Drying

[ewdudley]

Ran across a good paper about drying lumber that could give some good insights about drying firewood:

(broken link removed)

Although of course your best friends for drying are the sun and the wind, there were a couple things that caught my attention:

For multiple rows it may be preferable to have the rows parallel to the prevailing wind. Apparently if the stacks are perpendicular to the wind the first row does great with air moving through the stack sideways, but the next rows are shielded from the wind and sit in more stagnant air. When the rows are parallel to the wind the air cools and falls as it removes moisture from the stack and then flows between the stacks and leaves the yard with the prevailing wind. And since faces of the stacks will get more sun if the rows are running east to west parallel to the prevailing wind, so much the better.

Ideally stack should be elevated a foot or a foot and a half. Again, the air cools as it drys the wood and needs to fall away from the stack and leave the area. Also grass and weeds near the ground should be minimized to allow air to flow freely along the ground away from the stacks. So I guess a couple more layers of pallets might be worth a try.

Likewise drainage can be important. Even if the stacks don't get very wet from rain, wet ground will keep the relative humidity higher around the stacks until the ground drys out.

And this really surprised me: Drying time for twice the thickness takes four times as long. Although this is for boards whose shape is quite different from splits, it does seem to suggest that if you're really in a hurry to dry some firewood you might consider flat, thin splits, and it might even make sense to do some stickering in your firewood stacks.

Here's an interesting table:

Table 4.3—Effective air drying day calendar for the Upper Midwest

Month     Effective air drying days  
January             5 
February            5 
March              10 
April              20 
May                25 
June               30 
July               30 
August             30 
September          25 
October            20 
November           10 
December            5

And there's a lot more; dehumidifier drying, solar kilns, lots of stuff.

--ewd

 

[soupy1957]

"For multiple rows it may be preferable to have the rows parallel to the prevailing wind." (common sense)

"Ideally stack should be elevated a foot or a foot and a half. (Again, Common sense)

"drainage can be important." (duh)

Good basic stuff there.

-Soupy1957

 

[Hunderliggur]

"For multiple rows it may be preferable to have the rows parallel to the prevailing wind." (common sense)

"Ideally stack should be elevated a foot or a foot and a half. (Again, Common sense)

"drainage can be important." (duh)

Good basic stuff there.

-Soupy1957

Common Sense - something rarely found in a government document!

 

[My Oslo heats my home]

That was some good common sense stuff. I have some thoughts for other drying situations. I know the wood dealers pile, not stack, their wood. I can't imagine the wood under the bottom getting much air flowing through. The final drying from a typical wood dealer is up to the consumer. As in another thread about wood stacks this fall, the topic moved to covering the rows with topping plastic. I found the first two feet of the top of the pile to be much drier than the remaining stack due to the plastic covering the top.

 

[oldspark]

Effective air drying days is interesting, now if we can get some of the people who think wood dries as much in the winter to read it.

 

[billb3]

Effective air drying days is interesting, now if we can get some of the people who think wood dries as much in the winter to read it.

In those areas where there is less rain in the Winter than in the warmer months and those areas where the humidty sinks to levels approaching zero that article actually confirms the fact that wood can dry rather readily in Winter.
Those compensations ( again, allowed for in the article) are certainly true and valid here.

 

[oldspark]

Well I guess I was comparing 5 days to 30 for effective drying (34 years of burning wood also) silly me.

 

[Battenkiller]

Effective air drying days is interesting, now if we can get some of the people who think wood dries as much in the winter to read it.

Apples and oranges.

Lumber has to be dried down to at least EMC in the area - 12-14% MC in my parts of the country - preferably lower (using a kiln). We only need it in the 25% MC range in order for it to burn properly. Wood at that point has lost all of it's free water but very little of its bound water. Free water can easily be lost by sublimation during the coldest parts of the winter. The bound water, however, won't move through the wood at all when temps are below freezing. Diffusion comes to a grinding halt below 32ºF. So, it is entirely possible for firewood to go from 80% MC down to about 28% MC through sublimation alone. The rest (down to the ideal 20% MC) would occur within a few weeks in the spring and early summer.

