Wood Dryer

[Duetech]

Hi all,
Has anyone tried to build a wood dryer using their boiler as the heat source? I run my boiler in the summer for dhw and was thinking that would be a great time to shorten some of my wood dry time and since I was already using the boiler I could build a cabinet that would have about 48 cu. ft. of space (4' x2' x6') and dry the best part of a face cord using an old (or new) heater core from a car as the heat exchanger. I would just tap into the return line on the boiler and route through the heater core and back into the boiler from there. It would be a plywood/2x4 design vented at the bottom and top for gravity air flow and have simple cabinet hinges for the doors. The dryer would put a little extra load on the boiler so I would be getting a little less idling during the burn. The reason I ask is I am having trouble getting any real seasoned wood (I've been given an opportunity to cut green wood but don't have enough dry set up for next season) and know I am going to run into problems this coming winter. Any pro's/cons?

 

[jebatty]

I think it may aid the drying in a closed space, but you will be using return water heat, therefore burning more wood for DHW, also losing heat into the atmosphere, and I can't help but think it's a losing proposition. Get your wood split early, small splits, stack outside with good air movement, and let the sun do your drying for free.

 

[2.beans]

around here you can buy kiln dried cord wood. its pricey but maybe one cord of that to get you started if you were in a real bind. id take my chances and burn the wood you got.

 

[flyingcow]

I like the idea of using shipping container, or even seen the idea of using an old bus that was painted black. Just good old fashioned sun dried heat. I'm sure they were posted here. Just my search abilities are poor at best.

 

[peakbagger]

Heres a link to every thing you might want to know about kiln drying wood (boards) with solar. I expect a lot would be applicable to your proposed project.

http://www.woodweb.com/knowledge_base/Solar_Kiln_Designs_1.html

My first guess is that air flow is considerably more important than temperature. If you could come up with a stacking technique that maximizes the woods surface area and gets equal air distribution, that may be the best bang for the buck.

 

[Duetech]

Heres a link to every thing you might want to know about kiln drying wood (boards) with solar. I expect a lot would be applicable to your proposed project.

http://www.woodweb.com/knowledge_base/Solar_Kiln_Designs_1.html

My first guess is that air flow is considerably more important than temperature. If you could come up with a stacking technique that maximizes the woods surface area and gets equal air distribution, that may be the best bang for the buck.

Air flow just might be the best route after all it is present when the wood is stacked outside in the sun. The trouble I am having right now is I don't have a source for hauling wood and most of the "vendors" only have green wood and that is still at the price they would sell for seasoned and often enough it is something I still have to split down for the EKO. The basic result is that I will be getting what I can when and how but not much of that looks like it is going to be seasoned. I am not too worried about wood consumption in the summer as I don't have that big of a demand for dhw but is is still cheaper than LPG. The blower was not what I wanted to do but I think it might be best in the summer months. Any how I can buy the plywood and 2x4's I need for building a drying cabinet in a size I can haul in my car and it shouldn't be too expensive. It seems absurd but at the speed summers fly by it's almost winter and I wanted to be ready.

 

[TCaldwell]

cave, i built what you are talking about last year, a well insulated drying cabinet 4x4x6, with loading door in the wood storage area and a unloading door along side the boiler. the heat source is a ci radiator , with a johnson slab sensor controller for thermostat, a externally mounted dehumidifier with a dehumidastat and fan for moisture control. i have the temp set for 125deg and the rh setpoint for 15%. it will hold about 400 lbs wood on rebar racks. unless you have alot of time it will not season large green splits, it will dry small splits remove the dampness of seasoned wood stored outdoors. it will thaw frozen wood, it was a experiment with stuff that was lying around and being home for a few days with no winter work. yes it is supplied by the garn, and i do use it when i get in a pinch. I am told that the large commercial sized cordwod dryers run about 160deg with alot of air for 48 hrs to do any real drying, i think the 500kbtu/hr heat load is out of reach for most of us, good luck

 

[Duetech]

cave, i built what you are talking about last year, a well insulated drying cabinet 4x4x6, with loading door in the wood storage area and a unloading door along side the boiler. the heat source is a ci radiator , with a johnson slab sensor controller for thermostat, a externally mounted dehumidifier with a dehumidastat and fan for moisture control. i have the temp set for 125deg and the rh setpoint for 15%. it will hold about 400 lbs wood on rebar racks. unless you have alot of time it will not season large green splits, it will dry small splits remove the dampness of seasoned wood stored outdoors. it will thaw frozen wood, it was a experiment with stuff that was lying around and being home for a few days with no winter work. yes it is supplied by the garn, and i do use it when i get in a pinch. I am told that the large commercial sized cordwod dryers run about 160deg with alot of air for 48 hrs to do any real drying, i think the 500kbtu/hr heat load is out of reach for most of us, good luck

TCldwell, Thanks, you bring up another good point about warming frozen wood. My boiler is in a non-heated structure and even with seasoned wood I get a lot of condensation when I do a full load. I have been told it was just wood that was too wet but I know that the wood was seasoned before I stored it in my shed two years prior to its use and very soon after loading the wood was nearly dripping wet. My thought was to run the dryer at what ever the return temp from heating the dhw was which will probably be closer to 165 F. Do you know of a reason not to run it that hot?

 

[sdrobertson]

TCldwell, Thanks, you bring up another good point about warming frozen wood. My boiler is in a non-heated structure and even with seasoned wood I get a lot of condensation when I do a full load. I have been told it was just wood that was too wet but I know that the wood was seasoned before I stored it in my shed two years prior to its use and very soon after loading the wood was nearly dripping wet. My thought was to run the dryer at what ever the return temp from heating the dhw was which will probably be closer to 165 F. Do you know of a reason not to run it that hot?

