Charcoal

Place Hardwood billets in a Kiln and wait for them to heat all the way up. You get 4 per billet left after heating.
 * The Kiln may stay at 400 degrees to heat the billets, so the bellows are unnecessary and may cause you to use more fuel while waiting for the billets to heat up.


 * Charcoal is produced in the Kiln by adding up to 20 Hardwood billets and igniting it, by the time the Hardwood billets get to temperature the Kiln should have only burned off 1 Hardwood billets or Charcoal (if you are using this as fuel source), and then you can use the "Pull Out" option to turn 1 Hardwood billet into 4 Charcoal, which makes Charcoal 4x more effective than Hardwood billets as a fuel source.
 * The Hardwood billets will process faster if you use the "Use Bellows" feature of the kiln to increase the temperature.
 * Another large advantage for using the Kiln to produce Charcoal is that Charcoal weighs 1.00 and Hardwood billets weigh 10. Most smelting objects like the Furnace can only hold 100 weight or 200 like the Kiln so you will be able to add much more fuel (Or materials) using Charcoal since its weight is 1/10th of a Hardwood billet at 1.00.
 * Both Charcoal and Hardwood billets have a burning time of 10 minutes (3 minutes on a server setting of 60), and this is shortened by 1-2 minutes per use of "Use bellows". Because their burning time is the same it is recommended to only use Charcoal as a fuel source once your Kiln is operational.
 * If you have multiple fuel sources in the Kiln such as Both Hardwood billets and Charcoal when you "Light On" it will take from a random pile, so if you are using coal to heat your Hardwood billets it is recommended you remove the Hardwood billets turn it on so it uses Charcoal as the fuel source, using the bellows to get it to temperature, and then re-adding the Hardwood billets after to make more Charcoal.

Tips

 * Pulling out a load of charcoal damages a Kiln far less than pulling out the same amount of charcoal one at a time. Therefore, the best way to preserve the durability of a Kiln is to cook 13 Hardwood billets at a time without raising the temperature of the Kiln. One Hardwood billet will be consumed and the remaining twelve will be cooked, thus allowing you to pull out one load of charcoal.
 * Another option if more than 1 load of charcoal is need is to load the kiln with 20 Hardwood billets at a time, using the pull out command and adding 13 new billets to the kiln. When the piles of billets are then merged into 1 pile the heat-up time will be reduced. (the already heated billets heat up the new cold billets to about 1/3)

Video
Holzkohle Charbon Уголь