The moisture content of wood is directly related to the humidity and temperature of the surrounding air. The equilibrium moisture content (EMC) occurs when the wood has reached an equilibrium with its environment and is no longer gaining or losing moisture. Here is a calculator for computing the EMC of wood at or below the fiber saturation point (about 30% moisture content) given the temperature and relative humidity.
Examples for 70 F (21C):
5.3 % MCdb 5% MCwb 25% RH
11.1 % MCdb 10% MCwb 60% RH
17.6 % MCdb 15% MCwb 84% RH
19.0 % MCdb 16% MCwb 87% RH
25.0 % MCdb 20% MCwb 97% RH
28.8 % MCdb 22% MCwb 100% RH
33.3 % MCdb 25% MCwb 100+% RH
Equilibrium Moisture Content of Wood in Outdoor Locations in the United States and Worldwide
William T. Simpson, Forest Products Research Laboratory, Research Note FPL-RN-0268, August 1998
With relative humidity and temperature data from the National Oceanic and Atmospheric Administration, the average equilibrium moisture content for each month of the year was calculated for 262 locations in the United States and 122 locations outside the United States. As an aid for storage of kiln-dried lumber, a graph is presented for determining the reduction in equilibrium moisture content that results from heating air in an enclosed storage space above the temperature of the outside air. Keywords: Equilibrium moisture content, lumber storage, drying
Wood Equilibrium Moisture Content Table and Calculator
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