# Bone dry, but still Sizzle?



## FaithfulWoodsman (Dec 23, 2016)

Cut this cherry down last feb. It was dead, little punk outside, but bone dry when cut. Stored outside uncovered for most the summer. split and stacked in late August. Checked moisture again, <15%. Been in shed since then. Almost all the stuff has some small and short bleeding when tossed in the stove. For about 5 minutes the split has a few small water marks only around the edge (see pic). They burn great and water doesn't last long, just wondered if this is something anybody else has had or knows why. Again their bone dry and burn great. I'm stumped as to why I get any moisture at all. Maybe the punk holds a little still from summer rain? Been under shed for 3 months. ???


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## StihlKicking (Dec 23, 2016)

Just remember, unless their at 0% moisture there is still moisture in them. When you pitch a piece of wood into the stove that 15% of moisture has to go somewhere. Wood at less than 20% MC will still sizzle a little bit when that last tiny bit of moisture cooks out but it's nothing to be concerned over.


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## FaithfulWoodsman (Dec 23, 2016)

Very true. Maybe it's a cherry thing or the way they dried out. Cause they all do it just the same. A few spots on an edge.  None of the other ash or maple do it within the same moisture range. Oh well they burn awesome, which is all that matters.


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## Dantheman300z (Dec 23, 2016)

Gotta agree with StihlKicking, I am having the same thing with ash right now. Dead and cut late two years ago. Stacked under cover, still sizzles a small bit.


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## Firefighter938 (Dec 23, 2016)

i get it also occasionally, frequently with cherry also. I just burn it with a little more air until it takes off.


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## CentralVAWoodHeat (Dec 23, 2016)

Don't worry about it.  I have burned various types of wood at well under 15% and still get some moisture bubbles for a few minutes.  Like everyone else has said, it's totally normal.


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## Jay106n (Dec 23, 2016)

My black cherry does the same every now and then for the first few. Just the way the wood is for whatever reason. It still burns great!


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## Babaganoosh (Dec 23, 2016)

I've had the same issue with cherry wood. The bark really holds moisture. The sizzle lasts for a few minutes and then goes away.


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## lindnova (Dec 23, 2016)

Did you check the moisture content on a fresh split?  I am guessing there is still more moisture inside the splits than you think you have if it was only split in August.


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## Ctwoodtick (Dec 23, 2016)

I wonder if the punkiness is apt to hold some moisture?  Either way, sounds like the wood performs just fine.


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## FaithfulWoodsman (Dec 24, 2016)

lindnova said:


> Did you check the moisture content on a fresh split? I am guessing there is still more moisture inside the splits than you think you have if it was only split in August


Yep always check a fresh split. Split in August, but cut dead 6 months prior. I mean some of the stuff didn't even register freshly felled. seems like a cherry thing and also a punky water holding issue. But burns great.......so


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## Firefighter938 (Dec 24, 2016)

I have been burning some silver maple that has been c/s/s for two years. It is way dry. I keep about 1/2 cord in my garage to keep it dry and easy access. The latest maple I moved into the garage had been rained on about a week before I moved it. This morning I grabbed some to start a fire, and yep, it sizzled for about 5 minutes. I've been burning this maple all season with no sizzle. This load had a little.


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## Paulywalnut (Dec 29, 2016)

Years ago before I was schooled on 3 year seasoned wood, I would entertain the kids with foaming firewood. They thought it was great....me not so great


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## woodsHAM (Dec 30, 2016)

I burn alot of cherry and it always seems to have some sizzle to it. Sugar maple as well in my experience.


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## Babaganoosh (Dec 31, 2016)

Obviously it's not an accurate reading because it wasn't in wood per se but I took a piece of cherry that was outside in a rain storm and then sat a foot from the stove for 24 to 36 hours and resplit  it. It tested to 17%. Then for fun I jammed it into the bark and the area between the bark and the split. I was getting 25%. That thick  cherry bark definitely  holds the moisture.


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## Ashful (Dec 31, 2016)

I find I only get sizzle out of knotty splits, and a lot of the "Cherry" that grows around here is those flowery things that are all branches with almost no trunk, so if that's the case...


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## St. Coemgen (Dec 31, 2016)

FaithfulWoodsman said:


> Checked moisture again, <15%..... Again their bone dry and burn great..... I'm stumped as to why I get any moisture at all???



You answered your own question in your post. That is, 15% is not "bone dry" but instead wood with up to 15% moisture content. Which is still some water. And that measurement is just an average. Nothing in those numbers says there will not pockets of moisture with higher content in the wood. And wood came from a living thing, and while the "wood" xylem mostly transports water, there usually are some organic compounds, varying between species, there as well (which may bind some water), and what you see may be just some of that residual xylem "sap".

So in short, while an interesting biological question, for heating: don't worry about it.


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## FaithfulWoodsman (Dec 31, 2016)

St. Coemgen said:


> You answered your own question in your post. That is, 15% is not "bone dry" but instead wood with up to 15% moisture content. Which is still some water. And that measurement is just an average. Nothing in those numbers says there will not pockets of moisture with higher content in the wood. And wood came from a living thing, and while the "wood" xylem mostly transports water, there usually are some organic compounds, varying between species, there as well (which may bind some water), and what you see may be just some of that residual xylem "sap".
> 
> So in short, while an interesting biological question, for heating: don't worry about it.


Agreed and very scientific, which I appreciate. I was just surprised at how much water came out of some splits that didn't even register on the meter compared to other species that have no visible vapor spots at similar moisture levels. Most likely a variance between species as you stated and of no concern since they burn great.


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## fire_man (Jan 1, 2017)

Some of my 3 year old Oak sizzles but anything older never does.


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## CheapBassTurd (Jan 2, 2017)

*Learned a bit in this thread.  Thanx, fellas.
*


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## Easy Livin’ 3000 (Jan 2, 2017)

FaithfulWoodsman said:


> Cut this cherry down last feb. It was dead, little punk outside, but bone dry when cut. Stored outside uncovered for most the summer. split and stacked in late August. Checked moisture again, <15%. Been in shed since then. Almost all the stuff has some small and short bleeding when tossed in the stove. For about 5 minutes the split has a few small water marks only around the edge (see pic). They burn great and water doesn't last long, just wondered if this is something anybody else has had or knows why. Again their bone dry and burn great. I'm stumped as to why I get any moisture at all. Maybe the punk holds a little still from summer rain? Been under shed for 3 months. ???
> 
> 
> 
> ...


I have the same experience, and although I know it's fine, I eliminate it by removing the bark when I can.


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## PA. Woodsman (Jan 3, 2017)

On occasion, I will hear some sizzle coming from some of the smaller kindling splits that are in the garage which always gets like a hot house, especially this past Summer and I think "how the heck can there be any moisture in there?" but apparently there is, although I never see the ends sizzle, but like several have said unless it is 0% that moisture is there albeit very slight!


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## Woody Stover (Jan 3, 2017)

Yep, it's a "Cherry thing." Classic.


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## Ashful (Jan 4, 2017)

Nothing is "dry", in such close proximity to Shangy's.


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## Paulywalnut (Jan 10, 2017)

It has to be pretty moist to foam out the ends. 3 year red oak will hiss a bit


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## Easy Livin’ 3000 (Jan 10, 2017)

Ashful said:


> Nothing is "dry", in such close proximity to Shangy's.


