# Drying Wood Quickly Indoors



## Battenkiller (Jan 8, 2011)

I had a cord of freshly cut and split black birch delivered here last week.  I stacked up half of it outside and the other half inside (Sunday afternoon, January 2).   Monday night I went out and grabbed a fairly dense and sopping wet medium-size piece and brought it in and took a small slice off the end to get rid of any wood that may have dried while it was outside the last couple days.  Then I took a 2-3" slice off the end and weighed it on the old hippie herbal remedy weigh station (triple beam scale).  Came out to just a hair under a pound - 445.4 grams.  

I placed the remainder of the split on my old produce scale, and it weighed 10 pounds, 8 1/2 ounces (10.53 pounds).  I will leave it right there and weigh it each day and record the weight to get a drying curve established.  I will also take the relative humidity (RH) every day at the same time that I weigh it and record the result.  I have a large commercial floor fan blowing on the stack 24/7 to keep air moving through it.  It seems to be doing a very good job of moving air through the spaces between the splits so they can dry faster, just like being outside in a constant breeze.

I used the smaller sample to determine the moisture content of the sample split to get a baseline.  This stuff is way too wet to even think of using a resistance-type moisture meter on it.  I used the much more accurate oven-dry method to get the MC within a couple tenths of a percent.   I will use that info to evaluate the moisture content of the larger split as it dries out over the next few weeks.

I thought this was an exceptionally dense piece of wood.  I took it into the kitchen, filled the sink and dropped it in.  Sank like a rock.  

I then took it out of the water and went downstairs to chop it into little pieces with my trusty kindlin' meat cleaver (had to make sure I saved every little piece). That would allow it to dry much quicker.  I wanted to make sure I went slow with this one since the last time I did this I just wanted to demonstrate the method to the membership here.  This one's for the books.  Any unwanted charring of the wood will cause the sample to lose some volatile substances, skewing the result to show a higher initial MC than it really had.

I started out using my kitchen microwave to dry it, but that was taking forever and it was getting late, so I did it old school - overnight in an oven set at 215ÂºF.  Woke up and weighed the pieces on my triple beam - 282.9 grams.  There was no evidence of charring anywhere, so I think the stuff is a good. 


445.4 - 282.9 = 162.5 grams water lost = 36.5% water by weight (wet-basis), or 57.4% MC (dry-basis).  Not as wet as it looked, but certainly twice as high as any moisture meter will allow accurate measurement.


So, the 10.53 pound split sitting on the scale in the basement at 36.5% water contained 3.84 pounds of water when I placed it there and 6.69 pounds of wood fiber.  This is the figure that is needed to compute all further moisture loss using the changing weight alone to make the calculations.  The ramifications of this are that anyone can accurately determine the MC of there firewood at any time if they take a few representative samples during the season, weight them, determine the MC at that point, compute the dry fiber content, and use this at any point in the future to calculate the MC of their wood merely by weighing it.  No meter needed, no re-splitting, no sorting through piles looking for suitable splits.  And you don't need to be artificiality drying your wood indoors to take advantage of this technique.

The RH in the shop was determined using a Taylor sling psychrometer.  On day one, dry-bulb temp was 83Âº, wet-bulb temp was 66Âº.  17Âº wet-bulb depression at that temp = 40% RH.  Not as low as it will get when all the wood starts drying out.  The day before I started this I took in 1/2 cord from the same soaking wet load of black birch and stacked it 5' high, 42" in front of the stove (even with soaking wet wood I adhere religiously to clearances) with a large fan blowing against the back of it.  On day one it was acting as an gigantic organic humidifier with the wonderful scent of wintergreen emanating from it.


Results so far after four days of drying:


*Day #     Weight (lbs)     Water Wt (lbs)     Fiber Wt (lbs)     Rel. Humidity    MC (dry-basis)  MC (wet-basis)     *

One:        10.53                        3.84                               6.69                           40%                           57.4%                        36.5%
Two:        10.03                        3.34                               6.69                           35%                           49.9%                        33.3%             
Three:        9.56                        2.87                               6.69                           34%                           42.9%                        30.0%
Four:           9.38                        2.69                               6.69                           30%                          40.2%                        28.7%
Five:            9.13                         2.44                              6.69                           28%                          36.5%                        26.7%


As you can see, the 10 1/2 pound split lost a full 1/2 pound of water in one 24 hour period, 6 ounces the next day, 4 ounces the day after that and 3 1/2 ounces since last night.  MC at present is 36.5% (dry-basis), or 26.7% (wet-basis).  Just to compare methods, I grabbed a similar size split from the inside stack (it had been inside one extra day), split is and measured the MC.  It measured at 34% MC on the meter, which is a dry-basis measurement.  Pretty durn close, eh?


As my indoor stockpile of wood dries more and colder weather hits, RH down there should drop to about 20%, at which point all of the wood will be fairly well dried out and ready to burn (25% dry-basis, 20% wet-basis).


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## EatenByLimestone (Jan 8, 2011)

I love the taste of black birch....


Matt


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## jotulguy (Jan 8, 2011)

And to think he was just a janitor at harvard......how do you like them apples! 
Sorry guys. After my head stopped hurting from all the math to this post(all great info by the way!) That movie popped into my head.


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## pen (Jan 8, 2011)

The data table is nice but it would be better if the data were presented as a line graph   

pen


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## Dix (Jan 8, 2011)

BK, you need a vacation.


Seriously.


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## pen (Jan 8, 2011)

Doing The Dixie Eyed Hustle said:
			
		

> BK, you need a vacation.
> 
> 
> Seriously.



Oh dear god yes!

I just hope he takes me up on my graph suggestion so that he can go ahead and create a trend, then plot ahead into the future to find when this wood will actually be dry enough to burn, then continue letting it dry and see if it actually follows a linear path in water reduction as it dries.

I'll bet a beer that it's not so predictable.  

pen


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## EatenByLimestone (Jan 8, 2011)

Doing The Dixie Eyed Hustle said:
			
		

> BK, you need a vacation.
> 
> 
> Seriously.




Wait until after you are done weighing the wood so you don't have to do the experiment again.  

Matt


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## begreen (Jan 8, 2011)

Wow, sounds like the boiler video wasn't too far off. 3# of water is about 1.5 liters. Where are the control group stats?


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## woodgeek (Jan 8, 2011)

beekay,

sniff.  thank you!

geek


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## BrotherBart (Jan 8, 2011)

I only look at the PowerPoint presentations.


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## Big Al (Jan 8, 2011)

As folks say in my neck of the woods would say, Battenkiller is "wicked smott". 

But seriously man, your attention to detail and analytical mind never cease to amaze. Keep up the good work.

Al


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## nelraq (Jan 8, 2011)

Interesting thread!

I am a farmer, and make a lot of hay in the summer.  To ensure good hay for my customers, I have a moisture meter in the baler, and also a hand held meter which I can use to test hay that has already been baled.

To check the accuracy of the meters, ( especially the hand held one), I occassionally test a hay sample using  the microwave.

It's pretty simple really.  You start with a sample which weighs approx 50 grams.  In the microwave it goes with an 8 oz. glass of water.  When the water boils, take it out and put another 8 oz glass in.  Do this a 3rd time.  Take the water and the sample out and weigh the sample.  The difference, as a % of the 50g starting weight is the MC of the hay.  eg. 50g(start) - 42g (finish) = 8g.

(8g/50g) x 100 = 16% --the moisture content of the hay.  The water, by the way is in there to prevent the hay sample from catching on fire!

I've thought alot about trying this on firewood - so a couple of weeks ago I 'gave it a go"

I re split a split and checked the moisture with my meter - 11%.  Then I cut an end off of the split (to get away from the drier end piece) and then cut a small piece for testing.  Checked it with my meter and it was also 11%.

It weighed in at about 300 grams--exact #'s are on my desk somewhere -but I can't find them!

The rest of the experiment was carried out as above with the hay - with one exception.  Because of the weight of the wood, I microwaved it (with water) probably 5 or 6 times.  I weighed the wood after each 'bout' with the microwave and finished when the weight of the wood started going down in weight by only 1 or 2 grams.

Calculated the MC as I did for the hay and, low and behold, it was 11% - exactly the same as the meter.

Just for the heck of it, I put the wood back in the microwave with another glass of cold water.  In about 15 or 20 seconds, there was big smoke happening in the microwave!  The wood was obviously dry, and probably would have caught fire in another few seconds.  

I got the wood out with an oven mitt and took it outside - still smoking like crazy!!  The smoke was coming from the center of the wood--c/w good sized black charred area.   You couldn't touch it with your bare hand - it was really hot!

I certainly wouldn't do this test on a regular basis, but it was interesting to do it once anyways!  BTW, I already knew that my MC was dead on.  I took it to a local lumber mill last spring and compared a bunch of readings with their mega $ one.  Mine was +/- 1% on every test.

Cheers!!


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## remkel (Jan 8, 2011)

Analysis like this is woodburner porn....I look forward to the final results.


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## littlesmokey (Jan 8, 2011)

An observation from a non-technical guy, but your drying will not be linear. It will be a dramatic slope to a very shallow run. As they out parts dry, the inner parts must move the moisture to the air through the already dryer wood. Also, the closer the wood comes to the ambient moisture levels, it will slow also.

Just an aside, I use my microwave from time to time to dry wood turnings. Some are rough bowls of unusual woods I could not help but turn early, and others were contracts for special restorations when the only appropriate woods at hand were too high in moisture content. Like some clock finials in rosewood that came from Liverpool, England. Warehoused two hundred year old wood at 72% moisture. The warehouse was on the waterfront.


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## DanCorcoran (Jan 8, 2011)

I see where this thread is going:  stack a cord of wood to dry in your living room and you won't need to put a kettle of water on the stove to increase your humidity (but you will need to scrape the mold off the walls at least once a season).


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## Battenkiller (Jan 8, 2011)

DanCorcoran said:
			
		

> I see where this thread is going:  stack a cord of wood to dry in your living room and you won't need to put a kettle of water on the stove to increase your humidity (but you will need to scrape the mold off the walls at least once a season).



Not true at all.  Even at the highest humidity level, the RH down there never got over 40%.  That's still pretty dry.  For about three days I got some condensation on the big windows at the other end of the shop, but that stopped pretty quickly as RH dropped to 30%.  I do have mold down there, but it's all along the baseboards from the yearly springtime flooding I suffer with every snowmelt.  I've been doing this for 20 years now and I have never had to clean mold off of anything.  By the time I bring wood in here in that quantity, the wood in my housing structure is so dry that is sucks it right out of the air before it has the slightest chance to condense on surfaces.  It become liquid water again, but _inside_ the structural members and sheetrock, etc. by forming hygroscopic bonds with these substrates.  And when it does, it releases the heat initially lost through evaporation back into the home.




			
				BeGreen said:
			
		

> Wow, sounds like the boiler video wasn't too far off. 3# of water is about 1.5 liters. Where are the control group stats?



I never doubted the amount of water they claimed was in the split.  The issue was with the faulty way they numerically expressed both moisture content and heat loss.  The split they used as an example was 50% water by weight.  My birch was only 36.5% water.  My wood was so obviously wet that only an idiot or a wet-wood burning genius would try to heat his home with it, so I don't even see the point of comparing a piece of firewood that had much more water than mine has to a well-seasoned split.  No one is getting anywhere with wood that is half water by weight (100% MC as a wood technologist would express it).  That video would have been supremely unimpressive if they chose instead to demonstrate the difference between a split at 25% water (marginal firewood) and one at 20% (seasoned firewood).




			
				littlesmokey said:
			
		

> An observation from a non-technical guy, but your drying will not be linear. It will be a dramatic slope to a very shallow run. As they out parts dry, the inner parts must move the moisture to the air through the already dryer wood. Also, the closer the wood comes to the ambient moisture levels, it will slow also.



I never thought the drying would be linear, it should resemble an exponential decay function.  If you look at the amount of water lost so far each day, it mimics almost exactly a radioactive half-life function where the half-life is one 24-hour day.  That will change as the RH in the room drops.  In fact, it already did on the last day, where the wood dried more than the trend line would have predicted.  That's because the RH in the shop dropped to 28%.  At the wood dries and the RH continues to drop, I fully expect that the curve will be become slightly steeper than the original function would have been if that trend continued, although it will always be concave-up in shape.  An engineer would tell me I'd have to use differential equations to accurately model the drying, but we don't need to be that precise.  We're not trying to land a rover on the Martian landscape, we trying to get a fair idea of how fast wood dries so we can get a rough idea about when we can stick it in the stove.


As I said, you can still take advantage of this methodology without having to use it to speed-dry your firewood.  Next time you are bucking wood, cut several cookies from each wood type, weigh them and mark the weight in Magic Marker and toss them out in the sun to dry.  This will dry them most of the way in short order.  Take some splits from the same wood the cookies came from, weigh them, mark the weight and set them aside.   At any time after this, you can bring the weighed cookies inside and dry them out in a 215Âº oven (must be as close as possible to that temp) until they stop losing weight.  Record the final weight and use it to calculate the starting MC.  It will be the same starting MC that the splits you set aside had.  Now all you have to do is weigh the selected splits to see how much water they lost, giving you a very good idea how the rest of the entire load has lost water weight.  

By doing this little procedure at the onset of the season, you can check the MC of your wood at any time thereafter just by weighing the selected splits.  If you weigh them once a month, you can get a drying curve established that will allow you to predict about when the wood will be ready.  Not perfectly, but infinitely more accurate than saying, "Well, now... oak needs at least two full years... maybe three... in full sun and wind to season properly."  That ain't the least bit accurate.



I will be creating a spreadsheet that can be used to do all of the calculations needed to do this, so anyone interested in it can get it from me just by sending me an e-mail.  That way, even if you have a hard time understanding (no offense, some folks minds work differently than others) what, and why, and how to use the data, all you'll have to do is weigh, dry, re-weigh and punch in the numbers.  The spreadsheet will spit out the MC.


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## woodgeek (Jan 8, 2011)

Battenkiller said:
			
		

> littlesmokey said:
> 
> 
> 
> ...



Ahem, not exponential, but should be square root of time....


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## boatboy63 (Jan 8, 2011)

Interesting study, but if wife had seen me put a split into oven and heat overnight at 215*, I would be in a nice warm, rubber room by now. After further thought, it may not be a bad idea...warm surroundings and 3 meals a day.


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## herdbull (Jan 9, 2011)

I love this type of information. I'm an engineer by trade, a #'s guy by heart, toss in a huge dose of anality and this thread is right up my alley. Besides that it's great info to have. This may lead me to do the same type of testing. I store a full years worth of wood in the pole shed. It's already seasoned when I put it in there but this explains a lot. 

A this rate of losing water a guy could cut, split and stack it inside and have ready to use wood in no time. This would explain why the last weeks load or 2 I have brought in the house could practically be lit on fire with a lighter. I need to get a gauge so I can test it. I have a feeling it's too dry.


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## gibson (Jan 9, 2011)

Holy crap!  I think I need to start smoking weed!


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## Cal-MI (Jan 9, 2011)

Has anyone seen a wood fired firewood drying kiln? Or plans for one? I have a lot of red pine trees available. They are lying on the ground with the bark fallen off. Cured, dead over a year, but full of rainwater and ground moisture. And, of couse, now covered with snow.


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## tlingit (Jan 9, 2011)

Wow.  I am always so amazed by the intellegence and experience of the people who post here.  This information is so interesting and useful.  We do bring questionable wood in about a week early, especially in the fall.  It just hangs out in the garage until its time arrives.  I just thought I was giving the snow time to dry off, turns out there is science behind it.  Thanks BattenKiller.


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## tlingit (Jan 9, 2011)

Wow.  I am always so amazed by the intellegence and experience of the people who post here.  This information is so interesting and useful.  We do bring questionable wood in about a week early, especially in the fall.  It just hangs out in the garage until its time arrives.  I just thought I was giving the snow time to dry off, turns out there is science behind it.  Thanks BattenKiller.


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## pen (Jan 9, 2011)

I think some folks are jumping the gun here.  There simply is no quick way to dry wood w/out using a kiln.  There are many, many folks who advice not bringing in more than a day or two worth of wood into the house for other factors such as INSECTS!  There is no substitute for planning ahead and getting wood dried / protected properly.

Before you all bring the wood into your house or into your garage, read about Soupy's experience that he had a few weeks back.

https://www.hearth.com/econtent/index.php/forums/viewthread/66451/

If you think your house at 70 degrees w/ low air flow in the winter will dry wood well, try using a few 85 degree summer days w/ sunshine and wind.

pen


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## Battenkiller (Jan 9, 2011)

woodgeek said:
			
		

> Ahem, not exponential, but should be square root of time....



Ah..... yes.  :shut: 


I was trying to express the disappearance of water over time, but I accidentally used the amount of water lost each day rather than the weight of the water remaining each day.  If the amount of water remaining each day was half of what it was the day before, it would look just like a decay function with a half-life of one day.  But that's not what is actually happening.  The water is disappearing much slower than that, and not in an exponential fashion at all.  It's still a concave function, though, as can be seen in the graph below.  Thanks for catching that.  ;-)


BTW it's down to 25.4% water by weight (% MC wet-basis) after only 5 days drying.  Note in the chart how closely the RH in the room matches the percent water weight.  The wood is keeping the air humidified less and less each day, which is generating the RH curve seen.


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## Battenkiller (Jan 9, 2011)

pen said:
			
		

> I think some folks are jumping the gun here.  There simply is no quick way to dry wood w/out using a kiln.
> 
> If you think your house at 70 degrees w/ low air flow in the winter will dry wood well, try using a few 85 degree summer days w/ sunshine and wind.



You're way off, Pen.  Is my scale lying to me?  I can take photos each day if you want.  I already took the MC of one split from the stack.  Re-split it and used the moisture meter and it was down to 34% MC from a starting 56.5% MC four days before.  Is my meter lying as well?

BTW my basement ain't no 70Âº, it's about 82-88Âº almost all the time, with the RH dropping way lower (27% RH tonight) than it ever drops to outdoors in the summer, with good air movement through the stack 24/7.  My basement _is_ a kiln right now.


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## akennyd (Jan 9, 2011)

Good stuff!!  Thanks for taking the time to share with us...


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## partybob99 (Jan 9, 2011)

Sen. John Blutarsky said:
			
		

> Holy crap!  I think I need to start smoking weed!



LOL! x2!!


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## woodgeek (Jan 9, 2011)

sorry BK, should have been more specific--diffusion-limited rate of loss should go ~sqrt(time). (assuming diffusion inside the wood, and boundary layer in the wood that is thin compared to the split, i.e. quasi-planar)

looking at your data, _rate_ of loss at 1.0 day is ~0.47 lbs/day (to get a better estimate of the rate at 1 day age, take the loss from day 0 to day 2 and divide by two)
similarly, at 4.0 days age, _rate_ of loss is ~0.16 lbs/day, or less than half of the (estimated) rate after 1 day drying. Would have predicted day 4 rate to be 1/2 day 1 rate, day 9 to be 1/3 day 1 rate, etc.  Could be measurement uncertainty or a bad estimate for the day 1 rate (surface moisture or bad interpolation).  

It will be nice to see if the day 9 rate and the day 4 rate are in the ratio 2:3.  I would predict the loss rate on day 9 to be 0.16*0.67 = 0.11 lbs/day


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## pen (Jan 9, 2011)

Battenkiller said:
			
		

> pen said:
> 
> 
> 
> ...



Exactly, it's still way too wet to burn!  Is what you are doing better than nothing to get it dry?  Yes.  But it's pointless if the wood was seasoned properly in the first place.  Have any ash in that pile?  What a mess you will have when the bark borers come out of it!  (trust me, i've made this mistake before).

My bottom line, how long and under what exacting conditions in your basement will it take for your firewood to get down to a % moisture so that it's actually acceptable to burn?  I'm not denying that it's drying, just saying you haven't gotten to the promised land yet and therefore I think it's too early for people to be making conclusions based on this data since your wood, while being drier, is not dry enough.

pen


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## snowleopard (Jan 9, 2011)

I"m doing the `first year heating with wood getting by' thing, and was trying to dry out wood enough to burn that had gotten soaked in a (three-day!) winter rainstorm.  Some of it had probably been dampish before that because of the punk layer.  Then one day I looked at one of these pieces I was trying to dry inside, and realized two things:  one of my reasons for having a woodstove was to help reduce the humidity in my house, and bringing in wet wood wasn't helping with that goal.  The second realization hit me because a piece of bark dropped off and I looked at the squishy mess underneath, and realized that I'm bringing in a ton of mold spores with this wetish wood, and that's not a great idea either, particularly since the drying-off place is the sunroom, where most of my cherished greenery lives.  That chunk of wood, along with its damp breathren, went back outside to dry and burn on chilly days next summer or fall.  Thus endeth my drying-inside experiment.  Fortunately, I've found better wood underneath the damp stuff, so my heating-the-house-with-what-I've-got-on-hand experiment continues.


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## SolarAndWood (Jan 9, 2011)

Battenkiller said:
			
		

> My basement _is_ a kiln right now.



So how does the rest of your process work?  Have a bunch of trees outside a basement window that you cut, split and toss in a few days before you need them?  Or split them in the spring and finish them up in the kiln in the days before they become fuel for the kiln?  I would love to be able to go from heap to kiln to stove.  Would save a lot of time and energy.


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## JeffT (Jan 9, 2011)

I always like dry time info but how many kw-hr.are you using that proper planing and mother nature would take care of.Wood-fired kiln,yea lets burn wood to dry wood.


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## woodchip (Jan 9, 2011)

Although I have experimented with quick drying a couple of bits of birch near my fire, I would be a bit cautiousof bringing a load of wet wood into the house because all that moisture is going to go somewhere, either on the windows, behind some cupboards, or somewhere where you will end up with mould. 

It's a brilliant graph though, I would be curious to see one for a split laying outside in a woodpile on a few sunny breezy days in July, and as a comparison, a whole length of wood uncut, just to show how little wood does season before it is cut and split. 

Studying wood drying is actually much more interesting than watching paint drying. 

I just have to convince mrs woodchip


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## Battenkiller (Jan 9, 2011)

woodgeek said:
			
		

> sorry BK, should have been more specific--diffusion-limited rate of loss should go ~sqrt(time) Would have predicted day 4 rate to be 1/2 day 1 rate, day 9 to be 1/3 day 1 rate, etc.  Could be measurement uncertainty or a bad estimate for the day 1 rate (surface moisture or bad interpolation).  I would predict the loss rate on day 9 to be 0.16*0.67 = 0.11 lbs/day



I see what you're saying.  You're talking about Fick's Laws.  I wouldn't expect this process to rigidly adhere to a diffusion function, at least not in the beginning.  There are too many variables when water diffuses through a non-homogeneous porous media.  Biggest one I can think of is the difference between diffusion rates along the grain and across the grain.  Water moves along the long grain of the wood 10-15 times faster than it does across the grain.  As well, water diffuses across the tangential plane slower than it does in the radial plane, and this split is not quite square in cross section.  It's pretty funky, with a small crotch at the fat end.  

Then there is the difference between the movement of free water and bound water to consider.  Most of the free water left the wood pretty quickly, I imagine within a few days.  As long as the wood is at least 28-30% MC in the middle, there will be a combination of free water and bound water.  The outer parts of the split are much drier, so there is no free water left there.  Free water is able to move faster because it doesn't have to break the hygroscopic bonds that the bound water has to.  That should actually increase the steepness of the diffusion gradient until it has all moved out of the intercellular spaces, at which point I expect an even slower removal of the bound water to occur.

Lastly, as the wood shrinks as it drops below the fiber saturation point (FSP), the pores in the wood will get smaller and constrict the movement of the bound water molecules through them.  This will cause a further slowdown of the drying rate.

So, expect some very rapid drying in the beginning, then maybe it will dry in a slower but more predicable fashion.  I'll try to include a formula in the spreadsheet for computing the diffusion-limited rate of water removal and compare it to the actual rate, and then graph them out to see where and how they deviate.


It's possible that I could have made an error while computing the starting MC, but I was extremely careful and triple checked everything, so I think this is unlikely.  However, the remainder of the split has sat in the same position on my scale since day one.  That's the only thing I am measuring at this point.  The scale is an old but very accurate analog one that is very easy to read, and I used formulas within the spreadsheet to do all the calculations to convert the weights to decimal format.  You can see the wisdom of doing this when you notice that there is a difference between a few of the weights in my first post and the ones in the spreadsheet.  They were ones that I calculated quickly on my TI-85, and I must have made an error on them (probably rounding error).  Not the case with the figures in spreadsheet, which is dead on and calculates everything to several places before rounding to two decimal places at the end. 

After doing this successfully for about 20 years now, I think it's going just about the way I thought it would.  Somewhere before 21 days I predict that the curve will creep cross the 20% MC wet-basis line and it will be as dry as the high end MC of the wood used in the EPA testing procedure and be perfect for the stove.  I've never measured both the MC and the daily drying rates before (although I have used the scale before to let me know when the wood drying had come to a near standstill), but three weeks has always led to a very superior product for me on all but the most recalcitrant woods.


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## Battenkiller (Jan 10, 2011)

snowleopard said:
			
		

> The second realization hit me because a piece of bark dropped off and I looked at the squishy mess underneath, and realized that I'm bringing in a ton of mold spores with this wetish wood, and that's not a great idea either, particularly since the drying-off place is the sunroom, where most of my cherished greenery lives.



Yeah, never bring in really punky wood to do this with.  I've done it before and it's not a bright idea.  Given enough time, that punk can get so dry and light that it just blows all over the room every time you touch it, creating a major fungus hazard.  Also, the dessicated punk layer is extremely flammable.  One spark could set the whole stack ablaze.  The wood I move in _en masse_ like this has been cut and split in late fall or winter.  Bugs, peeling bark... any questionable wood stays outside where it belongs.  If it's really bad, it goes into the fire pit in the summer.





			
				JeffT said:
			
		

> I always like dry time info but how many kw-hr.are you using that proper planing and mother nature would take care of.Wood-fired kiln,yea lets burn wood to dry wood.



Ain'tcha reading?  It _is_ a wood-fired kiln, powered by my VC Vigilant while it heats my home.   ;-)   Cost of running the fan is negligible.  Anyway, it helps to move the air near the stove, so it actually is nothing everyone here hasn't been advised to do for improved heat circulation.





			
				woodchip said:
			
		

> I would be a bit cautious of bringing a load of wet wood into the house because all that moisture is going to go somewhere, either on the windows, behind some cupboards, or somewhere where you will end up with mould.



Doesn't happen if you do it in the dead of winter.  The moisture-hungry wood in your home sucks up that moisture like a sponge, with no chance for it to condense anywhere.  Two-three days of some minor condensation (frost) on the windows, then it's off to the races.  No time for mold to develop, and the windows will be too cold anyway.  In 20 years, I've never seen a trace of mold on anything but a spot or two of mildew on the occasional split.  Both air-dried firewood and that "kiln-dried" stuff at the supermarket is usually a lot more of a mold risk in the home.  The relative humidity in my basement was only 40% at the highest (the day after I moved the wood in).  Next day 35%, then 34%, then 30%, etc.  All too low for mold to grow.





			
				SolarAndWood said:
			
		

> So how does the rest of your process work?  Have a bunch of trees outside a basement window that you cut, split and toss in a few days before you need them?  Or split them in the spring and finish them up in the kiln in the days before they become fuel for the kiln?  I would love to be able to go from heap to kiln to stove.  Would save a lot of time and energy.



Like I mentioned above, the wood is cut and split by a commercial wood vendor just before I begin to dry it.  Ain't ever gonna be wetter that that, but it really doesn't make much of a difference.  The slow part is always getting it from the FSP (~30% MC) down to burnable wood.  The first part goes quickly at any starting moisture content.  

By putting all that wood into a gigantic heapen-hausen, you are doing what most large commercial kiln-drying operations do by pre-drying the wood.  You will save about a week or so over my method, but you will run a slightly greater risk of bringing unwanted strangers into your home (bugs, mold, hobos, etc.).  In general, though, you should be fine.  BTW the process won't work well until the outside air gets very cold and has very little water in it.  When you draw this dry air into the home (by burning your stove, or just natural air infiltration) and heat it up to living temps, the relative humidity of the air plummets.  

By putting it in the same room as the stove, you are elevating the temperature to a much higher 24-hour average than at any time during the course of the year.  In the height of summer, the RH will rise to near 100% most nights, effectively halting your wood drying, even setting it back for a few hours every morning until the dew evaporates.  This process beats that all to hell.  In fact, the daily average RH for out area is something like 75% RH.  Give 20% RH, steady temps in the 80s, and constant breeze a try and see what happens.  :coolsmile:


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## NH_Wood (Jan 10, 2011)

BK - cool stuff! I like the idea of regressing MC as a function of wood mass. My only problem would be knowing which splits came from the same tree (i.e. started at an assumed equal MC per unit mass) for the periodic determination of MC. In other words, you'd need to have a regression equation for each cohort of splits that originated from the same tree. Your situation of having a large group of splits from the same tree will allow a cool look at how well a linear regression fits a typical year of seasoning for that black birch. I wonder if you'll find the drying process to become non-linear under natural drying conditions (drying faster during some months vs. others - I'm guessing so). I have enough wood now that I know it'll be seasoned by the time it hits the stove, but this kind of stuff is fun! By the way, I'm heading out tomorrow or Tuesday to tackle a nice cluster of black birch at my work - looking forward to it! Love black and yellow birch - I leave white and gray for shoulder season. Cheers!


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## madison (Jan 10, 2011)

Hmmm, still hangin' onto the triple beam balance?  "Oh yea, it is for the kitchen."  BTW,  What's the MC of that ganja?


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## woodchip (Jan 10, 2011)

Battenkiller said:
			
		

> In 20 years, I've never seen a trace of mold on anything but a spot or two of mildew on the occasional split.  Both air-dried firewood and that "kiln-dried" stuff at the supermarket is usually a lot more of a mold risk in the home.  The relative humidity in my basement was only 40% at the highest (the day after I moved the wood in).  Next day 35%, then 34%, then 30%, etc.  All too low for mold to grow.



You would hate our winters then. 

Usually 3 months of 95% humidity outside, and struggling to get below 60% inside, damp everywhere. 

Current humidity as an example....... 96% humidity outside and 89% humidity in our bedroom, 80% in the lounge. 

That's why so many people over here have rheumatism problems, including me


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## woodgeek (Jan 10, 2011)

BK--

The anisotropic diffusion shouldn't change the rate vs time dependence (theoretically, of course), and the funky shape should not be a problem either, so long as the thickness of the dry layer is less than the split radius.  Of course, after a couple weeks, I expect that will not be the case, and the rate will drop through the floor relative to the sqrt(time) prediction--also a nice way to know when you are done.

I will think about free/bond water some more, but I have always assumed that water moves b/w these populations freely/quickly compared to later diffusion.  Theoretically, could create an isotherm/phase change front, but I don't think the binding is THAT strong.

I can buy 3+ weeks in a hot dry basement will do the trick.

Perhaps you might want to summarize the point for other readers thusly:

1) The wood drying process slows dramatically as it proceeds, in a diminishing returns sort of way, inside or outside.
2) If you find wood takes x days to dry in some circumstance, half of the drying or more might occur in the first x/4 days--naturally leading to arguments on the board about how long is long enough b/c a small difference in final dryness can lead to large difference in drying time required.
3) If you need the humidity anyway (requiring useful BTUs) and mold/bugs are not a problem, drying wood indoors in the winter is about 5-10x faster than doing it outdoors, but still takes *weeks*, not days to 'complete'.  Personally, I often end up with wood that has been drying outside for a few months, and is 'halfway there'.  I find after two additional weeks inside (not a huge amount as I am a WE burner), and it burns exactly same as wood that has been seasoning outside for about a year (ash), in my non-EPA POS stove.  The half-seasoning outside takes care of the bugs--the rare moldy piece (I dry under cover) is chucked in the stove. 
4) Putting wood close to the stove might further cut the drying time, but at distances/temps respecting combustion clearances you still need *>1 week*, not hours or days.  The limited space this close to the stove makes this approach a PITA, and of dubious safety, relative to having a somewhat larger store away from the stove, but still in a heated, ventilated low RH part of the house.  Reports from users about the benefit of stove drying wood are seeing effects from removing surface moisture only, or drying out a thin layer around the surface (helping take off).  BK and I are talking about getting the wood to a point equivalent to months of seasoning outside--through and through.
5) These gen'l findings summarize numerous more or less careful expts of this sort reported on this board over the years, conducted with scales and moisture meters, etc. but YMMV.


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## SolarAndWood (Jan 10, 2011)

Woodgeek, nice summary for the rest of us.  So, if you don't have a place inside to store a cord plus of wood at 80+ breezy conditions and need dry wood to make your stove operate properly, this might not be the best way.  



			
				Battenkiller said:
			
		

> SolarAndWood said:
> 
> 
> 
> ...



So, draw the dryest air of the year in which for us in upstate NY is when we want to burn anyway, heat it up and blow it across the splits until the RH of the room gets down to X%?  If you are not heating from your basement and essentially creating the kiln like conditions anyway, is there another option?  Something like instead of adding a stove to the basement, add an air furnace and direct the plenum into a pair of cord or so sized wind tunnels?  Then, keep track of the RH of the box and wait until it gets down to X% before switching the output of the furnace to the other box?  Maybe put a filter on the far end of the box from the plenum output to catch any potential nasties?


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## Battenkiller (Jan 10, 2011)

SolarAndWood said:
			
		

> So, draw the dryest air of the year in which for us in upstate NY is when we want to burn anyway, heat it up and blow it across the splits until the RH of the room gets down to X%?  If you are not heating from your basement and essentially creating the kiln like conditions anyway, is there another option?  Something like instead of adding a stove to the basement, add an air furnace and direct the plenum into a pair of cord or so sized wind tunnels?  Then, keep track of the RH of the box and wait until it gets down to X% before switching the output of the furnace to the other box?  Maybe put a filter on the far end of the box from the plenum output to catch any potential nasties?



First off, you can't monitor this process merely by watching the RH in the room.  In my case, the wood is keeping the RH up, and as it dries there will be lees humidification going on.  I didn't mean to imply that they would necessarily follow the same curve, just noting how it is following along so far.   There is absolutely no one-to-one relationship between the RH in the room and the MC in the wood in the room.  Given enough time, the wood would reach a EMC of about 6% MC at 30% RH and an ambient temperature of 84ÂºF.  In fact, right now all of the wood in my shop that's not firewood is so low in MC it won't even register on my meter, which means it's below 6% MC, even though the RH in the room is hovering around 27%. 

At some point the RH won't go down any further (I threw out the 20% RH figure off the top of my head), but the wood will continue to dry, although at a progressively slower rate.  This is because the remaining water in the wood won't be enough to compensate for the natural air infiltration rate in the home.  If my home was tight enough that air infiltration was minimal, I wouldn't do this indoors in the first place.  Nor would it be very effective, since the rate of dry outside air entering into the home would not be enough to get the low RH I am seeing here.

FWIW I think running a furnace to add heat in order to dry firewood seems extremely counter-productive to me.  You will lose way more than you gain in increased burn efficiency in the stove.  My place is custom made for this technique.  Smallish home, walk-in entrance to the basement, workshop in the basement with stove added, etc.  With the amount of wood you use, this would be more trouble than it's worth.  Best bet would be to build a 1-2 cord enclosed shed.  Insulating it will help keep temps up.  My best friend oversees a propane-fired firewood kiln operation.  They use old reefer truck boxes (not the kind of reefer I used to weigh on the triple beam) to conserve on the amount of propane used.  Just make sure it's leaky enough to allow the dry outside air into it and the moist air to exit it, that's critical to getting the fastest drying rate.  Heat it with an old box stove you got on Craig's List for $50 or so.  Get it ripping and start tossing in the green wood.  Add a couple cheap fans, and friend... you in _bidness_!  

Oh... I just looked at the scale and the split is now down to 8 lbs, 12 oz.  It has lost 47% of the water it originally had in it, and is now down to 23.6% water by weight.  Tonight at 9 PM it will have been down there one week and it's already burnable.


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## Battenkiller (Jan 10, 2011)

woodgeek said:
			
		

> The anisotropic diffusion shouldn't change the rate vs time dependence (theoretically, of course), and the funky shape should not be a problem either, so long as the thickness of the dry layer is less than the split radius.  Of course, after a couple weeks, I expect that will not be the case, and the rate will drop through the floor relative to the sqrt(time) prediction--also a nice way to know when you are done.
> 
> I will think about free/bond water some more, but I have always assumed that water moves b/w these populations freely/quickly compared to later diffusion.  Theoretically, could create an isotherm/phase change front, but I don't think the binding is THAT strong.



May be one of those times when theory don't quite explain everything?   :smirk: 

I think the main thing driving the more rapid removal rate in the beginning is that most of the free water evaporating from the end grain should be getting to the surface via capillary action rather than by diffusion.  This is a much faster process for bulk flow in wood.  Whatever the reason, the weight data for the test split is good, I can assure you.  There has to be some explanation why it dried slightly faster at a time when the RH was actually higher, but I do know there was no extra water on the outside at all.  This was cut and split right after it sat on the header for a week so during a dry spell we had, and I brought half of it in right away after the delivery.  The test split was taken from outside the following day, after a long, clear windy day.  The outside was essentially as dry as you will see for freshly split wood.

I think it's much more important to examine the drying rate at the end of the process.  By taking careful note of the tail end of the drying water losses, it should be possible for anyone to tell when the wood has dried sufficiently just by taking regular weight measurements and looking at the slope of the curve.  When the rate of weight change matches the rate gotten from the experimentally derived curves, the wood should by and large be ready to go, especially if drying at that point is strictly diffusion-limited.  Of course, matching the experimental conditions might require a kiln in some locations.  :coolsmirk:


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## SolarAndWood (Jan 11, 2011)

Battenkiller said:
			
		

> FWIW I think running a furnace to add heat in order to dry firewood seems extremely counter-productive to me.



Ha, it won't be a gas furnace.  I need to add a burner to the lower level before it is going to be usable any way.  Right now, the options on the table are a boiler or a second stove.  But, it could also be a wood furnace.  I'm not going to be heating from the lower level, so it won't be 80+ down there.  But, if I directed all the output of the wood furnace through a box or two, I could probably keep the box that warm.


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## Battenkiller (Jan 11, 2011)

SolarAndWood said:
			
		

> Ha, it won't be a gas furnace.  I need to add a burner to the lower level before it is going to be usable any way.  Right now, the options on the table are a boiler or a second stove.  But, it could also be a wood furnace.  I'm not going to be heating from the lower level, so it won't be 80+ down there.  But, if I directed all the output of the wood furnace through a box or two, I could probably keep the box that warm.



That sounds more like it.  Let me know if you decide to go ahead with it.  I'd be glad to provide design input.  In fact, I've begun an indoor firewood drying consultation firm.  Go to "BattenKilner.com" to see our list of services. ;-P


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## Battenkiller (Jan 12, 2011)

Quick update...

Week One ended yesterday at 9 PM.  Wood was down to 8 lbs, 11 1/2 ounces.  Drying is slowing to a crawl.  Lost another ounce today, so it's at 22.7% MC wet-basis.  Look at the graph.  As it drops below 8 lbs, 6 ounces, it will cross the 20% line.  Any guesses when that will be?

BTW the stuff is burning unbelievably!  Because the outside of the splits are so dry (~12-14% MC), it lights right up, and then goes on to get the stove hotter for longer than any wood I've used so far this season.  I split some of the smaller splits (4-5 pound range) and they are about 24% inside, 10-12% on the outside.  I toss them right it, they are like stove candy.

It is a rare treat for me to be able to burn straight black birch.  It's as good as it gets, both in the intensity and the length of the burn.  Not too many coals, either... unlike black locust and hickory.  

And the best part of all?  It went from the log to the stove inside a week.


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## SolarAndWood (Jan 12, 2011)

Battenkiller said:
			
		

> Any guesses when that will be?



I'm not sure it matters.  You took a year off in a week and it was a week in January.  That curve has to get pretty flat pretty quick doesn't it?


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## KWillets (Jan 12, 2011)

I got curious and looked up the heat of vaporization for water -- 970 btu/lb., and found a table of cord weight and "excess moisture" (above 20%) for red oak.  From these figures I get a total of about 1.13M btu to get a cord down to 20% MC, compared to 24M btu energy content.  So drying wood this way takes about 4.7% of the btu/cord, which isn't huge.  But you're still evaporating 1165 lbs. of water in your house.


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## Renovation (Jan 12, 2011)

KWillets said:
			
		

> I got curious and looked up the heat of vaporization for water -- 970 btu/lb., and found a table of cord weight and "excess moisture" (above 20%) for red oak.  From these figures I get a total of about 1.13M btu to get a cord down to 20% MC, compared to 24M btu energy content.  So drying wood this way takes about 4.7% of the btu/cord, which isn't huge.  But you're still evaporating 1165 lbs. of water in your house.



That's a very insightful point.  By drying the wood inside, wood is being burned to dry the wood, instead of solar energy.  So drying indoors lowers the wood's net energy output by the heat of vaporization--the net energy is the same as if the wood were never dried.  Very perceptive!


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## woodchip (Jan 12, 2011)

The other place wood could be dried quickly is to make a solar kiln using an open polythene tunnel which would get the airflow and also the additional solar heat.

The sun warming the air inside the tunnel would reduce the humidity, and the moisture would be taken out  of the wood by the continuous drier airflow. 

I'm going to try building one, after all, even if it's not that efficient, any improvement is a bonus if it's free. 

Almost like a simple diy solar heater for your house. You increase the BTU content of your wood using natural means, and utilise the increased power output in your house.

Who's going to turn down free BTU's


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## Rockey (Jan 12, 2011)

Very interesting experiment. In all honesty I wouldn't have expected to see such good results in such a short time period. In hindsight, it seems logical because the conditions in your experiemnt are much better than the most ideal outdoor drying conditions. The integrated temperature and relative humidity are one factor but the constant air movement via the fan is also significant. I've never been to a desert but I think trying to match all three conditions for a week straight(24/7) would be nearly impossible.

I for one would love to see how it would expedite the seasoning for red oak. Do you have any near you?


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## Battenkiller (Jan 12, 2011)

Rockey said:
			
		

> I for one would love to see how it would expedite the seasoning for red oak. Do you have any near you?



I've never tracked both MC and declining weight like I have in this experiment, but I tried to dry oak in here a long time ago.  Oak takes twice as long in my experience.  By the time it gets dry in here I have to move it back outside for the summer.  

There's really a small window of opportunity for this to work well in a home heating situation.  The relative humidity inside needs to be about 45% or less or you will quickly get mold on the wood.  That means you need to be heating with the stove already for long enough to get the water out of the slab, foundation walls, sheetrock, studs, etc.  By mid-November I'm ready to bring in the first load.  

It won't dry nearly as fast because I'm not running the stove full bore and the absolute humidity of the outside air is still up there.  Relative humidity outside is irrelevant, it's the temperature at that RH that dictates how much actual water vapor is in the air.  When the mercury dips into the single digits, even at high outside relative humidity there is very little water in the air.  When you draw that stuff in and heat it up, the RH in the living space drops like a stone and that's when the real magic begins.

Yes, you are correct about the air movement.  It's a crucial factor in rapid drying, but even without the fan going, the natural convection currents move the air through the splits OK, just takes longer.  I could also speed it up by using more fans, but the drying rate is dependent on the actual air speed passing over the wood.  In a wood stack I suspect you would see a point of diminishing returns trying to get the fans to significantly increase the speed of the air going through the splits.  I never tried, it dries fast enough as it is.


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## Hardrockmaple (Jan 12, 2011)

I have, for years now, brought 2 1/2-3 cords of air dried hardwood into my unfinished basement. I always wait until we've had a few heavy frosts (mid to late Nov.) before bringing it in. Every 5-6 wheel barrows full I spray liberally with a bug killer. Each spring I clean up my stacking area thoroughly. This supply represents my living area wood for another winter. I heat my house in late fall with another stove in the basement. Two birds/one stone, heat house/dry winter wood.

For the first 5-6 days after bringing the wood in I burn the basement stove (it's an aging smoke dragon that can handle 24 in. sticks of collected garbage wood) and run a dehumidifier. Within days the humidity in the basement drops to below 45% (since I insulated the basement totally).  By Jan. the wood I'm burning in the Dutchwest is tinder dry.


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## Battenkiller (Jan 12, 2011)

KWillets said:
			
		

> I got curious and looked up the heat of vaporization for water -- 970 btu/lb., and found a table of cord weight and "excess moisture" (above 20%) for red oak.  From these figures I get a total of about 1.13M btu to get a cord down to 20% MC, compared to 24M btu energy content.  So drying wood this way takes about 4.7% of the btu/cord, which isn't huge.  But you're still evaporating 1165 lbs. of water in your house.



As I said earlier in the thread:



			
				Battenkiller said:
			
		

> By the time I bring wood in here in that quantity, the wood in my housing structure is so dry that is sucks it right out of the air before it has the slightest chance to condense on surfaces.  It become liquid water again, but _inside_ the structural members and sheetrock, etc. by forming hygroscopic bonds with these substrates.  And when it does, *it releases the heat initially lost through evaporation back into the home.*



The natural infiltration rate of outside air into most homes is alarmingly high.  And unless you are using an OAK with the stove (I'm not) the stove pulls a lot of it out as well.  It's virtually impossible to keep that moist air in the home when the infiltration rate is at least 5 times a day in the very tightest homes.  Mine's an older one, so I might have closer to 10 times the volume of my house exchange with the outside air every day.  In fact, it's essential for that to occur, otherwise the RH in here would quickly climb to 100%  Thankfully, that never happens. 

Regardless, in this experiment, the RH in the home hit a peak of 40% after 24 hours, then dropped rapidly after that.  That's way too dry for any mold or moisture problems to occur.  A dew point calculation shows me that at 84ÂºF, the dew point is 57.1Âº.  That means that inside surfaces have to be lower than that for condensation to occur.  It does happen for a few days on the single pane windows (frost), but by day three in this case it was gone.  Some folks try everything they can do to get the RH up to 40% in their homes.  Even at more modest rooms temps, the dew point of 72Âº is still about 50Âº.  If your windows are below that temp (and they usually are), you will get condensation on them.  

Again, my 40% RH is a very short-lived event, not like someone keeping it up there 24/7 for the entire season.  Bottom line is that no matter how hard I try, I'm back down to 23% RH again after just a week, and everything I stick my moisture meter into in the basement right now that's not firewood is too low to register on the meter (<6% MC)

As far as the heat losses?  Well, there is no getting around that one, but it never is noticed in the home.  The stove continues to put out its 20-50K of BTUs and the average daily heat loss declines so rapidly that you might really only notice anything for the first day or so.  Bringing is frozen wood probably has a greater actual effect on heat loss than the evaporative losses.  I take care to bring it in at an advantageous time when I can (a few days warm, sunny weather before helps), but I can't ordain what the weather will bring, so I just live with the times that the weather doesn't cooperate.  

You can definitely feel the chill off all that wood, but every other burner here has the same net heat loss from bringing in cold wood by seasons end, it just happens one load at a time.  Also, as I said above, a lot of the water vapor initially formed turns back to water right inside the structural materials of your home, so the same amount of heat gets released again.  And then, sadly, it dries out and you lose it again for good, but at such a slow rate that it isn't perceptible.

Don't forget, using a humidifier or boiling pots of water on your stove does the same thing in the home.  Water evaporation by any means removes heat from the environment.  Ultra-dry air isn't good for you, so if you can do anything about it you should do so, and then accept any heat loss as a consequence of aiming for improved well-being.  Moister air feels warmer anyway, so it is likely a wash in the end, comfort wise... which is the final determinant of heating effectiveness IMHO.


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## Battenkiller (Jan 12, 2011)

Rockey said:
			
		

> The integrated temperature and relative humidity are one factor but the constant air movement via the fan is also significant.



I should have mentioned this before.  Although the fan is blowing on the stack 24/7, the actual test split is just sitting on the scale, completely out of the way of the air flow coming from the fan.  The somewhat twisted nature of this piece means that it is only contacting the scale tray in a couple of spots, ensuring good circulation around it, but the actual air movement passing by the surfaces is created solely by the convection currents arising from the stove.  The reality of the situation is that the main load is probably drying at an even faster rate, which goes a long way to explain why it is such an incendiary marvel in the stove at this point.


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## Wood Duck (Jan 12, 2011)

BK,
Maybe it is too late to ask this question, but how sure are you that the oven dried piece of wood you used to determine initial moisture content and dry weight of wood was fully dried? Is one night in a 215 degree (F) oven enough to fully dry the wood? The water lost from that piece of wood is the most critical piece of data in this whole experiment, because it is the basis for your calculation of dry weight of wood in the splits. I suggest that next time you bake that wood another night or two and keep recording the weight to be sure it is stable, i.e. the wood is completely dry.

As for the energy lost from the house by evaporating water from the wood, I'd say that is energy well spent. Unlike the report we got from England, most homes in the northern US are way too dry for my comfort in the winter, so the moisture from the wood would be welcomed. I could add a lot of moisture to my house without creating anything close to a moisture problem. My knuckles are bleeding right now from the effects of dry air. Sure, I could put something on my skin to help, but I don't (lazy) and don't need to except in the winter when it is very dry in here.


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## Battenkiller (Jan 12, 2011)

SolarAndWood said:
			
		

> You took a year off in a week and it was a week in January.  That curve has to get pretty flat pretty quick doesn't it?



Not if I change the scale of the chart.  %-P


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## Battenkiller (Jan 12, 2011)

Wood Duck said:
			
		

> Maybe it is too late to ask this question, but how sure are you that the oven dried piece of wood you used to determine initial moisture content and dry weight of wood was fully dried? Is one night in a 215 degree (F) oven enough to fully dry the wood? The water lost from that piece of wood is the most critical piece of data in this whole experiment, because it is the basis for your calculation of dry weight of wood in the splits. I suggest that next time you bake that wood another night or two and keep recording the weight to be sure it is stable, i.e. the wood is completely dry.



Good points.  

What I did was to dry it out in the microwave until the weight at the end of each cycle changed very little.  Then into the oven it went, and it didn't lose all that much more by the following morning.  Then I stuck the MM into a few pieces and got no reading at all... less than 6% at any rate.  SOP for small samples like this (I chopped them up into pieces about 3/4" x 1 1/2") is overnight at 215ÂºF, checked until the weight stops changing.  At most, I might be a few percent off.  

Even if I screwed up, the documentation of the changing weight is good information for the membership here.  "Skyline" did this in his experiment using fans at much higher RH, and that's really what got the ball rolling in my head.  

I'm not at all averse to doing this again, it wasn't really hard or time consuming to do.  Takes infinitely more time to post the results and answer questions here.  I have at least one more load of black birch coming from the same source (I'm gonna get all he'll sell me at $140/cord  ;-) ).  I can also ask him to throw some other species in with a load (he has hard maple, red oak, white oak, beech and cherry as well) to try to establish drying curves for them as well.

Let's wait for the data to all come in and then we can look at different ways to analyze it at that point.  There are differential equations that describe wood drying rates fairly well.  Maybe we can use them to compare the rates obtained from the experiment.  And, as a free thinking and obviously intelligent and analytical member here, your input is always very welcome.


