that produced heat for the kiln and not a “steam kiln “?

I thought walnut needed to be steam dried to stay dark?

 

[Mike1950]

@Mike1950 is there a chance that it was a steam powered boiler that produced heat for the kiln and not a “steam kiln “?

What kind of kiln do you use?

 

[Mike1950]

I thought walnut needed to be steam dried to stay dark?

@rob3232 is probably right. Steam powered.

 

[Mike1950]

I thought walnut needed to be steam dried to stay dark?

In my opinion air dry walnut has a lot more variations in color. Steam sorta blends all into more of same color. Easy to see difference side by side.