Humidity Relative Or Not?

[North of 60]

Everybody talks about this magic # of moisture content 23 32% or something for proper seasoned firewood. Can you measure this? Is there a tool/instrument? How does relative humidity for that geographical area compare? How can you lower your moisture content in your wood lower than your normal/average humidity? Is that not the moisture content reading in the air. In the north we are rated a semi arid climate. Averaging 35% in the summer & 20% in the winter. South eastern areas may never get below 45%.
Can that seasoned wood reach these magic #s. Hope I haven't given anybody a headache reading this. Ill re visit later to see if any brave souls not shaking there heads can explain this without getting typers cramp.

 

[karl]

Yes you can measure it with this thing. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=2757 It's accurate to within 1% if you believe the chinese. As for drying below the relative humidity. Sure you can. How do you think mud puddles dry up? Set a glass of water out in the sun for a few days and it will be empty. I'm too far removed from my flight instuctor days to tell you in a technical manner. We deal with humidity, vapor pressure, and heat alot, but basically the amount of water air will hold is greatly dependant on it's temperature. One of my old books has two pictures in it to help explain. One is the a desert on a hot sunny day and the other shows a winter landscape with snow falling. The caption reads something like. 5% humidity below the desert seen and 100% humidity below the winter landscape with the snow falling. The question is in which picture does the air contain more moisture. The answer is the desert scene. As air get hotters it becomes less dense and therfore the molecules are farther apart. So for lack of a better term, the air has more space inbetween it and therefore has more room to hold the water. Kinda like an air conditioner condenser. It cools the air and therefore the air can't hold as much water and is condenses out as liquid. So as long as its hot and not raining the air will suck moisture out of anything until a cloud forms. This makes it's easy to take 50% moisture wood and turn it to 25% moisture wood. But you also reach a point of diminishing returns. So to go from 25%-0% would take alot, and you would never get there. To explain that would take some serious math, but I think you get the point.

 

[North of 60]

Thanx for the intrument device. does anybody use one? As for the mud therory I under understand. There is a delta H there. As long as ther is a DIFFERANCE one will always give up to the other. Such as hot to cold.But ?????????

 

[karl]

Tell you what. Come down here to West Virginia right now. It's so hot and humid you can see the air. I'm not joking the visibility today was probably less than 3 miles and my wood is drying. If your're from Canada then, ten minutes outside in the middle of day here, and you would say who cares if this chit is drying or not I want to go hug an air conditioner. It's the middle of the night right now and I just yahoo weathered my zipcode, 25701. The humdity here is 93% right now. A living tree is only 50% water.

 

[North of 60]

Thought some more. The winter scene you talked about was below 0. the moisture / liquid had changed states. To a solid. Wood is a solid. The instruments specs only work above 0c/32f frozen wood or ice would have the same reading@ 0 or below. The moisture content has changed state. I do understand enthalpy and dew point. Iam a 21 year steam/gas fitter. Am i missing something.

 

[karl]

It has nothing to do with it being below 0 out outside. You can have water in the liquid state below 32 degrees. It's call super cooled water.

 

[Gooserider]

Yes... Air humidity and percent moisture in wood are two different things. Wood as it comes out of a living tree is mostly water, just as the human body is mostly water. As the wood seasons, the moisture evaporates and it dries out, just like your clothes or a sponge will dry out, although much more slowly as the moisture must travel through the wood to it's surface, which takes a while since wood is relatively non porous.

Bottom line - IF your wood is stored off the ground, preferably at least top-covered during the later stages of drying, etc. it should get down to about 20-25% moisture in a year or less for most woods - though some do take longer. It is mostly not practical for the average burner to get the moisture lower. A burner in a very humid climate will not get his wood quite as dry, and will take longer to get his wood seasoned than one in a very dry environment, but the difference is not that great.

However the dryer your wood is, the more heat you will get out of it, as any heat spent driving whatever moisture remains in the wood out is "lost", and in most cases the less creosote you will get as dry wood burns more completely. This may be one of the biggest reasons for the observed discrepancy between the test-lab produced emissions numbers you see in the stove manuals and the actual measured performance in the real world. The test lab uses kiln dried wood with an abnormally low moisture content compared to the moisture found in typical firewood

As to the meters - the HF meter is a cheapy, and while fairly reliable, it is also comparatively fragile and non-repairable. There are more expensive professional meters that are almost indestructable, but cost hundreds of dollars. If you do a search (see the upper right corner of the screen at the start of any thread) you will find lots of threads discussing the HF meter, and how to use it for the most benefit and accuracy.