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## homieg9999 (Jan 12, 2011)

littlesmokey said:
			
		

> An observation from a non-technical guy, but your drying will not be linear. It will be a dramatic slope to a very shallow run. As they out parts dry, the inner parts must move the moisture to the air through the already dryer wood. Also, the closer the wood comes to the ambient moisture levels, it will slow also.



Looks like an exponential decay pattern.  (which was my hunch from the beginning)


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## woodgeek (Jan 12, 2011)

Battenkiller said:
			
		

> Quick update...
> Week One ended yesterday at 9 PM.  Wood was down to 8 lbs, 11 1/2 ounces.  Drying is slowing to a crawl.  Lost another ounce today, so it's at 22.7% MC wet-basis.  Look at the graph.  As it drops below 8 lbs, 6 ounces, it will cross the 20% line.  Any guesses when that will be?



About 10 minutes after you get bored and throw the darned thing in the stove!


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## gyrfalcon (Jan 12, 2011)

Battenkiller said:
			
		

> It is a rare treat for me to be able to burn straight black birch.  It's as good as it gets, both in the intensity and the length of the burn.  Not too many coals, either... unlike black locust and hickory.
> 
> And the best part of all?  It went from the log to the stove inside a week.



Told you this was the absolute best stuff evah, didn't I?  Glad you're enjoying it.

BK, could you maybe distill all this into a paragraph of practical recommendation?  My eyes really start to cross with all the numbers.


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## gyrfalcon (Jan 12, 2011)

By the way, for folks who may be thinking of looking for some to burn, there's two species of birch in the East commonly called "black birch."  One grows primarily in wet, swampy areas from mid-Atlantic states south, the other in upland areas mostly in the northeast.  No idea how the swamp one burns, but the "black birch" BK and I burn, sometimes also called "cherry birch," is the other kind.   I gather the swamp one (betula nigra) has pretty elaborately peeling swaths of bark and is apparently sometimes used as an ornamental tree because of it.  The one here (betula lenta) mostly holds onto the outer layers of its bark.


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## Battenkiller (Jan 12, 2011)

gyrfalcon said:
			
		

> Battenkiller said:
> 
> 
> 
> ...



Hey, buddy!  I was thinking of you and your little stove (still sure you don't want to sell it to me?) when I started burning this stuff.  Now I get it.  You're right, this stuff kicks _ass_!  I've always found some mixed in with other wood, but never found anyone who'd give me a straight load of it until this year. Yes, sugar maple takes a distant second place to this stuff.  

I always knew what the BTU charts tell you about it, but they don't tell the whole tale.  Even though I still like my shagbark and my black locust, this is far and away the best wood I've ever burned.  Can't explain why it doesn't top the BTU charts.  Coaling properties are just right, ash residue is low, and it puts out the heat!  

I'll try to get together a little summary in the next day or so.  Hope it will help you.


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## cptoneleg (Jan 12, 2011)

partybob99 said:
			
		

> Sen. John Blutarsky said:
> 
> 
> 
> ...


     x 3


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## KWillets (Jan 12, 2011)

Another thing I wanted to check was how much humidity this would add, given that outside air is brought through the house to burn the wood.  The stoichiometric ratio for dry wood is 6.1, so if a cord of 20% mc oak is 3757 lbs. (got that from a 
table somewhere), it takes .8*3757*6.1 = 18334 lbs. of (dry?) air to burn.  If you evaporate 1165 lbs of water into that air, that's 6.35% by weight.  In other words if you seal off the house and only take in the minimum air for burning, you would have to add 6.35% by weight (444 grains/lb) to the air mass, which is actually several times 90% RH (100 grains/lb) at 70F.  The minimum stove airflow alone would not be enough to remove the water vapor. Darn.

However many stoves burn at higher ratios, eg, 35:1, so I doubt if humidity would be a huge problem.  There are also standards about how often air is supposed to be exchanged in a house, which I don't know offhand.

I guess the lesson is that it's technically possible to raise RH to mold-growing levels, so it's worth watching the RH meter, but normal ventilation will probably handle it.


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## gyrfalcon (Jan 12, 2011)

Battenkiller said:
			
		

> gyrfalcon said:
> 
> 
> 
> ...



Hey, you're not all that far away.  If I ever manage to get the coin together to get a bigger stove and need to dispose of this one, I'll let ya know.

It's counterintuitive until you really think about it, but you perforce have to closely observe and learn a whole lot more about not just stove operation but also the burning qualities of the wood and the size of the pieces and how the fire is built when you're seriously understoved.  Even a 50-degree difference in stovetop temp is big, and hard as heck to achieve with such a small firebox.  BBirch almost makes it easy.

The coin problem also makes it difficult to get more than a year's supply in at a time, so I seem to be doomed to perpetually dealing with not quite fully seasoned wood, and your summary would be very much appreciated here.


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## Renovation (Jan 13, 2011)

gyrfalcon said:
			
		

> BK, could you maybe distill all this into a paragraph of practical recommendation?



Since BK asked me to challenge his work, I'll see if I can light two fires with one match, and provide my own summary of BK's work, for debate, discussion, etc.

I'll present a quick summary, followed by an explanation.
*
Summary:

Indoor drying has the potential to dry green wood to the 20% dry-basis moisture content (which is what standard moisture meters read, and what most consider the threshold for convenient clean burning) in approximately 6 weeks, at the expense of about 5% less net energy out of the wood than if it were dried outdoors.
*
*Detail*

First I'll present my analysis of drying time, then net energy loss.

*Drying Time*

I'm simply eyeballing the red, dry-basis line on the drying chart, and guesstimating where it will cross the 20% line.  Given BK's analytical chops, I'm sure he can fit a curve to that data and tell us at what point it crosses the 20% level in nothing flat.  BK?  We can also wait and see when it gets to that point.
*
Net Energy*

KWillets Noted:



			
				KWillets said:
			
		

> I got curious and looked up the heat of vaporization for water -- 970 btu/lb., and found a table of cord weight and "excess moisture" (above 20%) for red oak.  From these figures I get a total of about 1.13M btu to get a cord down to 20% MC, compared to 24M btu energy content.  So drying wood this way takes about 4.7% of the btu/cord, which isn't huge.  But you're still evaporating 1165 lbs. of water in your house.



So the bottom line is it takes about 5% of the energy available in the wood to dry it to 20% moisture content.  This energy has to come from somewhere--outdoors it comes from the sun, indoors it comes from whatever you are using to heat your house.  This may not be perceptible, but it is a fact--barring extreme measures, the water evaporated from the wood will leave the house as vapor, and the energy required to vaporize it leaves along with it.  

Evaporative cooling may not be intuitive for wood, but it certainly is for humans.  This effect is why we sweat, and why the air feels so cold after swimming, showering, etc.  It takes energy to change water from a liquid to a vapor, and that lost energy cools off you, your room, etc.  In hot and dry Arizona, evaporative (or "swamp") coolers are the traditional way to cool during the summer--air is circulated over a damp pad, and back into the house.  As it passes over the pad, it evaporates water and in the process becomes cooler and more humid.  It is quite effective.

In the case of drying wood indoors, drying the wood turns the water in the wood into vapor, which cools the house.  Regardless of where or how many times that vapor condenses, as long as it eventually leaves the house in vapor form, the energy required to evaporate it is lost.   

An example of this is super-efficient direct vent gas furnaces.  To get the last bit of efficiency, they condense the water in the already cool flue gas, and drain it out as a liquid, thereby reclaiming the heat of vaporization.  In the case of indoor wood drying, I can think of no efficient way of condensing the water removed from the wood out of the air before that air leaves the house envelope--even if it condenses in the walls, it eventually leaves as vapor, taking its heat with it.  Unless of course the 1165 lbs of water/cord stays in your walls until Spring, in which case you have a whole other set of problems.

Finally, my analysis correctly ignores all the factors that are shared by indoor and outdoor drying.  For example, both cases require the same amount of energy to bring wood brought inside up to room temperature and evaporate whatever surface moisture happens to be on it. 

Okay, that's it for the analysis.  On a personal note, I enjoyed pondering this, and it helped distract me from the pain of my workout.  In school, I was known for caring more about a theory's consequences in concrete application than tweaking it's abstract equations.  I consider the math and theory a very valuable means to the end of applicability, and get little enjoyment out of them for their own sake.  This was called "picking the low-hanging fruit", and was either an asset or an annoyance, depending on one's priorities. 

Anyway, I hope this is useful, and invite questions, comments, concerns, challenges, etc.

My thanks to BK for his fascinating, rigorous, and educational experiment!  :coolsmile:


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## SolarAndWood (Jan 13, 2011)

(Curious) George said:
			
		

> educational experiment!  :coolsmile:



Educational experiment?  I've been trying to figure out how to build something that I can fill with the tractor and Battenkiln dry with a wood furnace.  That would eliminate moving it and stacking it in the shed on the windward side of the house, waiting a year, moving it and stacking it again in the shed on the leeward side of the house, tossing it in the bucket and carrying it to the stove.  It would also mean I wouldn't have to scrounge any wood for 5 years.


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## Renovation (Jan 13, 2011)

SolarAndWood said:
			
		

> (Curious) George said:
> 
> 
> 
> ...



Sounds good to me.  As I said, I enjoy applicable experiments, so "experiment" is not a criticism--it sounds like you're eager to be educated.

So you don't have enough sunny storage area, and are waiting with bated breath for the red line to cross 20%?


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## SolarAndWood (Jan 13, 2011)

I have plenty of sun and lots of wind.  Always looking for a better way though.


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## gyrfalcon (Jan 13, 2011)

(Curious) George said:
			
		

> Indoor drying has the potential to dry green wood to the 20% (dry-basis) moisture content (that most consider the threshold for convenient clean burning) in approximately 6 weeks



Um, six weeks?  He's at something like 22 percent in one week, unless I'm reading him cross-eyed, no?  If that's the case, seems to me there's no super-compelling need to wait another month to lose that last 2 percent.  If we're only talking a week to get green wood down that far, it's a much more practical enterprise for those of us with first-floor stoves to bring in a week's worth at a time.

I've lost track of how large these splits are, if I ever knew.  BK says "medium," but that's like "medium potato" in a cookbook to me, depends on your context.

How much faster would this be if your splits were, say, 2 or 3 inches, and/or shorter?  And does it make any difference what the moisture content is to begin with?

I have a couple days' stack of really small (1 and 2-inch, 14-inches-long) splits of not green but mostly not really ready for primetime beech sitting just outside the safe range of my stove, and I've been trying to figure out whether it's much drier after just three or four days or it's my imagination or I've lost track of where I put the dry stuff I do have.  (Yes, I have a moisture meter somewhere, but haven't been able to put my hands on it.  But by this time, I can recognize roughly how dry the wood is without it.)


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## gyrfalcon (Jan 13, 2011)

SolarAndWood said:
			
		

> I have plenty of sun and lots of wind.  Always looking for a better way though.



Yeah, so do I.  What I don't have is a woodlot or access to one, or the cash money to buy several years' worth of firewood in advance so it has time to really dry well.


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## Renovation (Jan 13, 2011)

gyrfalcon said:
			
		

> (Curious) George said:
> 
> 
> 
> ...



The red line on the chart is for the dry-basis moisture content, which is what moisture meters read, and currently stands at about 29%.  The line is also curving convex (dropping less rapidly with time).  So six weeks is my best guess, eyeballing the red line.  Remember, this is starting with very wet wood, so six weeks is nothing to sneeze at.

I'm sure BK could fit a curve to it and estimate the 20% point in a snap.


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## gyrfalcon (Jan 13, 2011)

(Curious) George said:
			
		

> The red line on the chart is for the dry-basis moisture content, which is what moisture meters read, and currently stands at about 29%.



Oh, HECK.  That went right past me.


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## Renovation (Jan 13, 2011)

SolarAndWood said:
			
		

> I have plenty of sun and lots of wind.  Always looking for a better way though.



Then why not split and store it in the sun, until you need it?

I'm impressed by your wood.  Oh, that sounded wrong.


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## SolarAndWood (Jan 13, 2011)

(Curious) George said:
			
		

> Then why not split and store it in the sun, until you need it?



That is what I do now, I have 35-40 cord in various states of the pipeline and no concerns of having to burn wet wood.  However, Gryfalcon nailed it here:



> Yeah, so do I.  What I donâ€™t have is a woodlot or access to one, or the cash money to buy several yearsâ€™ worth of firewood in advance so it has time to really dry well.



I would add that storing, moving, stacking, storing, moving, stacking and finally moving wood is a lot of work.  It also takes a lot of space and room under a roof on my suburban lot.

Battenkilner is offering a possible way around that.  But, you would have to be set up right to make it work without risk of having to burn less than ideal wood.  Which, I suppose is another thread in itself.


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## Battenkiller (Jan 13, 2011)

(Curious) George said:
			
		

> The red line on the chart is for the dry-basis moisture content, which is what moisture meters read, and currently stands at about 29%.




George, no offense, but for a guy who doesn't even have a stove yet, you seem pretty sure about how dry wood needs to be to burn well.



I started a fire with 100% BattenKilner rocket fuel exactly one week after I first brought it into the basement.  I set things up so that I would get the fastest possible startup I could achieve.  Well, things went so fast I didn't even have time to write much down.  Thankfully, I was able to get a timeline by looking at the EXIF data from the few shots I was able to take of the process:

I went down to check the stove just before 10 AM.  Top was at 125Âº, flue was about 75Âº (room temp).  I thoroughly cleaned out the ashes and pushed together the small pile of coals that was left from the night before.  In a departure from my usual starting practice, I decided to use a small wax/sawdust firestarter of my own making.  They are about 1" square - maybe 1/10 the volume of a Super Cedar (a type commonly used by Hearth members).

First photo is time stamped at 9:52:09, just prior to lighting the starter.
Second shot was taken at 9:55:44, 3 minutes and 33 seconds later.  I added more wood at this point and closed the doors.
Third shot was at 9:57:05, 1 minute and 21 seconds after the wood addition.  Closed the doors again.
Fourth shot was at 9:58:41, 1 minute and 36 seconds later.  I closed the doors, shut the intake damper to about 1/4 open, and waited while the temps rose.


Here are the stove top temps as they climbed:

10:00:38 - 350ÂºF  -  8 minutes and 27 seconds after lighting
10:03:17 - 525ÂºF  -  11 minutes and 8 seconds after lighting
10:05:40 - 600ÂºF  -  13 minutes and 23 seconds after lighting
10:09:00 - 700ÂºF  -  16 minutes and 51 seconds after lighting

About that time I started to smell that old familiar smell... screaming hot flue pipe.  My magnetic flue thermometer is pretty accurate, but it has a very long lag time.  It only said 525Âº, but I grabbed my IR gun and shot the pipe.  785ÂºF!  I quickly opened the top loading door to kill the draft a bit and help cool it off.  It dropped to about 715ÂºF, and I decided to toss in the main load.  Three splits of progressively larger size, loaded quickly, one after the other:  

7 lbs/3 oz, 9 lbs/7 oz, and 14 lbs/4 oz, for a total load of 29 lbs/14oz.  

The large splits ignited immediately upon hitting the wood below (see flames shooting around wood on the right), and I closed the load door.  I waited until the flue temps got up (about 600ÂºF flue, 750ÂºF stove top) and closed the bypass about 29 minutes after I struck the match.  At 10:32:52 I snapped the shot of the smoking (?) chimney seen in the lower right hand corner of the last sequence - exactly 40 minutes and 41 seconds after liftoff.  Went back inside and the stove was cruising at 700ÂºF, flue temp stable at 375ÂºF.  At no time after the first few minutes was the intake damper open more than about 1/4 of the way, and I only opened the stove doors for a second or so to take the photos (no glass on my stove), so there was no huge air boost needed to get the wood to take off.

This all happened during the time that most EPA stoves would have been functioning without secondary combustion yet occurring, operating strictly in an updraft, cold-start mode.  Therefore, I see no compelling evidence why it wouldn't go identically in a good EPA stove with decent draft, especially the first 30 minutes of the burn.

*EDIT:  The last photo in the stove top thermometer sequence is not the correct one.  That was taken a few minutes after the main load was loaded.  The actual time-stamped photo taken at 10:09:00 was showing 700ÂºF as I stated in the text.*


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## Renovation (Jan 13, 2011)

Battenkiller said:
			
		

> (Curious) George said:
> 
> 
> 
> ...



I'm far from sure how dry would needs to be, but willing to learn.  

No offense taken, but I must point out that, by attacking me (for being stoveless) and not my argument, you are making a classic mistake--what I say is true or not simply based on facts and logic, not on how experienced I am, whether I have a stove, or any other personal qualities.

This site is based on the idea that inexperienced people can learn from those with more experience--in other words, that the information on this site, viewed in total, is useful.  If you invalidate me even though I have correctly leaned the information here, you are invalidating the reason for this forum.

I'm simply repeating what I have learned from the many experienced and helpful members here, and hope others will correct me if I am wrong:

_Isnâ€™t it true that this forum recommends, over and over, when someone has burning problems, that, as a rule of thumb, their wood should be cut, split, and stacked for at least a year, and measure 20% or less on a standard moisture meter?_ (the common resistance-type, that measures dry-basis moisture)?

I hope other folks will chime in and say whether that is true or not.  If I am wrong I want to learn my mistake and correct myself.

