BattleMechs are incredibly heat inefficient - virtually everything you do, from moving to firing weapons, generates an excessive amount of heat. Too much heat and your onboard systems will overload and shut your 'Mech down. You monitor your current heat on the heat guage. Since 'Mechs disperse heat through their heat sinks, the more heat sinks your 'Mech has, the fast it dissapates the heat. Double heat sinks are twice as effiecient as standard heat sinks but take up more critical spaces.