For the OCD Moisture Content obsessives out there who test their MC regularly...

[53flyer]

Can someone tell me what they've discovered irt the impact of winter weather on the MC of wood? Meaning, has anyone measured their wood's MC at the end of summer (late Aug-late Sep) and compared it to a piece in Nov, Dec, Jan, Feb, Mar) to see how much the MC went up? I assume it would go up by anywhere from 3-4% to as high as 7-8% as the wood absorbs moisture from the air? Even though all me wood is under a roof, most of it is on the N side of the house so it doesn't get much sun on it. I'm sure if I had the setup to have it on the S side that the occasional sun would help offset the absorption of moisture in the winter.

Does all of this sound about right? Has anyone actually tested those measurements from summer through the winter burn season?

 

[BrotherBart]

The air is drier in winter than any other time of the year.

 

[ChillyGator]

low humidity, strong wind, mostly sunny, no snow..........winter drying is GOOD!

 

[53flyer]

I forgot about all the people on the E coast where the humidity is generally much greater (nasty sticky, summer heat, yukk :shut: ). For those who enjoy the W coast's relatively dry summer heat I think the winter may, at least at times, be more humid by comparison to summer. At least it seems fairly humid when we're getting the really wet, heavy snow that's full of moisture. We also get various weeks where we're getting lots of ground fog which equals 100% humidity so the wood's got to be soaking up some moisture then right?... In the shoulder seasons when it's raining that's also 100% humidity so shouldn't the wood be gaining moisture content then as well?.... Am I off base here? Where's our weather guy that posts on this board LOL ...

 

[bogydave]

My wood checked & cracked on the ends of the rounds quit a bit this winter.
But Alaska is known for for cold dry air & it definitely shows on my wood that I'd cut in Nov - Dec.
I'm having to burn some of it now & it's doing OK.
I don't have a moisture meter but I'm not sure a meter tells the whole story with so many varieties of wood.
1st pic Nov- Dec cut wood
2nd pic Jan cut wood
all were standing live Alaska white (paper) birch trees.

 

[BrotherBart]

It all gets into a long discussion of absolute vs. relative humidity. Anywhere you are the absolute humidity (actual amount of water in the air) is less in winter.

 

[oldspark]

My wood checks faster in the warm weather than the cold. I've got wood that is more checked than the picture above that has been split for about a month.

 

[Backwoods Savage]

I forgot about all the people on the E coast where the humidity is generally much greater (nasty sticky, summer heat, yukk :shut: ). For those who enjoy the W coast's relatively dry summer heat I think the winter may, at least at times, be more humid by comparison to summer. At least it seems fairly humid when we're getting the really wet, heavy snow that's full of moisture. We also get various weeks where we're getting lots of ground fog which equals 100% humidity so the wood's got to be soaking up some moisture then right?... In the shoulder seasons when it's raining that's also 100% humidity so shouldn't the wood be gaining moisture content then as well?.... Am I off base here? Where's our weather guy that posts on this board LOL ...

53, I understand your concern but please understand that wood is not a sponge. I can have a wood pile uncovered and then we get 2" of rain but within 24-48 hours (depending on the weather after the rain) that same wood will be just as dry as before. Just think of all the folks who leave their wood pile completely uncovered all the time. For instance, quads never covers his wood and he gets lots of snow. Then imagine that snow melting and freezing, melting and freezing and then come spring, melting and then raining, etc. He seems to have no problem.

I do feel it does make some difference with different types of wood though. For example, oak is very dense and it would take a lot for that to soak up any moisture. But then if you took bass or popple or even cedar which is not as dense, then that would theoretically soak up more moisture but methinks it would have to sit in water before one would have to be concerned.

Here is another example for the above. I can drop soft maple and leave them without cutting up to firewood length. Within 2-3 years they are worthless for firewood. Yet this past winter I cut up an ash log that had laid (flat on the ground) for 3 or 4 years and each year that area is under water for a couple months of the year. But that ash was good for burning. Very solid stuff.

