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Drying Wood With A Home Dehumidifier

58244 Views 11 Replies 8 Participants Last post by  PaGeorge
I have some nice Oregon White Oak that has air dried for one year. It is now at about 15% moisture content. The lumber is planed down to about an inch, and I am ready to finish drying it to build a dining table.

I stacked and stickered the lumber in a small insulated room, being careful to keep each layer flat and well supported every 2 feet. I am using an electric heater, a large oscillating fan, and a home dehumidifier. The heater keeps the room at 99 degrees, and the humidity is down to 20-25%. My plan is to run the heater and fan during daytime hours, and run the dehumidifier continuously. My dehumidifier is an appliance type unit rated for continuous duty. I will dry the lumber to less than 10% moisture content, which I figure will take 1-2 weeks.

Does anyone have experience with home kilns?
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I think it's pretty commonly done, although I guess some shoot for higher temperatures.

Example: LINK

See "Dehumidification Dry Kiln"

And … from Gene Wengert (knows all things wood): LINK

Good luck !
I am finishing a load in my home DH kiln. My temperatures run about 110-120 and I have the DH set to maintain 30% avg RH right now I constantly keep track of the water recovery and regulate temp and RH to not pull water out too fast so as not to cause too much degrade by drying too fast. It has been in the dryer for 2 months so far. My wood had not been air dried first so you have an advantage there. I think the oak may be somewhat more sensitive to degrade so go slow. The lower temperature you are using should help. By turning off the heater and fan at night you will slow drying. That may be good in your case. Lower RH, higher temperature and more air flow will speed up the process but could cause checking and warping etc.

Here's a plot of my temp and RH from a couple of days ago. The heavy blue area is the DH cyding.

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Seems like you are doing an ok job in my opinion, but I would recomend going to 6% instead of 10%, then allowing it a month or so to reacclimate to your home environment. Oregons oak is prone to bugs, which die above 133 deg f.; you may consider going up to that for enough time to get the woods core to that temperature. Best of luck!
I operate a DH kiln as part of my business. Because your oak is below 25%MC, you do not need to worry drying too quickly. Above 35%, the drying rate is absolutely critical, especially for oak. Below 25%, no big deal.

If you were to leave your DH unit set at 40%, you would equalize out between 7% - 8%MC. The problem is that your oak may not want to give up the moisture that easily.

There is no reason to turn the heat off at night either.

In a professional DH kiln, the final climate for oak is 120F and <40>t over-dry it at that rate.

The air flow rate through your stacks should be about 350FPM.

It is a good idea to sterilize the lumber at the end of the kiln run. This can be done by heating above 133F for 4 hours (measured at the core of the wood), or at 120F for about 7 - 10 days.
So far so good. After 5 days in my home dehumidifier kiln the oak has dropped to 8-10% or less. One more day otta do it. It has been interesting to track the water volume collected by the dehumidifier. The first couple days there was 3" of water in the tray every 12 hour period (amounted to 1-2 gallons). Now it is just a few dribbles of water every 12 hours. Because the environmental humidity has remained steady this week, I am confident I am reaching equilibrium. If someone doesn't have a moisture meter, they might be able to estimate MC with their dehumidifier. I found a nice used Maytag for $40. Since they tend to be an occasional-use appliance, it is easy to find one in good condition.

Interestingly, I didn't experience any warping or cupping at the 100 degree temperature. The oak is quartersawn though, which helps a great deal.
Be safe with your heat source and apliances, please don't risk a fire or do anything that doesn't feel safe!
I am about to dry some beech that is quarter sawn and I hope it goes well. I know you have to go slow with this stuff to prevent checking but fast enough to prevent damage from mold/fungus.

Thanks Scsmith42 for the input. Do you know anything about beech? I don't have the ability to steam it though I know that is what is commonly done in europe.

Have any experience drying beech anyone?
I have dried several batches of oak this way. Because it is a low temperature DH kiln, I think you could use it with most any lumber.
How are you checking the moisture content? I believe the EMC in your area is about 15% so the Oak will never fall below that moisture content without quite a but of energy involved. If the room is 100 degrees then that is not enough energy. The humidifier will have water in it because it will pull moisture out of the air and not the wood without the proper amount of energy input.
100 degrees is plenty of heat to remove moisture from lumber. This is evidenced by a moisture meter that tracks core moisture levels daily. It is not however, hot enough to kill bugs, so if you are concerned with that, run the kiln hotter for a couple days.
Cut a 1 inch strip of wood a foot from the end of the board. Weigh the strip in grams. Place the strip in an oven at 170 degree. Take the strip out every couple of hours to weigh it. When the strip stops losing weight you will know the oven dry weight of the wood. You can compare the numbers and get a true moisture content. I think you will find that a moisture meter often isn't very accurate. I have a degree in wood tech, and I think I know what I am talking about-but if you don't want the help then good luck to you.
I always scratch my head when the air drying topic comes up. So many charts,so many conflicting opinions. I guess that's to be expected because drying wood is probably somewhat like growing a vegetable garden in different regions of the country…I live in the NE corner of PA and I'm sure what methods work locally would be a flop somewhere else.
I'm a garage shop DIY guy and the amount of wood I use doesn't require a forklift to move around. Probably never had more than a 1000 board ft of wood at any time. As I see it heat and humidity bring us to moisture content along with time..
Seems the concensus is that water extraction done slowly produces the best results and to much heat/ drying to fast is not a best practice. I was thinking about using furring strips and plastic sheets to build a frame around it and stick a room dehumidifier in it with a tube to drain away the condensate…No heat applied.. Seems simple enough..The wood I'm planning to use has been air dried for over 3 years none thicker than 8/4..
Would that alone do the deed?
Garage is insulated and pretty much never go's below 65 degrees and the rh runs apx 70% inside it,,no ac and heat is sourced from electric coils…..I'd buy my wood ready to go from a place like woodcraft but I don't thing I'm gonna hit the mega millions lottery anyday soon.
I got a headache from all the youtube videos I've watched..
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