Is There An Ideal Moisture Content?

[Battenkiller]

From Adios Pantalones on another thread:

It’s documented that efficiency goes DOWN at really low MC, and I think that’s the reason Batt. particles need a cool surface or extra water to condense and form problematic creosote, so while emissions *may* go up, a hotter fire with soft wood (which is often the case) seems to compensate for any increase in emissions; at least it does not directly follow that increased particle necessarily means more creosote.

My answer:

Yes, you are correct, efficiency drops as MC gets very low (I'm someone who has actually provided this documentation here before), but at what point does it begin to turn downward? Many stove companies have begun hinting that firewood can be too dry (although they all fail to specify the magic number), but their concern seems to be in avoiding overfiring (a warranty issue) rather than improved combustion efficiency. While hotter burns with any wood will usually be cleaner and achieve greater combustion efficiency, overall heating efficiency can decline under these conditions since more hot air is allowed up the flue.

All of the studies that I have seen were done pre-EPA Phase I, and they seemed to show a general trend for combustion efficiency to peak between 25-30% MC, for heat transfer efficiency to drop steadily as MC increases, and for overall heating efficiency to occur at about 20% MC dry-basis (see chart below).

I have to wonder how have these figures have changed (or if they've changed at all) with the advent of modern technology? Therefore, I still feel this should be studied under controlled conditions.

BTW it has been experimentally determined that there is an extremely high correlation between particulate matter produced and creosote formation under similar burn conditions. Obviously, hotter burns and more excess air aren't similar burn conditions, but study after study have shown that very dry woods (both hardwood and softwoods) produce more measurable creosote under all burn conditions, at least in the old stoves (with fireplaces the opposite is true due to the dilution effect of the large mass airflow up the flue). If this has been totally reversed by the new technologies, it seems that this should be well documented, but I have not been able to find any studies that address this question. My instincts tell me that there has been no reversal of these trends, but merely a shift in the location of the peaks (likely to the left, or at lower MCs).

Regardless, we are all stewards of the environment, so clean burning should be the primary goal rather than just reduced creosote formation in the chimney. Should we aim for greater overall efficiency (more usable heat per cord of wood) or greater combustion efficiency (cleaner air)? At what MC are each of these goals achieved in modern stoves?

 

[Lynch]

hmmmm.
i would say the more heat i get the better and if the air is clean great if not. thats fine with me

 

[tfdchief]

BK, that is very interesting. Goes along with the study I quoted (done pre -EPA) a while back. I recently burned some very old hedge (15 years +) and was extremely surprised at how it burned. Nothing like 1 or 2 year seasoned hedge.

 

[gyrfalcon]

BK, that is very interesting. Goes along with the study I quoted (done pre -EPA) a while back. I recently burned some very old hedge (15 years +) and was extremely surprised at how it burned. Nothing like 1 or 2 year seasoned hedge.

Oh, come on. "Nothing like" in what way? Specifics, please!

 

[tfdchief]

BK, that is very interesting. Goes along with the study I quoted (done pre -EPA) a while back. I recently burned some very old hedge (15 years +) and was extremely surprised at how it burned. Nothing like 1 or 2 year seasoned hedge.

Oh, come on. "Nothing like" in what way? Specifics, please!

I have burnd a lot of hedge over the years and always found it to burn hotter and longer than anything else by a big margin. It would pop, crack, and throw sparks like no other wood....very difficult to reload the stove. This old stuff was slow to catch, did not burn nearly as hot or long, smokey, sooted up the glass, and did not pop and crack on reloads. I had no idea why, until I read about "to dry". I don't know if that accounts for the differences or not, but I can tell you it was sure different. BTW, I freshly split it and checked moisture level.....around 11%.

 

[Backwoods Savage]

Battenkiller, with your background you get turned on with studies and trying to get everything perfect and can quote many studies which show this or show that. However, I think you will find that better than 99% of all households will be far from that. After all, one has a wood stove and some fuel. He burns what he has.

To aim for perfection is not bad for sure. However, we surely will not find many who come even close. So the bigger question or maybe the better question rather than at what moisture content will be the ideal, why not, will my wood burn if I season it x months or years? Methinks this will answer more people's questions. However, if it turns on the engineers, carry on.

 

[gyrfalcon]

Battenkiller, with your background you get turned on with studies and trying to get everything perfect and can quote many studies which show this or show that. However, I think you will find that better than 99% of all households will be far from that. After all, one has a wood stove and some fuel. He burns what he has.

