# Ambient humidity - does it affect firewood?  (Newbie)



## M_ichel (Sep 5, 2017)

Hi all.

I searched the forum for "relative humidity" without success.  Here's my newbie question:

Our cottage is located on the edge of a fairly large body of water (Lac des Deux-Montagnes, QC).

Prevailing winds are from the lake to the land.

Therefore, relative humidity is usually "fairly high" (it's 64% inside the cottage as I type this;  no, we haven't had any rain for the last two days).  I didn't pay attention before (just had the stove installed last week), but except for the hottest (and dryest) spells at the height of summer, I bet the relative humidity is probably mostly in the range of 60-70%.

Even if the firewood read 15-20% humidity in the middle of the farmer's field, once it's been stacked near the lake for a few months, wouldn't it absorb moisture and stabilize around the average relative humidity of the area?

Thanks.


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## BenTN (Sep 5, 2017)

Here is a helpful chart.

https://www.fpl.fs.fed.us/documnts/fplrn/fplrn268.pdf

The wood can only get so dry in certain conditions so your theory is correct. If you are buying seasoned wood from a dealer or farmer then you shouldnt have any problems stacking at your place and burning thru the winter. Cold air is much more dense and holds less water, so 50% humidity in January is still far less moisture than 50% humidity in July.

Now if you are gathering and css'ing your own supply you may see extended times to reach your target 20%.


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## Rickb (Sep 5, 2017)

relative humidity will effect how fast wood seasons.  For example wood will lose water content faster in 20% relative humidity then 90%.  But relative humidity is the measure of moisture in the air at a given temperature it isnt actual moisture content.  So even at 80% humidity your wood will dry(slowly).

Does that make sense?

Ben beat me by a minute!


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## Poindexter (Sep 5, 2017)

I am a firm believer in emc as linked above by @BenTN .  I am running a passive solar firewood kiln setup at my place and emc works, within the limits of my test equipment.

Once temps are below freezing, and stay there, MC of your fuel isnt going to change enough to matter. 

Before freeze up, i was seeing my fuel stacks pick up a lot of moisture after the height of summer during my autumn rainy season. 

One key point to my kilns, two massive threads here, i got from @solarguy2000 , is a layer of plastic between the ground and my stacks.


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## kennyp2339 (Sep 6, 2017)

The theory sounds correct on paper but what about the houses built around the lake? Wouldn't everything be damp and moldy all the time? I think relative humidity plays apart of the whole drying process (speed of drying) but a micro climate from a lake wouldn't have a huge effect in the big picture.


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## sportbikerider78 (Sep 6, 2017)

Outdoor humidity is a factor.  Just like sun exposure, temperature and wind.


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## WoodyIsGoody (Sep 6, 2017)

M_ichel said:


> Even if the firewood read 15-20% humidity in the middle of the farmer's field, once it's been stacked near the lake for a few months, wouldn't it absorb moisture and stabilize around the average relative humidity of the area?
> 
> Thanks.



It's important to recognize that the percent of water in wood is not a humidity measurement, it's percent water by weight. And a humidity measurement is not percent water by weight, rather it's percent of it's total capacity. Thus, even a steady 50% relative humidity can dry wood to below 20% moisture content. This is what the EMC table provided by Ben illustrates (and how temperature plays into it).


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## Poindexter (Sep 6, 2017)

I have gotten down to 3 variables i have to control for.

1.  EMC of the air around my seasoning cords.  Certainly airflow is a small piece of this, replacing damp air with dry air allows more water to come out of the wood to get the new air more humid too.

2. Rain, including Ground Splash.  The wife and i put in an offer on a log cabin a couple years ago.  It had some issues.  Reading up on cabin maintenance, the sill logs should be 18" off the ground to keep them dry, up out of the splash zone.

3. Grond water transported as vapor.  Are the bottom couple layers of your stacks wetter than the wood in top?   Put a damp dish towel on a granite counter top.  The a rack for like cooling cookies.  Then a skillet.  Put a clothes iron in the skillet.  Put the skillet on a timer, 12 hours on, 12 off, just like sunlight.  Keep feeding water into the dishtowel from the side.  What happens to the bottom of the skillet?


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## johneh (Sep 6, 2017)

OK I'll bite what happen to the 
bottom of the skillet ?


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## WoodyIsGoody (Sep 6, 2017)

johneh said:


> OK I'll bite what happen to the
> bottom of the skillet ?



It gets wet/rusty.


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## Easy Livin’ 3000 (Sep 6, 2017)

My wood doors stick and wood floors swell when it gets and stays humid for a few days. Then, they both shrink when the humidity drops. This tells me something. Wouldn't have any idea the percentage moisture change.


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