Shangy's is a beer distributor in Emmaus, PA for anyone who is scratching their head.  You have a two track mind, Ashful.  Beer and wood heat.  I guess I can relate...


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## Ashful (Jan 11, 2017)

ED 3000 said:


> Shangy's is a beer distributor in Emmaus, PA...


Simply calling Shangy's a beer distributor, and leaving it at that, is like saying Los Angeles has a little traffic during rush hour.


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## SaltyWoodsman (Jan 11, 2017)

Phew! This was also a concern of mine. I'm a bit of a noob with my stove (it was in the house when we moved in), but did some reading. I bought 2 cords of "seasoned" firewood from a referral from a guy that my cousin sent me to. Fresh split did register < 20% MC (usually 16 - 18% range), but was sizzling. I thought I was taken for a ride, but there's no smoke/steam from the chimney, and the stove is maintaining 500°. I'll let 'em sizzle.


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## FaithfulWoodsman (Jan 11, 2017)

I checked under the bark on a few and a couple of them had much higher moisture content, some up to 26%. A fresh split on the same peice read 18%. I was never a proponent of removing bark as I felt it was losing some BTUs needlessly, albeit prob negligible. However bark will now go whenever I can get it off in processing.


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## Easy Livin’ 3000 (Jan 11, 2017)

FaithfulWoodsman said:


> I checked under the bark on a few and a couple of them had much higher moisture content, some up to 26%. A fresh split on the same peice read 18%. I was never a proponent of removing bark as I felt it was losing some BTUs needlessly, albeit prob negligible. However bark will now go whenever I can get it off in processing.


That bark sure hold the moisture in. Even 5 year old split wood, if stored outside in the rain, will stay wet for a long time under the bark. Often the bark will fall off given enough time, but not always.  It's not vascular moisture, but is still water that requires boiling off when burned.  A shed can help, but outside, rain will soak into the cambium layer like a sponge and remain there for a long time.  It's part of what nature designed it for!


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## PA. Woodsman (Jan 11, 2017)

ED 3000 said:


> Shangy's is a beer distributor in Emmaus, PA for anyone who is scratching their head.  You have a two track mind, Ashful.  Beer and wood heat.  I guess I can relate...




About 2 miles away from me, but I quit drinking many years ago so "it don't send me" HA !


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## Sodbuster (Jan 12, 2017)

Same thing with Cherry; Ash I can let the stove get almost cold if necessary and and it will fire right up and be blazing shortly thereafter. Cherry, I need a screaming hot bed of coals or it takes forever to get going.


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## fire_man (Jan 13, 2017)

ED 3000 said:


> That bark sure hold the moisture in. Even 5 year old split wood, if stored outside in the rain, will stay wet for a long time under the bark. Often the bark will fall off given enough time, but not always.  It's not vascular moisture, but is still water that requires boiling off when burned.  A shed can help, but outside, rain will soak into the cambium layer like a sponge and remain there for a long time.  It's part of what nature designed it for!



Finally someone else seeing the same thing I see. I've read too many posts that say external moisture is "no big deal". It depends on your climate.

Wood can season for three years but if there is moisture under the bark it burns terrible.


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## Marshy (Jan 13, 2017)

FaithfulWoodsman said:


> Yep always check a fresh split. Split in August, but cut dead 6 months prior. I mean some of the stuff didn't even register freshly felled. seems like a cherry thing and also a punky water holding issue. But burns great.......so


Simple answer to all of this is you are not burning seasoned wood. Cut in 6 months ago and split in Aug is half seasoned. To some its less than half seasoned. Don't put all your faith in a moisture meter. I like to remove the bark when its getting the final stacking at the house in Aug. Give it a chance to get the remaining moisture out of it. I also like to get it inside to warm up and dry out for a week before it burn it, it makes a noticeable difference.


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## FaithfulWoodsman (Jan 13, 2017)

Marshy said:


> Simple answer to all of this is you are not burning seasoned wood. Cut in 6 months ago and split in Aug is half seasoned.


If it was green then it would be a year and a half too soon, but like I stated. It was dead for a good while and was light and super dry when I cut it. Literally some splits didn't even register MC the day I cut it down. Cherry can be like that, dead standing and <15%. It was the rain soaked punk that never really dried out even under the shade for a while that caused some sizzle and even at that it was very little. Just surprised non registering splits could do that, but as others said, it's a cherry thing.


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## Marshy (Jan 14, 2017)

FaithfulWoodsman said:


> If it was green then it would be a year and a half too soon, but like I stated. It was dead for a good while and was light and super dry when I cut it. Literally some splits didn't even register MC the day I cut it down. Cherry can be like that, dead standing and <15%. It was the rain soaked punk that never really dried out even under the shade for a while that caused some sizzle and even at that it was very little. Just surprised non registering splits could do that, but as others said, it's a cherry thing.


Oak can get that pink out later too. Need to remove it or keep the rain off it. Do you bring the wood inside and let it dry for any period of time before you burn it?


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## FaithfulWoodsman (Jan 14, 2017)

I let it sit uncovered for a month or two, knowing I should cover it, but didn't have time. It then went in the shed for several months, but at the back with little air flow. We bring a week's worth into the basement so it gets a little dry time. Obviously that punk can sure hold the water. There really wasn't much sizzle, I was just surprised there was any at all being so dead and previously dry. Regardless it burned great. Now the stuff I'm currently using is a little different. But I gotta another post about that: "something's gonna have to change".


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## SaltyWoodsman (Jan 20, 2017)

Marshy said:


> I also like to get it inside to warm up and dry out for a week before it burn it, it makes a noticeable difference.



I stand some splits up around the stove (not too close) and let them bask in the heat to dry a little more before I burn them.


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## Ashful (Jan 20, 2017)

SaltyWoodsman said:


> I stand some splits up around the stove (not too close) and let them bask in the heat to dry a little more before I burn them.


I try to keep all wood outdoors, until I'm ready to put it in the stove.  The times I have left wood in a bin by the stove have occasionally resulted in moths or bugs in the house.


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## fire_man (Jan 20, 2017)

Firing up the stove is so much easier when there is a load waiting inside 24 hrs before reloading. 
Never had any bug problems, but that's probably because the stacks are covered for 5 years outside and are dry as a bone.


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## WoodyIsGoody (Jan 21, 2017)

SaltyWoodsman said:


> I stand some splits up around the stove (not too close) and let them bask in the heat to dry a little more before I burn them.



I've done that too but only when the wood wasn't properly seasoned. It helps a little but it takes time for moisture to migrate from the interior and there is simply not enough room around any stove to do a significant amount. Dry, seasoned wood burns fine straight from the chilly outdoors.


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## fire_man (Jan 21, 2017)

WoodyIsGoody said:


> Dry, seasoned wood burns fine straight from the chilly outdoors.



I'm not sure how cold it gets in the PNW but I find that filling a stove with 40 pounds of wood at 0F slows down the time it takes to get the stove up to temp so the cat can be re-engaged.


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## Marshy (Jan 21, 2017)

Some of the large uglies that I bring in that couldn't be split sit on the concrete floor with the cut end down. After a week you can move the chunk and see the concrete has wicked the moisture from the piece. I'll keep doing that until no more moisture come out of it, might take 2-3 weeks for some depending on the size. As you can see from my pile, I bring in about a face cord at a time. Only bugs that come in are the occasional moth and a few mosquitoes that were dorment.


