home built kilns

[Dobbs]

Any home built lumber kilns out there? How do they work? Any pictures?

Thinking of building a small one in the end of my shop 12' wide 8' high by 4' deep.

With a dehumidifer.

Dave

 

[Old Blue]

I havn't done it but there are some good threads on here about it that I have picked up a lot of wood drying knowledge from.

The basic technique seems to be to seal the ends of the logs as soon as possible after cutting. This keeps wood from losing moisture too fast. Some wood is very sensitive as to how slowly it needs to lose the first third or so of its moisture. Once the first third or so of the moisture is gone then it seems to be less likely to crack split or check.

There are some great sawyers and woodchuck here who have built some neat kilns. You'll learn a lot just cruising the various threads.

Old Blue
In the land of economically destructive taxation with no representation.
Kali-bone-ya

 

[SPM in King]

Kiln

Yes, indeed.

12 x 8 x 8 tall...inside dimensions.
Made with 2 x 6 rough cut hemlock and 3/4" concrete forming plywood (used).
7' high x 6' long doors on the long side for easy loading with forks.
Home made hinges with nesting pipes and 1/4" plate steel.
60 amp service for 3 10" fans, one dehumidifier and up to 2 220v 15amp heaters.

Works great. Make it TIGHT!


Steve.

 

[Dad2FourWI]

Sounds nice..... I want pics!!!!!

-Dad2FourWI

 

[TPA]

Virginia Tech Solar Kiln | Dept. of Wood Science and Forest Products at Virginia Tech

 

[Daninvan]

Some of the woodworking magazines have published plans over the years. I built mine (4x4x8) out of plans from American Woodworker #94 June 2002. FWW I know has also published plans. As other have mentioned, there are threads here dealing with kilns also. I built mine with a bunch of fancy control circuitry, heaters for lightbulbs, an attic fan, and a DH. Now, I just use the DH and the fan, don't bother using all the fancy circuitry.

12x8x4 will be a nice size, I guess kilns are like shops - never big enough! I air dry my wood two years, then put it in the kiln with the DH running full tilt, and a hose running out through the side of the kiln for the DH to drain. I collect the water in a bucket and keep track of how much is removed each day. The heat from the DH is enough to increase the temperature in the kiln to over 40 degrees C. After three or four weeks it usually gets down to less than 1/2 pint of water removed a day, and then I turn on the fan. That seems to raise the internal temp of the kiln over 50 C and draw more moisture out, but only for a few days then it is done. It usually gets the wood down to about 8 percent or so. I used to condition the wood afterwards by blowing steam in with a carpet cleaner, but have found no value in doing that so I stopped. I think the wood being air dried for two years minimizes the amount of stresses in the wood.

Make sure you insulate it, I just used 1" and 1 1/2" foam board insulation from the borg. I bought a cheap temp and humidity gauge that has remote sensors on it, I put the sensors in the kiln and leave the gauge part sitting on top of the kiln. Similarly, I use a pin type moisture meter, I just drive nails the right distance apart into a couple slabs and run wires from them outside the kiln to clip onto the moisture meter. So there is no need to open the kiln to drain the DH, check the humidity or temp, or to check the moisture content of the wood. Of course, some times I just open it up to 'take a look'!

Yours will have almost 4 x the volume of mine. I wonder if a single DH will be enough? I guess you can try and see what happens, always add one later if it turns out you need one.

 

[Cody Colston]

Since I only mill lumber for my own woodworking use, live in Texas and am away from home half the year (in two week cycles) I built a scaled down version of the VT Solar kiln.
Mine is sized for 300 bft although I can get more than that in it.

We get plenty of sun here and have mild winters so I can dry lumber all year long. Also, working like I do, I don't have time to play nursemaid to a charge of lumber...checking moisture loss against the safe drying rate, etc.

The fan is on a 24 hour timer and unless it's a light-colored wood being dried, I can basically just load it and forget it. It's designed for safely drying Red Oak and most species are much easier to dry.

 

[TPA]

Since I only mill lumber for my own woodworking use, live in Texas and am away from home half the year (in two week cycles) I built a scaled down version of the VT Solar kiln.
Mine is sized for 300 bft although I can get more than that in it.

We get plenty of sun here and have mild winters so I can dry lumber all year long. Also, working like I do, I don't have time to play nursemaid to a charge of lumber...checking moisture loss against the safe drying rate, etc.

The fan is on a 24 hour timer and unless it's a light-colored wood being dried, I can basically just load it and forget it. It's designed for safely drying Red Oak and most species are much easier to dry.

Hi Cody

Since I only live about 80 miles south of you, your experience is very relavant to me.

I suspect it takes much less time to dry in the summer than in the winter, but do you have an estimate as to average drying time for a full load? Do you change the air flow rate from summer to winter so that the dry time stays the same? Do you know how low the moisture content can be brought to using this kiln?

 

[Dobbs]

I have thought about the solar type putting a collector on the outside. Just hate to put the big holes in the side of my shop to transfer the heat in. An living in IL the winter time I dont think I would get much out of it.

 

[Leroy in Kansas]

I've often thought about building a kiln. I've also wondered what effect the relative humidity has on the wood once it is removed from the kiln?

 

[Sawyer Rob]

I've often thought about building a kiln. I've also wondered what effect the relative humidity has on the wood once it is removed from the kiln?

The RH of the wood will balance to what ever the RH is where the lumber is stored. SO, if you kiln dry it down to 8%, then move the lumber to an unheated, non air conditioned building, the lumber will start picking moisture back up.

SR

 

[Cody Colston]

Hi Cody

Since I only live about 80 miles south of you, your experience is very relavant to me.

I suspect it takes much less time to dry in the summer than in the winter, but do you have an estimate as to average drying time for a full load? Do you change the air flow rate from summer to winter so that the dry time stays the same? Do you know how low the moisture content can be brought to using this kiln?

In the summer, two-to-three weeks is about as long as it takes to dry any species. Oak is at the longer end of that period because I leave the vents almost closed for the entire time. Walnut will dry in two weeks because it is so forgiving. The temperature in my kiln routinely tops 140 degrees during the day.

Winter drying is dependent on the number of good drying days but add another two weeks to the summer drying time and that's close to the average.

I have the fan on a timer so that it comes on at 10:00 a.m. and goes off at 8:00 p.m. year round. On rainy days, I shut off the switch so that it doesn't run at all (or have my wife or one of the kids do it).

In the summer, I can get the lumber down to 6% MC. In the winter, I shoot for 8% MC.

The RH of the wood will balance to what ever the RH is where the lumber is stored. SO, if you kiln dry it down to 8%, then move the lumber to an unheated, non air conditioned building, the lumber will start picking moisture back up.

SR

The lumber will regain moisture if placed in an environment where the average RH is higher than 35%. However, if the lumber is indoors, even in an unheated/air-conditioned space, the EMC will remain much lower than it would be if it were stacked outdoors with a cover over it. That's because the inside of a closed building doesn't see the near-100% relative humidities hat the outdoors sees.

Even if the wood were dried to 8% and then placed in a 12% EMC environment, it would never regain moisture back to 12%. That is known as the hysteresis effect. It would never get beyond about 11% MC and even then it would take a long time.

Also, while the surface may regain moisture back to 11% the core will take many months to regain moisture back to even 9%. Once it is brought back into a 35% RH environment at 70 degrees F or more, it will quickly lose moisture back to near the kiln-dried value.

Or, one could simply wrap the kiln-dried stack in plastic and it would not change in MC at all, regardless of the RH or temperature.

 

[Dave Boyt]

The kiln dry wood won't be stickered, so there won't be any air flow through the stack. The outer layers of wood might pick up a little moisture, but it would take some serious moisture to affect the wood inside the pile. As long as it is in a shed, it should be OK. You're not going to hurt anything by putting plastic on it, though. The part about hysteresis is correct. The EMC Cody refers to is the "equilibrium moisture content". For any relative humidity of the air, there is a corresponding moisture content that the wood will eventually reach, if left in that environment long enough. Here's a link to an EMC graph http://www.woodweb.com/knowledge_base/EMCRH_ratios.html.

By the way, the acid from the moisture in the wood will eat away the insides of a household dehumidifier. Nyle sells stainless steel dehumidifiers designed for wood kilns. More expensive, but they'll hold up.

 

[Leroy in Kansas]

Thanks fellas, this clears up yet another mesterosity for me.

 

[Daninvan]

By the way, the acid from the moisture in the wood will eat away the insides of a household dehumidifier. Nyle sells stainless steel dehumidifiers designed for wood kilns. More expensive, but they'll hold up.

That is true, but the cheap DH units from walmart or where ever will still dry out many many loads. I've been doing it for years and am only on my second DH. The kiln cost works out to a few dollars per load.

 

[Dobbs]

That is true, but the cheap DH units from walmart or where ever will still dry out many many loads. I've been doing it for years and am only on my second DH. The kiln cost works out to a few dollars per load.

thanks for the info guys!!!!!!!!!!!!!!!!!!!!!! and Daninvan seem like everyone thinks they are only get a load or two out of the DH. I have this same type thread going on 3 or 4 forums.

An some one has spoke up on almost every one saying their DH has lasted 2 yrs +

 

[Dobbs]

a buddy of mine had a old Nyle L50 that he has stopped using. So I have drug it home to try to get it running . We will see how it works out

 

[Dobbs]

anyone out there have a Nyle L50 need to try to find the parts local. have a couple parts missing

 

[SPM in King]

Pics of kiln. 3 x 10" fans in bulkhead. Custom made hinges....and more:

Steve.

 

[markvanzee]

for anyone who want to build his own kiln, the sauno kiln unit from logosol would be a great and inexpensive way to dry lumber quick with great results. if i were to build a kiln myself, i would purchase one of these units for sure.