If your running the 165 degree water through a air handler then your air temps coming out of the air handler will not be 165. It'll be lower so I wouldn't worry about being to warm. If your doing this during the summer, I think the extra heat coming off the return water lines won't hurt anything, but the biggest issue will be moving allot of air through the stacks of wood. A uninsulated building closed up will get pretty warm in Michigan in the summer, it going to be a air movement issue.

 

[Duetech]

sdrobertson,
I have a small duct booster fan that I could use to force air through the unit. The building the boiler is in is fairly drafty but I will be sure to have a window or two open now that you bring up the probable humidity containment. Thanks...

 

[sdrobertson]

I've never used one but I always wonder how much those spinning things (wind powered ventilators?) that the used to use on barns and houses move remove hot air from the attics. A couple of those with the windy conditions we have here might be worth looking into as then you would get air movement with no motor running.

 

[blades]

Solar powerd roof vent perhaps?

 

[Duetech]

sdrobertson,
The barn vents work well when there is wind but I am intending to move the boiler into its own shed (20' x 14') with water storage and wood supply so modifying the current building will probably stick to window selection. The vents could be built into the boiler shed roof and the dryer could then act as a heater for cooler/cold weather if needed . Hopefully there will be about 5 cord of wood in the shed and the wood dryer would not be needed as a dryer.

blades,
There are some 12 volt blowers/fans that would work and solar panels are coming down to reasonable prices. That might be a worthwhile approach. I'll look into that thanks...

 

[Swamp Yankee]

We've got a Garn. When it is in 'standby' between burns there is a draft through the unit. The inside the combustion chamber is always whatever the water tank temp is....its like an oven/kiln. Towards the end of this season I experimented with loading it as soon as the burn is done, and blower is off. It acts as a wood kiln driving off more moisture from the wood. The wood gets real crispy and dry.

I doubt this improves the efficiency since the energy to drive off the moisture is coming out of the stored heat in the tank. BUT, it does make for a super clean burn. Seriously ZERO smoke at startup instead of the initial 4-5 minutes of smoke. I sometimes load it like I would for the next burn (say 1/2 full), then completely fill the combustion chamber to dry out some extra wood, then before I start the next burn remove the very dry extra wood. Make sense? Anyone else with a Garn try this, and does it impact efficiency? Thanks.

 

[Duetech]

Swamp Yankee,
Dry wood is the desired result with the draft you are getting through your Garn you are drying wood the way I want, but the EKO is down draft and my unit does not have storage so I couldn't do like you do with the Garn. I heat my dhw with the EKO in the summer and since I am having trouble getting wood for next season I thought I could try to dry fresh split wood with the surplus energy that I was generating while heating my dhw. During the summer I usually burn low btu woods like pine but the boiler has no problem achieving 165 F so I thought I could tap into the idling btu's and build up my winter supply of hard wood.

 

[603doug]

I read somewhere on line a freezer trailer was used for the kiln and they set up several fans stationed through out the box and it took about a week to dry. I have a insulated box trailer I use for storage and I have given some thought about throwing out the junk and setting one up, probably only cost 400 dollars a cord Right now I use my boiler for dwh only so I fill it up every few of days and run for a couple hrs each day to heat up the storage then shut it down and while it sets between firing it does dry the green pine I am using out pretty well. Some condensation in the fire box but it quickly burns out

 

[Duetech]

Right now I use my boiler for dwh only so I fill it up every few of days and run for a couple hrs each day to heat up the storage then shut it down and while it sets between firing it does dry the green pine I am using out pretty well. Some condensation in the fire box but it quickly burns out[/quote]

From what I understand condensation in a boiler during the summer months is best avoided as the water mixes with creosote and creates acid and shortens the life of the boiler.

The unit I was considering building would not hold a full face cord and I would want it to stay in the dryer long enough to dry the wood to about 20%. I am hoping that a week at 165 will pretty well get it down to the 20-25% mark. Maybe I will have to double the size or make two smaller units.

 

[michaelryba]

I too am behind the 8 ball for this winter coming up. My house and land is in a low liying area that's surronded by trees. I have a sun room on my house that has a very gentle pitch on the roof. I was thinking of tossing a buch of split wood up there this summer for a few months. I would think the combination of wind, black asphalt shingles & sun has got to result in a net drying of the wood.
Has anyone tried this?

 

[Gooserider]

I too am behind the 8 ball for this winter coming up. My house and land is in a low liying area that's surronded by trees. I have a sun room on my house that has a very gentle pitch on the roof. I was thinking of tossing a buch of split wood up there this summer for a few months. I would think the combination of wind, black asphalt shingles & sun has got to result in a net drying of the wood.
Has anyone tried this?

I would say that it might work, but you need to be REALLY careful about watching your deck load limits... It won't take a lot of wood up there to cause an overload, and that could be a really serious problem...

Gooserider

 

[Tony H]

Anyone ever try one of the large shop fans ? I had some wet wood at the end of last season and used a box fan in the boiler shed to blow warm air over it and it seemed to help .
I wonder if you had some fairly low moisture wood like box elder or silver maple and stacked it in a open pattern with a frame over it draped with black plastic and put one of those big shop fans (the ones that are about 4' across ) blowing thru the stack it would dry alot faster than normal.
Judging from rainfall and drying times it appears wind has much more to do with it that heat.

 

[DenaliChuck]

I too am behind the 8 ball for this winter coming up. My house and land is in a low liying area that's surronded by trees. I have a sun room on my house that has a very gentle pitch on the roof. I was thinking of tossing a buch of split wood up there this summer for a few months. I would think the combination of wind, black asphalt shingles & sun has got to result in a net drying of the wood.
Has anyone tried this?

You're liable to ruin your shingles...the grit on the shingle protects it from sun damage...