Humidity vs Moisture Content, Calculator

[skintigh]

I was a little confused because those terms sometimes seemed to be used interchangeably, and I didn't understand how wood could get ever under 20% if the air was 50%. Well I found all my answers in a single Equilibrium Moisture Content table (with sources!) plus a bonus calculator so I thought I would share:

http://www.csgnetwork.com/emctablecalc.html

The source is neat, too. I now know what the EMC is for my city for every month of the year. All I need now is data on how fast wood dries under different conditions (EMC vs drying time to 20%, and is it better to lower EMC or increase airflow, etc.) so I can optimize my firewood drying. I'm really hoping it is dry by winter...

 

[svk]

Oh man, you are going to get @Whitespider on the warpath now.

 

[bayard]

beware some wood will take up to several years to dry, red oak, elm,etc. some will take 2 or3 months under the right conditions. there are many reasons why wood will dry slowly. good luck

 

[skintigh]

beware some wood will take up to several years to dry, red oak, elm,etc. some will take 2 or3 months under the right conditions. there are many reasons why wood will dry slowly. good luck

This paper says 70-200 days for 1" northern red and up to 120-320 for 1" southern varieties when dried outdoors (page 24)
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr117.pdf
I assume thicker wood will take longer, though many claim that most of the drying is through the ends (so much so that lumber is sealed on the ends so as to not dry too fast).

Another interesting find, these researchers built a cheap, fan-less solar kiln with a plastic tarp and tested it against a control pile and against felled trees with their leaves left on. Turns out the clear tarp did not speed drying and leaving them in tree form made them dry slower. http://www.fs.fed.us/pnw/pubs/pnw_rn450.pdf

 

[svk]

Wood dries through the ends primarily when in round with bark on. When split dries from all split sides.

Not surprising that a fan less kiln didn't work. You need to remove humidity leaving the wood to help it along.

 

[olympyk_999]

This paper says 70-200 days for 1" northern red and up to 120-320 for 1" southern varieties when dried outdoors (page 24)
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr117.pdf
I assume thicker wood will take longer, though many claim that most of the drying is through the ends (so much so that lumber is sealed on the ends so as to not dry too fast).

Another interesting find, these researchers built a cheap, fan-less solar kiln with a plastic tarp and tested it against a control pile and against felled trees with their leaves left on. Turns out the clear tarp did not speed drying and leaving them in tree form made them dry slower. http://www.fs.fed.us/pnw/pubs/pnw_rn450.pdf

i had a few thousand BF of wide white pine (20" and under) for flooring dried at Hardwick Kilns in Hardwick MA earlier this year, they gave me a tour of their process, and they told me a minimum of 2 months for oak, they go through different kilns to slowly remove moisture and keep the lumber flat/straight...
my pine took 2-3 weeks along with air drying a week or so outside before it was sent into the kiln...near everything came out with no cracks and all of it was flat...they run A LOT of lumber through there from all over the world, they seem to have the process down!

 

[flotek]

When it comes to seasoning wood in your backyard There are too many variables to punch in a calculator to ever hope of an accurate reading

 

[svk]

Agree, lots of variables.

I've got silver maple that seasoned in 2 months in half sun and black ash (normally considered a fast drying species) in full sun for a year that's not even close to being ready.

 

[skintigh]

Wood dries through the ends primarily when in round with bark on. When split dries from all split sides.

Not surprising that a fan less kiln didn't work. You need to remove humidity leaving the wood to help it along.

I was referring to lumber - green boards - dry so fast through the ends that you need to seal them to prevent cracking. Obviously they can't dry only through the ends or else they would never dry one the ends were sealed (yet some people seem to suggest that...), but I guess it's faster from cut grain, fast enough to damage boards. Of course cracking is a good sign in firewood.

Their kiln had air holes at the top and bottom to allow warm air to pull away moisture and suck dry air in, yet the kiln still did nor improve drying. I wonder if the increase in heat and decrease in EMC is less important than the decrease in breeze cause by the tarp, and if so, would simply using a fan be even more effective that building a complex solar kiln with active venting? Or to put even more of a point on it, would using a solar powered fan to blow on your wood be more effective than building a modern solar kiln?