Like waste energy, waste heat is heat whose release during a process or the manufacture of a product is unavoidable. This heat dissipates naturally, but in some cases can be partly recovered and used. It can also be reduced. Waste heat falls into the same category as the heat releases associated with many common processes and actions. These include residential wastewater; cooling water, air conditioning and drying; defective insulation and doors and windows left open in cold weather; combustion gas from furnaces, boilers, incinerators and engines; product cooling by the glass, metal, cement and brick industries; and the heat radiated in steelmaking.