Heat is the least "noble" energy form. According to the second law of thermodynamics, heat cannot be transformed into higher forms of energy - like mechanical or electrical energy - without a loss, whereas the reciprocal process can happen loss free. While heat is a scalar and thus undirected, heat transfer always occurs from warm to cold, and never the other way around, unless work is added. As heat is at the end of a chain of energy transformations, it can be the tip of an iceberg of energy usage. Using "nobler" forms of energy to generate heat, e.g. using electricity to generate space heating, should be minimised, and waste heat from mechanical or electrical processes should be utilised to preserve energy sources.