In short, I do not think you have a thing to worry about especially considering your wood is under a roof. To get the best results though, I'd suggest leaving your wood stacked outdoors where wind will hit the side of the pile. Leave it at least through one summer before moving it under the roof. If you stack green wood in a shed it simply will not dry as fast as it will left outside. Wind is more important than sun.


Along with your concern, you might recall a recent post of mine where I have a neighbor who claims the wood will increase in size during the summer. I stacked wood at 54" and it has lost 6". He claims it will be over 48" by the end of the summer. I claim it is pure baloney but, I am willing to test his theory so I will check that stack this fall or at least late summer to see what the measurement is. Keep watching for the results.

 

[53flyer]

Savage- That's some good info there. It sure does seem strange though that if wood with say 15% MC is in air that's at 100% (even if it's just relative) that the MC would begin to move up from that 15% (even if by only 1%). Hmmm, very intriguing (at least to me). I'll look forward to the height check later this yr.

 

[DBoon]

I'm running the experiment now. See https://www.hearth.com/talk/threads/44360/

The short answer is "yes, covered wood is drying in the winter in an open meadow with good sun and wind exposure".

 

[Wood Duck]

Savage- That's some good info there. It sure does seem strange though that if wood with say 15% MC is in air that's at 100% (even if it's just relative) that the MC would begin to move up from that 15% (even if by only 1%). Hmmm, very intriguing (at least to me). I'll look forward to the height check later this yr.

53,
You have a point, but you're mixing up terms - sort of apples and oranges type of comparison. The moisture content of wood is percentage water by weight. I guess that is normally weight of water divided by total weight of the log including the water, or by weight of the solid, waterless wood in the log. Relative humidity of the air is the amount of water vapor in the air compared to the amount of water vapor the air could hold at the current air temperature. That means air at 100% relative humidity is holding 100% of the water it could hold. It does not mean the air is 100% water vapor. So, if you have wood at 35% moisture content and air at 55% relative humidity, which way would water vapor naturally go? You can't tell just by comparing 35 to 55 and saying water should move from the air to the wood because the air has more water. in fact, i bet it would go the opposite way.

The comparison you need to make is, I think, the partial pressure of wate vapor in the air compared to the partial pressure of water vapor in the interstitial spaces of your firewood. You could look up the partial pressure of water vapor in air at a given temperature and relative humidity, but figuring out the partial pressure of water vapor in the pores of your firewood would be more complicated. Once you know the two values, you'd calculate the rate of vapor diffusion based on the characteristics of the wood. A few simple calcs and you'll know exactly how fast your firewood is drying.

Nevertheless, I think you are right that seasoned firewood absorbs some water from the air if the wood has dried in a season of low humidity and then a season of higher humidity comes along. i don't think it is a lot of water, but many people report that the checks on the ends of firewood get smaller in humid weather. This must be due to the wood swelling as it absorbs water.

 

[michaelryba]

I'm not as scientific as WoodDuck, but agree with his logic. You can even "test" this concept today with a towel and a meter. Wet the towel in the sink. Insert moisture meter (mine said 38%) Lay towel out to dry. Note relative humidity in air (50% around here today). Come back a few hours later & WHA! the water has gone from the towel to the air. Your wood doesn't absorb & release water as fast as that towel, but it's a lot more dense than air & so can hold many times the amount of water.

 

[CJRages]

Nevertheless, I think you are right that seasoned firewood absorbs some water from the air if the wood has dried in a season of low humidity and then a season of higher humidity comes along. i don't think it is a lot of water, but many people report that the checks on the ends of firewood get smaller in humid weather. This must be due to the wood swelling as it absorbs water.

Here is another example to maybe help prove this point.

Last fall we installed 3/4 inch x 3 1/4 inch red oak hardwood flooring in our home. During the milling process those oak boards were (most likely) kiln-dried down to a very low moisture content. So...after purchasing the lumber and taking it home, the instructions were to open the ends of the boxes to allow the wood to acclimate to your home for 5-7 days before installation. Once moisture content had stabilized, then the boards could be nailed down to the sub-floor. Also note: installation instructions required that you leave a 1/2 to 3/4 inch "expansion gap" around the perimeter of the room in case of humidity fluctuation during the year.