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## WoodyIsGoody (Jan 21, 2017)

fire_man said:


> I'm not sure how cold it gets in the PNW but I find that filling a stove with 40 pounds of wood at 0F slows down the time it takes to get the stove up to temp so the cat can be re-engaged.



Cold wood does need to absorb a certain amount of energy to bring it up to combustion temperature but the difference is small if the wood is already of low moisture content, even if it's very cold.

But, yes, if your wood is not ready to burn, and you're lighting a cold firebox, anything you can do to reduce the amount of heat it absorbs helps increase the firebox temperature and reduces the amount of time needed for secondary burn to occur. Dry wood can be put in cold although, in practice, most people keep a small amount indoors for convenience and so it's already warmed. That's not of much benefit if you have good wood.

The difference between fully seasoned wood and almost seasoned wood is so huge I have made sure I never need to burn partially seasoned wood again.


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## fire_man (Jan 21, 2017)

My wood is seasoned 5 years top covered - so its definitely ready to burn. There is significant mass (including moisture mass) that must come up to temp in a hot stove. My experience says throwing a load of bone dry wood at 0F is not nearly as quick to get hot as 70F wood. Simple physics.

Part of the fun in burning is having a routine which I can count on to get the fire established in a relatively consistent manner. I guess we can agree to disagree on this one.


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## WoodyIsGoody (Jan 21, 2017)

fire_man said:


> Part of the fun in burning is having a routine which I can count on to get the fire established in a relatively consistent manner. I guess we can agree to disagree on this one.



We're not really disagreeing. The difference is there but it's small if your wood is low molsture content.

I'd rather have 18% moisture content at 0 degrees than 23% moisture content at 70 degrees. But, yes, if they're both 18% moisture, the 70 degree wood will light a little easier.


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## Hasufel (Jan 21, 2017)

fire_man said:


> There is significant mass (including moisture mass) that must come up to temp in a hot stove. My experience says throwing a load of bone dry wood at 0F is not nearly as quick to get hot as 70F wood. Simple physics.


I did a quick calculation and, for one pound of oak, the difference between starting at 0F and starting at 70F is equal to about 6 percent of the heat you get from burning it. So it actually makes more of a difference than I expected. I can see how that would affect stove performance. 

Of course, if you bring the wood in and let it warm up before loading the stove, you might get the stove to heat up faster but you're still cooling off your house and making the stove generate more heat to compensate. So if you're looking at overall energy efficiency, I guess the trick is to bring your firewood inside on a warm day!


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## fire_man (Jan 21, 2017)

I figured there was an equation in there somewhere that would help. All I know is especially with my Palladian it seems to take a really long time to fire up unless the wood is at room temp - the Progress less so. 

If my wife had to go outside to get the wood the stove would NEVER reach temp!


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## Babaganoosh (Jan 21, 2017)

Hasufel said:


> I did a quick calculation and, for one pound of oak, the difference between starting at 0F and starting at 70F is equal to about 6 percent of the heat you get from burning it. So it actually makes more of a difference than I expected. I can see how that would affect stove performance.
> 
> Of course, if you bring the wood in and let it warm up before loading the stove, you might get the stove to heat up faster but you're still cooling off your house and making the stove generate more heat to compensate. So if you're looking at overall energy efficiency, I guess the trick is to bring your firewood inside on a warm day!



The stove won't generate more heat. Less heat will be transferred to the house is all. 

Stoves generate a lot of btus. The btus needed to warm the wood up from say 32 to 70 is negligible compared to what's needed to heat a house.  

I don't see much difference in throwing cold wood into the stove as long as there's a good hot coal bed.  When there isn't a nice coal bed it's slightly harder to get it going but it's nothing big enough to write home about. I'd go on a limb here and say that 32 degree maple will go up before 70 degree locust 7 days a week and twice on Sunday.


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## Ashful (Jan 21, 2017)

Hasufel said:


> I did a quick calculation and, for one pound of oak, the difference between starting at 0F and starting at 70F is equal to about 6 percent of the heat you get from burning it. So it actually makes more of a difference than I expected. I can see how that would affect stove performance.
> 
> Of course, if you bring the wood in and let it warm up before loading the stove, you might get the stove to heat up faster but you're still cooling off your house and making the stove generate more heat to compensate. So if you're looking at overall energy efficiency, I guess the trick is to bring your firewood inside on a warm day!



This.  You can't argue with physics!


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## WoodyIsGoody (Jan 21, 2017)

Hasufel said:


> I did a quick calculation and, for one pound of oak, the difference between starting at 0F and starting at 70F is equal to about 6 percent of the heat you get from burning it. So it actually makes more of a difference than I expected.



I'd like to see your work because I got a different answer than you by a factor of 8+. And, at only about .7% of the btu value of the wood, my answer seems more intuitively correct. Here's my work:


The amount of energy required to raise the temperature of a substance 1 degree C is called the specific heat. The specific heat of firewood in this example needs two components, that of the wood and that of the water. Since we are measuring the amount of heat required to raise the firewood from 0F (-9C), it’s necessary to separate the two components because one (the H2O) will be going through a phase change (from solid to liquid) while the other (the solid wood) will not. The phase change absorbs a significant amount of energy without a change in temperature so our calculation would not be accurate without including the energy necessary to accomplish the phase change.

The specific heat of a pound of oven dried wood is roughly 1/4 that of a pound of water. If that water starts out as a solid (i.e frozen) it needs to go through one phase change transition, the change from a solid to a liquid. The amount of heat required for the phase change doesn’t involve ANY change of temperature of the water, that must be added on. It's also necessary to add in the energy required to raise the temperature of (dry) wood portion of the load to get a complete answer.

If that doesn’t have your head spinning yet, let’s look at some numbers.

Say your load is 40 lbs. of firewood w/ 15% moisture content and we will calculate how much heat energy it takes to bring that wood up to the same temperature it would be if the wood had been sitting at room temperature for a week.

At 15% moisture, a 40 lb. load contains 6 lbs. of water leaving 34 lbs. of 0% moisture "wood".

Now we’ll convert to metric to make it a whole lot easier.

6lb H20 = 2722g  34 lb. dry wood = 15,422g

First we’ll calculate the amount of energy required to raise just the water portion of the load (in this case a solid at 0F (-18C) up to 70F (21C). It takes 1 calorie to raise 1 gram of water 1 degree C. So, the heat needed to raise the water will be 39 cal/gram because we're raising it 39 degrees Celsius (from -18c to 21c). With 2722g of water, that’s 39 x 2722 calories or *106,158* calories.

To that figure we need to add the heat of fusion required (to convert 32 ice to 32 degree water). The heat of fusion (to go from solid to liquid) of water is 80 cal/g. With 2722g of water, that’s 80 x 2722 calories or *217,760* calories. Adding the temperature rise energy (106,158) to the heat of fusion (217,760) gives the total energy required to warm just the water portion of the wood. Which is *323,918* calories. You might notice that two thirds of the energy on the water side of the equation is consumed simply going from frozen to thawed (without contemplating any actual rise in temperature).

The specific heat of dried wood (0% water) is about .27 cal/gram/degree Celsius. This only varies slightly from specie to specie. This is the energy required to heat the wood without water one degree C. Since we need to raise 15,422g of wood 39 degrees C, it’s 39 x .27 x 15,422 or *162,394* calories. To calculate the energy required for the entire 40 lb. load (water and wood, we simply add the two totals together. 162,394 + 323,918 or *486,312 *calories. To convert calories to btu’s we multiply by .004 which gives us *1,945 btu’s*.


