DIY DH Kiln Performance

[kelLOGg]

I have put together an uninsulated DH kiln in the 2nd floor of my barn consisting of a large tarp, circulating fans and a room de-humidifier. It is sealed fairly well with duct tape on the seams and the ends tightly rolled. It is 350 cubic feet and loaded with 250 bd ft of 1" hickory that has been shed dried for 4 years. I want to dry it to use as flooring indoors. I have a hammer electrode moisture meter which over a 24 hour period showed a moisture content change in a test board from 11% to 10.2%. 5 inches of water has accumulated in a 5 gal bucket in the same period. As of this writing the outside temp and RH is 74 degF and 58% RH. Inside the kiln measures 90degF and 32% RH.

It seems to be working to me but I want comments in regard to the performance seen so far. Am I just drying my neighborhood 

This is a $100 investment in a bare bones DH kiln to see if I want to get into it more seriously. 

Bob

[TexasTimbers]

I have a similiar kiln in my shop, built fairly well though. Really tight. It sucked the moisture out of  several loads of various species right quick. My dilemma is storing it and controlling the re-absorption of moisture because most of it is going to be used for flooring.

I was talking with another member about it recently and based on his advice and my own wants, I thnk I am going to use a 40 gal DH unit inside a 12' tall x 25' long x 4' wide insulated chamber to keep the wood at a maintenance level. It would be too much wood to bring down from a high MC but I am hoping it will handle keep the wood from mositure absorption.

My point is plan ahead. Look beyond building the chamber unless you know you are going to place the wood in service immediately before it has time to go back up to 12% or whatever.

I have also talked to a member who pretty much only uses air dried wood even for furniture and has no problems. It's a confusing topic and sometimes I think ya just gotta quit reading blueprints and start hammering nails so to speak and let happens what may. Ain't nothin unfixable or unredoable.

[MikeH]

 Sounds like a great way to dry a small load. At 90 degrees and 32 rh the load will get down to just above 6%. I would try to heat up a little if possibe for faster results.

[brdmkr]

In the brief time I have been hanging out here, there have been numerous discussions of home DH units and kilns. In the back of my mind, I have several kiln designs that I would like to try, but I can't seem to get enough free time to chase any of these ideas.  One of the things I keep thinking about regarding the home DH units is their durability within a kiln.  So many folks talk about the acids eating up the coils.  Is there anyone with experience using home DH units to dry oak (supposedly the worse wood for the home DH units)?  If so, what were your experiences?  How long did the units last?

Another thing that I have been thinking about along these lines is the use of a charcoal impregnated filter to protect the DH unit?   Couldn't you just build a wooden box with a charcoal filter to house the DH?    Has anyone tried this?  Did it work?  Seems like it would do the trick.  Somebody try this and let me know as lately all I can seem to do is hit the forum a few times a day.  I am hoping this changes during the Christmas holidays.

[TexasTimbers]

I bought my 30 gal unit from walmart.com because it was the best price and was a goldstar unit which although chinese brand seems to put out good disposable junk. I purchase chinese junk as little as possible but it is practically impossible not ot do so these days. Don't wanna get that one started.

One line of thought says make sure to save the reciept so you can make sure and get a new one if the acids eat it up before the one year warranty. Another line of thought says that ain't exactly a nice thing to do. I can't instill your morals but for me I saved the reciept only for a tax write off.
I just can't bring myself to take it to my local wal mart for a swap knowing full well I am using it in a way it is totally not designed for, mega corporation or not. Ain't trying to come across as a saint but if the unit lasts one load or 10 I am going to buy another unit because as it averages out the cost. A $130 DH does not add but pennies per BF if you get the kind of use out of it I have so far.

What if it crashes in the middle of the second load? You got a whole load out of it for $130 . Say you had 300 BF of something worth $5BF kiln dried. You paid $130 for getting $1500 worth of wood dried but didn't have to haul it anywhere. If you get two loads you paid $65. Of course there is the electrica costs, and I have not done the math but ask donk to figger it for ya. Get what your payin per kw hour and figger the watts it uses over say a 5 week run saying the compressor runs 80% of the time over that 5 weeks. Donk and several others here like that kind of math I only studied up on it for tests and such. Or just ask daren i think he looked at his bills and guestimated an amount.