To aim for perfection is not bad for sure. However, we surely will not find many who come even close. So the bigger question or maybe the better question rather than at what moisture content will be the ideal, why not, will my wood burn if I season it x months or years? Methinks this will answer more people's questions. However, if it turns on the engineers, carry on.

Not sure why this kind of discussion seems to get your back up, Dennis. Somebody, maybe it was you, commented recently that we seem to hash over the same old subjects over and over again here. I agree with that. We all know the answer to how to make wood burnable-- stack it outside for a year or two, lots of air circulation, etc., etc., etc. That's a necessary discussion for new burners who are struggling to figure out what to do, and many of us dutifully chime in when somebody raises the question yet again.

I'm no engineer for sure, but I am interested in understanding more about what the processes at work are than just "leave it outside for a coupla years and throw it in the stove." I like to know why things happen, to the extent I'm able to understand it. On a purely practical level, that keeps me from repeating the same mistakes because I misdiagnose the problem.

Like last night, when I filled up my very small stove with some extremely dry beech I'd been saving for one of those sub-zero nights, and discovered to my dismay that it didn't give me anywhere near the heat I was expecting, less, in fact, than the roughly 20 MC stuff.

It's just the fuel equivalent to the endless discussions of the precise techniques for managing the air supply, particularly with cat stoves.

You can drive yourself nuts trying to figure out which of the many variables involved in stove/flue/wood/loading/burn cycle are making your burns better or worse. When you're working at the margins, as some of us are here, in very cold climates with stoves that aren't quite big enough and a less than perfect wood supply, this kind of info is enormously helpful. It's also, for some of us, just plain interesting.

It's not a question of "aiming for perfection," it's aiming for really good burns rather than barely adequate ones that leave you cold and frustrated. OK?

If these discussions irritate you, why not skip them?

 

[Battenkiller]

To aim for perfection is not bad for sure. However, we surely will not find many who come even close. Methinks this will answer more people's questions. However, if it turns on the engineers, carry on.

Dennis, I'm not aiming for perfection in burning, just perfection in understanding. There have been a lot of studies done that attempt to duplicate real-world burning scenarios. They often show dramatically different results than the EPA testing procedure gives. That's because in real life, folks don't burn small loads of doug fir 2x4s and 4x4s nailed together at a precise MC of between 19-25% MC dry-basis. So what's wrong with looking at the results of studies that show generalized tables and graphs that can give an idea of which way to go with the fuel/air/MC etc.?

Below is a table that shows the measured amounts of creosote accumulated over dozens of test burns in conventional stoves. Now, before you go crying foul about it not being valid information since everybody should be burning in EPA stoves, let's just look at fuel effect here. There is a consistent trend for increased creosote production by using pine instead of hardwood (oak here) at medium and high burn rates. That can only mean that it produces more excess smoke than oak.

There is also a trend for less creosote in both woods as moisture content increases from 5% MC to 25% MC during medium and high burn rates. This isn't the first study to show this. Every study done to examine this has had similar findings. Are they all incorrect? And if they aren't wrong, shouldn't folks know that getting their wood down from 25% MC to 15% MC will produce twice as much creosote, even when burning hot and hard? Are they to just blindly trust the new technology to burn all of that excess smoke even though they can clearly see evidence on their flue caps that it doesn't?

These things make me think long and hard, and I for one am not afraid to come to different conclusions than the masses come to, nor am I the least bit afraid to expose myself to public ridicule by posting these thoughts on a public forum. The hope is that they provoke careful thought and lead to greater knowledge. And if someone can provide clear evidence that my conclusions are incorrect (besides their descriptions of no smoke and clean flues and everlasting burns), they should go ahead and do so and not take cheap shots from the sidelines.

I'm sorry, I think this is vital information to share, a lot more vital to safe and efficient burning practices than pics of your wood stacks, or trip reports to Woodstock, or endless asides about the proper way to split wood, but I don't get on every thread you start and bash it. You seem to be here for the social benefits, I'm here to gather and share knowledge. Period. Is that so wrong that you need to get on here at every chance and malign that goal? Bottom line is that this is (still) a public forum. If you don't like the topic of an individual thread, why not just stay off it, OK? Have some respect for me, man, I have always shown you respect.

So the bigger question or maybe the better question rather than at what moisture content will be the ideal, why not, will my wood burn if I season it x months or years?

