Custom made kiln help

[dcrice]

Folks, I'm new to this kiln drying process so I appreciate any help or advice you can provide.

I recently built a custom made (insulated) box kiln 4' x 4' x 10' to dry my sawmill lumber in. I'm heating the kiln with 2X 500 watt shop lights. One of which I have plugged into the inkbird controller shown. Even though the actual temp (131deg F) is higher than the target temp (125deg F) this kiln is consistently holding the temp around 125 deg F to within +/-2 deg.  I just added a space heater, as shown in photo to help bring the temp up during the cold nights we've been having lately so that's why the temp was high. I also have 3 fans circulating the air and a dehumidifier to remove moisture.

Anyway, I have the kiln loaded with 8/4 live edge cherry. Most of it is between 15-20% MC. It's been running 3 days and my dehumidifier has yet to pull off any moisture. I was concerned that part of the problem maybe that I do not have any vents. Could this be a problem? Or do I need to add patients?

NOTE FROM ADMIN. PDF IS NOT ALLOWABLE FOR PHOTOS. YOU MUSTBUSE HPG AND YOUR GALLERY

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[K-Guy]

@dcrice 
Your household dehumidifier will probably cut out at 104°F. So you won't get anything at that temp.

[dcrice]

That's good to know. Thanks K-Guy!

[kelLOGg]

I, too, have a room dehumidifier in my kiln. Initially. I let it get as hot as 140°F and that temp would destroy the unit. Now, I don't let it get hotter than 100°F and the replacement unit has survived several years. When the wood is 7-8% MC I remove the dehum unit, crank the heat up to heat the wood core to 133°F for sterilization. That has consistently worked for me.

[GeneWengert-WoodDoc]

You do not mention any fans to move the air through the lumber pile.  Do you have fans or just the DH fan?

Do you also have 3/4” stickers? 

 How are you measuring MC...pin meter with insulated needles driven 1/2” deep on a face or ??

About how much lumber is being dried in your box?

[dcrice]

I, too, have a room dehumidifier in my kiln. Initially. I let it get as hot as 140°F and that temp would destroy the unit. Now, I don't let it get hotter than 100°F and the replacement unit has survived several years. When the wood is 7-8% MC I remove the dehum unit, crank the heat up to heat the wood core to 133°F for sterilization. That has consistently worked for me.

Good to know. I think part of my problem is what K-Guy mentioned. I've been running the kiln at a high temp (125 deg F) and the household DH wouldn't work. I guess I'll need to keep at the lower temperatures for now. It may take longer to dry but it is what it is. How long does it normally take you to dry out Cherry and Walnut to 7-8%? Thanks for the help.....Dr.

[dcrice]

You do not mention any fans to move the air through the lumber pile.  Do you have fans or just the DH fan?

Do you also have 3/4” stickers?

 How are you measuring MC...pin meter with insulated needles driven 1/2” deep on a face or ??

About how much lumber is being dried in your box?

Yes, I have 3 fans, two in the back and one in front. Yes, I'm using 3/4" stickers.
I'm using a Wagner 220 Moisture Meter.
Currently, I have about 200 to 300 bf of wood in my kiln but it has a capacity of about 400 to 500 bf.
Thanks.....Dr.

[doc henderson]

the thicker slabs will take longer.  you mentioned that at night it requires aux. heat, but you could follow the solar cycle and let the temp drop below 100 at night and let the DH work at that time.  what is the RH in the kiln?

[kelLOGg]

I have not yet dried cherry or walnut although I have each soon to go into the kiln. I usually dry oak in the kiln after air drying which will take about 2 weeks to get to 7 or 8%. Operating my kiln in the summer is general not a good idea because the ambient temp is close to the max operating kiln temp. So, when the weather is hot drying in the kiln takes longer. Now is a good time to use my kiln and it is busy.  

[dcrice]

the thicker slabs will take longer.  you mentioned that at night it requires aux. heat, but you could follow the solar cycle and let the temp drop below 100 at night and let the DH work at that time.  what is the RH in the kiln?

I have not checked the RH. I was planning to add a wet bulb to the kiln but haven't got around to it.

[doc henderson]

not as industrial, but I have had good luck with the 14 dollar accurite temp and humidity monitors with a remote.  I can read from inside a metal container from 200 feet away in my shop.  I also got the sensor push that @YellowHammer  uses and recommends.  they both read about the same.  I have got the accurite monitors from WM or amazon.  if the RH is too low, it will create more stress depending on the MC of the slabs.  if you cycle it like solar it will relieve stress at night when the RH comes up in the air, near the wood surface.

[scsmith42]

Was the cherry air dried before it went into your chamber, or was it green?  IF AD; what was the MC% when it went in?

[dcrice]

Was the cherry air dried before it went into your chamber, or was it green?  IF AD; what was the MC% when it went in?

I was air dried to around 20%.

[dcrice]

not as industrial, but I have had good luck with the 14 dollar accurite temp and humidity monitors with a remote.  I can read from inside a metal container from 200 feet away in my shop.  I also got the sensor push that @YellowHammer  uses and recommends.  they both read about the same.  I have got the accurite monitors from WM or amazon.  if the RH is too low, it will create more stress depending on the MC of the slabs.  if you cycle it like solar it will relieve stress at night when the RH comes up in the air, near the wood surface.

I'll have try one of those. Pardon my ignorance, but how low of a RH is too low and whats a good stable level?

[doc henderson]

well if the wood is air dried, it is starting low.  the degrade starts early in the drying process.  each thickness and species will have its own schedule of temp and RH or wet bulb depression.  If the relative humidity is low, it is the same as drying in a house or airconditioned shop with heat.  Lets see what @GeneWengert-WoodDoc and others have to say.  @Southside @YellowHammer  @customsawyer   @WDH  and others

[doc henderson]

@dcrice if you have a sealed unit and no leaks, and the DH is not running, then heat is the only thing dropping your RH, so it will go back up when the temp drops.  If it is high, you need to get some out.  if it is low then you have leaks or you are opening it every day, and loosing the water that way.  good luck.  there is lots the has been written, and you first have to see where you are in the schedule.  I am a student of wood drying, but the afore mentioned guys do it every day, and or are experts in the field!  good luck

[YellowHammer]

As @doc henderson has said, it's important to know the wet bulb or relative humidity to know what is really going on in the chamber.    

[customsawyer]

When running the kiln the more information you can get the better off you are.

[farmfromkansas]

Question about room dehumidifiers, if you keep a dehumidifier in your wood dryer during cold weather, and it gets down below freezing, will it ruin your dehumidifier?  Looked in my trailer this afternoon and it was above 80 degrees, but I took out the dehumidifier when it started freezing at night.

[Ianab]

Question about room dehumidifiers, if you keep a dehumidifier in your wood dryer during cold weather, and it gets down below freezing, will it ruin your dehumidifier?  Looked in my trailer this afternoon and it was above 80 degrees, but I took out the dehumidifier when it started freezing at night.

I killed one from letting it freeze up in winter. It built up so much ice it got into the electronics in the top and shorted it out.

The dont work very well if the temp is down below about 10C anyway. So may as well turn it off unless you have some heat in there.