Waste heat occurs especially in thermal power stations, and many modern stations use efficiency measures that make use of this thermal energy as heat or electric power and thus increase a power station's efficiency rate.
Waste heat sometimes called Secondary heat or Low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat. A heat engine can never have perfect efficiency, according to the second law of thermodynamics, waste heat is regarded as a waste by-product of this process. When produced by humans, or by human activities, it is a component of anthropogenic heat, which additionally includes unintentional heat leakage, such as from space heating. Waste heat is thought by some to contribute to the urban heat island effect. The biggest point sources of waste heat originate from machines such as electrical generators or industrial processes, such as steel or glass production. The burning of transport fuels is a major contribution to waste heat.