Because we all have different climates that we live in, giving widely different equilibrium moisture contents, that's why. Your wood may sit under cover at 18% MC until the day your great-grandchildren decide to burn it, but someone in the high country may get the same results in 6 weeks in the summer and go down to <10% MC after a year or so. If we are to use modern stoves, I see no earthly reason to use antiquated MC assessment methods when modern, accurate, and extremely affordable instrumentation is now at our disposal. C'mon.... $12 for a moisture meter and you're resisting? Let's find out once and for all if your 5+ year old stuff is any drier than the stuff I make in my basement in a three weeks. If I send you a cheap $12 Harbor Freight moisture meter, will you at least put your ancient wood to the test for us so we can have a definitive answer.

I might as well sign off this thread now, I'm sure it will be locked or deleted momentarily. :roll:

 

[Battenkiller]

Like last night, when I filled up my very small stove with some extremely dry beech I'd been saving for one of those sub-zero nights, and discovered to my dismay that it didn't give me anywhere near the heat I was expecting, less, in fact, than the roughly 20 MC stuff.

When you're working at the margins, as some of us are here, in very cold climates with stoves that aren't quite big enough and a less than perfect wood supply, this kind of info is enormously helpful.

Ha, ha! No surprise when you look at the table I provided, eh? ;-)


Gyrfalcon, you are certainly doing some amazing things with that little heater of yours. So amazing, in fact, that I am now leaning toward installing one in my fireplace rather than getting a bigger EPA stove for the basement. My stove burns extremely cleanly and efficiently for me (as long as I don't get the wood too dry %-P ), but I would be best served to use it for overnight burns only, and heat the upstairs with a much smaller stove. There is only the Tribute that I know of that would be fit for the task in my small fireplace. I wish I sprung for one last fall when the tax credit was higher.

How would a slammer install work with a small soapstone I wonder? :cheese:

 

[Backwoods Savage]

Battenkiller, with your background you get turned on with studies and trying to get everything perfect and can quote many studies which show this or show that. However, I think you will find that better than 99% of all households will be far from that. After all, one has a wood stove and some fuel. He burns what he has.

To aim for perfection is not bad for sure. However, we surely will not find many who come even close. So the bigger question or maybe the better question rather than at what moisture content will be the ideal, why not, will my wood burn if I season it x months or years? Methinks this will answer more people's questions. However, if it turns on the engineers, carry on.

Not sure why this kind of discussion seems to get your back up, Dennis. Somebody, maybe it was you, commented recently that we seem to hash over the same old subjects over and over again here. I agree with that. We all know the answer to how to make wood burnable-- stack it outside for a year or two, lots of air circulation, etc., etc., etc. That's a necessary discussion for new burners who are struggling to figure out what to do, and many of us dutifully chime in when somebody raises the question yet again.

I'm no engineer for sure, but I am interested in understanding more about what the processes at work are than just "leave it outside for a coupla years and throw it in the stove." I like to know why things happen, to the extent I'm able to understand it. On a purely practical level, that keeps me from repeating the same mistakes because I misdiagnose the problem.

Like last night, when I filled up my very small stove with some extremely dry beech I'd been saving for one of those sub-zero nights, and discovered to my dismay that it didn't give me anywhere near the heat I was expecting, less, in fact, than the roughly 20 MC stuff.

It's just the fuel equivalent to the endless discussions of the precise techniques for managing the air supply, particularly with cat stoves.

You can drive yourself nuts trying to figure out which of the many variables involved in stove/flue/wood/loading/burn cycle are making your burns better or worse. When you're working at the margins, as some of us are here, in very cold climates with stoves that aren't quite big enough and a less than perfect wood supply, this kind of info is enormously helpful. It's also, for some of us, just plain interesting.

It's not a question of "aiming for perfection," it's aiming for really good burns rather than barely adequate ones that leave you cold and frustrated. OK?

If these discussions irritate you, why not skip them?

Ummmmm. gyrfalcon, I know not why you think I am irritated. Please do not think that as I certainly am not.



EDIT: The same goes for Battenkiller. Do not think I am irritated because I am not. I just go by the KISS principle. If this sort of thing turns you on, by all means, carry on.

 

[oldspark]

Who said any thing about aiming for perfection, we all know that will not happen, but getting the most out of your time is well worth striving for.

 

[Battenkiller]

The same goes for Battenkiller. Do not think I am irritated because I am not. I just go by the KISS principle. If this sort of thing turns you on, by all means, carry on.

I never thought you were irritated, just acting dismissive. Thanks for clarifying, though.