The accepted btu value for one lb. of wood (any species) at 0% moisture level is 8660 btu’s. Since we know our wood weight without moisture is only 34 lbs., our 40 lb. load of 15% moisture wood has *294,440 btu’s *(34 x 8660) Since *1,945 btu’s *will be consumed simply warming the wood from 0C-21C, we will be deficient by that amount vs. using wood already thawed and warmed to room temperature. Instead of starting with 294,440 btu’s we’ll be starting with *292,496* btu's or 99.3% of the amount that would have been available had the load been pre-warmed warmed to 21C (70F).

That's only 0.7% difference! In other words, only 0.7% of the total btu value of the wood goes to warming it up to room temperature from 0F.




> So if you're looking at overall energy efficiency, I guess the trick is to bring your firewood inside on a warm day!



Good luck finding a winter day so warm that this isn't the small loss that it is (remember, these calculations are based on wood that is frozen solid at 0 degree F!) You would have to bring your entire season's worth of wood inside before it got cold in the fall to avoid this 0.7% heat loss. But you can keep this loss as low as possible by only bringing good, dry wood inside!


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## FaithfulWoodsman (Jan 22, 2017)

Nice work. Without checking your values and conversions, your calculations appear correct. However, even as thorough as you've been there are still variables unaddressed. For one if pressure is constant and the air dry, which it would be, sublimation may occur on a super hot bed of coals. Don't remember specifics, but I do recall that sublimation takes considerably more energy than phasing from solid to liquid, whether provided by the coals or wood, result would still be a larger net loss. Regardless i think we are in danger of getting a little too far into the weeds with this one. 
Cause.........


WoodyIsGoody said:


> Good luck finding a winter day so warm that this isn't the small loss that it is (remember, these calculations are based on wood that is frozen solid at 0 degree F!) You would have to bring your entire season's worth of wood inside before it got cold in the fall to avoid this 0.7% heat loss.


1. It's been within 15° of 70° for two weeks here, 65° today
And
2. I bring 1/4 cord from the shed outside my basement at a time. It reaches 70° within hours and lasts for 7-12 days depending on the weather. 
Love this forum.


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## WoodyIsGoody (Jan 22, 2017)

FaithfulWoodsman said:


> Nice work. Without checking your values and conversions, your calculations appear correct. However, even as thorough as you've been there are still variables unaddressed. For one if pressure is constant and the air dry, which it would be, sublimation may occur on a super hot bed of coals. Don't remember specifics, but I do recall that sublimation takes considerably more energy than phasing from solid to liquid, whether provided by the coals or wood, result would still be a larger net loss. Regardless i think we are in danger of getting a little too far into the weeds with this one.



I like the way you think!

The heat of sublimation is equal to the heat of fusion (solid to liquid) + heat of 100C temperature change (from 0C-100C) + heat of vaporization. But I didn't count that because we are only going to room temperature with this exercise. However, you're right. My calculations don't take into account the energy of any moisture that evaporates from the wood (regardless if it sublimates or evaporates). If the wood dried through this process, we would no longer have 15% moisture content! So I was trying to do the calculation for the warmed wood assuming a steady 15% moisture content. And even though the amount of energy required to sublimate water is quite high, the amount of water that sublimated (or evaporated) would be very low (assuming we are just bringing the wood to room temperature).

Things get complicated real fast when we try to mathematically model the real world.


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## Hasufel (Jan 22, 2017)

WoodyIsGoody said:


> I'd like to see your work because I got a different answer than you by a factor of 8+. And, at only about .7% of the btu value of the wood, my answer seems more intuitively correct. Here's my work:
> 
> 
> The amount of energy required to raise the temperature of a substance 1 degree C is called the specific heat. The specific heat of firewood in this example needs two components, that of the wood and that of the water. Since we are measuring the amount of heat required to raise the firewood from 0F (-9C), it’s necessary to separate the two components because one (the H2O) will be going through a phase change (from solid to liquid) while the other (the solid wood) will not. The phase change absorbs a significant amount of energy without a change in temperature so our calculation would not be accurate without including the energy necessary to accomplish the phase change.
> ...


I think I figured out the problem--I was the victim of bad data. Also, I calculated for dry oak and ignored water entirely, and I think some of our physical property data might be off as well. Here's how I did the math:

H=mcT [where H = change in enthalpy, m = mass, c (actually c-sub-p) = specific heat, and T = temperature change]

I did this all in English units to keep it simple, so...

H = 1 pound X 5.73 BTU/lb F X 70 F = 401 BTU needed to raise 1 pound of oak by 70 F. The heat capacity value was for oak timber, found at http://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html .

The figure I used for the heat value of oak is 6388 BTU/lb, which is a bit different than the figure you used (source = https://en.wikipedia.org/wiki/Wood_fuel but because I don't blindly trust Wikipedia I calculated a similar figure for oak at http://www.engineeringtoolbox.com/wood-combustion-heat-d_372.html .

So we have 401/6388 = 0.063 or 6.3 %.

HOWEVER, I ran the calculation in metric and came up with an order of magnitude difference...0.63 % rather than 6.3 %. I traced the problem to the heat capacity of oak, which the site I listed above gave as 5.73 BTU/lb F. The same site gave the corresponding value as 0.57 cal/g C but that should calculate out to be almost exactly the same as BTU/lb F, so it appears that the heat capacity value I used was 10 times too large. Using the smaller value, I now get a number much closer to yours.

And now that my brain hurts, it's time to go outside and play with wood!


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## WoodyIsGoody (Jan 22, 2017)

Hasufel said:


> I think I figured out the problem--I was the victim of bad data. Also, I calculated for dry oak and ignored water entirely, and I think some of our physical property data might be off as well.



I agree, the engineering toolbox gives a value for the specific heat of wood that is 10 times higher for the imperial measure vs. the metric. They also give values for different species of wood that vary from .31 cal/g/C (red beech) to .60cal/g/C  (pockwood, a tropical hardwood) and yet they fail to state the all important factor, moisture content. I would assume the all the readings between .3 and .38 are for kiln dried wood around 10% moisture or less but that some of the other figures could be culled from different sources and represent wood with higher moisture content. To further complicate matters, the specific heat of dry wood (and most organic materials) increases linearly with temperature, from around .27 cal/g/C at 0C to .37 cal/g/C at 100C.

My calculations used .27 cal/g/C but assumed 0% moisture. If you assume 20% moisture (H2O has specific heat of 1.0) then the .27 cal/g/C that I used for dry wood becomes .38 cal/g/C for 15% moisture wood and .42 cal/g/C for 20% moisture wood.

If I were to calculate this again, I would adjust the heating value of 0% moisture wood from 8860 btu/pound to 7974 btu/pound  because I forgot to adjust to account for the fact that stoves are not 100% efficient at extracting the heat. In other words, a lb. of 0% moisture wood has around 7974 btu's useable heat when burned optimally. This number, reduced a further 20% to account for water content, will correspond almost exactly with the number you used for 20% moisture wood. A good explanation of firewood btu values is offered here:

https://chimneysweeponline.com/howoodbtu.htm

In a future discussion we will need to explore the effect of water content on USEABLE heat. This will get into the heat of vaporization and the numbers are quite astounding! Without recalculating everything, I can see that the heat to bring wood from 0F to room temperature could be up to 1% of the actual heating value of that wood. And anyone who likes numbers can see that almost half of this heat is the phase change of just the water portion of the wood. And if your wood is much over 20%, thawing the water in the wood (from 32F to 32F) will take more energy than raising the temperature of the wood AND the water from 0F to 70F!  Just wait until we start comparing the heat of vaporization to the relatively minor heat of fusion (melting). Now my goal is to have the driest wood possible (at least as dry as is possible here in the dank PNW).

