Just what exactly is is and is all wood firewood
BTU’s are a measure of heat. It stands for British Thermal Unit which is a defined unit of heat. The measure is what amount of energy it takes to raise one pound of water one degree. There are seven pounds of water in a gallon. As a frame of reference there can be up to about 1,000 to 1,500 pounds of water depending on how it is dried. So the effect of water content in the wood can really impact the energy available in the wood you go to burn.
To answere this question, I take this to be specifically about the how, not the why of kiln dried firewood. But the bottom line action of what is done and why people do it.
Moisture in the wood can be as high as 60% of the wood when it is first cut. So to burn well there is a need to remove most of that moisture so it is easy to light and burns brightly not just smoldering. So to put it briefly kiln dried mean firwood has been placed in a large over and monitored to reduce the moisture content from 60% down to 15-20% for consistantly good burning firewood. For a brief video done by the company that claims to be the inventor you can see a video description of what Kiln Drying is on our youtube channel.