OK to burn 22% moisture mixed with 12%-14% ?

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bikedennis

Member
Jun 21, 2021
121
Nor Cal
Maybe dumb question. Anyway when I stacked and covered some fir it was about 18% moisture. Just checked it with the meter and it reads above 20%(22%-23%). If I mix it with about 1/3 12%-14% pine is it all good and safe for the stove(BK)?
 
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stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
I'm not familiar with fir, but I suspect it's heavier than pine.

If you take the average of the moisture contents, (2/3 @ 23 pct, 1/3 at 14 pct), you're exactly at 20 pct. But of the fir is heavier, I'd mix in more pine. It's borderline imo.

How did you measure?
 

bikedennis

Member
Jun 21, 2021
121
Nor Cal
Used a digital moisture meter. Inexpensive, maybe not real accurate, but I read somewhere that the cheapies were accurate within 1%.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
Sure, otherwise you wouldn't have an actual number.

But how did you measure. Precisely. It matters a lot.
 

TheBigIron

Feeling the Heat
Dec 23, 2014
274
Peru, IL
Used a digital moisture meter. Inexpensive, maybe not real accurate, but I read somewhere that the cheapies were accurate within 1%.
@stoveliker is wanting to know if you take a split from your pile and test it, or if you take a split from your pile, resplit that piece and let get to room temperature then test it. You’ll find a huge difference in moisture readouts. Just my input
 
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stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
@stoveliker is wanting to know if you take a split from your pile and test it, or if you take a split from your pile, resplit that piece and let get to room temperature then test it. You’ll find a huge difference in moisture readouts. Just my input

No, not split, let get to temp, and then measure.
Get a split, let it be in a room for a day, then resplit and measure. If you reverse the order, you'll measure a number far lower than it actually is.
 
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TrippRick

New Member
Mar 22, 2022
15
Central Mass / Poland ME
No, not split, let get to temp, and then measure.
Get a split, let it be in a room for a day, then resplit and measure. If you reverse the order, you'll measure a number far lower than it actually is.
Not sure where I found this chart (maybe in this forum?) but does this look relatively accurate? Does anyone use these or similar correction factors?
1651165551509.png
 
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moresnow

Minister of Fire
Jan 13, 2015
2,083
Iowa
Not sure where I found this chart (maybe in this forum?) but does this look relatively accurate? Does anyone use these or similar correction factors? View attachment 295140
This graph. Along with a concise description of moisture meter operation should be a sticky that every new member could be directed to right off the bat::P
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
I don't know how accurate it is as I did not verify this experimentally myself. I do use this, and have seen other places where similar order of magnitude corrections are advocated.

I do vaguely remember that if one digs down one will find that this was once done by some forestry department of some state university.

So, yes, I think the table is correct.

I do note though that it is likely "more or less correct", because measured values are also affected by whether the wood split nicely or has more cracks, how deep the moisture meter is in, the type of wood (I believe they are calibrated for soft woods, not e.g. oak), etc. etc. etc..

I.e. the numbers are not an exact truth, but a good and usable indicator. And that suffices for our goals here, generally.


(These are the reflexive caveats that scientists always come up with to confuzzle the audience about what is scientifically true... I.e. I can't help it. ;P )
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,455
South Puget Sound, WA
To answer the question, yes, It probably will be ok. I did a test on this a couple weeks ago with fresh doug fir that measured 22% mc. Doug fir has high oil/resin content that will help it burn. Mixing it with known dry wood also helps. If you note that water and foam are bubbling out the ends then the wood has more than 22% moisture. If you can bring a box or two of the wood into the house for a week it will shed quite a bit of moisture, especially if the splits are under 6" wide.
 
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blades

Minister of Fire
Nov 23, 2008
3,785
WI, Leroy
most of the wood moisture meters are calibrated for furniture type wood. some of the better ones have mutiple ranges but are still under apx $60.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
most of the wood moisture meters are calibrated for furniture type wood. some of the better ones have mutiple ranges but are still under apx $60.
The General Tools mmd4e has two modes. "Wood" and "building materials". I read that as firewood and lumber.
And is only < $30 on amazon.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,455
South Puget Sound, WA
That's the model I have. Works well.
 
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TrippRick

New Member
Mar 22, 2022
15
Central Mass / Poland ME
To answer the question, yes, It probably will be ok. I did a test on this a couple weeks ago with fresh doug fir that measured 22% mc. Doug fir has high oil/resin content that will help it burn. Mixing it with known dry wood also helps. If you note that water and foam are bubbling out the ends then the wood has more than 22% moisture. If you can bring a box or two of the wood into the house for a week it will shed quite a bit of moisture, especially if the splits are under 6" wide.
Good point about bringing in some wood to further dry before putting in the stove. I'm thinking of buying / building a small rack or 2 to do that. 1 would be near the insert, the other close to that. It's a lot dryer there than in my garage, where my winter wood is. For oak, maple, ash, cherry....how long do you folks recommend? I know the longer the better but only have so much room.
 

AstroBoy

New Member
Feb 9, 2022
23
Philadelphia suburbs
The General Tools mmd4e has two modes. "Wood" and "building materials". I read that as firewood and lumber.
I think it’s more like firewood+lumber (both are wood, just finished or not) vs. drywall or plaster. The manual isn’t specific, but has sentences like “To locate the source of a leak behind wood, plaster, drywall or a ceiling, make measurements at different locations.”

In any case “Wood” mode is certainly what we want for testing firewood. 😀

Also, Home Depot has a version of the General Tools moisture meter if you want to pick one up locally.
 

GrumpyDad

Minister of Fire
Feb 23, 2022
562
Champion, PA
Am I understanding this chart correctly? If the temp is 40 F and my meter reads 20 the actual moisture content is 24, or do I have that backwards
I too would like to know this answer.
At around 65 degrees outside, after splitting the wood I have had sitting for a couple years Im around 16%-18%. So when it gets cold out I am now at above 20% optimal burn moisture content? That doesnt make sense to me, because when it gets cold in my area moisture goes away. To that point that we must add humidification into our living space in order to not have bloody noses and hair standing up like a science experiment. That's inside and out. Moisture gets SUCKED from everything.
I will do my own experiment and report back.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
It is not an issue of the outside humidity (equilibration takes a lot of time).

Instead the measurement will indicate a lower mc than it really is when it is cold, because the conductivity of the wood decreases with temperature, and dry wood has a lower conductivities (higher resistance), so the device interprets it as drier wood.

in other words the calibration of resistance measured to moisture content is done at 70 F. (And with firnor pine I believe, not oak.)

That is why it's best to bring a few splits into the home, let them get to room temp for 24 hrs, then resplit them and measure.
 

GrumpyDad

Minister of Fire
Feb 23, 2022
562
Champion, PA
It is not an issue of the outside humidity (equilibration takes a lot of time).

Instead the measurement will indicate a lower mc than it really is when it is cold, because the conductivity of the wood decreases with temperature, and dry wood has a lower conductivities (higher resistance), so the device interprets it as drier wood.

in other words the calibration of resistance measured to moisture content is done at 70 F. (And with firnor pine I believe, not oak.)

That is why it's best to bring a few splits into the home, let them get to room temp for 24 hrs, then resplit them and measure.
So if you read 28 mc at 20f it's actually 20 mc ?
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
No, the other way around. If you read 20 mc at low temperature, it is actually higher. I don't know the exact numbers.

The real mc is higher than what the meter tells you when the temperature is lower than 70 F.