 

[billb3]

My solid wood front door is about 3/16 inch wider in the Summer vs Winter and the door opening varies a quarter inch for the same period.
I installed the door in October and the next July I had to take it off and plane the side to get it to close and open without struggle.

 

[bogydave]

It all gets into a long discussion of absolute vs. relative humidity. Anywhere you are the absolute humidity (actual amount of water in the air) is less in winter.

Right
Because the air temperature is colder & colder air cannot hold as much moisture.
So 90% humidity in the winter at say 30°f, (is 90% of what 30 degree air can hold) in the winter, the air is dryer than
if it were 90% humidity in the summer at 80°f . (80 degree air can hold more water so 90% humidity of 80 degree air is more water in the air)

30 degree air will contain less water (than 80 degree air) to be at 90% of the maximum it can hold before fog (small water droplets forming in minute particles ie condenstion) & a slight drop
in temperature (air will hold less) we will get dew (or frost) on the grass like on cool clear nights.
As the temperature drops, the water in the air has to go somewhere because the air is cooler & will hold less water. When the temp drops
to where the cooler air has more than it can hold, the water has to go somewhere.
Dew is the air wringing itself out like a saturated sponge drips.

humidity is % of water the air can hold at given temperature at a given barometric pressure

Now that I confused myself

It all just Relative bye

 

[WoodPorn]

My solid wood front door is about 3/16 inch wider in the Summer vs Winter and the door opening varies a quarter inch for the same period.
I installed the door in October and the next July I had to take it off and plane the side to get it to close and open without struggle.

+1
I have the same issue every summer!

 

[Backwoods Savage]

It all gets into a long discussion of absolute vs. relative humidity. Anywhere you are the absolute humidity (actual amount of water in the air) is less in winter.

Right
Because the air temperature is colder & colder air cannot hold as much moisture.
So 90% humidity in the winter at say 30°f, (is 90% of what 30 degree air can hold) in the winter, the air is dryer than
if it were 90% humidity in the summer at 80°f . (80 degree air can hold more water so 90% humidity of 80 degree air is more water in the air)

30 degree air will contain less water (than 80 degree air) to be at 90% of the maximum it can hold before fog (small water droplets forming in minute particles ie condenstion) & a slight drop
in temperature (air will hold less) we will get dew (or frost) on the grass like on cool clear nights.
As the temperature drops, the water in the air has to go somewhere because the air is cooler & will hold less water. When the temp drops
to where the cooler air has more than it can hold, the water has to go somewhere.
Dew is the air wringing itself out like a saturated sponge drips.

humidity is % of water the air can hold at given temperature at a given barometric pressure

Now that I confused myself

It all just Relative bye

Dave, you may have confused yourself but you are correct with your analysis. The warmer the air, the more moisture it can hold. That is another reason we will see some winter days with snow flurries. The dry air cannot hold onto that moisture so it falls as snow. On the other hand many have seen virga in the summertime, which is nothing more than rain coming out of a cloud but evaporating before it gets to the ground.


Along with Pondman's analogy with the towel, try it with a sponge!

 

[53flyer]

This was just a duplicate post (not sure what caused the duplication). I would've delete it instead of writing this explanation but apparently you have to be a Mod to do that (even to your own posts) so this will have to do...

 

[53flyer]

yes, bogydave, that is all true. I realize the difference between the capacity of air to hold water at different temps but thanks for posting the explanation for everyone to read.

My question came from the fact that my summers are generally only in the 70-80's with around 30-40% (relative) humidity unless it rains which usually doesn't happen during our hottest periods. By comparison, in the winter it's routinely around 20-60°F but with 70-100% (relative) humidity. Given that low (relative) humidity of summer, I'm not so sure that the actual moisture in the air would be "less" in winter as compared to summer (even with the warmer summer temps).

It would be very different if I lived in an area with summer temps of 80-100°F and 60-80% (relative) humidity which is why I mentioned the difference between dry W coast climate vs. sticky/wet E coast climate.