I have always bought my wood in the fall and dried it in the basement during the cold weather. I try to keep at least a cord left over because wood won't dry well in the basement until the infiltrating outside air get real cold and dry. That leftover cord in springtime is a hell of a lot lighter than when it was delivered green in the fall. Never actually measured the MC, but I've been burning for a little while myself, and IMO the stuff is mostly there by the end of March.

28% MC is nowhere near good enough for hardwood lumber, so that is where some of the information coming from the lumber industry can be misleading. Water loss through sublimation is a well-documented fact. A couple years ago we had a heated argument about this, and I came up with research done in Canada with waterlogged lumber and sub-zero drying via sublimation. It was highly effective, and as a bonus, ended up causing less damage to the lumber than drying it in a kiln did.

 

[oldspark]

BK thanks for that explantion and I will stay out of these discussions abut winter drying from now on (learn something new every day).

 

[Battenkiller]

BK thanks for that explantion and I will stay out of these discussions abut winter drying from now on (learn something new every day).

Not at all. Your subjective experience is as valid as anybody's, even more due to the length of that experience. There is always a good reason for what we observe. It may not be what you think the reason is, but that doesn't invalidate the observation.

A good example is unseasoned wood and creosote production. Scientists have shown quite conclusively that very dry wood leads to an increase in creosote production and accumulation on the flue walls over that seen when burning unseasoned wood, yet almost everyone who isn't a scientist observes just the opposite and disagrees vehemently with their conclusions.

Why?

I suspect it is because most folks burning unseasoned wood have a hard time getting the stove hot enough to burn it cleanly in the first place. Then there are the old school burners who actually liked green wood as it slowed down their leaky stoves, who then bought an airtight and found they could slow it way down by choking the intake air and ended up with a smoky mess.

Most of the scientists who have done these experiments are cautious with their recommendations regarding the burning of unseasoned wood in spite of their findings. They know full well that many folks won't be able to (or desire to) manage the air correctly for unseasoned wood burning, so they say things like, "In many cases", when in actuality the cleaner burns occur in every case in the lab because these guys are smart... and because they are using many thousands of dollars worth of equipment to monitor the burn cycle 24/7.

 

[oldspark]

I have never counted on the wood drying in the winter and noticed that wood cut and stacked in the winter did not crack on the ends very much, so I found the information about the water logged lumber in Canada drying with less damage than a kiln very enlightening.

 

[Battenkiller]

Here's a table from that same publication that shows what happens to 4/4 red oak dried outside beginning at various times of the year. Notice that the green wood that started at 80% MC in January took almost twice as long to dry (11 weeks) down to 20% MC as wood that was started in June (6 weeks). But... it did dry to 20% MC by the end of April. And look where it is by the end of March. Just about exactly at the fiber saturation point (FSP) of almost all woods, the point where all free water has been lost but the all of the bound water remains.

 

[Battenkiller]

I have never counted on the wood drying in the winter and noticed that wood cut and stacked in the winter did not crack on the ends very much, so I found the information about the water logged lumber in Canada drying with less damage than a kiln very enlightening.

Again, our individual experience tells us different things. Here's a couple photos to show what I mean. The first one is some cherry that was c/s/d in November, 2009. The other of a mix of hickory and oak that was cut down in the middle of December and bucked, split, and delivered to me the next day. Both photos show wood that was stacked in full sun and wind outside until February 7, 2010 when the photos were taken. Nothing intense as far as cracking goes, but there are definitely cracks throughout. This can only occur after the wood has gotten below the FSP since wood won't shrink at all until it has lost all of its free water.

