Question

When a fuel is burnt some of the energy produced is given off as waste heat?

Answer 1

Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility (or in thermodynamics lexicon a lower exergyor higher entropy) than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms, for example, a refrigerator warms the room air, an internal combustion engine generates high-temperature exhaust gases, and electronic components get warm when in operation.