I'm not saying that any of your data is wrong, or that the wood does not burn great in your stove and your particular setup, but simply that it is incorrect to assume that wood that measures 29% MC on a standard moisture meter is suddenly the standard for great burning, because I do not believe it is.

And, if you want to talk stoves, isn't it true that your stove is a pre-EPA model, and not representative of the burning requirements of modern stoves?  Is this thread wrong?

https://www.hearth.com/econtent/index.php/forums/viewthread/27521/#288864

Back to my original point--I'm asserting that if we want to use this forum's usual standard for dry-enough wood, we care about when your wood gets to 20% dry-basis moisture.  Of course that standard may not apply here, but I want BK's moisture charts to be interpreted correctly, and a number of people have mistaken the lower line on the chart for the forum's usual dry-weight MC measurement, and it's not.

I hope we can all remain civil and friendly, and refrain from personal attacks, for that is what is great about this place, and the standard that I want to maintain.

If I am being rude, inappropriate or wrong, please correct me so that I can learn.

Thanks!


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## Renovation (Jan 13, 2011)

SolarAndWood said:
			
		

> Battenkilner is offering a possible way around that.  But, you would have to be set up right to make it work without risk of having to burn less than ideal wood.  Which, I suppose is another thread in itself.



So are you going to give the BattenKiln a try?  It seems easy and quick enough to do, and I'd love to know how it works with a King.   :wow:


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## Battenkiller (Jan 13, 2011)

(Curious) George said:
			
		

> No offense taken, but I must point out that, by attacking me (for being stoveless) and not my argument, you are making a classic mistake--what I say is true or not simply based on facts and logic, not on how experienced I am, whether I have a stove, or any other personal qualities.
> 
> I'm not saying that any of your data is wrong, or that the wood does not burn great in your stove and your particular setup, but simply that it is incorrect to assume that wood that measures 29% MC on a standard moisture meter is suddenly the standard for great burning, because I do not believe it is.
> 
> And, if you want to talk stoves, isn't it true that your stove is a pre-EPA model, and not representative of the burning requirements of modern stoves?  Is this thread wrong?



Hold on, Curious feller.  I ain't attacking you.  I really like most of your posts, and your general style as well.  It's just that I ain't about to agree with a forum consensus that claims something is true in general just because it appears to be true for them.  And I don't think you're rude, either.  A bit thin-skinned, maybe, but that's OK.

I'm not now, nor have I ever, claimed that wood that is 20% MC dry-basis is "the new standard for great burning".  The purpose of this thread is merely to demonstrate how quickly wood will dry in the right conditions, and how predictably it will do so once you have established a drying rate for it.  I have stated repeatedly on numerous occasions that wood should be in the "ideal" band of MC, its just that I prefer to accept the industry standard regarding what that is rather than a handful of the most vociferous posters on an Internet forum.  Doubt me?  Fine.  Back it up with statements from the stove industry itself.  Or call the EPA and ask them why they test stoves at fuel MCs above the ideal range.  Hell, nobody seemed to have ever heard of wet and dry basis MCs a years ago.  Now it's a point of contention?

Anywho, let's remain friends and take what I say in light of how it was intended, K?

Regarding my old "smoke dragon", I am just trying to show how well wood like this will burn in any stove at startup.  EPA stoves don't really vary in how they burn at this point, it's the secondary combustion that sets them apart at a point later on in the burn than I showed here.  I feel very strongly that if somebody can't get a roaring fire with this stuff in hand, they need lessons in how to burn, not in how to season wood.  In short, nothing will help them until they accept they need to learn to operate the stove better.  Whether or not I will achieve peak efficiency with this wood would have to wait until I get that hip flue setup with all the fancy sensors and flow meters and such.  But it is extremely clear to me that this stuff would come close... _real_ close.  All you have to do is open up the top load door and look at the quality of the flame, and feel the intense heat come ripping off this stove for hours to know that.  That's the kind of knowledge you only get from long experience, not by agreeing with a forum's membership.  And again, I mean no offense.

I get so weary of new burners having their wood constantly called into question when it's so obvious from reading their complaints that _no_ wood will burn well they way they are running things.  Is this ruining my life?  Does it really matter that much to me?  Well, no, it really doesn't, but it means _something_ or why else are we here in the first place?  I often think for days about whether or not I should post some controversial bit of info.  Surely I will be held in contempt by many who disagree with what I am saying.  That's the real beauty of the Internet.  Even though I try hard to help, in the end, I really don't give a shite what folks here think of me.


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## pen (Jan 13, 2011)

Why is it every time I read this thread that things like this keep popping into my head



> The TV Guide of June 16-20, 1984, had an R. J. Reynolds Tobacco Co. ad. headed Second-hand smoke: Letâ€™s clear the air. The copy continued:
> 
> There is little evidence â€“ and certainly nothing which proves scientifically â€“ that cigarette smoke causes disease among non-smokers.













Hmm, yea, just not sure why I keep shaking my head as I am reminded of misinformation like these.  Strange coincidence I suppose. 

pen


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## Renovation (Jan 13, 2011)

Battenkiller said:
			
		

> Hold on, Curious feller.  I ain't attacking you...    ...And I donâ€™t think youâ€™re rude, either.  A bit thin-skinned, maybe, but thatâ€™s OK.



Thanks, great to know, and likewise! 



> I'm not now, nor have I ever, claimed that wood that is 20% MC dry-basis is "the new standard for great burning".



That is not what I said.  If you reread my post, you'll see that I actually said:



> it is incorrect to assume that wood that measures *29%* MC on a standard moisture meter is suddenly the standard for great burning, because I do not believe it is.



The reason I said that is because,  in response to a newb asking about rules of thumb for MC, you said in your thread here:

https://www.hearth.com/econtent/index.php/forums/viewreply/778755/

which is now included in the Wiki here:

https://www.hearth.com/econtent/index.php/wiki/Determine_moisture_content_of_wood/



> As far as a definite cutoff number, I donâ€™t believe it exists.  The way you load the stove, the type of wood, the way the wood is split, the amount of coals in there, the internal stove temps, the timing and size of wood additions, the strength of your draftâ€¦. all things that can and sometimes do have a more profound effect on the burn then just MC and draft opening.  *For me, the theoretical cutoff is 25% MC wet-basis (33% MC on the meter).  Thatâ€™s 5% more water in the wood than the maximum allowable MC in the EPA test loads.  Above that, you will likely have a progressively harder time burning your wood without micro-managing the stove.*



Which I think could lead a newbie reading this thread, searching the threads or reading the Wiki to believe that 29% (as mentioned here) or 33% MC on a standard meter is the rule of thumb.  I think that entry in the Wiki is misleading, since the usual advice here is 20% MC or less on a standard, dry-basis meter.

It seems to me that the Wiki should reflect the advice that is generally given, and if that is now to be 33% or less MC on a standard meter, perhaps that should be acknowledged and discussed?

That is my concern, and has been all along.

This takes nothing away from your thread, your innovation, or your ideas, all of which I respect.  I simple want newbies to get good rule-of-thumb advice about what sort of wood will generally burn cleanly and easily, and don't want your unique experience and beliefs, in threads and the Wiki, to confuse that.

Fair enough?



> Anywho, let's remain friends and take what I say in light of how it was intended, K?



Absolutely, and likewise.



> I get so weary of new burners having their wood constantly called into question when it's so obvious from reading their complaints that _no_ wood will burn well they way they are running things.



That cuts to the heart of the matter.  You are questioning the general assumption here, and that seems a very valid topic, worthy of discussion in it's own thread.  But if you're sick of the whole thing, I certainly understand.  

Best Wishes!


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## homieg9999 (Jan 14, 2011)

I ran some analysis on my TI-86.

I fit an exponential function to your data:

Dry Basis:  y = 53.2185341(.92112541^x), this equation fits the data about 98%

Wet Basis:  y = 34.831669(.943085961^x), this equation fits the data about 98.4%

Just plug in days into the x variable, and you'll get an extrapolated moisture content, orrrr you could plug in what moisture content you want for y, then solve for x (days) with logarithms.

I hope this is helpful.


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## Renovation (Jan 14, 2011)

homieg9999 said:
			
		

> I ran some analysis on my TI-86.
> 
> I fit an exponential function to your data:
> 
> ...



Thanks HomieG! 

I know that Excel has similar wizards, that will curve-fit data.  I was hoping BK would click his up, and let us know.

Could your solve for 20% wet-basis, and 20% dry-basis, and tell us how many drying-days you get for each, if you haven't hit the "clear" button yet?


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## homieg9999 (Jan 14, 2011)

I did it by hand using log properties:

Dry:  11.91 days

Wet: 9.46 days

I'm going to bed now, but if there is anything else you'd like me to run, I'll try to get to it tomorrow


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## Battenkiller (Jan 14, 2011)

(Curious) George said:
			
		

> Battenkiller said:
> 
> 
> 
> ...



Yeah, the "9" and the "0" are real close on my keyboard.  I was letting my typing finger fly on that one 'cause Lady BK was tapping her foot waiting for me to go to the store.  I meant to write, "I'm not now, nor have I ever, claimed that wood that is 2*9*% MC dry-basis is "the new standard for great burning".    Which is the truth.  Sorry for the poor proof reading.




			
				(Curious) George said:
			
		

> homieg9999 said:
> 
> 
> 
> ...



Yeah, I fit an exponential curve to the data and found it fit pretty well.  I was reminded of what an organic chemist friend told me once.  He said, "Lewis structures are too good to be true, and ligand theory is too true to be good."  That really sunk in for me, and I try not to describe things with mathematical models unless I really understand exactly what is driving them.  Which in this case, I don't.  I'll try to play with it when I have a chance, and thanks for the input, guys.

BTW the wood is now 8lbs, 7 1/2 oz.  RH is down to 22%.  MC is 26.6% dry-basis, 21% wet-basis after 10 full days.  The split has lost 2.06 pounds of water, or 54% of the original water weight of 3.84 pounds.


And as "Pen" has wisely pointed out, in my ganja-addled delusional state, I am fudging all the data, doctoring up both my photos and the time-stamps in the EXIF data, and lying through my teeth about all of this... just like Big Tobacco does.  If you don't die of a chimney fire using this method, the copious amounts of smoke produced will give you all lung cancer.

Good efin' grief.  :roll:


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## pen (Jan 14, 2011)

I'm sorry, but I just honestly don't see what this will prove or gain over preparation considering the other possible negatives associated with drying a month's worth of wood indoors constantly.  We all know a "kiln" will dry wood.  I don't agree that making your basement one is a good idea.  

Additionally, my concern is that people will take bits and pieces of this data and believe that just throwing their wood indoors for 3 weeks means it's good to go.

My concerns are honest in that I don't think people will interpret your data correctly.  The tobacco companies weren't lying in those adds either, but people were able to make the wrong impressions based upon those statements.  I don't want people making the same mistakes w/ your information.  Data is meant to be interpreted, it in and of itself is not the conclusion.  

pen


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## Renovation (Jan 14, 2011)

homieg9999 said:
			
		

> I did it by hand using log properties:
> 
> Dry:  11.91 days
> 
> ...



  Sweet dreams.

Is that more days, or days total?

Which data are you fitting to, the values in BK's Jan 11 data?  Your values don't seem to fit, because that data stand at 29% and 23% at day nine, and  looking at the chart it's hard to believe the red line would reach 20% only a couple of days after the green one...


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## Battenkiller (Jan 14, 2011)

pen said:
			
		

> Additionally, my concern is that people will take bits and pieces of this data and believe that just throwing their wood indoors for 3 weeks means it's good to go.



And I'm concerned about 75% of what I see hyped up on this forum that I know flat out not to be true at all.  So what?  I have gone well out of my way to explain why this works, and for whom and where and in what situation this might work.  At no time did I recommend anybody actually do this, but if asked, I can give a clear explanation of why this may or may not work on a case by case basis.  Otherwise, it's just an experiment that has many other interesting things that are coming out of it, like the data analysis others are pitching in with that may help establish drying curves that will be able to be used to reasonable predict when wood will be ready when dried outside.  

I suppose we shouldn't post links to scientific studies, either.  They might be misinterpreted, and folks would be creosoting themselves to death with wet wood, or giving themselves third-degree burns by touching hot wood, or dying of CO inhalation, or... whatever.   So keep coming in here and trashing the thread, who cares?  Maybe you'll save the world... or get the thread locked, as may be your real intention by trolling it.



Disclaimer:

This is only a topic on an Internet forum.  Proceed at your own risk.


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## Battenkiller (Jan 14, 2011)

(Curious) George said:
			
		

> Which data are you fitting to, the values in BK's Jan 11 data?  Your values don't seem to fit, because that data stand at 29% and 23% at day nine, and  looking at the chart it's hard to believe the red line would reach 20% only a couple of days after the green one...



Gotta agree there.


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## pen (Jan 14, 2011)

You just proved my case in point.  You chose which statement to pick and chose from my post that fit your argument.

What about this quote from my post 





> other possible negatives associated with drying a monthâ€™s worth of wood indoors constantly



Are the other concerns (ie, insects, mold) about storing a large quantity of wood indoors bunk?  What is the benefit of drying firewood in this manner versus simply planning ahead and having it ready by drying outdoors?  

pen


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## gyrfalcon (Jan 14, 2011)

Battenkiller, seems we've got increasingly varied interpretations of the practical implications of your experiments.

So I renew my plea for a simple bottom line summary.

You do appear to have said in one of your posts that you took medium-sized splits (what does that mean, please?  You talking 4-inch, 5-inch, 6-inch?) of recently cut green Black Birch, left it in your warm cellar (70 degrees? Or is it more than that?) for one week with a fan blowing on it, and then popped it in your stove and it lit right up.

Can that possibly be right? (I don't give a rip what the measured moisture content is, personally)

Beyond that, I have questions about what the effect might be of having smaller splits, a lower room temperature, no fan, etc., but I'd really like to know whether I understood the basic premise correctly or I've gotten it completely bolixed up.


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## gyrfalcon (Jan 14, 2011)

pen said:
			
		

> Are the other concerns (ie, insects, mold) about storing a large quantity of wood indoors bunk?  What is the benefit of drying firewood in this manner versus simply planning ahead and having it ready by drying outdoors?
> 
> pen



Gee, the benefit is for those of us who are entirely capable of planning ahead but lack the resources to put such plans into effect, no?

Insects and mold are not an issue in the winter in cold climates.

And I sure haven't seen Battenkiller crusading for drying firewood indoors in preference to drying it outdoors.  He's just been carrying out a fairly rigorous experiment and reporting the results, which may well turn out to be incredibly helpful for some of us.


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## Battenkiller (Jan 14, 2011)

gyrfalcon said:
			
		

> So I renew my plea for a simple bottom line summary.
> 
> You do appear to have said in one of your posts that you took medium-sized splits (what does that mean, please?  You talking 4-inch, 5-inch, 6-inch?) of recently cut green Black Birch, left it in your warm cellar (70 degrees? Or is it more than that?) for one week with a fan blowing on it, and then popped it in your stove and it lit right up.
> 
> ...



Gosh, give a guy time to breathe (and tend to his lovin' wife, eh?)  :cheese: 


Yes, it _can_ possibly be right.  Look at the data, look at the photos, look at the timeline of the course of the fire.  Nothing fudged here.  If that's the attitude, I'm done here.  I value nothing in life more than truth.  I don't fudge data, or intentionally deceive.  It's just not my style.  Just because something seems incredible to you doesn't mean it ain't true.  This all makes perfect sense to me, and the experiment is playing out fairly close to how I suspected it would based on previous years doing this... only faster.

Did I say I took medium splits into the house?  Then I misspoke.  These are _huge_ splits, some of them in excess of 15 pounds, even dried down this much.  7" x 7" x 20" long a few of them.  The biggest one I stuck in that fire was over 14 pounds.  Burned like sugar, lasted for hours, heated the whole place to 71Âº until mid-afternoon.

The effect on smaller splits is enormously better.  The smaller splits I started the fire with came into the basement that way, I never claimed otherwise.  They measured 12% MC on the outside, and they are small enough that they were likely close to that on the inside.  Is it any secret that smaller splits dry much faster than fatter ones?  

Another thing.  Someone said at one point that these would be dried to a low MC all the way through.  Sorry, but I never claimed that.  It's simply not true, impossible, in fact. There is a very steep moisture gradient inside all of these splits.  They will take months to reach full equilibrium.  So what?  The same thing might take years if done outside.  

This has absolutely zero effect on the way these burn, as you can see in the photos.  The fact that they are so dry on the outside means they ignite almost instantly, and the residual moisture inside gives a long, stable burn, better than the stuff I've had outside all year (yes, I do some both ways, always).  Net heat loss through evaporation will be equal to a split at full equilibrium that has the identical total amount of water, but I really feel I will get a better total combustion efficiency and overall efficiency, at least in my stove.  YMMV. 


You live close enough.  Make the trip over and see for yourself.   We'll torch off a 100% BattenKiln-dried black birch fire in my stove and let you be the judge.  I'll even send you home with some for your little rock stove to keep you warm when you get home, and feed you well while you're here.  :coolsmile:


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## Battenkiller (Jan 14, 2011)

gyrfalcon said:
			
		

> pen said:
> 
> 
> 
> ...



Thanks, friend.  I really needed that.