 

[gyrfalcon]

Ummmmm. gyrfalcon, I know not why you think I am irritated. Please do not think that as I certainly am not.

EDIT: The same goes for Battenkiller. Do not think I am irritated because I am not. I just go by the KISS principle. If this sort of thing turns you on, by all means, carry on.

OK, you're not irritated. I guess it's me that's irritated. With respect, your habit of popping up to pooh-pooh these discussions every time they start is getting a little maddening.

There's actually a KISS principle involved in this thread, as well-- as in don't knock yourself out trying to overdry your wood and think it's going to give you more heat and/or a cleaner chimney. Just stick to the tried-and-true and aim for the 20 MC. The idea is by no means obvious. It's actually counterintuitive, and therefore takes a little scientific exploration to prove.

 

[tfdchief]

I have great respect for both of you. I have listend to both of you. I will continue to do so. I will say however, that being a scientist by education, I am like BK, I have to know why (if possible) and will endlessly seek all the knowledge I can get, both from experience and science, in order to "know why". My common sense would tell me that Dennis is right about dry wood. However, I have experienced the opposite and seen scientific results of the opposite. As BK has said, there are so many variables that conclusions are hard to make. Let's all do what this forum does so well, and that is share in our love for burning wood, whatever that means to you. :smirk:

 

[gyrfalcon]

Like last night, when I filled up my very small stove with some extremely dry beech I'd been saving for one of those sub-zero nights, and discovered to my dismay that it didn't give me anywhere near the heat I was expecting, less, in fact, than the roughly 20 MC stuff.

Ha, ha! No surprise when you look at the table I provided, eh? ;-)

Gyrfalcon, you are certainly doing some amazing things with that little heater of yours. So amazing, in fact, that I am now leaning toward installing one in my fireplace rather than getting a bigger EPA stove for the basement. My stove burns extremely cleanly and efficiently for me (as long as I don't get the wood too dry %-P ), but I would be best served to use it for overnight burns only, and heat the upstairs with a much smaller stove. There is only the Tribute that I know of that would be fit for the task in my small fireplace. I wish I sprung for one last fall when the tax credit was higher.

How would a slammer install work with a small soapstone I wonder? :cheese:

No surprise indeed, but an "A-ha!" moment for sure. I only wish I'd figured it out a couple days earlier...

As for the Tribute-- it's a good little stove, but it absolutely takes a lot of fussing and very great care to get the most out of it. The burn cycle is very short, and at the bottom of it, it's too small to provide noticeable heating. Also, because the burn cycle is so short, the window of opportunity for doing a reload that will go well or adjusting the primary air, etc., is very short. Miss it by 10 or 15 minutes, and you have to struggle to recover.

Also, bear in mind that the amazing things I'm doing with the stove are not keeping my space anywhere near as warm as most people would want. Acceptable heating for me means mid to high 60s in the area right around the stove for much of the winter, and downright chilly elsewhere. (Of course, if I had more o' that magical black birch, I'd do a little bit better than that.) I would think that putting one even part-way into a fireplace would dramatically decrease even that heating capacity. Every square inch of exposed surface is deeply precious with a stove this small, and you'd presumably also lose the bit of extra heat from the flue pipe if it goes directly into the chimney. Mine goes straight up through the room to the ceiling (double-wall, alas for the heat factor, because of my minimal clearances).

My open first floor, which is all I'm trying to heat, is something less than 800 sf, with decent but hardly state of the art storm windows and insulation and 8-foot ceilings, for comparison purposes.

Um, what's a "slammer install"?? Doesn't sound good...

 

[Lumber-Jack]

For me wood burning is a hobby and I for one always appreciate BK's post because they generally tend to be well thought out, researched and based on some sort of documented studies as evidence (which he generally provides as proof). This is in stark contrast to a lot of other members post's which simply state their opinion, not that there is necessarily anything wrong with that either (enough opinions pointing in one direction can be a strong force), but a single personal opinion doesn't carry nearly the weight or depth (or interest) of a well thought out researched point of view does.
It all comes down to food for thought. Everybody knows (or ought to know) that it's beneficial to make sure one's wood is seasoned before burning it. Certainly there are variety of ways of obtaining that seasoned wood, whether they attempt to buy it pre-seasoned, cut and season it themselves (like Dennis does), or cut trees that are pre-seasoned (like I do), all food for though, and there is no one right (or wrong) way of doing it. Everyone has there own unique circumstances and being open minded enough to see that there is more than one way to skin a cat adds to the dialog, interest and entertainment of this forum (or any forum for that mater).

BK, as you know I've been learning the intricacies of burning very dry wood in my EPA stove, and have found that the best way to get the heat out of it is by burning smaller loads, however that doesn't work too good for overnight burns, but by knowing that there is a problem with wood that is too dry I often look for splits that are bigger and have a little more weight to them and are likely have a slightly higher MC. Doing so generally moderates the initial burn better (not as much off gassing) and gives me a longer overall burn.
I don't worry too much about the smoke coming out of my chimney though, as just about all my neighbors are dirty burners, and even I have an old smoke dragon in the shop that the only way to get long burns out of is by damping down the fire and burning dirty. (me bad) :red:

 

[Battenkiller]

And back to the discussion at hand...

I posted this before, and again yesterday but that thread got locked. It is a chart that shows the interrelatedness of moisture content, combustion efficiency, and overall heating efficiency in a particular conventional wood heater that was tested at a medium burn rate (average output = 17K BTU). To clear up the confusion about the two methods of expressing MC, the author (Dr. Jay Shelton) labeled the horizontal axis with both methods (the numbers at the top represent the ones you would get using a simple resistance-type moisture meter).

Looking at combustion efficiency alone, it is pretty clear that efficiency rises dramatically in a liner fashion as MC increases from 0% MC up to 20%, then rises at an increasingly slower rate to a final plateau of about 88% at between 25-30% MC, then drops at roughly the same rate as MC rises to 50%. Curiously, the combustion efficiency at 50% MC is just about the same as it is at 15% MC... about 85%. All along that range, the combustion efficiency only varies by 3%, but as the wood drops to 10% MC, combustion efficiency drops to only 80%, and oven-dry wood (0% MC) burns at an astoundingly low 70% efficiency... 15% less efficient than wood at 50% MC.

The question is, how much has this changed with the advent of efficient secondary combustion? I would predict a shift of the peak combustion efficiency to the left (toward lower MC), but there is simply no possible way I can see to fit any real-world data set onto a curve that would show a steady decline in combustion efficiency as MC increases from 0% MC to 50% MC.

Any (rational) thoughts?

 

[gyrfalcon]

BK, as you know I've been learning the intricacies of burning very dry wood in my EPA stove, and have found that the best way to get the heat out of it is by burning smaller loads

Boy, that's also certainly counterintuitive, but since you first mentioned it a while ago, I've been observing a little bit more carefully with that in mind and noticing the same thing-- assuming by "very dry wood" you aren't talking about super-dry down around 10 or so, are you? Why do you suppose that is? Is it just a simple matter of combustion needing sufficient air?

Just curiously, how big is your stove? And how small a load are you talking about?

As I type, I'm getting a nice (for soapstone) 400-degree fire with just a few splits of my nice 20 MC kiln-dried maple, maybe between a third to half a stove load.

 

[Battenkiller]

BK, as you know I've been learning the intricacies of burning very dry wood in my EPA stove, and have found that the best way to get the heat out of it is by burning smaller loads

Boy, that's also certainly counterintuitive, but since you first mentioned it a while ago, I've been observing a little bit more carefully with that in mind and noticing the same thing-- assuming by "very dry wood" you aren't talking about super-dry down around 10 or so, are you? Why do you suppose that is? Is it just a simple matter of combustion needing sufficient air?

Just curiously, how big is your stove? And how small a load are you talking about?

As I type, I'm getting a nice (for soapstone) 400-degree fire with just a few splits of my nice 20 MC kiln-dried maple, maybe between a third to half a stove load.

Check out CL's location and wood source. He has no choice but to burn very dry pine because it is all he has and it's basically free. Long experience has probably shown him that burning the way he does is the most efficient and clean way to go. If you look at the labs test loads and the EPA test loads, they don't fill the box completely at all. Maybe 1/3 to 1/2 full. You need an amply mixing chamber above the wood for turbulent fuel/air mixing to occur. Check out my avatar photo (taken at the instant the stove was opened for more wood). I use that shot deliberately for two reasons:


1. There is only a small load in there and yet the box is filled with flame with not a trace of smoke.

2. The wood was black birch, split rather small, and at about 30% MC.


That particular fire had the stove blazing like no tomorrow, 750ºF in no time. A brief writeup of it was in my "Drying Wood Quickly" thread.

