Nineteen days hath September: a wood drying calendar

[Jon1270]

It won't be news to anyone that wood dries faster when it's hot outside, but it turns out that the rate varies in a fairly predictable way. There's a rule of thumb (one that's backed up by actual science, not wild speculation) that wood dries twice as fast for every 20 degrees Fahrenheit increase in temperature. Using that rule, along with historical daily average temperatures I got from the National Weather Service, I generated this wood drying calendar. It's 365 days long, but the months look a little different than you are used to. With this calendar, wood dries just as fast in January as it does in July, but January is over 10 weeks long, and July is just over 2 weeks.

One limitation: it's based on Pittsburgh climate data. It's probably not far off for most parts of the country where hardwoods grow and people burn them for heat, but some areas (deserts, coastal areas) would look very different.

Enjoy.

 

[Jon1270]

And the last 2...

 

[Ralphie Boy]

Well there goes my best tool for checking the moisture content of my firewood.... the multi-year calendar! Someone always comes up with a better mouse trap.

 

[Jon1270]

Well there goes my best tool for checking the moisture content of my firewood.

Nah, a full year is still the same as it ever was. It's only the fractions of years that get confusing.

 

[Blue Tornado]

What day is your birthday on your calender?

 

[bmblank]

Jon, you must be an engineer. I hate myself for completely understanding your calendar.

@those who don't understand it,
If your going for 2 years of seasoning, its obviously the same no matter when you start it. But if you want to go for 18 months, its gonna take longer if you start in November than it would if you start in May or June.

 

[oldspark]

Yep wood drying over 6 months of winter is not the same as wood drying over 6 months of summer.

 

[Applesister]

Jon I love your imput, I look for your Avatar. And Im not peeing in your cornflakes here. But I just dont get it. But then Im just a dumb hick that only has sex with farm animals, well not only. I went to bed last night trying to figure out why I couldnt get past conceptualizing a 10 week month of Jan. Being a graphic artist and minoring in accounting I tried to reconstruct your information. So I could understand it. Im sure its the male/ female species thing. But I took the one stationary variable which is the 365 days. And I decided that I would have used a pie chart and colored each month with a color code. Like a weather map and represent each month by a percentage amount(time). January and December being the largest pie slices. The information became easier for me to grasp. With the color spectrum going from cool to warm.

 

[Jon1270]

Yeah, a pie chart would be a much simpler way to convey virtually the same information. It even occurred to me to use one, but this seemed more fun. You should post yours here!

 

[Applesister]

So my conclusion from your shared research...which is very nice of you. Is that perhaps you may be leaning toward a heated woodshed construction? All of this information is pointing toward the use of a wood kiln. Or a solar woodshed?? The threads on the solar kilns here are interesting. I have two greenhouses Ive been eyeing up here. You know...if us farmer types can extend a growing season with hoop houses cold frames...why not use the sun??? A woodshed with clear plastic roofing? A drum of calcium chloride to absorb water.

 

[Jon1270]

And I decided that I would have used a pie chart and colored each month with a color code. Like a weather map and represent each month by a percentage amount(time). January and December being the largest pie slices.

You could approach it another way, and use the size of the pie slices to indicate how fast wood dries in any given standard-calendar month, in which case the winter months would be smaller rather than larger.

 

[Jon1270]

Sadly I don't have sufficient sunny area for a solar kiln unless I want it to fill my tiny suburban front yard, which I doubt my neighbors would appreciate.

 

[Applesister]

what would be really cool would be a formula that you plug in information and get a simple read out for actual time span of drying for each species. Like if you cut birch in November. when will it be dry. Since each species has a sapwood moisture and a heartwood moisture content that doesnt vary significantly. A starting MC and an ending MC and time it takes to get there...based on the month of imput??

 

[oldspark]

Or you could get ahead a couple of years and stack it out in the wind and sun.

 

[Jon1270]

Yeah, I have a fantasy of developing a model like that but I suspect it would take a few years of testing and data gathering. You'd also have to correct for climate differences, and minimize variables by specifying that the wood be top-covered, stacked in single rows so far apart, with so much sun exposure... pretty difficult to make it usefully accurate.