 

[joefrompa]

Here's a table from that same publication that shows what happens to 4/4 red oak dried outside beginning at various times of the year. Notice that the green wood that started at 80% MC in January took almost twice as long to dry (11 weeks) down to 20% MC as wood that was started in June (6 weeks). But... it did dry to 20% MC by the end of April. And look where it is by the end of March. Just about exactly at the fiber saturation point (FSP) of almost all woods, the point where all free water has been lost but the all of the bound water remains.

The observations of wood cutters would disagree with that graph, though it might come down to lumber condition. That graph says though that red oak can dry to 20% MC in ~4 months, at least in lumber form.

 

[gpcollen1]

"For multiple rows it may be preferable to have the rows parallel to the prevailing wind." (common sense)

"Ideally stack should be elevated a foot or a foot and a half. (Again, Common sense)

"drainage can be important." (duh)

Good basic stuff there.

-Soupy1957

Nope - most mention perpendicular to the wind not parallel..

 

[jimbom]

Here's a table from that same publication that shows what happens to 4/4 red oak dried outside beginning at various times of the year. Notice that the green wood that started at 80% MC in January took almost twice as long to dry (11 weeks) down to 20% MC as wood that was started in June (6 weeks). But... it did dry to 20% MC by the end of April. And look where it is by the end of March. Just about exactly at the fiber saturation point (FSP) of almost all woods, the point where all free water has been lost but the all of the bound water remains.

The observations of wood cutters would disagree with that graph, though it might come down to lumber condition. That graph says though that red oak can dry to 20% MC in ~4 months, at least in lumber form.

It starts as a 4/4 (one inch) thickness. That is thinner than most all of my splits.

 

[oldspark]

"For multiple rows it may be preferable to have the rows parallel to the prevailing wind." (common sense)

"Ideally stack should be elevated a foot or a foot and a half. (Again, Common sense)

"drainage can be important." (duh)

Good basic stuff there.

-Soupy1957

Nope - most mention perpendicular to the wind not parallel..

For multiple rows I thought you were supposed to stack so the wind would flow over the wood the best way possible, parallel would be the best choice would it not?

 

[Jags]

Scientists have shown quite conclusively that very dry wood leads to an increase in creosote production and accumulation on the flue walls over that seen when burning unseasoned wood, yet almost everyone who isn't a scientist observes just the opposite and disagrees vehemently with their conclusions.

I believe this in part, is also the reason that most stove manuals state 20%MC as ideal. Kiln dried stuff has the reputation of overfiring, but the secondary part of the puzzle is the rate it off gasses and the stoves ability to consume that.

 

[oldspark]

Scientists have shown quite conclusively that very dry wood leads to an increase in creosote production and accumulation on the flue walls over that seen when burning unseasoned wood, yet almost everyone who isn't a scientist observes just the opposite and disagrees vehemently with their conclusions.

I believe this in part, is also the reason that most stove manuals state 20%MC as ideal. Kiln dried stuff has the reputation of overfiring, but the secondary part of the puzzle is the rate it off gasses and the stoves ability to consume that.

Thats what makes sense to me, it off gasses so fast that the stove cant handle it.

 

[Battenkiller]

Scientists have shown quite conclusively that very dry wood leads to an increase in creosote production and accumulation on the flue walls over that seen when burning unseasoned wood, yet almost everyone who isn't a scientist observes just the opposite and disagrees vehemently with their conclusions.

I believe this in part, is also the reason that most stove manuals state 20%MC as ideal. Kiln dried stuff has the reputation of overfiring, but the secondary part of the puzzle is the rate it off gasses and the stoves ability to consume that.

Right. Most folks figure that since they have secondary combustion tubes, any smoke produced will be consumed before it gets out of the box. They neglect the most important part of the equation - combustion air. Smoke doesn't just mysteriously turn into flame, it needs oxygen. Lots of smoke need lots of oxygen, leading to an overfire situation at best, or a chimney fire ignition in the worst scenario. Even cat stoves need the correct amount of air to burn up the smoke. All a cat does is to lower the reaction temp, it still needs every bit as much oxygen.

Little story from my sweep...

