container kiln for firewood

[lumberjake]

Hi,
im in the process of building a firewood kiln from a container. My biggest question is how do i vent it to let the moisture out without loosing to much heat? And is it better to hang the fans from the cieling pointed down or across. any help what so ever would be greatly appreciated.
thanks
jake

[GeneWengert-WoodDoc]

In any kiln there is always the question or concern about venting and subsequent heat loss.  The more you can vent without affecting the internal temperature (that is, the heater is running full time to keep the temperature at the desired level) , the faster the wood will dry.  Of course, the energy cost will be higher, as you are not taking full advantage of the low humidity from the incoming air.  The extreme case would be venting so much that the outside air would come, be heated, pass through the firewood and then be exhausted...very energy inefficient.  So, venting less so that when you do vent, the out going air is at higher humidity, will take longer and use less energy from your heater per hour and overall.  I suggest that with auto vents you use about 60% RH as your guide...when more humid, vent and when less humid, close the vent.  Or if you have manual vents, crack them open and monitor the RH, adjusting them to achieve the correct RH.  As the wood dries, you will find that the vents will be closed more and more.  Also, when the wood is quite wet, you may wish to open the vents wide and use no extra heat...just pass the outside air across the wood using the "free" outside heat.  In this case, do not run the kiln when the outside is above 90% RH.  As the wood dries, then after a few days or so, close the vents and add heat.

Ok?

[lumberjake]

thank you very much
jake

[allagashwoods]

Jake, I built a firewood kiln with a container that works quite well but it's a little different from most. I have a forced hot air wood fired furnance that dries the wood so it costs  me next to nothing to dry the wood. I set my exhaust fan to go on for 5 minutes every 2 hours, not to accurate but it does the job. I have a 10,000 cfm fan that runs for the whole drying process. I keep the temp at about 180 to 200 degrees for 3-4 days depending on the type of wood I'm drying. I check the moisture with a meter every day and dry the wood until it get it about 10-15 percent moisture. The down side to this is I have to fill the furnance 5-6 times every 24 hours. Don't get caught up with the hype of  the kiln makers about the kiln having to be perfect, heat air and moisture removal will dry the wood as well as anything manufactured.Good luck.
                           Len

[GeneWengert-WoodDoc]

Although your operation using firewood for energy costs you nothing, I am wondering if that firewood you used were dried and sold, how much it would be worth.

[allagashwoods]

Gene, not alot, the wood is dropped off by local tree companies and it's not great stuff. I get all the saleable wood sorted out and split to dry and about half the wood left is prepped for the kiln. My kiln takes 4 ft wood so anything I can lift is already to go. While my kiln works well most of my business is still seasoned wood, I'm slowly getting a customer base that will hopefully allow me to become an all kiln firewood business, but I'm still a ways from that

[lumberjake]

I really appreciate the information thank you very much!

[Handymark]

Are you guys referring to the large cargo shipping containers?

[allagashwoods]

Handymark, yes, but you have to start with an insulated container or go through the process of insulating the container yourself, the more insualtion the less the furnance has to work to keep the temps at the numbers that are required to dry the wood in 3-4 days

[Handymark]

I have never seen an insulated container around here but spray foam or foam board should work. I could also see using a short refrigerated semi trailer or the box off a refer straight truck. I am a few years off but I am trying to look at options for a kiln enclosed within my planned barn that would use heat from the outside wood burner as well as excess summer heat in the greenhouse I plan to have attached to the southern side of the barn.

[WoodenHead]

How are you planning on stacking the firewood in the kiln for best drying?  What are roughly the sizes of your pieces?

[allagashwoods]

Newbee, I stack the firewood in 1/3 cord bins as I sell the kiln dried by the face cord. The bins are made up of pallets, not the prettiest but free.I load the bins in kiln with my skidsteer and take them out and put them in my truck with the skidsteer,this saves a lot of time and energy. I stack the wood rather than throw it in the kins because I can get more wood in that way.The wood is split  small as compared to regular seasoned wood because it dries much,much faster.

[WoodenHead]

Is your kiln any different from a typical lumber drying kiln?  The reason I ask is because I have a DH kiln for lumber.  A local firewood supplier is interested in drying a portion of their firewood, but isn't certain of their market.  I was wondering if my kiln is suitable for drying firewood as well.  For lumber the idea is to force the air through the sticker spaces.  It is a little more difficult to force the air through firewood piles.  I'm curious as to how your setup might be different from the typical lumber drying kiln.

[GeneWengert-WoodDoc]

A DH kiln will dry firewood, but the cost may not be attractive.  One cord may require $25 or more electricity...depending on electric rates and MC levels.  It is common to put firewood in a largenwire-wall bin randomly and then put bins into the kiln.  Prior air drying is financially attractive if you can keep the rain off.

