DH Kiln Minimum RH?

[firefighter ontheside]

I thouhgt I remembered reading an answer to this question at one time, but I can't find it.  What would be a minimum RH that I wouldn't want the kiln to drop below?  I dry lumber in my shed with a dehumidifier.  I only put air dried lumber in there.  I assume there is much less risk of case hardening with previously air dried lumber, but is there still a risk.  My kiln got to about 106deg and RH of 18% after about a week of drying.  I am not supplying additional heat, just the DH running constanly supplied the heat.

[K-Guy]

If you are at 30% RH, the wood will be around 5% which is too dry, Aim for 6-7% for hardwoods and 10-11% minimum. Now if you DH has just quit, then it may only be the air that is that dry and it will rise again as the wood gives off more moisture. I would begin checking with a moisture meter from 40% down to prevent over drying it.

[firefighter ontheside]

The wood was all at around 15% moisture content when I put it in.  My target is to get it down to about 7%.  I have a very large DH in there right now since my little residential one bit the dust.  It doesnt have any kind of humidistat.  It's just on or off.  I just checked and its back to 100deg and 19% RH after having had it turned off for 36 hours.  During the time I had the DH turned off, it got down to 80deg in there and about 35%RH.  I still had fans going.  I'm going to switch it off again for a while I guess.  Of course this is all just to get this load dried and perhaps one more load before I remodel the chamber and add an L53.

[kelLOGg]

Firefighter, I have used a room DH unit for 10 - 15 years - actually, several units. I started out letting it get as hot as the DH unit would get it (~140°) and it wouldn't take the heat and I had to replace it. Now I don't let it get over 90° so drying takes longer. Been using the same unit for ~5 years now. How did you decide on 100°? I can get below 30%. Kiln meaures 6 x 6 x 16.

[doc henderson]

What is the MC of the wood now?  If it is done then just maintain.  If it has a ways to go, then leave the fans on and let the wood catch up.  Maybe if your DH is that big, it is getting ahead of how fast the moisture can leave the wood.  also the end MC will be based on the average not minute to minute RH.  I have a container that I store dry wood in, and only run the DH once a month, and usually when it is cooler and the RH is higher.  I would keep the fans on low and use the capacity you have paid for (electricity) and keep moving water from the wood.  If the humidity is 45% at night when the temp drops you should be ok.

Edit:  It took twice to write this as we had a few minutes down, but the second one I copied and made 3 tries to past and send.  now we are up and I was able to paste my response from an hour ago and not have to re-write.  

[firefighter ontheside]

With letting the kiln sit idle, but making sure the RH didn't get about about 25 or 30%, the moisture level in the walnut in question is about 8.5% using my hammer probe on the delmhorst.  I think that is going to turn out just fine assuming that when I heat it up to sanitize it will lose another percent.  I assume that in letting it sit with the DH off, the moisture in the core was able to move toward the outside and even out the level throughout.  

 @kelLOGg I chose 100 deg as a temp that I assumed would not kill the DH.  My original question was about not letting the RH get too low.  I was concerned an RH too low could cause checking or case hardening if the core was still in the teens and the edges were getting down to around 6% or such.  I have to decide if I'm going to dry anything else in the shed before I buy the Nyle.  If I want to dry more before then, I need to get a replacement room DH.  This big dryer I have is just too big for the job.  It overpowers the shed.  Plus I can't plug it into my little digital Inkbird controller that I have.  The DH doesn't come back on just by having power.  I have to push the button.  So I could set it to turn off when the temp gets to 100, but then I would eventually have to turn it back on manually.

[doc henderson]

how big is this thing?  can you run a contactor/relay or does it reset off each time with no power?  what is it out of?  glad you have lots of options.

[firefighter ontheside]

Once the power is turned off to the unit it takes a finger to press the on button to get it to turn back on.  My old room DH would turn right back on as soon as power was restored.  It's a Drizair LGR2000 and weighs 132lbs.  It's upper temp limit is listed as 100deg which is why I don't want it to get hotter than that in there.  I don't mind ruining a little residential unit, but I don't want to ruin this thing.  We bought it when my wife's office basement flooded and I needed to dry it out.  I got it used, but still wasn't cheap.

[doc henderson]

well you can hold it in reserve for those type emergencies and or when you start a wet load in the kiln if needed.  cool (and dry)!
like a magnetic switch.

[firefighter ontheside]

I tried it when I put my first load of wood in the kiln.  The temp outside was in the 90's and the thing overpowered the kiln within hours.  It works Ok when the temp outside is cool like now, but even then it eventually heated up over 100 in there.  Yeah, we will keep the thing and it will go back to her office to live in the basement, because I don't have room for it here.  That thing is not easy to get up in the truck at 132lbs.

[doc henderson]

Well, have that son of yours help you.  It would work great in a larger storage area, that just needs a lower RH to store dry wood.  I bet if you had a buddy that does heating and air, you could find a connection to cycle the compressor on and off, if it was important to you so it could be controlled.  humidity and temp control.  If you are ever this way, I have a friend, and we do stuff like this for each other on a trade basis.

[firefighter ontheside]

Oh he does when he's around, but I do most of my business work on weekdays when they are in school.  It's on wheels and I figured out that I can use some 8' boards as ramps and roll it up and down.  That requires that I remember those boards to bring with me to the office.  Having that type of control on this unit would make a big difference, especially if I had somewhere to keep dried wood like your container.  I will likely buy one of those containers one of these days.

[doc henderson]

I think the price of those is still in the "bubble" but good to follow the price, or find one that someone wants to get rid of.  I bought mine at Sturdy built and I think the price is double what I paid.  Lets call it the "double bubble"!

[firefighter ontheside]

Yeah, they appear to be coming down a bit.  $1800 for a 20' container.  I've been hoping to find one at auction.

[doc henderson]

Mine is open on the ends, and 4 doors that all open up nearly the whole side (18 feet out of 20) and have a heavy frame to keep the whole thing aligned.  they are 5 K now last I checked.  I may check back.