I have rented here for the last 21 years, and the same guy that sweeps my chimney does the landlord's, as well as his son's. We got to talking and he told me that he just got done doing the landlord's chimney and he had 15 gallons of creosote! The son had 10 gallons with a new Quadra-Fire 5700 step-top. They both burn wood that is drier than what I usually burn because they have their help do all the wood duties. I had 2 gallons from my Vigilant. Yeah, that's a lot to some folks but I have a 25' masonry chimney with square flue tiles, so you are always going to get buildup. In my case it was light, flaky stuff with a few expanded pieces from burning real hot. In the landlord's son's case, he has a stove that is way oversized for his tiny home, so he chokes it down as far as he can (probably modified it as well). He not only had 10 gallons of flaky stuff, he has almost 1/4" of glaze creosote.

He is most definitely not smarter than the wood he is burning.

 

[Adios Pantalones]

When I want to produce a lot of smoke at once I use very dry, thin split pine.

 

[Battenkiller]

When I want to produce a lot of smoke at once I use very dry, thin split pine.

Yeah, that'll do it for sure. But at least you're glazing something a lot more beautiful than the inside of a chimney. ;-)

 

[red oak]

I have never counted on the wood drying in the winter and noticed that wood cut and stacked in the winter did not crack on the ends very much, so I found the information about the water logged lumber in Canada drying with less damage than a kiln very enlightening.

Again, our individual experience tells us different things. Here's a couple photos to show what I mean. The first one is some cherry that was c/s/d in November, 2009. The other of a mix of hickory and oak that was cut down in the middle of December and bucked, split, and delivered to me the next day. Both photos show wood that was stacked in full sun and wind outside until February 7, 2010 when the photos were taken. Nothing intense as far as cracking goes, but there are definitely cracks throughout. This can only occur after the wood has gotten below the FSP since wood won't shrink at all until it has lost all of its free water.

So does this mean that when wood begins to crack on the ends and throughout that it is fire ready? I knew this meant it was seasoning but I didn't know it meant that it was definitely ready to go in the fire. Am I reading this correctly?

 

[bogydave]

If you dry your wood for 1 year at least, you go thru all 12 months & best drying days.
IMO, 2 years is even better. Covering the top of the stacks during your rainy season helps also.

So, if you cut (or bought) your CSS wood last Oct, it will be good dry wood ready to burn this Oct, with or without a chart.
(Oak being one exception) Very few folks cut, split & stack wood in the spring (but may be a good time to buy , save some $$)

The area you are in matters allot too. In the PNW, it's hard for me to believe wood dries much at
all in the Seattle winter, rainy, misty moist conditions but in Alaska at -10°f & low humidity it will dry better here.
The chart may help you know when the wood "should" be drying,

 

[My Oslo heats my home]

Again, our individual experience tells us different things. Here's a couple photos to show what I mean. The first one is some cherry that was c/s/d in November, 2009. The other of a mix of hickory and oak that was cut down in the middle of December and bucked, split, and delivered to me the next day. Both photos show wood that was stacked in full sun and wind outside until February 7, 2010 when the photos were taken. Nothing intense as far as cracking goes, but there are definitely cracks throughout. This can only occur after the wood has gotten below the FSP since wood won't shrink at all until it has lost all of its free water.

BK, you should be promoted to wood scientologist, they should creat a position here for you. Thanks for the visual aids and description, it caught my attention. I would like to run this by you with hopes you can assist with your moisture expertise.

I have 2 yr old red oak that has been on the racks drying. The 1.5 cords should be ready but after reading you material on free water I'm not so sure. After removing some of the splits from various places in the rack I went to re-split and check the MC with the meter. It was reading 20% or less (but nothing less than 17%) The weight felt right, the sound was there and the numbers seemed good from the meter. The only part missing was the checking on the end grain, the entire 1.5 cord had hardly and checks. I ran this by in another thread and I got thumbs up just based on the MC numbers. Your information now has me concerned whether or not this wood is ready. Tell me what you think plz.