Relative Humidity

• In the Northern Hemisphere, above the tropics, wood can dry out fully because of the low relative humidity. The winter months cause dry skin in many people, and something similar happens to your cordwood. The dryness of winter air is attributable to the low average temperatures. The colder air is, the less water vapor can be suspended in the air. When wood is stored under these dry conditions, moisture is wicked out of the wood, and the low amount of water vapor in the air means that little water reenters the wood during storage.
  
  

Length of Storage

• Wood that has been split and stacked for storage as fuel is more readily able to lose moisture, since more of the inner wood is exposed and the bark on the trunk no longer encases the wood. Because wood is often cut during the warmer months and then stored, it has many months to slowly desiccate. If you can purchase wood cut during winter for use next winter, it will have even longer to dry out.
  
  

Winter Dormancy

• Deciduous hardwood trees go into a dormant phase during the winter. After losing their foliage in the late fall, the tree no longer has to supply nutrients to the tips of every branch. With sap no longer flowing, the moisture content of the intact tree is lower during the winter than at any other point in the year.
  
  

Style of Stacking

• When firewood is delivered to your home for use in a furnace or wood stove in the winter months, it is stacked by a certain method that prevents the wood from getting too moist. When firewood is stacked, it should be placed in a "cord." A cord is a unit of measuring firewood that involves neatly placing it in a stack that measures no larger than 4 feet by 8 feet, with a depth of no more than 4 feet. This stacking method is a time-honored way to ensure efficient drying and air circulation around the wood.