The big takeaway here is that moisture content of your wood affects your comfort and safety in multiple ways.




> And now that my brain hurts, it's time to go outside and play with wood!



Let 'er rip!


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## FaithfulWoodsman (Jan 22, 2017)

WoodyIsGoody said:


> The big takeaway here is that moisture content of your wood affects your comfort and safety in multiple ways.





Hasufel said:


> And now that my brain hurts, it's time to go outside and play with wood!


Yes and yes. I'm a MS science teacher, so it's been fun delving into this much pyro-physics. I must know what both of your professions are as my instincts tell me they involve engineering, physics, or chemistry. Plz tell.


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## Hasufel (Jan 22, 2017)

FaithfulWoodsman said:


> Yes and yes. I'm a MS science teacher, so it's been fun delving into this much pyro-physics. I must know what both of your professions are as my instincts tell me they involve engineering, physics, or chemistry. Plz tell.


You're very perceptive! Chemical engineer. It's rare that I get a chance to apply my (admittedly dated) knowledge on such practical matters.  Although I did get a free drink at Starbucks one time because I knew Avogadro's number...


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## WoodyIsGoody (Jan 22, 2017)

FaithfulWoodsman said:


> Yes and yes. I'm a MS science teacher, so it's been fun delving into this much pyro-physics. I must know what both of your professions are as my instincts tell me they involve engineering, physics, or chemistry. Plz tell.



Ha! I'm semi-retired from commercial salmon fishing in Alaska and Washington, carpenter, laborer and freestyler who has been a ski bum his entire life. I've made more $$ sitting on my ass in front of my monitor playing the stock market than I've ever made using my hands and back. Otherwise I'd still be fishing. Now my wife and I just manage our one beach vacation rental on Kauai and continue to invest.  My dog doesn't understand what is so attractive about my laptop (considering it doesn't have good smells or seem to do much at all). He shows more interest when I fire up my Green Egg! He loves fires, the sunny spot on the carpet (even in mid-summer, go figure) and, oddly enough, following me on my skis for miles, even when the snow is above his chest, in which case he stays in my powder tracks even if they make SS's down a steep slope. This never fails to entertain others who might chance to be close enough to observe.  Because it looks like he is imitating a skier (when actually he's just being practical and trying to keep his head above the surface of the snow). But I think he has more fun than I do.

The equations and conversions here made me delve into areas that hadn't been exercised much since I was in HS and college ~30 years ago because I'm more of a back of a napkin, seat of the pants thinker.


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## Oldman47 (Jan 23, 2017)

So why are you guys stopping at 70ºF or 21ºC? Wood cannot burn at that temperature. I am not sure where it starts but I know that even paper will not burn until 451ºF. My bet is wood would be a bit higher. By that time you have boiled off all of the moisture, latent heat of vaporization, in either case and the BTUs to heat your wood from frozen to 70F becomes insignificant compared to making that steam and heating the wood that much. If you are going to run the numbers, why not be complete about what we do know?


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## Hasufel (Jan 23, 2017)

Oldman47 said:


> So why are you guys stopping at 70ºF or 21ºC? Wood cannot burn at that temperature. I am not sure where it starts but I know that even paper will not burn until 451ºF. My bet is wood would be a bit higher. By that time you have boiled off all of the moisture, latent heat of vaporization, in either case and the BTUs to heat your wood from frozen to 70F becomes insignificant compared to making that steam and heating the wood that much. If you are going to run the numbers, why not be complete about what we do know?


In all this thermodynamics excitement I've kind of lost track of how this started but I think the point was to highlight the difference between loading cold wood from outside directly into the stove vs. loading wood that had reached room temperature, and that difference was on the order of 0.6% of the wood's heat value. You are right that there's a lot of additional heat needed to get the wood to its ignition temperature (and boil off the water in the process) but that would be the same in both cases (0F vs 70F wood). I don't anticipate people preheating the wood to 450F and then chucking it into the stove. Doing the math, however, would probably highlight just how much energy is needed to boil off the water, and reinforce the importance of burning dry wood.


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## FaithfulWoodsman (Jan 23, 2017)

Hasufel said:


> Doing the math, however, would probably highlight just how much energy is needed to boil off the water, and reinforce the importance of burning dry wood.


Bingo! That's the info to change your ways. But I already burn dry and I assume most everybody on here has been educated and is working towards that goal. Knowing what you need and how to get it are two different things. I have two year  CSS beech and ash right now that are in the low 20's, some lower. But I expected nothing but teens, low at that. Split to big, not enough air and tarps that really didn't do much. Water also drains to where wood is stacked, but there's nothing I can do about that. Adjustment will be made. Found half a cord of burn now (15%) cherry to add, so all is well. But I find myself saying what was said last year when I had to supplement the last month with dead standing......."next year I'll have 5 cords of super dry wood". Ironically this year this year is worst than last (middle stacks). Next year for sure.


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## WoodyIsGoody (Jan 24, 2017)

Oldman47 said:


> So why are you guys stopping at 70ºF or 21ºC? Wood cannot burn at that temperature. I am not sure where it starts but I know that even paper will not burn until 451ºF. My bet is wood would be a bit higher. By that time you have boiled off all of the moisture, latent heat of vaporization, in either case and the BTUs to heat your wood from frozen to 70F becomes insignificant compared to making that steam and heating the wood that much. If you are going to run the numbers, why not be complete about what we do know?



I hear you. When I have more unallocated free time I would like to do just that. The heat of fusion (ice to water) is an eye-opener but pales in comparison to the heat of vaporization. And the energy loss as the water in your wood vaporizes hurts more than the lost energy would indicate. By consuming heat, the evaporation of water cools the combustion process and causes a less complete burn. So more unburnt gases escape up your chimney without contributing to the heating of your home. And some might say, that's ok, I'll burn the less dry stuff when the weather is mild and I don't need the extra heat. But that's the worst time to burn damp wood because that's when you want to be able to burn low and slow which is precisely when you don't want your combustion cooled further. Creosote city.

Here's a brainteaser that I don't know the answer to. My ski cabin is in a PNW rainforest at 1000 foot elevation. It's quite rare for the humidity to drop below 50%, at least for any length of time. Typical humidity is close to 100% (generally 80%-100%). So how is it that my woodpile ends up at 20% humidity after a couple of years? It's a mystery to me.


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## Oldman47 (Jan 24, 2017)

Just try telling someone who doesn't understand the math that boiling is a cooling process. They will think you have lost all of your marbles.


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## Firefighter938 (Jan 24, 2017)

I've noticed a big change in my wood lately. It has been warm and wet in central Indiana for several weeks. I am burning standing dead ash that has been stacked for 1.5yrs. It was probably burnable the day I stacked it, but I didn't need it. 
Anyway, it has been burning great until just a few days ago. Now on cold starts(which is happening more often because of mild temps) I'm seeing some moisture come out the ends. Not for long, and it doesn't bubble, but you can see it. It is a little more difficult to start fires also. 
This is all from the same tree, the same stack, and it has been sitting in a pole barn for 2 months, so it hasn't gotten rained on. 
I think the constant high humidity we have had has added moisture to the wood, to the point it is now noticeable. It only lasts a few minutes and is gone, but definitely changed the characteristics of the fire. 
It is possible that the wood I'm burning now was the lower portion of the tree, or the bottom of the stack when it was outside also.


