oldspark said:
"Because 25% MC dry-basis is the moisture content the stoves are designed to burn, and the moisture content that the EPA test procedure specifically demands, and the moisture content that those idiots in white lab coats have been saying for over 30 years burns most efficiently in an air-limited wood stove. Or to say it another way, a 25% MC reading on a moisture meter IS the Holy Grail of 20% MC by weight."
This is from a post by our resident wood expert BK.
God help us all if I'm the resident wood expert, but I do know a wee bit about moisture meters and wood drying.
OK... I just ran around the place sticking my cheap little blue HF meter into every unfinished piece of wood I could find. Looks like a snake's been attacking everything, but I'm being forced out of here, so what do I care?
Results? Just about every dang thing in the place reads about 10% MC, with a few items in the kitchen up around 11-12% MC. With no heat or AC running, this is just about exactly the EMC that any furniture maker or lumber dealer would tell you to expect to find indoors in my location during this time of year.
I went down to the basement to check a split of black birch. It read 14% MC. This wasn't just any old piece of black birch, it is the same one that I tracked the changing weight data on during last year's wood drying experiment. At the end of that experiment, BG suggested that I put it outside to see how much more weight it lost. It didn't. It
gained weight (as I knew it would).
As you can see in the table below, after 42 days in the Battenkiln it had lost 3.11 pounds (3lbs, 2oz) and was down to 11.06% MC. I put it out in a recessed place on top of the AC for my shop where it wouldn't get a drop of rain on it all season. A few weeks ago, I brought it in and weighed it. It had gained 3.4 ounces, and the MC had reached equilibrium with the outside air at 14.19% MC.
When I just went down and stuck it with my meter, guess what it read? Like I said - 14%. Exactly what it should have read according to my weight data.
Just last week I changed the batteries on this unit and tested a few of my outside splits. One was a cherry split that had sat all winter in the Battenkiln and then was put into my shed to keep it from getting rain on it, so it was at least as dry as the black birch test split. It read 14% MC.... the same as the black birch stored in similar conditions. Then I grabbed a cherry split that had sat in all the rain we have had the last two months. A re-split showed in to be 17% MC... 3 points higher than the wood that never saw a drop of rain. So yes, wood IS like a sponge (albeit a very slow acting sponge). Wetter? Yup. Still burnable? You betcha!
So, should there be any reason to doubt the accuracy of my meter? It seems to me to be spot on with any expected MC I can come up with. What more can I say? Buy one for $12 and trust the damn thing. They are really only resistance meters with a scale calibrated for wood MC instead of ohms. Do you doubt the accuracy of your multimeter just because it ain't a $300 Fluke? C'mon, they all are using the same chips and printed circuit boards made by our good friends in China.