Heat is generated by a ship's Power Plant and other modules while it is operating under its own power, and by certain environments. The rate at which a ship accumulates and dissipates heat defines the number of intensive activities that ship can perform in a given period of time. The amount of heat that a ship currently has is displayed in the Heat Indicator on the HUD.
Generating and Dissipating Heat
In most situations, heat is generated by the ship itself when it is not docked in a Landing Pad or parked on a planetary surface. The Power Plant accounts for the majority of heat, with more expensive Power Plants offering lower heat generation, but other modules, especially weapons, can significantly boost heat generation. The power consumption of a given module can be tracked in the Modules tab of the HUD's right-side Internal Panel. Modules with high power consumption generally produce more heat as long as they are active. Firing weapons or receiving weapons fire can cause heat levels to spike rapidly. Heat can also rise dramatically when in close proximity to a star, such as during Fuel Scooping, or when inside the docking bay of a recently-damaged station.
To dissipate heat, all ships are built with Heat Vents that draw a ship's internal heat and radiate it out into space. Heat Vents have limited capabilities, however, and their rate of dissipation is easily overwhelmed by intensive power consumption or approaching stars. Heat Vanes are shuttered and heat will build up continuously while Silent Running is active. Heat dissipation can be bolstered by the Heatsink Launcher utility module, which can absorb all of a ship's heat, no matter how high, in seconds and eject it into space via a disposable heatsink. Strategic use of the Heatsink Launcher can mean the difference between victory and defeat in battle, or prevent an unlucky explorer from damaging or losing their ship far away from civilisation.
Detection and Stealth
A higher amount of heat will increase the ship's signature range on the HUD's radar, which means that the ship will be more easily detectable by other ships nearby in normal space. A heat level below 15% will allow a ship to be nearly undetectable by the radar of most ships, although no amount of heat suppression will conceal a ship from visual observation. Silent Running allows a ship to outwardly imitate 0% heat while it is active, but the trade-off is internal heat build up with a risk of module and hull damage. This can be countered with the timely use of a Heatsink Launcher.
When the ship's internal temperature exceeds 100%, modules will suffer damage continuously. In particular, the Cargo Scoop is delicate and often becomes one of the first modules to fail, which then causes losses to any onboard cargo. If heat rises above 150%, then the ship's hull integrity and health will also be damaged continuously, which can result in ship loss very quickly.
Managing Heat via Engineering
Some modules can be modified by Engineers to significantly reduce the heat output of a ship. The Low Emissions modification available for Power Plants can cut heat most effectively, and the Thermal Spread Experimental Effect can be helpful on multiple modules.