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## pen (Jan 14, 2011)

Well, I've done this myself at one point putting a cord and a face of wood in my basement.  That year I hit 101 on the wall thermometer 20 feet from my wood stove.  W/ that much wood in my basement at all times I had a solid month of firewood on hand even in the coldest weather.  In this "experiment" of mine, I lacked a moisture meter but I did have a non-epa woodstove much like BK and I'm willing to bet an even hotter environment consistently.  I too can say that the wood will dry, but still is nothing like having fully seasoned wood on hand as I would get into wood from time to time that would burn completely differently from the previous load which made it very difficult to plan on load sizes / when to close the drafts and how much, etc.  I also spent a month vacuuming the window sills every day because of the bark borer beetles that I had leaving the wood.  My window's sills would literally be covered in an 1/8 in layer of beetles from end to end.  Thank god my wife is an understanding woman who didn't mind the "experiment" as well (so long as I was the one to clean the window's every day).  I also had 1 chimney fire that year.  

Since then I have learned better, I have not had another chimney fire and I have not had window's filled w/ beetles.  

BK is doing nothing new here, others have tried this and my point is there are many variables involved which makes his data nearly worthless.  If you want to be safe do it right.  If you are just getting by, remember, you are also taking on the burden of the extra risks involved.  

Education / knowledge is the key to power.  His data is certainly part of that.  However, I want to make sure that everyone realizes that it needs further interpretation and that baselines can't be set here since there are simply too many factors involved.

I don't mean to knock what BK is presenting, it's foolish to argue that a hot dry environment will dry wood (duh) I am simply concerned that the results are being misinterpreted in terms of the "BIG PICTURE."  The big picture to me is safety.  So, for this procedure to work for everyone else, they too have to get the triple beam balance out and make such careful measurements to ensure they have gotten their wood to the "promised land" (whatever that is).  In in the meantime, what will they be burning too add heat to the room to even get the wood dry?  

This practice is reactive rather than proactive and that is the problem.  

pen


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## gyrfalcon (Jan 14, 2011)

Battenkiller said:
			
		

> gyrfalcon said:
> 
> 
> 
> ...





> Whoa there, sugar!  Did notnotnot suggest you fudged the data.  Suggested I might have it bollixed up in my own head, right?



Did I say I took medium splits into the house?



> Probably not.  I just remembered wrong.



 Then I misspoke.  These are _huge_ splits, some of them in excess of 15 pounds, even dried down this much.  7" x 7" x 20" long a few of them.  The biggest one I stuck in that fire was over 14 pounds.  Burned like sugar, lasted for hours, heated the whole place to 71Âº until mid-afternoon.

The effect on smaller splits is enormously better.  The smaller splits I started the fire with came into the basement that way, I never claimed otherwise.  They measured 12% MC on the outside, and they are small enough that they were likely close to that on the inside.  Is it any secret that smaller splits dry much faster than fatter ones?



> OK, that's what I'm getting at.  What size were the splits you started the fire with?  Forgive me if I've lost track, but there are a whole lotta numbers in your posts on all this and I figure it's easier to ask than try to dig it out myself.
> 
> No, it's no secret smaller splits dry faster outdoors, but I just wanted to be sure there wasn't something involving the RH in an enclosed space like a house that might counteract that.



Another thing.  Someone said at one point that these would be dried to a low MC all the way through.  Sorry, but I never claimed that.  It's simply not true, impossible, in fact. There is a very steep moisture gradient inside all of these splits.  They will take months to reach full equilibrium.  So what?  The same thing might take years if done outside.  

This has absolutely zero effect on the way these burn, as you can see in the photos.  The fact that they are so dry on the outside means they ignite almost instantly, and the residual moisture inside gives a long, stable burn, better than the stuff I've had outside all year (yes, I do some both ways, always).  Net heat loss through evaporation will be equal to a split at full equilibrium that has the identical total amount of water, but I really feel I will get a better total combustion efficiency and overall efficiency, at least in my stove.  YMMV. 



> I still need to pin you down a bit more here, if I could, about the stuff that burned so nicely for you.  It was how big?  It was green?  It had been inside a week?  It was in what temperature?
> 
> And while I'm at it, any kind of guess as to how much this whole process would be slowed down if your splits weren't sitting in constant 70-degree-plus heat but 5 or 10 degrees cooler and/or didn't have a fan running on them the whole time?


You live close enough.  Make the trip over and see for yourself.   We'll torch off a 100% BattenKiln-dried black birch fire in my stove and let you be the judge.  I'll even send you home with some for your little rock stove to keep you warm when you get home, and feed you well while you're here.  :coolsmile:[/quote]



> Can't see any reason at all why a road trip over your way wouldn't be a fun thing to do at some point.  It'd probably have to wait until most of snow season is over, though, since my big 4WD Jeep just died and I'm driving my elderly little Honda for a while.


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## gyrfalcon (Jan 14, 2011)

pen said:
			
		

> Well, I've done this myself at one point putting a cord and a face of wood in my basement.  That year I hit 101 on the wall thermometer 20 feet from my wood stove.  W/ that much wood in my basement at all times I had a solid month of firewood on hand even in the coldest weather.  In this "experiment" of mine, I lacked a moisture meter but I did have a non-epa woodstove much like BK and I'm willing to bet an even hotter environment consistently.  I too can say that the wood will dry, but still is nothing like having fully seasoned wood on hand as I would get into wood from time to time that would burn completely differently from the previous load which made it very difficult to plan on load sizes / when to close the drafts and how much, etc.  I also spent a month vacuuming the window sills every day because of the bark borer beetles that I had leaving the wood.  My window's sills would literally be covered in an 1/8 in layer of beetles from end to end.  Thank god my wife is an understanding woman who didn't mind the "experiment" as well (so long as I was the one to clean the window's every day).  I also had 1 chimney fire that year.
> 
> Since then I have learned better, I have not had another chimney fire and I have not had window's filled w/ beetles.
> 
> ...



Yikes!  That's a whole lotta beetles.  I don't wonder you're leery of the whole idea.  I sure would suggest if you've got wood that's full of beetles (or ants) that this is probably not a useful way to go for you.  Personally, I've never had a single beetle in the house, an ant or a spider only once or twice in three or four years, and I already store several days worth of fuel in my living room next to the stove.  I wouldn't even want to pick up a piece of wood crawling with beetles like that, thanks very much!

I would respectfully suggest, though, that having it in as high temperatures as you apparently did and for as long as you did perhaps caused eggs to hatch in great numbers, something there's little risk of in a week.

Beetle-infested cordwood aside, what possible risks could be involved in burning wood dried outside versus inside?  I know when I've gotten my wood to the "promised land," and so do you.  It burns easily and cleanly and without hissing and oozing.  I don't see what difference it makes where it was while it was getting to that point or how long it took.  Do you make those careful measurements to make sure your wood is ready to burn now?  I sure don't.  I can recognize dry wood by the heft and feel of it, and when I'm in doubt, I throw a piece in the stove to see what happens.  And for whatever it's worth, seems to me there's always patches here and there in my wood stacks that clearly aren't ready and don't burn well, even when the rest of it is fine, for no discernible reason.  Again, I don't really see how that would happen more often just because the wood was dried in a different location.


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## SolarAndWood (Jan 14, 2011)

Oye.  BK, as soon as I figure out how to build a Battenkiln in my basement, I will forward it to you for a peer review.  Maybe drinkin more Kool-Aid, but I am pretty sure there is a benefit to hot dry moving air in the drying process.


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## pen (Jan 14, 2011)

The wood crawling with beetles was from a bunch of beautiful ash trees cut live in an attempt to protect a house / garage from a wind storm.  The wood was cut / split / stacked outside for a few weeks before I moved it into the house.  After a few weeks in the house I started noticing very fine saw dust on the cat.  I went investigating and sure enough, my wood had a layer of dust on it and pieces looked as if they were shot w/ a shot gun.  The holes were from the beetles exiting after they ate their full under the bark of the unseasoned wood.

This was with a very common wood, ash.  The very same stuff that people like to burn under seasoned because "ash wet or ash dry a king will warm his slippers by."

Now in my neck of the woods we don't have termites, no poisonous spiders, in all, the creepy crawlers are very tame.  As such, the ones of these that I was afraid might start attacking my house and furniture fortunately could not due to the beetle type.  However, for someone who lives just a few hundred miles south of here, the "bugs" to be concerned with can be much more fierce.

So in the end, the wood I brought in was just as fresh and beautiful as the birch presented here just a different species.  Had the ash been seasoned 1 year outdoors the bugs would have innocently left outside of my home and the living phloem would have dried so that it was uninhabitable for them.  At the point of bringing the wood indoors, there were no visible signs to predict what was going to happen.  

Point:  Bug's generally don't dig dry wood.  If you make the wood dry in your home, the bugs that are in it will need to exit as they are not content with folding up and dying as their food source literally dries up.  

pen


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## woodgeek (Jan 14, 2011)

The bottom line is that if an indoor drying method like this 'works' for you, then you are free to do it.  Period.

As a group, we have in the past been unable to agree on an outside seasoning time suggestion, b/c of all the variables of climate, split size etc.
The gen'l guideline 'one year, except dense species which get two' is great (conservative) advice for folks who have the ability to put up a year or two of wood--a
lot of us don't. In reality, with outdoor drying, YMMV.  The nature of wood drying has this diminishing returns (decelerating) characteristic, after a fraction
of the time it is most of the way there.  So, it is def _possible_ for folks to get a clean/safe burn using wood that has been outside for a good bit less than
a year.  To tell folks that it is impossible, or that they shouldn't try stuff and judge for themselves does them a disservice.

Alternatively, the indoor drying process does work (wood in a a dry environment dries, what else would it do?).  There have been posters in the past that
have said something akin to 'I bring my just split wood into the house, stack it 5' from the stove, and it is fully seasoned (i.e. it burns great) two days later'.
No one on this thread is suggesting that, in fact it is countering it.  In those old threads the methodology was pretty shoddy--folks didn't weigh anything, 
own a moisture meter, or have a thermometer on their stove--just said 'yup, goes up really fast after two days in the house, not so much otherwise'. 
The service BK is providing is to detail his successful, practical alternative to a year of outside drying.  Beyond just telling us 'it works', which we should
believe based on his sage advice over the years, he is providing numerical data that supports his claims (a weight curve), and a timescale--a week or two,
not a day or two.  

Whether you decide to try something similar is really up to you once you know the timescale involved.  Do you have enough heated, ventilated
space in your house to store *2+ weeks* of wood, your wood is reasonably free of bugs/mold to the point you wouldn't lose sleep over visions of beetles
crawling everywhere (thanks pen), and you're already paying an energy/$$ cost to humidify your otherwise too dry house?  If the answer is yes, then indoor drying 
is an option for you.

It really comes down to volume: for a 24/7 burner, the amounts can be so large, we are talking about a large commitment that eats a lot of indoor space.
If you are burning less than a cord of wood a year, then it is probably not that big a deal.

I also think BK is being conservative--I suggested that a split might be dry through and through after several weeks indoors.  Clearly, neither he nor I would
claim that w/o data.  But if half of the wood volume is at 15% MC and half is at 25%, it will burn just as well as a uniform 20%MC split.  This is the nice thing
about the weight method--it tells you about the average MC, which is the most important thing.  Having the outside dryer than the inside helps with take-off,
as BK has demonstrated.  This is what has fooled less careful burners into thinking their wood was dry--after one day inside it took off fast (and then died
later).  BK is getting enough water mass out that over the whole burn cycle, the splits are functionally equivalent to those dried outside after a reasonably short
(but not conveniently short) length of time.

thanks again BK for the experiment!


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## gyrfalcon (Jan 14, 2011)

Well said, Woodgeek.

I would just add that the other huge factor people seldom want to consider (because it means more work, I guess) in drying time, indoors or out, is the size of the split.  When burner after burner confidently and authoritatively announces "Oak takes two or three years to dry"-- yeah, true for really large splits.  Split 'em in half and it takes much less time.


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## Battenkiller (Jan 15, 2011)

I had to bring another face cord of birch inside.  I'd love to be able to run the entire experiment under the identical starting conditions, but the reality is I have to heat this place with this wood, and it's gotta get dry first.  Beside, the extra moisture will do my aching sinuses some good.

The only effect should be a slight rate decrease for a day or two as the wood raises the RH in the room.  Should also be about 5Âº cooler down there for a few days until the wood heats up.  I know... more heat loss, but it's happening all at once instead of one load at a time like normal folks experience (and don't even notice).  Physics provides no free rides.

Test split is down to 8lbs, 6 1/2 oz.  MC is 20.4% wet-basis. It should cross into the promised land of burnability sometime tonight during my sleep.  I had to move the stack around to fit in the extra wood and rotate things so I had the wettest wood directly across from the stove for fastest drying.  While I was at it, I pulled three different size splits out of the stack, re-split them and took a MC reading with my meter.  

Split 1:  3lbs, 14 oz   MC outside - 10%   MC inside - 24%
Split 2:  5lbs, 4oz.     MC outside - 10%  MC inside - 24%
Split 3:  9lbs, 7oz.     MC outside - 10%  MC inside - 25%

How do ya like them apples!  I got pics of the splits and the readings if anyone really needs to see them.  You can really tell the difference in handling the fresh splits compared to the dry ones.  This s*** is hea_vy_ when it's wet!  The dry stuff hefts like, well... dry wood.

The reason why the splits in the stack are drier is because they have had the fan blowing directly on them the whole time, while the test split is sitting on the scale back in the corner behind the stove.  Air circulation speeds up the process considerably.

I intend to run this thing out for the original 21 days planned.  That's only good science.  But AFAIC, this stuff is dead-ready to burn in anything made.


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## gyrfalcon (Jan 15, 2011)

Battenkiller said:
			
		

> I had to bring another face cord of birch inside.  I'd love to be able to run the entire experiment under the identical starting conditions, but the reality is I have to heat this place with this wood, and it's gotta get dry first.  Beside, the extra moisture will do my aching sinuses some good.
> 
> The only effect should be a slight rate decrease for a day or two as the wood raises the RH in the room.  Should also be about 5Âº cooler down there for a few days until the wood heats up.  I know... more heat loss, but it's happening all at once instead of one load at a time like normal folks experience (and don't even notice).  Physics provides no free rides.
> 
> ...



It is heavy stuff, but of course, so's all high-BTU wood.

Just before whacking myself in the eye with my safety goggles, I almost whacked myself in the face picking up a small split of beech that was a lot lighter than it was when I put it down a few days ago.  I've been running my own experiment unintentionally by getting sick for a few days-- not seriously, but enough that I couldn't face dealing with the stove or the wood-- so put on the dollar-bill-burner in the basement and retreated to bed with a hot toddy for a while, leaving about a day's worth of unready, very small splits stacked near the stove to mix in with my dwindling supply of really good rock maple.

With no fan, no stove going, just a baseboard a few feet away and the thermostat set only to 60, these things turned into really nice dry wood in no more than 4 days-- no hissing, no spitting, no drooling foam out the ends, lit up immediately and burned beautifully and thoroughly, practically no coaling at all.  My crappy little moisture meter said 13 when I stuck it in, compared to high 20s when I brought it in freshly split.  (These things are so small, not worth the effort to split the dry ones again for a fresh reading.)

Yowza!  I'm a believer.


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## RRJ22 (Jan 15, 2011)

BK
Thanks for the experiment.  I have been following it with great interest, mainly because I am way to lazy to take the time to document wood drying!  I too have multiple weeks worth of wood in the room with the stove though, because after a minimum of one week inside it burns dramatically better.  I had six cords c/s/s by April 15, 2010 of mixed silver maple, cherry, mulberry, and other assorted wood that was stacked outdoors.  I upgraded from an old Wonderwood smoke dragon in April to a Summit which took shorter pieces, so I started cutting the wood to size as I brought it up to the roofed woodshed it late Sep.  Since I usually try to bring in a few days worth of wood at a time, I noticed that wood stored inside would start getting the drying checks in the fresh cut end in the course of 24-28 hours, which really surprised me because this stuff had been drying outdoors all summer long.  My next door neighbor gave me a few armfuls of his wood, which was dry... c/s/s over 5 years ago, and under roof in a super drafty old barn the last several years.  His wood burnt hotter and longer than mine, and considering the checking in mine, I assumed mine was wetter than I wanted.  I have room in the stove room, (and Pen's bugs aren't a concern) so I brought almost half a cord in and stacked it inside.  Observation told me that after one week indoors the checking on the ends had stabilized, and the wood burnt better and the coaling issues almost went away.  

My conditions are different than yours, because I also have an OAK.  My indoor humidity has hovered around 40 % according to the decorative hygrometer, it feels comfortable and the wife is happy.  Hopefully next year I will be able to dry my wood adequately outdoors (it is all cut, and most is already split and stacked) and I won't need to Battenkiln it, but it definitely is making a difference this year.  As I already said, your experiment has been fascinating, because you documented with numbers what I was observing.


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## elmoleaf (Jan 15, 2011)

For reference, here's how a kiln dried fire wood operation describes what they need to do to dry wood:
_The wood remains in the kilns for 2 days at over 160 degrees; removing over 1000 pounds of water from each cord. This in turn increases the firewood's burning efficiency by nearly l million BTU's per cord over green firewood, and increases the heat value by 25%. The kiln dried firewood is dried to an average of 25% moisture content_ http://www.coltonenterprises.com/process.htm


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## SolarAndWood (Jan 15, 2011)

elmoleaf said:
			
		

> http://www.coltonenterprises.com/process.htm



That place is an impressive operation.