It has long been known that a partially filled box will put out the same amount of heat (or more) as a full box. One reason is the aforementioned gas mixing. The other is that wood is a pretty decent insulator and keeps the flames from hitting the interior walls. The downside is more frequent reloads, (which can mean somewhat dirtier burns as well as the inconvenience involved) but it's the best way to get the maximum heat output and greatest combustion efficiency from most wood heaters. For overnights or long days at the office with no one home, however, you do what you must to keep the place warm.

 

[Lumber-Jack]

BK, That graph show a steady decline in the Heat Transfer Efficiency. What exactly is the difference between Combustion Efficiency and Heat Transfer Efficiency?
If the combustion efficiency is based simply on the particulate emission measured out of the top of the chimney, then perhaps the measured emission is less with higher MC wood because the particulates are more readily being captured , or filtered, by the chimney before they reached the top of the chimney where they placed the measuring device??? Just guessing here.

Gyrfalcon, as far as what the MC content of some of the wood I'm burning is, I can only go by what my moisture meter is reading, and I know there is a certain amount of error in these things especially at the low and high ends of the scale. but I am getting readings as low as 5% in some of the freshly split pieces. I have been wanting too do the microwave MC test like BK has done, but just haven't gotten around to it, because I don't yet have the right type of weight scale and I'm a little hesitant to buy one just for this experiment.
I think BK answered the reason why those small loads burn more efficiently by comparing it to how pellet stoves burn. As you suggested, by making sure the wood gets sufficient air, and burning hot. I can't do that with the big loads because I'll overheat my stove.
My stove is a Regency F2400 which mid range stove and has a 2.3 cu. ft. box. and by small load I mean as small as two 3-4" splits on top of a nice bed of coals. If I don't have a hot coal bed I can generally build a larger fire and open the draft more without worrying so much about over heating the stove. But again, I don't get as clean burn with a larger, colder start, fire like that.

 

[Battenkiller]

BK, That graph show a steady decline in the Heat Transfer Efficiency. What exactly is the difference between Combustion Efficiency and Heat Transfer Efficiency?
If the combustion efficiency is based simply on the particulate emission measured out of the top of the chimney, then perhaps the measured emission is less with higher MC wood because the particulates are more readily being captured , or filtered, by the chimney before they reached the top of the chimney where they placed the measuring device??? Just guessing here.

Combustion efficiency is simply the percentage of the available wood fiber contained in the fuel that actually combines with oxygen to create H2O and CO2. PM isn't the only fuel loss, nor is it the largest component of fuel loss. There are so many fuel products that leave the combustion zone as unburned and invisible vapor that it is impossible to test for them all, but the labs use sensors and filters to account for all of the major players (see charts below). Carbon monoxide, methane, hydrocarbons, formaldehyde, benzene (and other toxic aromatic compounds) are all released in the gram to tens of grams range per kg burned. All of these are medium to high energy fuel gases that are part of the total lost fuel when determining combustion efficiency.

With the exception of a few studies that tried to deliberately "harvest" creosote, flue temps in lab situations are kept too hot for much PM to condense as creosote, so there is no subtractive "filtering" of PM by deposition onto the flue walls. PM is gathered from filters sized for the capture of selected sizes (i.e. PM 5, PM 2.5) to determine the fractions of each size (PM in the 2.5 micron range is particularly troublesome for asthmatics, for example).

However you slice it, more PM is produced with very dry wood than with wet wood, so the potential for creosote accumulation is always greater, not less. Burn wet hardwood hot enough and you will get very little PM produced by comparison to very dry wood, but you will get less significantly less usable heat in the living space. Therefore, woodburning scientists still recommend burning well seasoned wood instead of green wood because of the net heat loss and inconvenience (or inability in the case of the inexperienced) of maintaining high stove temps.

Heat transfer losses are obvious if you think about it. More air needed with wet wood, more heat up the stack. As well, more excess water evaporated means more unrecoverable heat up the flue as water vapor. And yet, there is increased combustion efficiency with wetter wood, so there is more available heat to spare. These three conflicting phenomena combine at about 20% MC for hardwood to yield the maximum overall heating efficiency, which is why 20% MC has always been recommended by the hearth industry... which depends very highly on the results of these tests.

 

[tfdchief]

BK, Absolutely facinating! I now at least partially understand why my 15+ year old hedge burned so uncharacteristicly.

 

[-PB-]

I also find this very interesting. It is something to think about and another great example of something learned on this site. Not trying to rehash anything but I also very much enjoy and respect hearing other opinions such as Dennis' KISS opinion. I think it helps, for me at least, to hear as many perspectives as I can on different subjects.
Once again... thanks for the info, and opinions!