We all know that wet wood is more difficult to burn but there is actually many more reasons why dry wood, and in particular, kiln dried wood is far superior.
When we talk about wet wood, we aren't talking about wet to touch, but we are actually talking about the total amount of water stored in the wood. This is important, because a dry piece of wood that has rain water on the surface, is far superior to wet wood that appears to be dry on the surface. Dry wood is dry all the way to the core, whereas wet wood may appear to be dry on the surface but a few mm in, it is still wet.
When wood is dried, it shrinks, this means buying wet wood you actually get less, because each cubic meter is filled with swollen wood.
Have you ever noticed that heating cooking oil takes a lot less time than heating water? Well, that's because water requires a lot of energy to heat up compared to many other substances. What's more, is that in order to turn water into steam requires even more energy. The wetter the wood is, the more the heating potential of the wood is used in warming up the water, and turning it into steam. Most of this steam then goes out chimney without you ever seeing the benefit.
Drier wood means a higher percentage of the energy in the wood is pumped into your house as heat. Wetter wood means a higher percentage of the energy in the wood is absorbed by water and lost.
Higher moisture content also prevents the wood from burning hot. Burning hot is crucial for burning clean, therefore wetter wood, means more smoke. Smoke is actually unburnt gases, meaning that not only are you creating smog, but gases you could have burnt in your fire are escaping out the chimney.