Method used makes a big difference of MC% http://dnr.wi.gov/topic/ForestBusinesses/documents/BiomassMoistureContent.pdf
Wonder how a MM % is calculated. ? DC electrical Resistance inside a 1" portion of the wood fibers ? Any salinity of the moisture inside the wood used &/or wood type ? (Thought like this are symptoms of "Cabin Fever" )
My MM is 3 years in the stack! % will always be less than 20% if it is stacked and top covered right.
Pretty much. Moisture meters don't measure moisture at all; they measure electrical properties that correlate reasonably well to moisture content. All the relatively affordable moisture meters are just glorified ohmmeters. Below about 6% MC the resistance of wood is so high, and above 28% the resistance is so low, that electronic meters can't make heads or tails of the situation, but inside that range they do reasonably well, give or take a couple percent for variations of temperature and species.
Yup, given such time out of rain/snow to approach EMC (equilibrium moisture content) with local atmosphere, MC of wood stacked outdoors here will settle at 10-12%, dry basis. So goes the theory, and the way it happens. Stacked near the stove for a while, it won't budge a MM.
Oven dry. As noted up at the top, oven dry basis is the standard for lumber, plywood and similar products, and those are the products that moisture meters are primarily designed and used for. Firewood is kind of a niche application.
It's worth noting that the difference in the numbers gets smaller as moisture content gets lower. Bogydave's example uses very wet wood, so the difference is dramatic, but 15% dry basis is the same as 13% green basis. If you're dealing with kiln-dried hardwoods meant for furniture, trim, etc. then you might be looking at 7% dry basis vs. 6.5% green basis. It becomes an almost meaningless distinction.
Except in the case of the EPA stove tests. The test specifications are done on a wet basis. 20% wet = 25% dry.
The standard for emission tests is to burn cribs of doug fir lumber at between 16-20% wet. Far from everyday real world use.