[lumberjake]

we also have dh kilns for lumber but ours run off of electric ebac units. For me to dry firewood in those kilns would just cost way too much. the dh kilns have to vents the unit sucks in all the moisture and the water drips out of a hose. the kiln im building for the firewood is from a 40' reefer trailor, i figured that was easier than building and insulating. my biggest concern was the venting but im think with everyones input on here i can figure it out. im going to look at the furnace today that im planning on using to blow the hot air in and have a fan or two just circulating the air. im also using stackable metal baskets that hold roughly a 1/3 cord to but the wood in and made a gate on the front so i can dump the wood out, i just fasten the basket to the skid steer and dump. no handling.  hopefully in the next two weeks or so ill have it up and running and let you guys know who she works.
thanks again for everyones input

[allagashwoods]

Lumberjake,  couple of things I've learned along the way, keep your motors for the fans outside the kiln, the heat and moisture will ruin them in a short amount of time. I have my motors set up with a shaft through kiln wall to a pulley for the circulation and the exhaust fans. I went through a couple of motors before I figured it out, Don't worry about the openings not being sealed, the venting is not an issue. I have seen a couple of kilns set up with no venting other than the cracks and holes in the kiln and they worked fine. USDA did and study a few years back on kiln drying and the kiln they used had only natural venting.

[WoodenHead]

Would a solar kiln work well for drying firewood?  In some regions it might cut down on heating costs.

[allagashwoods]

Newbee,
   It would but, it takes a long time to dry it,a month or so depending on the solar kiln and location. The problem is unless you have a giant kiln you won't be able to do any volume. It would be perfect for a homeowner that didn't need a more than half a dozen cords or so. I thought about a great big greenhouse but the cost and the land needed made it impractical

[roundwood]

Lumberjake, Did you sort out your furnace, what have you decided on and how big is it (kw),
I have an insulated container and fans for air circulation, just need to know the best way to generate the heat i need,  I'm looking at a Moderater Multi Fuel boiler, what's the best way to heat the chamber?  Heat coils or blow in hot air?

Cheers

[roundwood]

allagashwood, can you give me a little more info on the type of furnace you have, sounds like it's just the job i'm looking for,
really appreciate any info you can give me,

Cheers

[allagashwoods]

Roundwood, goggle hopscoenergy, they have  a furnance that will work quite well for a kiln. They also have a couple of people that are using them now and can give you some feedback which will save you time and money trying to figure things out as you go. I didn't go with this co. and instead went with an off brand. Wish I had gone with Hopscoenergy, live and learn.

[lumberjake]

round wood,
i have a coal/wood furnace and i cut a hole in the front of the trailor and set the furnace inside but kept the doors on the outside so i wouldnt loose any heat. it's not a real big furnace i fill it about four times a day with scrap wood. when i burn coal with it i only fill it twice a day. but the wood is free so i dont mind fixing it a few more times seeing how i drive past it when i leave the mill. i have two fans inside moving the air and i plan on putting in two more. I have a vent at the back side of the trailor to let out the moisture and im planning on hooking up an exhaust fan to help it out. I also drilled a four inch cold air intake in the front to let fresh air in. I went from green to dry in 9 days on the first load. im looking to get down around 5 hopefully after i get it all figured out. 9 days isnt bad but im only drying 3 cords at a time so the faster the better or i might just build another one come sumer. 

[NWP]

I had a kiln that sounds exactly like yours and Allagash's.  I loaded 1/3 cord loose per basket.  My stove was inside with the door on the outside.  I put a thermostat controlled fan with shutters on the rear of the kiln.  I set it to the max setting.  It would kick on and vent moisture and then shut itself off.  If the outside temp was below 32 F, it was hard to make the kiln work.  It would take a long time (7-8 days).  That would end up being too much time invested for 6 cords of wood.  If the outside temp was 50-60 degrees, I could knock out a load every 3 days.  I ended up quitting using it to dry wood and now just use it for storage. 

[Ado101]

Hi, Im hoping that I might get some answers as to why my firewood is taking so long to dry out. 
I have an insulated small container with about 3 cord of split logs, temperature between 100/150 F and a couple of fans, albeit small fans. I don't have a venting extracting fan , I leave to door open for about half and hour every 6hrs hoping this will remove some of the moisture, not sure if it is though. The wood stacks holds the temp so re heating dosen't seem to take that long, but they just don't seem to be drying as quickly as I first envisaged. This is an experiment at the moment as I'm looking to convert my 40' container if I can master it. Any tips and help would be appreciated.

[barbender]

I'd think you need to be moving more air. From what I've read, kiln drying firewood takes as much heat and airflow as you can get.