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## Battenkiller (Jan 15, 2011)

elmoleaf said:
			
		

> For reference, here's how a kiln dried fire wood operation describes what they need to do to dry wood:
> _The wood remains in the kilns for 2 days at over 160 degrees; removing over 1000 pounds of water from each cord. This in turn increases the firewood's burning efficiency by nearly l million BTU's per cord over green firewood, and increases the heat value by 25%. The kiln dried firewood is dried to an average of 25% moisture content_ http://www.coltonenterprises.com/process.htm




Thank God I can do it at a much slower rate.  160Âº is mighty toasty.  Of course, it sure would eliminate the bug factor.:lol: 


Interesting info, and I like the way it is presented.  Drives a few important points home:


1. There is a lot of water in a cord of green wood

2. Evaporating all that water doesn't use all that much energy.  There's a much bigger difference between red and white oak than 1 million BTU/cord.

3. There are very significant heat losses from other factors besides water evaporation.  These would be in the form of lower combustion efficiency and more sensible heat lost up the flue (due to the higher air flows needed).  A 25% heating loss comes as no surprise to me.

4. Kiln-dried firewood ain't the same as kiln-dried furniture wood.  Note the *25% MC* they are selling it at.  They don't mention how they are determining the MC, either.  If they are doing it by a weight loss estimation and are expressing it as water lost divided by green weight, it is actually at 33% MC dry-basis, which is the way a resistance moisture meter would read.


H-m-mmm.....  I wonder how much I can get for the BattenKiln wood?  It is now officially below 20% MC wet-basis, 25% dry-basis.


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## gyrfalcon (Jan 15, 2011)

Hmmm.  The kiln-dried firewood I've used is done differently, according to the lumber yard's Web site.  They say say 180 to 200 for four or five days to get to 15 to 20 percent average MC.  (http://www.vermontlumber.com/firewood.php)  Perhaps that's because they do bigger pieces (I'm reluctant to call them "splits"), 8 to 10 and sometimes more inches across.  Which puzzles me since pretty much the only people who would buy kiln-dried wood in bulk would be people who don't cut their own wood and wouldn't own a splitter to cut them down farther.  (And I see to my dismay they've upped their prices by about 40 bucks a cord since I bought from them to get myself out of a jam this winter.)


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## SolarAndWood (Jan 15, 2011)

gyrfalcon said:
			
		

> (http://www.vermontlumber.com/firewood.php)  Perhaps that's because they do bigger pieces (I'm reluctant to call them "splits"), 8 to 10 and sometimes more inches across.



What an elegant way to make firewood.  BK, have you figured out what the rest of that curve looks like yet?  If it takes a week to do what would take a year to do outside, how long does year 2 take?

What do you think about an alcove Battenkiln?  Pull the stove out from the wall, put a somewhat low header in a few feet in front of the stove, then circulate the air up around and behind a stack of wood behind the stove.  The air then finishes by blowing past the stove on its way to the rest of the house.


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## Battenkiller (Jan 15, 2011)

Hey, Solar... Did you check out the "seasoned" wood Colton is selling?  They cut and split about 500 cord in the spring and dump it on the pavement, then they sell it as seasoned in the fall.

Kicks your heapen-hausen's ass! :lol:

I'm calling my buddy up to see when I can check out the firewood kiln-drying operation he oversees.  It's nowhere as sophisticated or energy efficient (they use propane-fired heaters and old insulated truck boxes with the same type holding cages), but it should be interesting.  I'll go with camera (and moisture meter) in hand and bring back a car full and compare it with the BattenKiln product and give a report.


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## Battenkiller (Jan 15, 2011)

gyrfalcon said:
			
		

> They say say 180 to 200 for four or five days to get to 15 to 20 percent average MC.  (http://www.vermontlumber.com/firewood.php)  Perhaps that's because they do bigger pieces (I'm reluctant to call them "splits"), 8 to 10 and sometimes more inches across.



Gyrfalcon, you have to remember that they are doing this year round.  It's hard to get RH low inside the kiln when you are drawing in air that has more water in it.  They need to get the kiln a lot hotter to do that in the summer when there's more water in the air.  Temperature does help to increase the diffusion rate inside the wood, but if it ain't evaporating fast enough at the very surface, the wood won't dry fast.  Low RH inside the kiln at all times is the main driving force for rapid water removal.

Like I mentioned somewhere above, this works best for me when the weather is at the coldest because that is when there is the least amount of water in the air.  I'm not talking RH, I'm talking absolute water content on a grams of water/air volume basis.  That's what drives this in the cold weather, and why it won't work well at all in warm weather.

Interesting to see we have yet another professional opinion about the dangers of using wood that is too dry.  Maybe it's just a New England phenomenon. %-P 



> *Seasoning and Heat Treatment*
> 
> Our firewood is kiln-seasoned so that most of the pieces are in the 15 to 20 percent moisture content range, with a general maximum of 25 percent in the bigger pieces. When we dry lumber, we dry it to 6% to 8% moisture content, which is fine for kindling but not for larger pieces of firewood. Trying to burn a number of pieces of firewood at 10% moisture or less can be difficult to control in a wood stove, possibly damaging the stove or your home by causing overheating. *The increase in heat value of very dry wood over wood at 20 percent moisture content is small, generally not more than 3 percent*, and is outweighed by the potential for overheating.


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## SolarAndWood (Jan 15, 2011)

Battenkiller said:
			
		

> Kicks your heapen-hausen's ass! :lol:



Ha, producing 1/20th of that last year kicked my ass.  

What do you think of the alcove Battenkiln idea?  How sensitive do you think the Battenkiln is to temperature?


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## Battenkiller (Jan 15, 2011)

SolarAndWood said:
			
		

> What do you think of the alcove Battenkiln idea?  How sensitive do you think the Battenkiln is to temperature?



Sounds like a slow and laborious process to me.  You won't get much wood in that space and it will have to be emptied and refilled every 2-3 weeks or so.  Knowing how much you feed that King, I don't think you'll come close to meeting your demand.  Might want to consider looking for a big-ass pre-EPA radiant heater in the basement.  You'll have enough heat down there to drive the process and you'll really be surprised just how much warmer your place will be with heat coming up from underneath as well as from the living space itself.

What seems the best thing is to try to arrange separate drying bins that each hold a one-day supply.  Once they all get dry enough to burn, you start burning the wood from one, then refill it the next day and burn the wood in the next compartment.  The numbers of compartments = the number of days it takes to bring the wood down to 20%, and you have a perfect rotation with ready wood that is always at the proper MC.  I've been thinking of doing this for years now, but every year I start the season without having built it.  I'd want mine to be easy to take apart and store since I desperately need the space in the shop.  I really welcome the end of the burning season if for no other reason than I get to have my shop back.

For a guy burning less than a cord a month, that means you never have much more than 1/2 cord inside at a time, and the only chance you have of bringing in any unwanted nasty things is in a single day's worth of wood (if you keep your eyes open for them).  I never saw anyone here being chastised for bringing in a few days worth of wood, I don't see why what I'm doing is really any different.  The only thing I'm doing that hundreds of other burners aren't doing is weighing a piece of wood on a scale every day.

As far as the drying curves, we'll all have to be patient.  The data hasn't come in yet, and it's not going as predictably as one might hope for.  I'm still losing water from the test split at a fairly rapid rate.  Even starting at a RH of 32% several hours after I brought the next load in, the split lost 1/2 ounce in 12 hours.  That's the same 1 oz/day rate I've been seeing for a few days now, and I'm not sure what is causing this.  That's why it's best to let all the data come in (it's only a bit more than a week away) and then analyze it and begin a discussion about what it all means.

Temperature is critical to this in that you need to artificially drive down the RH in the kiln.  A 20Âº increase in the internal wood temp would speed up the diffusion rate inside the wood very little, but it would make a huge difference to the RH inside the kiln.  There is no getting around this.  If you can't get the kiln down below 30% RH, drying will proceed too slowly to be useful.  Might as well (gasp!) dry it outside.

BTW, I didn't see close to the same spike in RH from the latest wood addition.  32% RH as opposed to the 40% I saw with the first load.  And even after the coldest night of the year, there was only a tiny bit of condensation on the single-pane basement windows, and none on the double-glazed ones.  Why?  Because the wood has been sitting outside drying the whole time.  It already had tons of fine end-checking going on when I brought it in, a result of free water moving out of the ends.  So much for wood not drying outside in the cold weather.


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## SolarAndWood (Jan 15, 2011)

Battenkiller said:
			
		

> What seems the best thing is to try to arrange separate drying bins that each hold a one-day supply.  Once they all get dry enough to burn, you start burning the wood from one, then refill it the next day and burn the wood in the next compartment.  The numbers of compartments = the number of days it takes to bring the wood down to 20%, and you have a perfect rotation with ready wood that is always at the proper MC.  I've been thinking of doing this for years now, but every year I start the season without having built it.



That is exactly what I was thinking.  The "alcove" would be 15 feet wide with shelving behind the stove. I have some old 20" deep heavy metal warehouse shelving that I have been on the edge of tossing for a while now.  Create a trap for the hot air on top of and slightly in front of the stove, put blowers above the stove directing the hot air behind the shelving and back down around through the wood.  So, would have something like a cord and a half going all the time.  Or 3 if it worked out that I could get away with two rows.


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## Battenkiller (Jan 15, 2011)

SolarAndWood said:
			
		

> The "alcove" would be 15 feet wide with shelving behind the stove. I have some old 20" deep heavy metal warehouse shelving that I have been on the edge of tossing for a while now.  Create a trap for the hot air on top of and slightly in front of the stove, put blowers above the stove directing the hot air behind the shelving and back down around through the wood.  So, would have something like a cord and a half going all the time.  Or 3 if it worked out that I could get away with two rows.



If done correctly, on that scale and in that manner, you have already designed a much better kiln than I have. ;-)


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## Battenkiller (Jan 19, 2011)

Quick update...


Yesterday was the two-week mark.  2/3 of the allotted time for the experiment has passed.  Test split is at 23.4% dry-basis, 18.9% wet-basis. Drying has slowed to a crawl - 1/2 to 3/4 oz/day.  The split has gone from 10.53 pounds all the way down to 8.25 pounds, and has lost 2.28 pounds of water, which is 0.27 gallons of moisture - over a quart.  That's a _lot _of water in a single split! 

I will have to stop measuring the split in ounces lost and use another method.  This old produce scale has a scale across the top that gives the amount in dollars and cents as well as in pounds and ounces.  By using the $1/lb scale, I can get a good eyeball measurement down to 1/100 of a pound, so I'll stop using the spreadsheet weight formula and just enter the weight directly into the cells in the "Weight" column.  Just mentioning it so it won't look suspicious when you look at the data.

You can see by looking at the charts that the RH has been higher for the last several days.  That's partly because I brought another face cord of wood in again, but also because it's been warmer outside, and with more actual moisture in the air (snow, sleet, and freezing rain).  That may be affecting the drying rate.  I'll know better when the RH drops in here again over the next several days.  I think it has more to do with the fact that this is, as Woodgeek pointed out, a diminishing-return-for-time-spent proposition.  Same thing happens outside, but a lot slower.  Once the wood drops the free water, the diffusion-limited water loss rate gets slower and slower with the passage of time.  Wood at two years will be only marginally drier than one year old wood.


FWIW there was a huge study about moisture meters that someone linked to in another thread.  In reading it, I saw that the method they used to prep the samples (almost 3000 of them!) was to leave them in climate-controlled lab conditions at three different relative humidity levels for at least an entire year.  That was after pre-drying at 40ÂºC until they were close to the target levels.  Talk about patience!  The idea was to eliminate the moisture gradient inside the samples.  In short, it takes a very long time for the wood to get evenly dry all the way from the outside to the very center.  And that wasn't for big-ass splits like we love to stoke the stove with.  The general rule of thumb in the woodworking trade is to air-dry under cover - stacked and stickered - for at least one year per inch of thickness in order to get the entire board dry through and through.  That would be 4-8 years for the size wood I like to burn.  Sorry, folks, I just ain't waiting that long.


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## SolarAndWood (Jan 20, 2011)

Battenkiller said:
			
		

> Wood at two years will be only marginally drier than one year old wood.
> 
> In short, it takes a very long time for the wood to get evenly dry all the way from the outside to the very center.  And that wasn't for big-ass splits like we love to stoke the stove with.  The general rule of thumb in the woodworking trade is to air-dry under cover - stacked and stickered - for at least one year per inch of thickness in order to get the entire board dry through and through.  That would be 4-8 years for the size wood I like to burn.  Sorry, folks, I just ain't waiting that long.



Did I get the cliff notes right?  This is true for 10 lb splits, but how does it scale?  I think you and I must like to burn the same thing as my random sample of split this spring ideal splits just ranged from 25 to 35 pounds.

I think my ideal setup may be a mulit-year JagsLeeesque windheapenrowsen with a 2 week stop in the BattenKiln before it hits the stove(s).  Then, my current 8 cord under the roof right outside the door solution as a backup for when that doesn't work out quite right.  It is a lot less work than I do now and should yield even better results.


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## Battenkiller (Jan 26, 2011)

At 9 PM last night, the BattenKiln wood-drying experiment reached its conclusion.  After 21 days, a 10.55 pound split of freshly cut black birch lost a total of 2.52 pounds of water, just sitting in the same place is a very warm and arid environment.  It went from an accurately determined moisture content of 57.5% MC (dry-basis) all the way down to 19.9% MC (16.6% MC wet-basis) in a mere three weeks time.  Since last night, it has dropped down to 7.98 pounds, and is at 19.1% MC dry-basis, or 16.0% water by weight.  It is now exactly at the low end of the EPA range (16-20% water by weight) for water content in the Doug Fir test loads that are used in testing stoves for emissions.

The first photo shows the starting and ending weights.  I should have taken the readings directly from the lower scale from the beginning.  By looking at the "100" column (see numerals along the bottom), I could have read the weights directly by hundredths of a pound instead of using the spreadsheet formula.  In the end, I ended up having to use it because the daily weight loss was less that 1/2 ounce.  I adjusted the initial reading that I had entered on the spreadsheet to coincide with was that column read in the starting photo (see lower left ). All direct readings used are highlighted in bright yellow on the spreadsheet.  For the remainder of the readings it was close enough to just eyeball the line to the nearest 1/2 ounce and apply the spreadsheet formula.

The column to the far right is the daily ratio of the previous day's weight divided by the current weight.  Disregarding the first week's figures, you can see that for most of the last two weeks there was a fairly consistent constant of proportionality of about 0.96, which would indicate that the drying rate might be accurately modeled using an exponential decay function.  I'm hoping that the more mathematically astute members who contributed some of the earlier posts might shed a little light on this, since once a constant was established for a given species in a given drying situation, a fairly accurate prediction of when the wood would be finished might be made.

Looking at the data, I'm almost disappointed.  I really had no idea that the test split would dip below 20% water by weight at exactly 21 days, but that's the way it played out.  Results like that look fudged, but this is not at all the case.  Not really a good guess, either, since I originally thought it might get to 25% water by this time if I was lucky.  Apparently, black birch is an even faster drying species that I suspected.  I will continue to take daily weights of the split until it ceases to dry at the rate of 1 ounce per week.  Later in the season I will post the results.


So, guys, look at all the data and give it some thought.  Now's the time for discussion if anyone cares to.


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## gyrfalcon (Jan 26, 2011)

[quote author="Battenkiller" date="1295131800"

Gyrfalcon, you have to remember that they are doing this year round.  It's hard to get RH low inside the kiln when you are drawing in air that has more water in it.  They need to get the kiln a lot hotter to do that in the summer when there's more water in the air.[/quote]

So water in the air is all, which I believe you've been trying to tell us for some time now.  I think I finally get it... So that's why it seemed to go faster in these days of well below zero temperatures.  Duh.

It's funny how you can observe things but doubt your own observations because you don't know enough to know why it's happening the way it seems to be.  That's me and unready firewood drying out within just days next to the stove.  I've thought I'd seen this over the last few years, but didn't trust my own sense and figured it must be wishful thinking or some other observer bias.

Since you started posting on your experiment, I've been stacking small splits of my unready wood in open "log cabin" style next to the stove and really paying close attention, and they really are drying out very rapidly, maybe three or four days.  That's with no fan.  (I've got a good amount of dry rock maple, but it doesn't burn hot enough for these cold mid-winter days, so I need to use as much of the unready beech as possible.)

So profound thanks.  Really.

If you're at all, at all inclined to do more experimenting on this, I think it would be particularly fascinating to try it with the same kind of wood-- freshly cut black birch-- but do it without the fan to see just how much of an effect the moving air has on drying rate.  And of course, running the experiment with a different species of wood would be awfully interesting, too.

Can't thank you enough for taking the trouble to do this.  I do so much prefer facts to guesswork and assumptions.


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## SolarAndWood (Jan 26, 2011)

gyrfalcon said:
			
		

> Can't thank you enough for taking the trouble to do this.  I do so much prefer facts to guesswork and assumptions.



+1, thanks for sharing the experiment.  The most promising thing I see is that the Daily Ratio has held steady even as the MC has gone down.  Makes me think that if you can get to the low 20s MC outside which seems relatively easy, a couple weeks in an appropriately sized Battenkiln for ones heat load will give you a continuous supply of ideal wood without needing 3 years of neat single row stacks outside.  For me, I hope it means no stacks at all other than in the kiln.


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## Battenkiller (Jan 30, 2011)

Well, that was a lively little discussion.  I expected more naysayers telling me I must have made a mistake because drying wood this fast is just plain impossible.

Six weeks to 20% water content someone claimed?  This wood was stove worthy by day 12.  How's that crow taste right about now? :-/ 


Day 26 data and chart below.  Test split is at 14.3% water content and still dropping steadily.  There is something interesting going on, and I can't for the life of me figure it out.  The test split seems to be losing water at a much faster rate than I predicted it would by this time.  I expected the shape of the graph to change as the new green wood was brought in, but I didn't expect this later increase in water loss rate.  

Unfortunately, I stopped taking the three daily RH readings and averaging them after the three weeks was up.  It's a PITA to do, and I actually have a callous on my right pointer finger from holding onto the handle of the sling psychrometer as I spun it for several minutes each day - a meteorological occupational injury.  I do have a small chemical indicator that I have learned to rough guess the RH just by sight, and I know that it is very dry down there.  At any rate, once this thing stops losing weight for a week, I'm putting it back outside in a dry place to see how much weight it gains by sitting out there in the winter air.  That should _really_ spin some heads around.  :lol: 

Gyrfalcon, I thought I was clear in my explanation.  There was no fan on the test split at any time.  In fact, it was shielded from the fan by a 6 1/2' tall stack of wood.  The fan was on the stack itself, to get it dry for me to burn.  I can only say that I think that stuff has even less water left in it than the test split sitting back on the scale all this time.  The only air movement the test split received was through natural convection currents... which, I must say, are pretty strong several feet away from a 650Âº stove.

Solar, I think you have your work cut out for you drying out 30 pounds splits this way.  The thickness always works against you, even inside a real lumber kiln.  Pre-drying outside will take some of the time off, but just looking at the graphs you can see how much the drying slows down at the tail end of the process.  I wouldn't be surprised if it took almost as long to go from 30% to 20% as it would to go from 70% to 30%.  I'd do a little improvising right away before you make a major commitment to this and then end up disappointed.



I can't help but notice the attention this thread has gotten so far.  3284 views and 121 replies.  Given that, I think a few caveats are in order:



- Unless you thoroughly understand why this is working so well in my case, I'd strongly advise anyone not to attempt this on a large scale.  Truth told, when I first started doing this 20 years ago, I didn't understand any of it.  I was merely bringing my wood in to make it convenient to load the stove.  After a few weeks, I started to notice that it was burning a lot better.  After all, green oak don't burn for s***.  Getting it to burn at all by using this method was a real epiphany for me, but I didn't fully understand the whole outside RH/inside heat thing for years.  A very bright 18 year old apprentice explained it all to me, and it was like a bolt of lightning.  Then I fired his ass.  Can't have anybody smarter than the boss.

- Different species dry at very different rates.  If white oak takes three times as long as cherry to dry outdoors, it will take three times as long to dry indoors.  The same chemistry and physics are at play at all times.

- Air movement certainly helps, but the main thing driving this is the lowering of the indoor relative humidity.  While increasing the temperature does increase the diffusion rate of water inside the split itself, you aren't really raising it up that much to make that big a difference.  The primary thing that getting the air hot does in this improvised kiln is to force the RH indoors to a very low level.  In short, if you can't get your storage temps up to at least the mid 80s, this will not work much better than six weeks in the hottest part of the summer.  I am always certain that this will occur in my case.  Are you certain it will in _your_ situation?  If not, try this out in small quantities before you commit to it, or you may be facing a long winter re-splitting your wood to get it to burn well for you.

- As I mentioned above, large splits can take a very long time to dry out.  Diffusion rates are inversely proportional to the distance traveled, so they are very rapid for short distances (veneer thicknesses) and tediously long for long distances.  Everybody knows this intuitively after a single year of seasoning wood.  Split it small if you want it to dry quickly.  Which brings me to the final warning...

- You can easily get your wood too dry using this method.  Guys... it's a _de facto_ kiln in here.  Real kiln-dried wood is not a good thing in almost any stove.  Knowing that so many here are of the belief that "the drier the wood, the better it burns" is actually my worst fear here.  You're simply not gonna get extra heat out of your stove by getting the wood down to 10% MC... you will get less.  You'll either run so hot that you lose tons of heat up the flue, or you'll choke it down and lose lots of wood gases up the flue.  Please do not attempt to super-charge your already seasoned wood by doing this or you will be sorry.  I'm already at the too dry stage for a lot of this wood.  I've been burning off the smaller stuff as fast as I can and saving the huge splits because they dry much slower.  You have to really think this through all the time.  It's not at all as simple as leaving it out in a covered and breezy location for a couple years.  I know some will laugh out loud at this notion, but I am in earnest.  This method dries wood fast.. _too_ fast in many cases.  Trier beware.


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## woodgeek (Jan 30, 2011)

Much thanks BK for the definitive experiment and nice summary!


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## Renovation (Jan 30, 2011)

Battenkiller said:
			
		

> Six weeks to 20% water content someone claimed?  This wood was stove worthy by day 12.  How's that crow taste right about now? :-/



Okay, since you asked for it, one last time.

In one sentence, you demonstrate why thoughtful dissenters--those who could help you clarify your thinking--no longer bother replying to your posts.

Once again you mis-characterize the feedback you've received, blur the distinction between dry and wet basis to your advantage, and insult and condescend to those who took the time to disagree and have a conversation with you.  

PM me if you have something friendly or constructive to say. I'll leave the last here word to you, since there's no upside for me in following this thread.

But go ahead, use global warming and safe following distances in your defense, and imply that those who disagree are lazy idiots who are calling you a drug-addled liar.  This lazy idiot certainly isn't--I think you're a well meaning, smart guy who lets his emotions get in the way of good science.

As you were.


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## Battenkiller (Jan 30, 2011)

George, I'm really stunned here.  I had to go back through this entire thread to see what's got your knickers in a knot...



			
				(Curious) George said:
			
		

> No offense taken, but I must point out that, by attacking me (for being stoveless) and not my argument, you are making a classic mistake--what I say is true or not simply based on facts and logic, not on how experienced I am, whether I have a stove, or any other personal qualities.
> 
> I hope we can all remain civil and friendly, and refrain from personal attacks, for that is what is great about this place, and the standard that I want to maintain.
> 
> *If I am being rude, inappropriate or wrong, please correct me so that I can learn.*



Nothing I said in my last post was directed at anyone in particular, just my way of saying that the predictions of failure were incorrect.  I had no idea who said what 3-4 weeks ago.  Apparently _you_ were the guy who incorrectly predicted it would take 6 weeks to dry down to 20% MC dry-basis and you assume that I was directing that comment specifically at you?  Not true at all.


But then you go on and attack my character with the following? 




> In one sentence, *you demonstrate why thoughtful dissentersâ€”those who could help you clarify your thinkingâ€”no longer bother replying to your posts*.
> 
> Once again you mis-characterize the feedback youâ€™ve received, *blur the distinction between dry and wet basis to your advantage, and insult and condescend to those who took the time to disagree and have a conversation with you*.
> 
> But _go ahead, use global warming and safe following distances in your defense, and imply that those who disagree are lazy idiots who are calling you a drug-addled liar._  This lazy idiot certainly isnâ€™tâ€”I think youâ€™re a well meaning, smart *guy who lets his emotions get in the way of good science*.



Just what do you know about my emotional status?  I'm a pretty cool-headed guy, but I do have my limits.  This is supposed to be fun and educational.  Having to deal with multi-pronged attacks against my integrity is not something I care to endure _ad nauseum_.

To finally answer your question about being rude, inappropriate, or wrong.... 

In a word, yes, I believe you are.  

Now if you have anything useful to add, and if you can handle the heat of my disagreement with your beliefs, feel free to continue to contribute here.  I have absolutely no intention of sending you a PM regarding this matter, but if you want to PM me to explain the real cause and nature of this outburst, I will reply in a courteous and thoughtful manner... like I have to dozens of PMs in the past.  For the record, I have received my own share of negative comments on the public forums, but never a single negative by PM.  Perhaps if folks are so offended by my unintentional insults, they should bring their grievances up in private rather than to try to perform a character assassination in the public view.


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## Battenkiller (Jan 30, 2011)

woodgeek said:
			
		

> Much thanks BK for the definitive experiment and nice summary!



You're welcome!  Glad I could do this for those who will appreciate it.

So, Woodgeek... what do you think about the way the curve is turning?  This is unexpected to me, perhaps you can shed some insight into this.  You seem to have a much better grasp of the physics and math behind diffusion rates.  Am I incorrect in seeing that there seems to be an exponential component to the graph, at least for the middle part of the curve?  Now it seems to be almost liner, with a loss of nearly 1/2 ounce of water each day.  Ain't supposed to happen that way AFAIK, but the scale disagrees.  Your thoughts?


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## KWillets (Jan 30, 2011)

http://en.wikipedia.org/wiki/Wood_drying#A_simple_model_for_wood_drying







M is the MC at time t, M_e is the equilibrium MC, M_0 is the beginning MC, and tor is a constant in this case, so as you suspected it's an exponential decay down to M_e.

Interestingly, they give  a figure of about 10x faster drying along the grain than across it.


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## woodgeek (Jan 30, 2011)

Theory of course has its limits, but if we started with (1) a 'half-infinite' slab (basically, big and flat), that was (2) uniformly charged with water that (3) (effectively) diffused within the slab, AND (4) any water that reached the surface effectively disappeared, then the result is easy.  The cumulative amount of water lost is NOT an exponential function of time, but goes like time^0.5.  Interestingly, this formula predicts that the initial drying is not only fast, it is infinitely fast at t=0, and moreover, that the curve will stretch out much longer in time than it would if it were exponential (or you fitted the original data to an exponential).

I think assumptions (2) and (3) are pretty aok.  (4) requires a little thought--at finite RH there is an equilibrium MC that is reached, perhaps we can adjust our definition of mobile water to be the water that is excess of this equilibrium amount.  (1) is ok so long as the thickness of the (growing) dry zone is less than the radius of the split, so it is ok for early times, and then at late times the rate of loss should go faster than the planar model (cuz we run out of water when the dry layer reaches the center). In the past you have suggested that the mobile water diffusivity must depend on MC, like there is cellular water and bound water.  I don't think so, as a matter of opinion, I would expect water to move between these two populations rapidly--they would move together with an effective diffusivity.  I guess that much of the mass movement is due to the small fraction of the water in vapor form diffusing in the pore spaces, and so should be roughly proportional to the saturation vapor pressure of water.

The little published data I have looked at does suggests that the time to air dry dimensional lumber goes like the square of the minimum dimension, a 2" thick plank will take 4x longer to dry than a 1" plank.  (for heat diffusion reasons, it might also take four times longer to burn).  It also seems to take about 2-3x longer at winter temps (and 0%RH) than at summer temps (at 0%RH), consistent with my idea that is proportional to the vapor pressure of water at those two temps.

I was a little busy at work recently, so didn't get to plot up/fit your data.  I predict that if you plot the square of the cumulative water loss versus time, it will start out pretty linear, and flatten out at the longest time (when you reach the center of the split).  I will not be cranky if the wood drying process differs from my simplistic expectations....


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## Battenkiller (Jan 30, 2011)

KWillets said:
			
		

> http://en.wikipedia.org/wiki/Wood_drying#A_simple_model_for_wood_drying
> 
> 
> 
> ...




Yes, that's the one I was looking for!  Thanks so much.  

I was trying to apply a standard exponential decay function starting with the original water weight like you would with a pharmaceutical half-life in the bloodstream, but when I put it into my TI-85 and graphed it, the amount remaining at each time interval wasn't coming close to what the results were showing.  I'll have to play with your formula some more.  I'll also have to bone up on graphing with the TI-85.  It's been ten years since I've had to do that for anything.

Funny, I remember finding that Wiki entry and posting a link on the forum, but then couldn't find it in my bookmarks later on.  Yes, the accepted estimate for water movement along the long grain is 10-15 times as fast as across the thickness.  My own experience has shown that wood dries a lot faster when cut shorter.  I believe that rate changes after all the free water is removed from the wood, but I'm not sure.  I'll have to read that Wiki entry again later on.

Does anyone know of a down-loadable graphing calculator that I can use to enter these functions into so that I can try to display the graphs on this thread?


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## Reggie Dunlap (Jan 30, 2011)

My experience drying wood in my garage is pretty similar. The garage is heated to around 70 by my Tarm boiler, and I run a de-humidifier when the RH goes above 50%. I also aim a big box fan at the wood. If it's below zero I turn on the radiant heat to warm the slab up a little.

On Jan 8 I stacked a very green cord of hard maple, cherry, and yellow birch in the garage. I split the wood fine, no bigger than 4-5". I weighed one of the biggest chunks of hard maple at 7 lbs. 14 oz.  Over the next 18 days the weight dropped to 5 lbs. 14 oz, so it lost a full two pounds of water weight. I don't have a moisture meter so i don't  know the moisture content, but I'm burning it mixed in with some really dry wood. The smaller splits burn fine with no sizzling, the bigger chunks burn with some sizzling.

I think the biggest factor in drying wood quickly is splitting it very fine. Then you need heat and air movement from a fan.


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## woodgeek (Jan 30, 2011)

It would be cool to see if you can get the exponential thingy to work. I'm skeptical--the major way one gets such forms is if the rate of loss is proportional to the amount remaining, which would be correct if the water remaining were 'well mixed' and its vapor pressure was proportional to the amount left.  I would expect neither of these to be true--but I guess I should go read the wiki link. 

Just wanted to throw down a friendly gauntlet.


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## Hogwildz (Jan 30, 2011)

I am not very analytical, nor good at graphs etc.
I bring in approx. 1/2 cord of wood into the living room(stove room). Now I have two sets of tubs I store the wood in/on. So when one set of bins is empty, I reload and start burning the other set of bins. This always gives the new load plenty of time to dry any moisture that may be in the splits to the point that it all burns very nicely.
I get approx. 3 weeks of burning out of a full load in the house. 
And it also helps humidify the house for a few days.
Not very scientific, but works for me.


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## Wet1 (Jan 30, 2011)

BK,
I'd like to thank you for taking the time to do this experiment and documenting it.  I can't say I'm completely surprised at the results, but I too would have guessed it would have taken a little more time than it did to get down to 20% MC, at least based on my own informal drying I do near the stove.  Then again, I do tend to burn larger splits and most of it is oak... so I'm sure your decay would have been a lot less with such a subject.

Looking forward to your continued results from these weekly weigh-ins.  If you happen to do another, I'd love to see what would happen with 10 and 25 lb. splits of red oak!

Thanks again for all your efforts!


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## DanCorcoran (Jan 30, 2011)

Anybody know anything about drying apricots?


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## Battenkiller (Jan 31, 2011)

DanCorcoran said:
			
		

> Anybody know anything about drying apricots?



Stack them loosely under cover in a windy location for at least 2 years.


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## pen (Jan 31, 2011)

Battenkiller said:
			
		

> DanCorcoran said:
> 
> 
> 
> ...



That's good drying advice for most anything to go in the stove in my opinion  :coolsmile: 

pen


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## Battenkiller (Jan 31, 2011)

pen said:
			
		

> That's good drying advice for most anything to go in the stove in my opinion  :coolsmile:



I thought you'd agree with that one. ;-)


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## Battenkiller (Feb 8, 2011)

Week Five Update...

Test split is at 7.56 lbs, down 2.99 lbs since the start.  Dry-basis MC is 12.8%, wet-basis MC is 11.4%.

I tried to mess around with some of the more sophisticated drying models, but there are too many variables and unknowns.  When I look at the data, I can see that a consistent daily drying ratio began to emerge after the initial drying period was over (faster initial rate driven in part by the more rapid end-grain drying).  This varied from day to day, partly because I am unable to measure the weight of the split to the nearest thousandth, so I had to continually round off.  The other reason is probably that the RH in the room varied from day to day, due to changes in outdoor absolute moisture content, indoor air demands and the periodic addition of wet wood to the room.  I decided to average this ratio and use the most basic exponential growth function starting on the first day that the ratio appeared to be showing some consistency.  This day was on Day 10 of the experiment, when the accumulated weight loss amounted to 1.77 lbs.

The column in light green contains all of the daily drying ratios.  I averaged these and got a daily weight loss ratio of 0.971439.  I entered this into my TI-85 as Y= 1.77(.971439^X), set the range for decimals and traced along the graph to get the value at each integer along the "X" axis (each day).  The results are is the pukey lime green columns on the right.  This simple exponential decay model proved to be remarkably predictive in this case.  The largest deviations were -0.04 lbs, and they all occurred during the time period shortly after bringing in large amounts of green wood.  The charts show a similar deviation from a smooth exponential curve during this general time period.

I continued tracing along the graph for the next seven days.  I used the outputs to make daily drying predictions for the next week.  I will continue to record the actual daily weight loss (real slow at this point) to see how close to the predictions the model continues to be.  I will report back next week with the results.  If all goes according to the predictions, we will have a furniture grade kiln-dried specimen in six weeks total time.

Cheers!


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