The term "biomass boilers" refers to all boilers and plants that run on organic fuels: industrial and municipal waste of plant or animal origin that can no longer be utilized but may be converted into electricity and heat. Because the carbon dioxide exhaled during the combustion process is similar to that absorbed by plants throughout their lives and released after their natural death, biomasses and the fuels derived from them are a source of renewable energy. Therefore, the burning of biomass does not result in an increase in carbon dioxide in the atmosphere, which is the primary source of the greenhouse effect, but rather provides an extra benefit to the environment due to the biodegradability of the substances burnt.