All kilns require energy to operate.
Heat is used to warm the chamber and evaporate the moisture from the wood. The heat is circulated through out the kiln via the fans. Heat is usually in the form of hot water or steam which is produced by a boiler which heats the water. The water is then circulated through the kiln in pipes and heating coils, which act as a heat exchanger to radiate the heat from the water to the air. A heating coil is normally a Copper pipe with fins which help to expedite the transfer of heat from the water to the finned pipe, and from that to the air.