 

[Jon1270]

It would be relatively easy, though, to assign speed-of-drying numbers to particular locations, to clarify the differences between, say, Northern Michigan and Texas...

 

[Seasoned Oak]

Yep wood drying over 6 months of winter is not the same as wood drying over 6 months of summer.

What about the fact that the humidity around here is 80% in summer and 20 % in winter. At 20 % the air will suck the moisture out of just about anything even if its frozen.

 

[oldspark]

What about the fact that the humidity around here is 80% in summer and 20 % in winter. At 20 % the air will suck the moisture out of just about anything even if its frozen.

Have you ever read up on the subject, there are two types of moisture in wood, bound and free, the one type goes no where below 32 degrees but the othere does, plus higher temps dry things faster then low temps so the humidity can be higher and still have quicker drying. So if you have 80% humidity is your wood at 80%?

 

[Applesister]

Virginia Tech University has a phone APP tree identification system. It brings up all the tree/ plant species that grow in your GPS recorded position. It also gives GPS elevation coordinants. Its free but it uses alot of memory. It works like Leafspot. A special hand held moisture meter that tracks your GPS location factoring relative humidity time of year and moisture content of the wood being tested. All you do is plug in which species you are testing?? It gives you a drying time.

 

[Woody Stover]

What about the fact that the humidity around here is 80% in summer and 20 % in winter. At 20 % the air will suck the moisture out of just about anything even if its frozen.

It ain't 20% often enough. Last week here has been rainy/snowy and a lot of days the humidity doesn't drop much below 70%. Couple the lower RH in summer with 'twice the drying with every twenty-degree rise in temp' and you are really kickin' some arse. Now, if you get a drought like we had here last summer, you get a fair amount of 20% RH minimum days (unheard of here)...wow, that's awesome. All that said, my wood was still not all dry enough. There is no substitute for time.

This calendar has confirmed one thing for me; I need to get a buttload of wood stacked right now!

 

[Jon1270]

What about the fact that the humidity around here is 80% in summer and 20 % in winter. At 20 % the air will suck the moisture out of just about anything even if its frozen.

I think you may be thinking of indoor relative humidity, which is dramatically lowered in the wintertime by our stoves and furnaces. From what I've read, outdoor RH is a lot more stable than that in most areas of the country. (Currently 100% and snowing in Pittsburgh).

Also, even at 80% the equilibrium moisture content of wood is 16%, much drier than most firewood ever gets before it's burned. More speculatively, I doubt humidity is the bottleneck that limits drying speed except maybe early in the process when there's a lot of moisture near the surface of a chunk of wood, ready to leave on the first bus that comes along. Further into the process, I would guess that water's ability to move through the wood (density, cellular structure) would be more important. Temperature helps with that because the added energy makes the water more mobile even deep inside a split.

 

[Jon1270]

Virginia Tech University has a phone APP tree identification system.

What, you tease us with that and don't provide a link? Have you no manners? (Oh wait, farm animals... )

This calendar has confirmed one thing for me; I need to get a buttload of wood stacked right now!

Exactly. Weeks of delay in January or February (the conventional ones) don't matter much, but the warmer it gets the higher the cost of waiting (unless you're stocked 4 years out, in which case who cares?)

 

[oldspark]

"Get her done" as early as possible in the spring

 

[Applesister]

Sorry..I meant maybe Jon could invent an in the field hand held meter...with your location based on GPS And the known humidity levels for the time of year and species of wood.

 

[Jon1270]

Have you ever read up on the subject, there are two types of moisture in wood, bound and free, the one type goes no where below 32 degrees but the othere does

Yep, have read quite a bit on the topic. The 32 degree threshold doesn't actually mean much unless your woodpile is coated in snow and ice. Trees contain a natural antifreeze that prevents the water from freezing unless it gets ridiculously cold (way below zero F). That's why you don't see trees cracking and splitting all the time.

Sorry..I meant maybe Jon could invent an in the field hand held meter..

Oops. Also, rats.