Temperature (Subnautica)
Temperature is an environmental game mechanic that, like Radiation, affects the player. In most circumstances, extreme temperatures are harmful to the player. However, unlike Radiation, the player can also harness heat sources for Energy applications.
Heat Sources
High Temperatures are typically generated by underwater volcanic activity. Such sources of heat include Lava Geysers, which can be found on the seafloor in a few biomes, and Thermal Vents, which can be found in some of the deeper biomes. Certain biomes are also quite hot, such as the Inactive Lava Zone and Lava Lakes. Direct contact with lava will instantly kill the player.
Heat Protection
The player starts taking damage when in an area with a temperature above 50°C. The UI will indicate that the player is too hot by showing glowing orange lines around the edges of the screen. The player can equip a Thermometer to show the current temperature on their HUD.
The player's thermal resistance increases to 70°C if they equip a Reinforced Dive Suit. This will protect the player from most harmful temperatures. However, water near lava in the lava zones is hotter than 70°C, which the suit cannot protect against, so the player must be careful when exploring in these areas.
To survive any higher temperatures will require the use of a vehicle such as the Cyclops or the Prawn Suit. The Prawn Suit is especially useful for collecting resources near heat sources as it can resist the extreme heat, but care should still be taken as direct contact with lava will still damage it.
Energy Production
The player can build a Thermal Plant to generate Energy from heat sources. A Thermal Plant must be placed close to the heat source (in an area that is at least 15º), so the player must use Power Transmitters if their Seabase is not built near the heat source.
The Prawn Suit Thermal Reactor and the Cyclops Thermal Reactor Module can be installed in a Prawn Suit or Cyclops, respectively, to allow these vehicles to generate power when near heat sources.