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## FaithfulWoodsman (Jan 24, 2017)

WoodyIsGoody said:


> Here's a brainteaser that I don't know the answer to. My ski cabin is in a PNW rainforest at 1000 foot elevation. It's quite rare for the humidity to drop below 50%, at least for any length of time. Typical humidity is close to 100% (generally 80%-100%). So how is it that my woodpile ends up at 20% humidity after a couple of years? It's a mystery to me





Firefighter938 said:


> I've noticed a big change in my wood lately. It has been warm and wet in central Indiana for several weeks. I am burning standing dead ash that has been stacked for 1.5yrs. It was probably burnable the day I stacked it, but I didn't need it.
> Anyway, it has been burning great until just a few days ago



Something tells me atmospheric pressure plays a large role in determining how RH is going to affect the drying of cellular moisture and the expansion/contraction of seasoned (burn ready) wood. Any woodworker knows humidity can drastically affect the size and characteristics of wood. My current batch was questionable already, but I've noticed it has gotten even worse since the constant bombardment of moisture in the air for about a month now. Many splits sizzle for at least 10 minutes and some even have moisture escaping through the sides under the bark, visible once it lifts. I take in a week's worth at a time and things get better within a few days.


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## Hasufel (Jan 24, 2017)

WoodyIsGoody said:


> Here's a brainteaser that I don't know the answer to. My ski cabin is in a PNW rainforest at 1000 foot elevation. It's quite rare for the humidity to drop below 50%, at least for any length of time. Typical humidity is close to 100% (generally 80%-100%). So how is it that my woodpile ends up at 20% humidity after a couple of years? It's a mystery to me.


I think the answer is that air and wood are different substances with different properties. Moisture in your wood is not technically humidity because it's sitting there in the liquid state, whereas in air it's a vapor. Theoretically, any liquid water will tend to evaporate if it's exposed to air below 100% RH. However, in wood, there's capillary action and other processes that cause it to hold on to some of the water. So moisture in wood reaches a certain equilibrium point that depends on the RH and maybe other factors (like air pressure perhaps?). I ran some tests here and found that firewood that's not exposed to rain can still gain weight when the humidity goes up. Another factor to consider is that you have sunlight helping; that heats the wood above the air temperature and increases the vapor pressure of the water inside, which makes it more likely to evaporate. And the more wind you have, the less likely you are to have the air in contact with wood reach saturation...so that increases drying too.


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## Oldman47 (Jan 24, 2017)

If you really want to get into what goes on with wood moisture content try here, but only if you are very serious about it. It makes for heavy reading but does tell you that relative humidity and wood stable moisture content are very different. The wood will hold a lot less than you might think using just RH. I find that page 3 and 4 help my understanding in the broad sense.
http://www.woodbodger.com/wp-conten...Relations-and-Physical-Properties-of-Wood.pdf


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## Hasufel (Jan 24, 2017)

Oldman47 said:


> If you really want to get into what goes on with wood moisture content try here, but only if you are very serious about it. It makes for heavy reading but does tell you that relative humidity and wood stable moisture content are very different. The wood will hold a lot less than you might think using just RH. I find that page 3 and 4 help my understanding in the broad sense.
> http://www.woodbodger.com/wp-conten...Relations-and-Physical-Properties-of-Wood.pdf


That's a fantastic resource, thanks! So per the brainteaser that @WoodyIsGoody posed, Table 4-2 shows that at, say, 70F and 90% RH, you can still dry wood down to 20.5% MC. Very interesting!


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## Sodbuster (Jan 25, 2017)

Firefighter938 said:


> I've noticed a big change in my wood lately. It has been warm and wet in central Indiana for several weeks. I am burning standing dead ash that has been stacked for 1.5yrs. It was probably burnable the day I stacked it, but I didn't need it.
> Anyway, it has been burning great until just a few days ago. Now on cold starts(which is happening more often because of mild temps) I'm seeing some moisture come out the ends. Not for long, and it doesn't bubble, but you can see it. It is a little more difficult to start fires also.
> This is all from the same tree, the same stack, and it has been sitting in a pole barn for 2 months, so it hasn't gotten rained on.
> I think the constant high humidity we have had has added moisture to the wood, to the point it is now noticeable. It only lasts a few minutes and is gone, but definitely changed the characteristics of the fire.
> It is possible that the wood I'm burning now was the lower portion of the tree, or the bottom of the stack when it was outside also.




Ditto,ditto,ditto on this, with temperatures in Michigan hovering in the 40's to near 50, I've had several cold starts, all of which take hours. If I don't let the stove go cold, I have no problem, but a cold stove in this climate is a very slow start.  This is using dead Ash that has be CSS for 1-1/2 years and was 12% when I cut it.


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## WoodyIsGoody (Jan 25, 2017)

Hasufel said:


> That's a fantastic resource, thanks! So per the brainteaser that @WoodyIsGoody posed, Table 4-2 shows that at, say, 70F and 90% RH, you can still dry wood down to 20.5% MC. Very interesting!



Good eye on that. Humidity does drop here in the summer which helps as well.

Another chapter of the same book has more relevant info:
http://www.woodbodger.com/wp-conten...3-Drying-and-Control-of-Moisture-Content1.pdf

Sadly, no discussion of how deep freezing green wood might affect it's future drying speed. Also, the drying table (4-2) doesn't extend below 30 degrees. I've often felt that some freeze/thaw cycles contribute to better drying in my climate.


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## Ashful (Jan 25, 2017)

Sodbuster said:


> Ditto,ditto,ditto on this, with temperatures in Michigan hovering in the 40's to near 50, I've had several cold starts, all of which take hours. If I don't let the stove go cold, I have no problem, but a cold stove in this climate is a very slow start.  This is using dead Ash that has be CSS for 1-1/2 years and was 12% when I cut it.


Hours?  For me, a cold start in cold weather takes 6-8 minutes from lighting match to active and engaged catalytic combustor.  In mild weather, when my shorter (15 feet) chimney gets lazy, it can take up to 15 minutes, but never more.  The last time I spent more than 15 minutes waiting for secondary combustion was my first year burning, when I was trying to burn poorly-seasoned wood, and even then we were looking at more like 30 minutes to reach secondary combustion.  If I read your post correctly, and you're belching creo for several hours waiting for secondary combustion to kick in, something is horribly wrong!


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## Sodbuster (Jan 25, 2017)

Ashful said:


> Hours?  For me, a cold start in cold weather takes 6-8 minutes from lighting match to active and engaged catalytic combustor.  In mild weather, when my shorter (15 feet) chimney gets lazy, it can take up to 15 minutes, but never more.  The last time I spent more than 15 minutes waiting for secondary combustion was my first year burning, when I was trying to burn poorly-seasoned wood, and even then we were looking at more like 30 minutes to reach secondary combustion.  If I read your post correctly, and you're belching creo for several hours waiting for secondary combustion to kick in, something is horribly wrong!



