The core principle of the heater is energy conversion, the most widely is the electrical energy into heat. For example, electric heater, eddy current in the alternating magnetic field and the heat absorbed by the metal, is the electrical energy into light energy; such as solar water heater, solar radiation energy and solar energy (photoelectric effect) converted to heat both; biomass energy is to raw material as a carrier of the solar energy to chemical energy a form of energy storage, and it directly or indirectly from photosynthesis. In addition, nuclear energy, wind energy and the energy conversion model, but generally need to be converted into electrical energy use.