Just how dry is your firewood?

I buy my firewood by the truckload.
Mainly smaller tops consisting of Tamarack and Douglas Fir.
All cut standing green and piled in huge log decks on the mountain.
They sit there for the remainder of the summer, winter, and spring.
Early the next summer, they deliver a long load to my property.
It is stacked on runners to keep it off the ground where it sits in the sun, and when the fall rainy season starts, it is covered with a large tarp for the winter.
That sits until the following spring when I cut, split, and stack it in a south-facing wood shed. After baking all summer, that is the wood I burn for the coming winter.
No bark, seemingly kindling dry, quite a bit of it dry checked to the core
I don't have a moisture meter to get a true reading, but this wood is undoubtedly ready to be dragon chow... Or so it seems...

Shorty has her morning meal around six a.m. By 10 a.m., she has coaled out, and I shut her air intake for the day.
With a heavy firebrick core wrapped with 1" of Morgan Superwool, it stays mighty hot in her gullet.
I use a waxed canvas tote to move firewood. One full load in it is enough for Shorty's evening and morning meal.

The other day, with high temps in the low teens and the night, predicted to be just above zero; I decided to bring in some extra wood.
In the late afternoon, I brought in a small load of wood and preloaded Shorty with her evening meal, but I did not light it.
I then reloaded the tote so I would have plenty of wood on hand if the house felt chilly.
While doing other chores outdoors, I suddenly noticed wispy steam coming from the house chimney.
I suspected that perhaps the wood had reached 456F and self-ignited...
What I found when I came indoors surprised me.
No, all the dragon chow was still waiting to be lit, including the newspaper and kindling, I'm guessing it was preheated to over 400F.
However, I could only see that after opening the door. The entire 7x7 glass window was dripping with moisture—the first time that glass had been anything but clear!
Who would have guessed there was still that much moisture in the wood?
When I touched the lighter to the paper, that pile of wood burst into flames. It always lights easily, but not this easily!
A couple of hours later, as she was all coals, her window was almost clear again!

No matter how dry your wood seems, there is always more moisture trapped inside!

Some (probably most) of that moisture may have come from heating the wood to the point of thermolytic breakdown, which starts happening just over 200 C (392 F). Hemicellulose is the first to decompose and those molecules have lots of hydrogen and oxygen atoms begging for sweet release. Burning oven-dry wood will yield combustion gases that are about 25% water by mass.

For the J-tube owners playing along at home, this is why you can put in really dry sticks and they still ooze a lot of liquid out the top end as they get going...it's the steam from thermolysis moving under pressure up the sap channels in the wood.

Phil Stevens wrote:For the J-tube owners playing along at home, this is why you can put in really dry sticks and they still ooze a lot of liquid out the top end as they get going...it's the steam from thermolysis moving under pressure up the sap channels in the wood.

I see that oozing liquid, but only infrequently and in specific pieces of wood. Any idea why it only happens some of the time?

Wood will never stay dryer than the average humidity of the air around it. I live in a humid region and the wood is always a bit 'wet'.

Coydon Wallham wrote:I see that oozing liquid, but only infrequently and in specific pieces of wood. Any idea why it only happens some of the time?

The channels need to be open for the pressurised liquids to travel to the end. Lots of wood has dried sap blocking the way. You're more likely to see it in hardwoods that were cut when the trees were dormant.

I typically only burn spruce, White, Engleman, Black, and lodgepole pine anymore. No experience with any wood from back east.
Regards oozing liquid, any conifer fighting disease or injury forms pitch of varying viscosities/dryness in or around the affected areas. The only liquid I ever see.
Collect it off when running your stove/campfire, will harden after cooling. My dad told me the Native Americans used it for an adhesive. He once glued a spinning rod tip back on when we were backpacking.

The humidity out here seems to be around 50-60% all winter, but firewood continues to dry. Diffusion, capillary action. Fact. Maybe slower, but does not stop. Speed (diffusion/vapor pressure) more accurately guesstimated by dewpoint rather than Relative Humidity. Low dewpoint means dry air regardless of what RH says. Be my take.
Two kinds of water in wood, just like your body. Water in cells and tissues, and water in the cell walls or physical structure. Water in the veins and cells leaves far more rapidly than water in the cell wall's structure. Wood seems dry, but still has the work of cell walls contracting to expel the last of the water.

Stove length firewood dries out the end grain for the most part, so any 'hardening' of the circumference makes little difference. Also why wood being stored for future milling often has it's ends sealed.  
Why I like 'standing silver' conifers for 'this seasons' wood. No bark to retain recent precipitation, already had years and years to dry. Horizontal wood catches/holds the water upright trees shed.

I also dislike poplar for heating somewhat. It burns fast and hot, my wife loves it for cooking and canning on the woodstove. I dislike it because because of speed of burn and it seems to have more water, never ready the first season no matter how early you cut it.

Along those lines. Will somebody explain to me how a "moisture meter's" little metal prongs stuck 1mm into the end grain of a length of cordwood tells me anything useful about the dryness of the center of that 22inch piece of stove wood. Those meters function similar to a pH meter, they measure electrical resistance in wood of 2 prongs about an inch apart, and infer a local value.

You can tell how ready a piece of conifer is as soon as you start to handle it, especially the 'ring' sound dry wood makes.
Steel, likewise. Piece of high quality steel has a different "feel" from common mild steel. Just me.
If that big processor does not strip the branches and some of the bark from your firewood before stacking it out, then maybe that is your answer.
Fondle your wood, man. Might not be as dry as you think.
Hijacked your thread, sorry.

Tommy Bolin wrote:
Along those lines. Will somebody explain to me how a "moisture meter's" little metal prongs stuck 1mm into the end grain of a length of cordwood tells me anything useful about the dryness of the center of that 22inch piece of stove wood. Those meters function similar to a pH meter, they measure electrical resistance in wood of 2 prongs about an inch apart, and infer a local value.

If you have a woodpile you want to test, take one of the thicker pieces from the pile, split it, and get the reading from the center of the wood where you split it.  It will give you a pretty good indication.  Most readers are accurate to 5% or so if you test that way, and I think that's close enough to tell if my firewood is ready to burn.  I also generally don't burn for 2 years after cutting, so I don't use a meter often.  I normally only use it on a pile if I don't know when it was cut.

Tommy Bolin wrote:You can tell how ready a piece of conifer is as soon as you start to handle it, especially the 'ring' sound dry wood makes.

I find my red pine cordwood sounds like bowling pins with a year plus of aging...

Trace Oswald wrote: split it, and get the reading from the center of the wood where you split it.  It will give you a pretty good indication.

That makes far more sense than what I've heard in the past.
Fine idea, but I'll leave the meter to the kiln driers and furniture makers.

Tommy Bolin wrote:

Trace Oswald wrote: split it, and get the reading from the center of the wood where you split it.  It will give you a pretty good indication.

That makes far more sense than what I've heard in the past.
Fine idea, but I'll leave the meter to the kiln driers and furniture makers.

I get it Tommy. I rarely use one either. I've been cutting firewood since I was a kid for our family business. At this point, I stay far enough ahead that I always have wood that has been drying for at least two years, and I have some now that is three years. Ideally, I'll get to the point where I'm several years ahead all the time.