These small DH kilns are not for high production obviously but you can't hardly ruin a load in them and you can run small woodworking specific loads and within 6 to a year months have alot of differnet species on hand if you started with AD wood.

I doubt I will discontinue this thing even when my big kiln is running because they are so versatile with small loads. I like to do mixed loads (only have done one but all the species eventually came down to < 6%; while one species was still coming down the others were being "maintained" is the way I look at it.) and these things are great for that in my totally non-professional humble opinion.

I have got 3 loads so far and will put another in when I get some time like hopefully within a couple weeks. It will definately be a mixed load and one species that is going to go in that I haven't tried in any volume yet is box elder. I got my finger crossed on that. YMMV

I got most of my info about this from a member but i wouldn't do him any favors by mentioning him because he actually sells the plans with all the info you need.

[Daren]

I got most of my info about this from a member but i wouldn't do him any favors by mentioning him because he actually sells the plans with all the info you need.

I got 90% of the info here for free  . The electricity was less than $.05 bft on stuff already a/d to around 20% the month I checked it. (I had $.05 a bft in gas just dragging my wood to the nearest kiln drier. And had to wait forever on my small loads, handle it all twice as much...)

I ain't mentioning any names either. But I bet the guy with the plans wouldn't sell them to a long standing FF member, he'd just give them to them if they p.m.ed him.

 I have ran the same d/h for 2 years, so if blows up today it is not even worth factoring the price of a new one into the $ per bft I have already dried. It would be a very small faction of a penny. Funny thing, I did blow one up though, and expensive one, right off the bat. I went out and bought the cheapest one I could find like Kevin is talking about and it has lasted 2 years, go figure  .

A guy could just do a search here of "air conditioner kiln" and "homemade dehumidifier kiln" and other related searches. It has been discussed here plenty.

[solidwoods]

Don't know if the moisture loss rate is within tolerance or not.
Lumber below 30%mc is more forgiving to dry (meaning you aint on no known kiln schedule).
Hickory is a harder wood to dry (meaning its drying schedule has little tolerance for variance).
Air drying, because of a lack of good control of the rate of moisture loss,, can be hazardous to the lumber.  A Properly set up air dryer can be more work than a basic kiln because the kiln goes straight to a known proper temp/humidity.
I'm not knocking air drying, I air dry most all woods I work.

If you have a wood shop with the space, a combination room of finishing and Kiln works well.  I have one that holds 2kbf,  I use waterbased topcoats ,, so when I finish in the room, I turn on the kiln heat and keep the heat a little higher.

Stickering your lumber in the house would also dry it (from 11% it's not too long).

I like the burning wood to heat hot water to do a whole bunch of things concept.
If you are a home based woodworker with a kiln you will have no problem paying off the equipment quickly.  Not to mention heating the shop/home (can't see the state your in from here but if its cold,, you could be loosing $)

jim

[TexasTimbers]

jim,

I know you weren't talkng to me, but I am in north Texas and it gets darn cold for about 3 months of the year - not always a full 3 - but I have looked at the hot water via wood burner option and think it's smart even in a mostly year round warm and hot environment because waste wood at a sawmill is plentiful enough to keep it stoked for the shop, kiln, and home. I have also looked at the condensation kiln route because my dad gave me a huge commercial condensation tower off the roof of a shopping center that is still good, and that is the always the biggest cost of a CK - a new one like this is huge bucks i don't wanna guess. The only other big cost would be the wood furnace big enough to use even half the potential of such a tower. I talked to a guy in NC that has been running condensation kilns and wood fired water boilers for 10 years and swears by them because of the low operating cost and says they dry as quick as DH kilns which he and his dad used to use before they switched to condensations. Well I got off topic again didn't mean to get into a CK versus DHK comparison.

I air dry because I have to not cause I want. When I get the big kiln (well, 4000BF) going that need will be reduced dramatically but I will probably still have to air dry - I'll just pick the friendliest species for that.

I like that woodweave cieling on your website and might experiement with making really thin slices of ERC to tighten the gaps, because spiders are bad down here and I would think it might be hard to maintain because of webs etc. Have you found that to be the case? I reckon Tennessee has as many spiders as we do down here unfortunately. 

