Temperature (Below Zero)

The temperature in Subnautica: Below Zero is a major environmental game mechanic that the player must manage. Extreme temperatures (both hot and cold) are harmful to the player.

Temperatures and rate of exposure can be affected by the weather conditions. The current weather and forecast can be seen in a base Control Room. Robin's current warmth is indicated by teeth-chattering sounds.

Cold
Certain consumables boost the player's warmth, such as the Spicy Fruit Salad, Heat Fruit and the Thermos. Thermal Lilies, Geothermal Vents and hot springs can be found on the surface to provide warmth to the player.

The Cold Suit exists to protect the player from low temperatures, and the PDA will warn the player about cold weather and hypothermia (extremely low heat in the body)

Heat
The player starts taking damage from temperatures above 50°C. The UI will indicate that the player is too hot by showing glowing orange lines on the edges of the screen. However, the player's thermal resistance increases to 70°C if they're wearing the Reinforced Dive Suit.

Energy Generation
High temperatures can be used to generate energy for Seabases through the Thermal Plant; because these are external generators that have to be placed at specific locations to work (any source above 25°C, which can be found in the HUD of the Prawn Suit or on the Thermal Plant), the Seabase needs to be close, or otherwise connected via Power Transmitters.

Prawn Suits can generate energy from heat using the Thermal Reactor upgrade (any source above 30°C), and the Seatruck will do the same using the Heat Recharging Upgrade

Fumaroles
Fumaroles are large volcanic structures found only in the Purple Vents biome. They can be seen bursting from their rocky shell and spewing a violet stream of smoke. Unlike most thermal structures in Below Zero, the Fumaroles will burn the player when they are close to them.

Hot Springs
Hot springs are flatbeds of water located all over the Delta Island. Some hot springs contain Crystalline Sulfurs lining their edges. When standing in a Hot Spring the player’s temperature increases.

Hydrothermal Spires
Hydrothermal Spires are a type of hydrothermal Vent chimney-like structures that emit black material resembling smoke. They are found commonly in the Thermal Spires and in lower number in the Tree Spires. They produce heat that can be harnessed for energy, but are not harmful to the player.

Hydrothermal Vents
are large, narrow thermal structures located in the Arctic Kelp Caves, Crystal Caves and Deep Twisty Bridges. The area around Hydrothermal Vents is generally charred, showing their extreme heat output. Many vents have nearby resources such as Diamond, Lithium, Magnetite, or Gold Outcrops. It is unknown what effect Hydrothermal Vents will have on the player in the future, but they will likely act similarly to geysers.

Lava Geysers
Lava Geysers are areas of the ocean floor that spew out lava and steam. Every few seconds, the craters erupt, throwing steam and chunks of lava into the water surrounding it. They can only be observed from a safe distance, as their eruptions will cause massive damage to the player. Even approaching the area near the geyser hurts the player due to the extreme amount of heat.

Steam Vents
Steam Vents are surface vents channeling gas out from underground pockets. The vents are only active for a few seconds at a time, and intermittently start and stop spewing gas. The player can use these vents to increase their Temperature by standing on or near them. As a bonus, they can also be used to launch the Snowfox in the air.

Thermal Lilys
Thermal Lilys are large Flora species found only on Delta Island, but will most likely be found in more locations in the future. When a player is not near them they remain dormant with their petals folded around their eyes. However, when the player approaches them, they will stare at the player which will heat them up. If the player is too close to the Thermal Lily, it will slowly burn the player.

Tree Spires
Tree Spires are large, heat sources that can be found exclusively in the Tree Spires biome and neighboring areas. They behave similarly to Hydrothermal Spires, creating a black smog as well as heat in the process, yet not being harmful to the player.