It is heated to and is then cooled back down to . As an example, consider air as it is heated or cooled. Swimming pools may be heated or unheated. Instead, the engine is heated by recapturing exhaust heat. Then the mixture is heated over a stove. Incoming water is sprayed onto pipes which are then heated to generate steam. The oven is typically heated to well over . Then the acidified whey is heated to near boiling. The windshield could be heated electrically. The furnace is heated using burning gas. I boils when it is heated and contracts when its temperature is lowered. This mixture is then heated for several days, stirring constantly. The mould was then heated to melt the thermoplastic. The rear seats can also be heated. The front seats with heated and climatised system were offered.