[scsmith42]

Bob - it seems to me that what you're doing is working.  A little more heat would probably help, but as you increase heat you need to increase the RH%, else you risk overdrying the lumber.  Be sure to take MC% readings that will indicate what the % is in the center of the board - that's going to be the wettest part.

Brkmaker, I don't have any experience with the home DH units in a kiln, but I've dried a lot of oak in my DH kiln and it's pretty corrosive on metal parts.  Re a home DH unit, what I'd suggest is to take it apart and clear-coat everything that could corrode with a couple of coats of clear polyurethane (including the condensor and evaporator coils).  That should double or triple the life of the unit.

Scott

[Daren]

  Re a home DH unit, what I'd suggest is to take it apart and clear-coat everything that could corrode with a couple of coats of clear polyurethane (including the condensor and evaporator coils).  That should double or triple the life of the unit.

Or radiator spray paint, the stuff you can buy at an auto parts store. It keeps road salt and other corrosives from eating aluminum/copper car radiators. It oughta help with the tannic acid  .

[Part_Timer]

 

Mine is not much more high tech than yours.  plywood sides, plastic peg board in the back, small fan and a box store DH.  $150 total.  Works like a dream.  250bf x  $1.75bf ash = plenty of money for a new DH when necessary. 

[brdmkr]

I have been contemplating a model that would double as a workbench in the shop.  I know that Daren likes 30 - 40 pint DH units, but I have found a 65 for about the same money.  I almost bought it today, but then I began to wonder if the larger unit might dry too quickly.  Any thoughts?  Right now, I am thinking that I would like to be able to dry about 250 - 300 bdft at once. 

[Daren]

Any thoughts?   

, thanks for the slap in the face. Now burn the plans I sent you (without even trying a proven system) and offer your own when you get it "figured out" next year (?). No more free plans from me here, they are worthless.

[brdmkr]

Any thoughts?   

, thanks for the slap in the face. Now burn the plans I sent you (without even trying a proven system) and offer your own when you get it "figured out" next year (?). No more free plans from me here, they are worthless.

Daren,

I think you took that question the wrong way.  I really appreciate the plans.  My question was simply that I found a DH with a higher capacity for about the same money.  I was only asking if purchasing the larger unit would hurt anything (i.e., dry too fast).  I also did not imply in any way that the plans were worthless.  If I had thought the plans were worthless, I would have just purchased the larger DH unit, as I would have figured bigger is better.  Instead, I came  here to ask.  I certainly did not mean any offense to you, and I am sorry that I upset you.   

[Daren]

  I certainly did not mean any offense to you, and I am sorry that I upset you.   

Wow , I sounded rude didn't I. Man I was grouchy last night ...and it showed, sorry that is not my nature. You are going to make too much heat with your 65, it is going to short cycle and not dry anything. Bigger is not better, what I recommended is best. How's that? I should have just stayed out of this conversation. 

[brdmkr]

No problem.  You have been a huge help.  I could see that you thought I was questioning your approach, but that was not what I intended.  Besides, going with the smaller unit will save me about $20

I'll likely buy the 40 pint today.

[Dana]

What has been your experience with the kiln when the temps are below freezing? I realize that it all has to do with how well its insulated but is it a seasonal type of kiln, if it is built outside? I'm thinking Michigan temps here 10's and 20's and a few minus number days.

[Part_Timer]

Dana if your asking me, mine is insulated and in the garage.  It will run  in the winter but have to run an electric heater in it instead of a heat lamp.   

brdmkr, good thinking about the workbench top.  Maybe I have a new spring project.

[kelLOGg]

So far I've been pleased with the measurements - after a week the test board is down to 7.5% RH and water continued to collect. A cold front moved thru on Sat and the kiln stopped working as expected.

I'm also pleased with the feedback - lots of good ideas. Part_timer, I like the pegboard diffuser idea. I just may copy you on that. Some of the upgrade possibilities based on everyone's comments include rigid sides, polystyrene boards if I decide to make it non-seasonal, walk-in, controls and readouts on the outside, etc. - the possibilities are limitless and exciting.
Bob

[pineywoods]

I have built 2 kilns that are a combination D/H + solar. Details are on here in a thread about solar kilns. Works good. Dries wet cypress at 100% down to 6% .