Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics. The radiator is always a source of heat to its environment, although this may be for either the purpose of this environment, or for cooling the fluid or coolant supplied to it, as for . Despite the name, most radiators transfer the bulk of their heat via convection instead of thermal radiation (the main exception to this rule being the radiators on spacecraft, see below), though the term "convector" is used more narrowly; see , below.