Hours may be a bit long now that I rethink it. Basically with my steel stove,if I let it get stone cold, it takes a while before it's throwing serious heat. That's starting the logs, that are cold, with Fatwood. If I catch it with some hot coals the whole process is much quicker. I guess that was my poorly made point.


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## Ashful (Jan 27, 2017)

Sodbuster said:


> Hours may be a bit long now that I rethink it. Basically with my steel stove,if I let it get stone cold, it takes a while before it's throwing serious heat. That's starting the logs, that are cold, with Fatwood. If I catch it with some hot coals the whole process is much quicker. I guess that was my poorly made point.


Save your smaller splits for those cold starts.  It does take longer if you're loading all 6" or 8" square splits on top of that kindling.  Nothing wrong with an occasional box of 4" splits, for getting things hot fast.


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## venator260 (Jan 29, 2017)

Marshy said:


> I also like to get it inside to warm up and dry out for a week before it burn it, it makes a noticeable difference.


This is what I do. My current t basement full has been processed for 1.5 years, but has been about 7-8 stacks deep in my dad's woodshed for that time. I pick a warm day and put a bunch in the basement. I get the sizzles for about 3-4 days, and then it stops. I figure that being in the basement that stays about 70-80 degrees and about 30% RH takes off enough surface moisture that it stops being an issue. At my current rate of burning, I have about 3 weeks to a month's worth in the basement currently. It's been there since last Saturday. I stopped getting sizzlers Wednesday or Thursday. 

My plan for next year is to reconfigure my space and get at least 1/2 a winter's worth in there in the fall. I'll pick my best wood, but any drying that occurs will help the burn and add moisture to the house, however little it may be.

And as another poster said, I try to pick warm days to bring in wood, but that's more about short term heat loss through the window I throw the wood in through.


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## FaithfulWoodsman (Jan 29, 2017)

venator260 said:


> I get the sizzles for about 3-4 days, and then it stops.


I am getting sizzle now, but wasn't with my stuff stored for several months under shed after two years CSS. Current stuff was also 2 yr CSS but wasn't under shed until few weeks ago. I can only bring in 1.5 weeks worth, but notice a big diff after a few days. Designing a better plan for the future.


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## JotulOwner (Jan 30, 2017)

I get some noise and less than perfect burn from 7 year old splits (species doesn't matter) if the wood has been exposed to rain water (even a little bit) and hasn't fully dried out before I use it. I try to avoid that but sometimes it happens.


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## Marshy (Feb 1, 2017)

Each fall my neighbor buys his wood split and delivered. He brings all of it into his basement and stacks it and runs dehumidifiers. I told him he's crazy and should buy 2 years worth and get one year ahead. His furnace doesn't care too much I guess...

My pile looks a little thin for the time of year it is. I was really expecting to see a decrease in consumption by going with this BK King but so far I'm on track to use the same as my old non-epa stove. I have 2/3 of a cord that I did not bring up to the house because I didn't expect to need it. Looks like I should go get it once the ground hardens up again. That pile was not covered so there  is a fair amount of snow on the top right now. I'll be sure to give it extra time indoors before it gets burnt.


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## FaithfulWoodsman (Feb 7, 2017)

I just cut some dead cherry last Friday. It was super dry and very light, so I stacked it in the shed. Most of it had about an inch of punky wood around the good heartwood. Went to put some in the house yesterday and most of it has soaked up moisture and are much heavier. Only the punk has taken in the water as the heartwood is testing at 10-15%. It hadn't rained, all the weight is from very humid air. Will be interesting to see how long it takes for the water to release from the wood now that it's inside.


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## jatoxico (Feb 7, 2017)

Came home and started evening fire the other night. Have red oak that has been CSS for 3 years in a single row outside then in my wood shed since the end of Sept. Little triangular split with base (largest edge) only 1.5", kindling sized really. Yup, began steaming and boiling water like crazy. Go figure.


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## Ashful (Feb 7, 2017)

jatoxico said:


> Came home and started evening fire the other night. Have red oak that has been CSS for 3 years in a single row outside then in my wood shed since the end of Sept. Little triangular split with base (largest edge) only 1.5", kindling sized really. Yup, began steaming and boiling water like crazy. Go figure.



Red oak is most of what I burn.  Mine is seasoned 2.5 years, and I haven't noticed many sizzlers.  It burns like a dream, with very long active-cat coaling phase.


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## jatoxico (Feb 7, 2017)

Ashful said:


> Red oak is most of what I burn.  Mine is seasoned 2.5 years, and I haven't noticed many sizzlers.  It burns like a dream, with very long active-cat coaling phase.


Yeah steady diet of red oak here too though I have some other stuff ready to play with.

Most all burns beautifully, it's just the odd stick here and there that's wet but that one being so small surprised me.


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## Hasufel (Feb 10, 2017)

WoodyIsGoody said:


> I hear you. When I have more unallocated free time I would like to do just that. The heat of fusion (ice to water) is an eye-opener but pales in comparison to the heat of vaporization. And the energy loss as the water in your wood vaporizes hurts more than the lost energy would indicate. By consuming heat, the evaporation of water cools the combustion process and causes a less complete burn. So more unburnt gases escape up your chimney without contributing to the heating of your home. And some might say, that's ok, I'll burn the less dry stuff when the weather is mild and I don't need the extra heat. But that's the worst time to burn damp wood because that's when you want to be able to burn low and slow which is precisely when you don't want your combustion cooled further. Creosote city.


I'm stuck at home with a bad cold so I figured I'd finally work on this problem some more. What I did was put together an Excel file that calculated what percent of red oak's total heat value is expended in getting the wood up to the ignition point (and boiling off any water in the process). I looked at MCs from 0% to 25% and starting temps of -20C (-4F), 0C (32F), and 20C (68F). Not too many surprises in the numbers themselves but here's what I came up with...starting temperature has a small effect but not as much as the MC:



This takes a set quantity of wood (dry weight equivalent) and calculates the energy required to heat it to the boiling point, boil off any water, and then continue heating the dry wood to the ignition point (for which I used 250C...if you want to use a higher value the percentages will increase slightly but the proportions should still be close). Then you divide that by the heat value (3574 kcal/kg) to get a percentage. I calculated the heat capacities from 
https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr09.pdf . What surprised me is that there's no solid-liquid phase change to worry about if the wood is below the fiber saturation point, according to the document. So that simplified the calculations a bit.

To break this down a little further (and allow others to check my work, because cold medicine makes me loopy), 1.2 kg of 20% MC red oak (1 kg dry equivalent) at 0C/32F would need about 66 kcal to heat it to 100C, 108 kcal to boil off the 0.2 kg of water, and 71 kcal to heat the 1 kg of dry wood to 250F. So 27% of the "wasted" energy goes into heating the damp wood and a whopping 44% goes into boiling off the water. The remaining 29% is "overhead" that's pretty much unaffected by the starting conditions. Add them all up and divide by 3574 and you get the 6.9% figure that's on the chart.

I hope I did this right--give me a shout if any of it doesn't make sense!


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## WoodyIsGoody (Feb 10, 2017)

Hasufel said:


> I'm stuck at home with a bad cold so I figured I'd finally work on this problem some more.