 

[Battenkiller]

53flyer,

I don't know how far east you are, but in Spokane, WA the equilibrium moisture content (EMC) for wood stored outdoors is 8.6% in August, while in December it is 18.7%.

http://www.woodweb.com/knowledge_base/Equilibrium_moisture_content_of_wood_in_outdoor_lo.html

That's a 10% difference, so you are correct. But the larger point is that, even at RH near 100%, your wood will eventually dry to about 30% MC. That's the fiber saturation point for almost all domestic woods. Once is gets down to that point, only constant immersion in water can raise it any higher. The attached chart is all anyone handling wood needs to know about moisture content.

 

[Bootlegger]

I split some maple back in early December, it was 30-35% at that time. It is now in the low 20's.

My house is in the woods so my piles get more sun in winter than summer. Last summer I had piles of rounds that only got a couple hours sunlight a day and had big fungus growing on them by fall. That stuff was 35-40% when I split it.

 

[oldspark]

I split some maple back in early December, it was 30-35% at that time. It is now in the low 20's.

My house is in the woods so my piles get more sun in winter than summer. Last summer I had piles of rounds that only got a couple hours sunlight a day and had big fungus growing on them by fall. That stuff was 35-40% when I split it.

Piles (thats your problem right there) of rounds?

 

[Bootlegger]

Piles (thats your problem right there) of rounds?

Sorry, stacks, on gravel with space between rows.

 

[oldspark]

Piles (thats your problem right there) of rounds?

Sorry, stacks, on gravel with space between rows.

My wood is stacked on the southern edge of my grove so it gets some shade in summer and unless it rains it stays very dry and I do not cover it until winter.

 

[Intheswamp]

I forgot about all the people on the E coast where the humidity is generally much greater (nasty sticky, summer heat, yukk :shut: ). For those who enjoy the W coast's relatively dry summer heat I think the winter may, at least at times, be more humid by comparison to summer. At least it seems fairly humid when we're getting the really wet, heavy snow that's full of moisture. We also get various weeks where we're getting lots of ground fog which equals 100% humidity so the wood's got to be soaking up some moisture then right?... In the shoulder seasons when it's raining that's also 100% humidity so shouldn't the wood be gaining moisture content then as well?.... Am I off base here? Where's our weather guy that posts on this board LOL ...

53, I understand your concern but please understand that wood is not a sponge. I can have a wood pile uncovered and then we get 2" of rain but within 24-48 hours (depending on the weather after the rain) that same wood will be just as dry as before. Just think of all the folks who leave their wood pile completely uncovered all the time. For instance, quads never covers his wood and he gets lots of snow. Then imagine that snow melting and freezing, melting and freezing and then come spring, melting and then raining, etc. He seems to have no problem.

I do feel it does make some difference with different types of wood though. For example, oak is very dense and it would take a lot for that to soak up any moisture. But then if you took bass or popple or even cedar which is not as dense, then that would theoretically soak up more moisture but methinks it would have to sit in water before one would have to be concerned.

Here is another example for the above. I can drop soft maple and leave them without cutting up to firewood length. Within 2-3 years they are worthless for firewood. Yet this past winter I cut up an ash log that had laid (flat on the ground) for 3 or 4 years and each year that area is under water for a couple months of the year. But that ash was good for burning. Very solid stuff.

In short, I do not think you have a thing to worry about especially considering your wood is under a roof. To get the best results though, I'd suggest leaving your wood stacked outdoors where wind will hit the side of the pile. Leave it at least through one summer before moving it under the roof. If you stack green wood in a shed it simply will not dry as fast as it will left outside. Wind is more important than sun.


Along with your concern, you might recall a recent post of mine where I have a neighbor who claims the wood will increase in size during the summer. I stacked wood at 54" and it has lost 6". He claims it will be over 48" by the end of the summer. I claim it is pure baloney but, I am willing to test his theory so I will check that stack this fall or at least late summer to see what the measurement is. Keep watching for the results.

Howdy Dennis, sorry for dragging up an old thread but I started at the back of the forum and I'm working my way to the current threads...I'm on page 40-something now. Anyhow, I was wondered if you measured your test stacks or not...to see if they actually "grew"??

Ed