Gooserider

 

[North of 60]

thanx to both of you. Higher the average relitive humidity reguardless of temp the longer to reduce the moisture content of the wood. Now for Karl... Smile 1st
your sub zero water must be under a vacume /one atmosphere (14.7 A) not to change state. cheers!

 

[thephotohound]

I personally use this meter:

http://cgi.ebay.com/Digital-Wood-Mo...oryZ1504QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Cheap, but does the job... Watch out, though... it can be misleading. After a few months in the sun, you may go to check the moisture of that red oak you split back in April and get a reading of 26%. Split that bad boy again, recheck the moisture level, and you're right back at 38%.

 

[GeeWizMan]

Whenever you check the moisture content of wood, it should always be a fresh split.

The HF one mentioned works fine for me.

I believe the term is supersaturated for when air contains more water vapor than it should at a given temperature. That usually only happens when there is no condensation nuclei present for water vapor to condense on to.

George

 

[hilly]

Relative humidity is how much water vapour is in the air vs. how much the air could actually hold. If you imagined a piece of wood in low humidity air, most of the air that moved over the wood, would be able to take some moisture with it because the air's capacity to hold water hasn't been reached. I would expect wood in a humid climate to dry a bit slower than in an arid climate because as the air passes over the wood it isn't able to take as much moisture from the wood, because it may be close to its capacity to hold moisture already.

It's kind of the same in people. We cool by having sweat evaporate from our skin. In dry climates this happens quickly because the air can absorb lots of moisture and we cool ourselves quickly. In a humid climate the sweat doesn't evaporate very quickly because the air already has so much moisture in it and if the sweat doesn't evaporate, we don't cool down much.

 

[karl]

Northof 60,

Supercooled water doesn't have to be in a vacuum to avoid changing states. My dad was a chemist and he didn't know such a phenomenon existed until long after he got out of school. Back then no airplaines flew high enough to experience it. Here's a web quote on it.

Droplets of supercooled water often exist in stratiform and cumulus clouds. They form into ice when they are struck by the wings of passing airplanes and abruptly crystallize. (This causes problems with lift, so aircraft that are expected to fly in such conditions are equipped with a deicing system.) Freezing rain is also caused by supercooled droplets.

A liquid below its freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form. However, lacking any such nucleus, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. The homogeneous nucleation can occur above the glass transition where the system is an amorphous—that is, non-crystalline—solid.

Water has a freezing point of 273.15 K (0 °C or 32 °F) but can be supercooled at standard pressure down to its crystal homogeneous nucleation at almost 231 K (−42.15 °C).1If cooled at a rate on the order of 1 million kelvins per seconds.



It's wierd stuff and dangerous too. The water is well below freezing and is still a liquid until it touches something and then it freezes instantly.

 

[jpl1nh]

I think there is one other factor to consider in how wood gives off and reabsorbs moisture to and from air. The composition of wood is primarily bundles of microscopic tubes, the xylem and phloem of past seasons, which transport water and nutrients up and down the tree. Imagine what happens in a straw. Air will definitely evaporate water from the straw, but even fully saturated air will not refill the straw. This is not a completely accurate view of wood however because the xylem and phloem tubes are so small, some moisture can start to renter the tubes from capillary action. It won't get far since the air inside will be blocking its passage (like air bubbles in a straw stop water from entering). Wood floats in water because it has so much air in those little tubes. Leave wood exposed to lots of liquid water over time and you can resaturate it. Even wood protected from exposure to liquid water is always somewhat changing its moisture content in relation to the humidity; we all see that all the time with doors and windows swelling in humid weather, shrinking in dry, but overall due to the ease with which wood can give up its water in the driest weather, and the very slow and limited absorption of moisture from air in humid weather, I think that wood which is not exposed to liquid water will end up at a substantially lower moisture level than the average humidity of a given area.

 

[North of 60]

relitive or not. Awsome feed back to all. THe length of seasoning in the north for me would be 6 months. 95% of my wood is dead standing so I think there is a good jump on it right there. When i see 2 year seasoned wood quotes on peiples hard woods it raised some questions. Our pine spruce and poplar grains are less dence. The poplar carries more moisture content therefore I even split the smallest peices to allow alarger surface area to evaporate. That bark just willnot breath. farther south I guess is what makes this wood less desirable if you do not have the space to cure it.