Ha! I did my calculations when I was stuck at home with a bad cold. Great minds think alike! ;-)



> What I did was put together an Excel file that calculated what percent of red oak's total heat value is expended in getting the wood up to the ignition point (and boiling off any water in the process). I looked at MCs from 0% to 25% and starting temps of -20C (-4F), 0C (32F), and 20C (68F). Not too many surprises in the numbers themselves but here's what I came up with...starting temperature has a small effect but not as much as the MC:
> View attachment 194473



Very nice. I think it would be even better if it went up to 35-40% MC because it would illustrate the effect of the drying curve better. I know you know this but I wanted to mention it for those who may not. Your table doesn't represent the true loss of heating value caused by the evaporation of water during the burn because it doesn't attempt to account for the fact that the cooling allows more volatile gases to escape unburnt that would otherwise have burnt without the evaporative cooling effect illustrated in your table. And this is a huge factor why well seasoned wood produces so much more heat than less well seasoned wood.



> What surprised me is that there's no solid-liquid phase change to worry about if the wood is below the fiber saturation point, according to the document. So that simplified the calculations a bit.



That's a great document and thanks for posting it! My interpretation of it is that various researchers results vary considerably on that point and the likely reality is that some of the frozen water bound in wood does go through solid-liquid phase but that as the MC content of the wood decreases the percentage of water molecules that are bound (frozen) to other water molecules declines and thus the effect of solid-liquid phase change declines as well. Oddly, it also appears that as the moisture content decreases, the temperature at which the phase change happens also decreases. Interesting stuff.



> To break this down a little further (and allow others to check my work, because cold medicine makes me loopy), 1.2 kg of 20% MC red oak (1 kg dry equivalent) at 0C/32F would need about 66 kcal to heat it to 100C, 108 kcal to boil off the 0.2 kg of water, and 71 kcal to heat the 1 kg of dry wood to 250F. So 27% of the "wasted" energy goes into heating the damp wood and a whopping 44% goes into boiling off the water. The remaining 29% is "overhead" that's pretty much unaffected by the starting conditions. Add them all up and divide by 3574 and you get the 6.9% figure that's on the chart.
> 
> I hope I did this right--give me a shout if any of it doesn't make sense!



I haven't checked your numbers (I got sidetracked by unit conversions and then other related topics) but the figures seem very much in line with what I can believe intuitively. Keeping in mind the single biggest loss of wet wood is the way evaporative cooling that prevents all the volatile gases from burning! Which is also the source of most wood smoke pollution. Unfortunately, there is no good way to mathematically model that loss due to all the variables involved.


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## Hasufel (Feb 10, 2017)

WoodyIsGoody said:


> Ha! I did my calculations when I was stuck at home with a bad cold. Great minds think alike! ;-)


When you can't go outside and play with firewood, what else is there to do? 



WoodyIsGoody said:


> Very nice. I think it would be even better if it went up to 35-40% MC because it would illustrate the effect of the drying curve better. I know you know this but I wanted to mention it for those who may not. Your table doesn't represent the true loss of heating value caused by the evaporation of water during the burn because it doesn't attempt to account for the fact that the cooling allows more volatile gases to escape unburnt that would otherwise have burnt without the evaporative cooling effect illustrated in your table. And this is a huge factor why well seasoned wood produces so much more heat than less well seasoned wood.



Partly I figured that the lower MCs were more in line with the discussion that triggered this whole thing, but the main reason I didn't go higher is that the thermodynamic properties data started getting complicated at subfreezing temps and higher MCs. I didn't want to make too many assumptions. I guess if I were to add higher MCs I could start by running them at just 0C and above, which I think would still illustrate your point.



WoodyIsGoody said:


> That's a great document and thanks for posting it! My interpretation of it is that various researchers results vary considerably on that point and the likely reality is that some of the frozen water bound in wood does go through solid-liquid phase but that as the MC content of the wood decreases the percentage of water molecules that are bound (frozen) to other water molecules declines and thus the effect of solid-liquid phase change declines as well. Oddly, it also appears that as the moisture content decreases, the temperature at which the phase change happens also decreases. Interesting stuff.



I think what is happening is that there is a fixed amount of sugars and other things dissolved in the unbound water. The water starts off fairly dilute but as the wood dries the concentration of dissolved materials increases, so you get freezing point depression. As for the phase change point, my expert interpretation is that it's...complicated. 



WoodyIsGoody said:


> I haven't checked your numbers (I got sidetracked by unit conversions and then other related topics) but the figures seem very much in line with what I can believe intuitively. Keeping in mind the single biggest loss of wet wood is the way evaporative cooling that prevents all the volatile gases from burning! Which is also the source of most wood smoke pollution. Unfortunately, there is no good way to mathematically model that loss due to all the variables involved.



I just reread some of the older posts and I see that the figures I posted are in line with the temperature effects we were discussing in posts 51 and 54, so that's a good sanity check. But to really do this issue justice you'd need to factor in the heat flux and various transport phenomena, which I'm pretty sure is beyond my abilities (or at least my motivation). Real life performance gets really complicated really fast! Great chat, thanks...


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## WoodyIsGoody (Feb 10, 2017)

Hasufel said:


> I guess if I were to add higher MCs I could start by running them at just 0C and above, which I think would still illustrate your point.



Yes, plus I like bringing in 3-6 days/wood at a time so the wood I burn is almost always room temperature. Fortunately, my wife has never said a bad word about that big pile of wood in the living room.  Having a big stack of dry, well seasoned wood sitting handy makes the entire cabin smell so sweet and good. Wood smells better than leftover cooking smells (no matter how delicious the actual food). And I really dislike the smells that have crept into modern life like plastics, any scented products, and engine exhausts. I've been know to sneak in some unseasoned wood for it's more powerful smell. Of course I pack it back outside and trade it for fresh periodically. 

It's so rainy here the entire heating season, if it's not raining you never know when it's going to start again. And when it's raining, you never know how long it will continue. The location in the Cascade Mountains makes it much wetter than Seattle. A big stack allows me to replenish at my leisure when it's not as wet outside.  So, yeah, my interest is mainly in the heat of evaporation (although I understand the wood absorbs room heat to reach room temperature).




> I think what is happening is that there is a fixed amount of sugars and other things dissolved in the unbound water. The water starts off fairly dilute but as the wood dries the concentration of dissolved materials increases, so you get freezing point depression.



I'm not a chemist but I believe the water content of the wood would need to be at or above the fiber saturation point to consider that anything is dissolved in the water. Otherwise the sugars, etc. are not dissolved in the "water" but merely present in the wood. But I admit I don't know whether the presence of those sugars would affect the freezing point of the remaining moisture (or for that matter whether an individual water molecule can actually freeze). Seems to me, water is only "frozen" or solid when it is surround by other water molecules and bound into "ice" and thus the diminishing heat of fusion as the moisture content decreases is simply due to a lack of adjacent water molecules with which to adhere to.


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## Hasufel (Feb 10, 2017)

WoodyIsGoody said:


> I'm not a chemist but I believe the water content of the wood would need to be at or above the fiber saturation point to consider that anything is dissolved in the water. Otherwise the sugars, etc. are not dissolved in the "water" but merely present in the wood. But I admit I don't know whether the presence of those sugars would affect the freezing point of the remaining moisture (or for that matter whether an individual water molecule can actually freeze). Seems to me, water is only "frozen" or solid when it is surround by other water molecules and bound into "ice" and thus the diminishing heat of fusion as the moisture content decreases is simply due to a lack of adjacent water molecules with which to adhere to.


Strangely enough, wood can have both freezing and unfreezing bound water. See http://forest.uef.fi/~karenlam/petri/measur/4361Naka.pdf for some fascinating reading!


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