New kiln idea...

[metalspinner]

...or maybe not.

I was thinking of ways to pull heat out of my attic into an insulated box to dry some slabs.  The box will be on ground level at the gable end of the house. Do you guy's think an insulated duct with a booster fan inside is capable of pulling the hot attic air down into this box?

Then once the box is heated, will a couple of simple vents in the sides of the box give enough draw to expel the built up humidity.

My thinking is that it would work similar to a solar kiln because of the heat cycle in the attic.  A thermostat on the fan can regulate the cycle.  The box can be built around a pile of lumber and screwed together.

I wonder what kind of dissipation of the air as it enters into the box would be needed?

Just a developing idea I thought I would share. ;D

[Riles]

It's sorta been done already.

http://my.execpc.com/%7etmbrgrn/page18.html

The heat from the "attic" is routed to whichever drying compartment is ready, leaving the others to continue air drying.

[Tom]

I don't think you would have too much trouble getting the hot air into the box.  I have doubts about being able to get the humid air out.  It takes a pretty good breeze to move wet air from the center of a stack of wood.

[metalspinner]

Riley,
That is more complicated than what I had in mind. That is a nice set-up, though.  Everytime I stack my solar kiln, I walk away thinking that there has to be a better way.  I spent all day Saturday in and out of that box carrying one board at a time.

This would be more of a small chamber to dry a couple hundred feet at a time. 

Tom,
If the stack were, say, three feet wide, eight feet long, and about four feet tall do you think I would have the problem you mentioned.  Maybe a small exhaust fan rather than vents would move the air a little better.(?)

[Tom]

You may not need fans, but I think you would rest easier.  The fan moving the hot air from the attic, might be enough to purge the stack if baffled properly.  Why don't you look at WoodMizer's solar kiln and think about building something like that.  It was really simply.  It had one permanant wall (the back one) and the rest of the kiln was a plastic sheet box with fans that was hinged on top of the back wall and had a roof for a counter weight on the back.  You could just lift the whole front of the kilna and load it with a tractor if you wanted. 

I don't think they sell it anymore, but I thought it was a good idea.

[metalspinner]

Tom,
I can picture it.  I guess this annual thread of mine about a better kiln is more just complaining about having to load the one I've got. Remember the panels assembled around the stack idea? 
I have no support equipment - just my back.  Luckily, all the wood is for my personal use, so 1500bf or so will get me through many projects.

The duct from the attic to the box idea could work, I think.  A little more head scratching on air flow and ventilation could make this an inexpensive reality.

[getoverit]

I really like the idea of building the kiln around the stack

Thats one thing I have never thought of, but I dont see why it wouldnt work.I'm just wondering if the hot air from the attic will get hotter than the kiln would get if left alone?

[beenthere]

I really like the idea of building the kiln around the stack .........

I once saw a kiln that was on tracks, and moved over the lumber stacks. Made stacking and unstacking easier, and the kiln building was lighter than the wood stacks. Just made me think of it with this discussion going. 

[Dan_Shade]

What did DanG ever do with his horse trailer kiln?

[Tom]

It's just so easy to oversimplify the situation by thinking that a kiln is nothing but a hot box.   Don't let yourself get into that frame of mind.   Drying wood is accomplished by moving the water from the wood to the air and then getting rid of the humid air by either replacing it or condensing the water.  Heat and Vacuum are just ways of helping to get the water out of the wood.

There's been a lot of study done on air movement, and the other puzzle pieces.  Talk to a kiln operator about Schedules sometime and you will realize just how complicated it can become.

[metalspinner]

It's just so easy to oversimplify the situation by thinking that a kiln is nothing but a hot box

Yes, but.... ;D

Wood dry's by itself naturally.  As a hobbiest I only need to get a little bit of wood down the last few percentage points from air dryed.  I'm not trying to force several thousand BF from green to 6% in a couple of weeks.

Drying wood is accomplished by moving the water from the wood to the air and then getting rid of the humid air by either replacing it...

This type of drying is a simple procedure for sure.  The way to achieve the temperature seems to be the only thing that can complicate it.  Harnessing the hot air in the attic seems like the trickiest part of the idea above.  If a constant flow of hot dry air passes over the boards, then that hot moist air is expelled, then we have a simple system.  The self regulating drying cycles of the solar heated air makes the procedure even easier.

The "attic heat pumped into a box idea" could serve a hobbiest woodworker very well.  All of the customers you guy's cut a few hundred bf for could benefit from an easy and inexpensive way to dry their wood.

I guess a full blown expierment is in order. ;)

[fencerowphil (Phil L.)]

Hey MetalSpinner,

I think you are right.   Just go for it and play with it.

Taking your lumber from air dry on down a few points should be a cinch.
Hot air rises, so if you bring in the air low, diffuse it through the stack, then
let it exhaust out high, just the static pressure of the incoming air should
work with convection and get it done.  Add a simple timer on your fan and
play with the intervals.    With the fan on the pressure side (incoming), you
won't have moisture or acidic Ph to worry about, so any old fan will do.

Phil L.

[Steven A.]

Why not just stack the lumber in the attic and put a fan in the attic vents?
You might have to cut the boards a little short to get them up the stairs and through the little attic access hole but at least you would not have to build a kiln. 

[metalspinner]

Why not just stack the lumber in the attic and put a fan

Steven,
I have a solar kiln now that is frustrating to stack.  I have to carry each board in there one at a time, then get the block in there at the top of the stack.   I'm tired of  the handleing of the lumber in and out of the little hot box.

[mur]

Hi metalspinner:
One quick solution might work for you.  A lumber cart.  Load from the outside,
- easy all around access - then just push into the kiln on an end door that hinges open.  I just bought some heavy duty 8" wheels for 2 carts a friend is building for me.  Cost under 50 bucks each - Canadian pesos.  They are rated for 1,000 pounds per tire.  This idea for carts came from the last time I toured some specialty wood shops down in Vancouver, BC.  The workers there were moving thousands of board feet per cart around like nothing.  I was impressed.  Sold me on the spot to have carts made. 
Also thinking about "beenthere's" kiln covering on wheels idea.  Simple and elegant.  You could have a stack air drying while a load was in the kiln.  Load finished in the kiln and you would just slide the kiln over the air drying load.  Back and forth.  Definitely would have some possibilities to work in some situations. 

[Murf]

There's a fella near here built a similar sorta contraption, but fer dryin his firewood not lumber.

He built two big air ducts, one up the north side, and one on the south side, neither is insulated. The air is not in them long enough for it to matter. The key is the airflow, he get's it moving and keeps it moving. At the bottom of the duct on the north side is a large forced air furnace blower. It is connected to an A/C thermostat in the attic, anytime the attic temperature reaches about 70° the blower comes on and stays on till it drops back below that.

He claims he can get green firewood, neatly stacked, down to 20% in less than 3 months.

I question the amount of electricity required to do it compared to just waiting another year before burning it.  :

[Modat22]

I'm hoping to build a couple small solar kilns soon. One for lumber and one for firewood. I like the idea of killing off all the bugs before bringing them in the house.

[metalspinner]

Mur,
Here is a discussion we had last year.

Solar kiln

My moaning and groaning starts each time I'm in and out of the kiln.  Tom's pic looks like a good idea because no support equipment is needed.  Also, the Modular system will work with a little more effort.  This attic thing could work with a little air flow study... maybe.

I guess all of this will just be put on the list.... :-\

[Duncan]

When trying to dry a very small amount of wood (say >100bf) I have just stacked and stickered it in my attic.  I limit the amount due to limiting the amount of moisture in the attic not due to weight limitations.  If you are just talking about a few slabs just throw them into the attic.

Otherwise you could just put an electric heater in the area and end up cheaper than you will by the time you set up an attic heat reclamation unit.

[Riles]

Another option, if you're only on a hobbyiest scale, is to just bring it into the house after it air dries. Basically, you continue the air drying to the next level. You just have to have the room in the house... Works best for people with workshops in the house, and room for things like wall rack storage.

[scgargoyle]

I have a friend who builds very expensive guitars. He built about an 8 X 12 room in his shop, sealed up good. He has a big house-type dehumidifier running in there, and its amazing how fast it dries his wood. When a fresh batch is brought in, he sometimes has to empty the dehumidifier a couple times a day. My brother built a solar heater in college. They took aluminum shavings from a machine shop and painted them flat black. They put them in a clear box, and hooked up a blower. It provided continuous very hot air as long as the sun was shining. Maybe something like that on a bigger scale would work for a solar kiln. Should be able to get aluminum chips from a scrap place, and they never wear out. If you really want to cheat the power company, run the blower off a solar panel. That way the blower would stop automatically when the sun went down.

[Murf]

SC, tell your friend to lift up his dehumidifier and look underneath, nearly every one of them has a fitting to take a garden hose. If you pull out the pan, you'll usually find a fitting in there, and a hole in the case directly below it.

If you set the dehumidifier up a few feet on something it will gravity drain a long ways without anyone having to touch it.

[Left Coast Chris]

I have the oposite problem here in N. Calif. Sacramento Valley.   Last few days have been 7 or 8% humidity and is that way most of the summer.  The air drying goes so fast that I have to cover with tarps.   Would still like to build a killn to get temps up to kill bugs.   I like the aluminum shavings idea....... increased surface area letting off heat.

[fencerowphil (Phil L.)]

I know that one day I will build a couple of solar kilns.  From study here and
on Woodweb,  It seems certain that a well-designed solar can develop temps
sufficient for sterilization.   

To make that certain, the concept of an in-coming air preheater makes sense.

The aluminum shaving idea would be workable for that supplemental heat.
I have also heard of another means to do the same thing - using aluminum
cans painted flat black.  Of course, scrap black poly pipe or sheeting could be
used as the absorber as well.  Even shredded rubber tires can work.

My general thought would be to add this sterilizing heat in the last stages of
drying, so that you could reduce air outflow to almost nothing and bring the
temperature up significantly - maybe even 175-180 F (around 75 + Centigrade).

You could just set up the aux. heat when needed, near the end of the drying cycle
on that given load.  Nothing elaborate.  Lay down two sheets of duct board (1"
fiberglass) on the ground; cover with black poly; put the cans/shavings/etc. on the
poly;  lay clear poly over that;  channel the heat to kiln intakes; and there you have
it.  The kiln would need to be very well insulated, with a night-time roll down cover
to minimize heat loss.

Phil L.