 

[North of 60]

I hope here people still beleive that there is still such a thing of there is 'no such thing as a stupid question.' This site has a lot of wood veterans and a wood burner would be stupid not to tap in and utilize this. THanx for everyones time on there responces. Exspecialy Karl. Must of given you a hand cramp.
north of 60

 

[jpl1nh]

relitive or not. Awsome feed back to all. THe length of seasoning in the north for me would be 6 months. 95% of my wood is dead standing so I think there is a good jump on it right there. When i see 2 year seasoned wood quotes on peiples hard woods it raised some questions. Our pine spruce and poplar grains are less dence. The poplar carries more moisture content therefore I even split the smallest peices to allow alarger surface area to evaporate. That bark just willnot breath. farther south I guess is what makes this wood less desirable if you do not have the space to cure it.

I too use mostly standing dead, and with poplar, if I don't get it soon after it dies, it starts to get punky in a hurry. Doesn't have a lot of BTU's relative to almost everything else I have available so I will often pass it by unless its in great shape, or really conveniant. Tough to put your time and energy in to poplar when you have oak, maple, black locust, etc.. Having said all that, you're proof that all wood is good, you use what you have, and you learn how to process it and burn it to its fullest. Bet it still keeps you warm and happy too! :coolsmile:

 

[jpl1nh]

I hope here people still beleive that there is still such a thing of there is 'no such thing as a stupid question.' This site has a lot of wood veterans and a wood burner would be stupid not to tap in and utilize this. THanx for everyones time on there responces. Exspecialy Karl. Must of given you a hand cramp.
north of 60

No question too stupid for this gang. We'll all talk far too much about wood, stoves, hell, almost anything. We do pride ouselves on especially stupid comments however. %-P

 

[North of 60]

I know my spelling wontgive me any browny points

 

[Gooserider]

relitive or not. Awsome feed back to all. THe length of seasoning in the north for me would be 6 months. 95% of my wood is dead standing so I think there is a good jump on it right there. When i see 2 year seasoned wood quotes on peiples hard woods it raised some questions. Our pine spruce and poplar grains are less dence. The poplar carries more moisture content therefore I even split the smallest peices to allow alarger surface area to evaporate. That bark just willnot breath. farther south I guess is what makes this wood less desirable if you do not have the space to cure it.

My understanding is that the cimate in your area is relatively low humidity, so it will tend to dry wood faster. We are talking how to get optimally dry wood, under average conditions, as opposed to "dry enough to burn" under ideal conditions. A lot of us are also burning hardwoods that take longer to dry because they are more dense.

I'll admit to not doing any measuring on my wood, but all reports are that standing dead is somewhat helpful in getting a start on seasoning, although it usually isn't as much help as people would like to think it is.

I would also say that the reason those of us who are lucky enough to have good Oak and other hardwoods available to us tend to pass on pines and poplar, etc. is not a question of how much room it takes to cure, but rather the fact that even after curing, it is not as good a fuel... Any wood is better than no wood, but given the choice between high BTU/split wood vs low BTU/split which would you choose? It takes about the same amount of work to turn a tree into a pile of splits, so which tree would you want to work on if you have a choice?

Gooserider

 

[North of 60]

Gooserider Burning poplar means you need more space because to store more because you would burn more due to its heat output.
I myself have over 15 cord of mixed poplar spruce & pine. Was out today gettin more. Most Yukoners get theres in Sept, Oct
to burn this winter. Go figure. Thanx for the input.

 

[Gooserider]

Gooserider Burning poplar means you need more space because to store more because you would burn more due to its heat output.
I myself have over 15 cord of mixed poplar spruce & pine. Was out today gettin more. Most Yukoners get theres in Sept, Oct
to burn this winter. Go figure. Thanx for the input.

I don't think we're disagreeing on the conclusion - we just get there different ways... :coolsmirk: I'm willing to bet that if you had an oak forest in one direction and a poplar forest in the other you wouldn't be going to the poplar forest for the wood (or spruce or pine or....) even if you have lots of space. I'll grant my space is somewhat limited by the size of my woodshed, but if I were told I could only burn poplar, etc. it wouldn't be that big a deal to build a second shed...

I figure you burn what you got, but if you have a choice, you will get the best BTU output wood you can get your hands on because it's better fuel, not because it takes less room...

Gooserider

 

[North of 60]

Well shes gone full circle. The posting of my thread was humidity relative or not. Shes all relative. Geographically for sure. A drier climate, less dense woods (soft woods) Dead standing as its all we are allowed to cut up here. No live trees Six monthes or less to season. Humid or higher humidity climates, denser wood (hard woods), one to two year seasoning time. Send me up some oak. Seasoned of course. :coolsmile: