Temperature

Players can switch the in game display to Celsius (°C), Farenheit (°F), or Kelvin (°K). This Wiki will list values in both Celsius and Farenheit. Kelvin is the same as the Celsius scale, but shifted by +273.15° - if you have a desire to use Kelvin, you probably don't need help with it.

Internally, the game uses Celsius (°C) for all temperature functions, such as "too hot" or too "cold". As the game always rounds temperature to an integer ("whole number"), you can get a misleading indicator while using Farenheit. This normally isn't big, around 0.3°F. But if you want reliable temperature values, and especially if you are modding, use Celsius or Kelvin.

Temperature Changes

Outdoor temperature usually fluctuates slowly by day and season and is bounded by the climate of your biome. Be careful though, because unpredictable events like a cold snap, volcanic winter or heat wave can also change outdoor temperature unexpectedly. No amount of added heat, even with modding tools, will affect or change the outdoor temperature. Otherwise, the outdoors is simply treated as another room, albeit a large one.

The maximum temperature is 1,000 °C (1,832 °F) and the minimum is -270 °C (-454 °F), very close to absolute zero. The minimum temperature is not encountered during normal unmodded gameplay, but fires in small enclosed spaces can reach the maximum temperature.

Any place enclosed by walls and other structures are considered indoors. Rooms that are Unroofed - no or minimal roof tiles - are considered outdoors in regards to temperature, and unable to be changed from outdoor temperatures. Rooms that are fully roofed are entirely subject to heat changes, and removing roof tiles will quickly equalize temperature with the outside. The exact flipover point between this and "uses outdoor" is not static and seems to change with room size.

Heat Transfer Between Rooms

Temperature change within a room is instant.

Heat will also transfer from enclosed rooms to other rooms, and the outside. Heat travels through roofs, walls, and doors. Open doors and roofs will quickly "equalize" temperature to the outside. eat transfer only occurs in cardinal directions. Thus the corners of rooms can be eliminated without negatively affecting the insulation of a room. Adding another layer of walls increases insultation, but only up to 2 layers of wall. Gaps between each layer will decrease insulation, but stil have an effect.

Larger rooms have more thermal "mass", and their temperature changes more slowly than smaller rooms, but temperature equalization with the outside is proportional with a room's perimeter. A square (shape with the most volume/perimeter) will lose heat slower than thin, rectangular hallways. Rooms with more wall tiles exposed to the outside will lose temperature faster.

See Temperature#Temperature mechanics for more details.

Functions

Unsuitable temperature will cause food to spoil, plants to rot, and pawns to die, or at least feel uncomfortable.

On Crops

All biomes have a listed growing season. Some are very short (or, in extreme cold, non-existent) and others are "year round". Colonists avoid planting outdoors if it isn't growing season. Many players pick their starting location based on this, with year round being the easiest option.

However, a year round climate is no guarantee of trouble-free farming experience. Just getting close to freezing will slow plant growth, reducing the output of crops. More, climates that do not freeze tend to get very hot in the summer season, hot enough to kill crops in some instances. In Rimworld, even equatorial locations have a "winter". Cold snaps can drop the temperatures below freezing for short periods - but long enough to, again, kill crops.

The short-term solution is to immediately harvest everything to save what you can. The long-term solution is some sort of greenhouse, making use of temperature controlled indoor structures, walled and roofed, with heaters, coolers, sun lamps, and possibly hydroponics.

On Food

Warm temperatures rot food and corpses, the hotter the faster, and even "durable" foods like corn and rice will eventually rot away. Colder temperatures preserve food and corpses by slowing spoilage. Freezing temperatures stop spoilage entirely and preserve these items indefinitely. Coolers will preserve food, so colonists starting with Electricity will quickly want to build a dedicated room.

Fertillized eggs will "ruined by temperature" outside of its comfortable range of 0 °C – 50 °C (32 °F – 122 °F). "Ruined" eggs may still be eaten as normal, but won't hatch into an animal.

Deterioration is an entirely different mechanic, and items left outside will lose health regardless of temperature. Rotting doesn't effect the health stat of an item.

On Creatures

Pawns have a Maximum Comfortable Temperature and Minimum Comfortable Temperature. Going over 10 °C (50 °F) beyond these limits will start giving them heatstroke or hypothermia. Too hot or cold will cause burns or frostbite over time. Insectoids will instead experience hypothermic slowdown. Pawns will also recieve negative mood]lets based on how extreme the temperature is. The Gear tab shows aggregate stats about comfy temperatures.

For humans, clothing will increase both comfortable thresholds, depending on the clothing type and material. Colonists will try and wear items suitable for the temperature, unless they are forced otherwise. Colonists' moods ignore clothing when considering Slept in the Cold/Heat. So piling on the warmest clothing doesn't avoid a "slept in the cold" bad thought if a bedroom is not adequately heated.

Animals tend to have much higher comfortable thresholds. However, in extreme biomes, it may be necessary to build a "barn" of some sort with temperature control and designate indoor animal sleeping spots to keep your herd warm/cool.

Fire

Temperatures above 235 °C (455 °F) will ignite flammable items and structures, depending on their material's flammability. All stone types and uranium have their flammability set to 0% and therefore objects made from them will not ignite or burn in any temperature. Steel, plasteel, silver, gold and jade are flammable as materials, but not as items.

Managing Temperature

Temperature management is important for any colony, regardless of climate. It can be simply managed with a good power supply and the following structures. Temperature changing buildings will still work while "outdoors", but have no noticable effect.

Temperature Thresholds

It is important to know where Temperature might become an issue. Often multiple aspects have to be considered with Temperature: Pawn Limits, Sleeping Pawn Limits (which exclude clothing values), Workbench Limits, Plant Limits.

Temperature	Effects
1,000 °C (1,832 °F)	Maximum value
~235 °C (455 °F)	Items spontaneously catch fire
50 °C (122 °F)	Animals max temperature
44 °C (111.2 °F)	Plant growth slowed
30 °C (86 °F)	Campfire max temperature
26 °C (78.8 °F)	Default human upper comfort limit
21 °C (69.8 °F)	Heater and Cooler default target
17 °C (62.6 °F)	Passive cooler min temperature
16 °C (60.8 °F)	Default human lower comfort limit
10 °C (50 °F)	Below this value plant growth and food spoiling slowed. Food spoiling is divided a factor of (10-Temp)/10, in Celsius.
5 °C (41 °F)	Food spoiling rate divided by a factor of 2. Bad temperature bench modifier
1 °C (33.8 °F)	Food spoiling rate divided by a factor of 10.
0 °C (32 °F)	Plant growth and food spoiling stopped.
-10 °C (14 °F)	Most plants die.
-270 °C (-454 °F)	Minimum value.

Cooling Buildings

Passive cooler

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The passive cooler is a very low-tech option automatically unlocked for all default starts. They operate at the same strength as a Cooler and will cool rooms to a very comfortable 15 °C (59 °F). Passive coolers last for 5 days; it needs to be fueled with wood when it runs out of fuel. Due to the temperature limit, passive coolers are unable to preserve food.

Passive coolers are a life saver in extremely hot climates as they can be quickly built, are immune to electrical events and are easily massed in a heat wave. Use passive coolers to keep your living spaces survivable and chill rooms surrounding a freezer to further protect the products inside.

Cooler

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The cooler is primarily used to lower the temperature of a room. It has two states of power consumption: low and high. In its low state, the cooler produces no heat or cold but still requires 20 W. It can be used to lower the temperature of a room to a comfortable 20 °C (68 °F) (room temperature) in the summer or create a walk-in freezer for your food. In hot biomes such as desert or rainforest, having comfortable air conditioning is a necessity for any base.

Coolers are heat pumps that produce both a cold side and a hot side. The hot side is rarely useful and should be directed to an outdoor space (or a 1x1, unroofed room) to not inconvenience your colony. The heating side is useful when outdoors temperature is uncomfortable, but not freezing. This is between 1 °C – 16 °C (33.8 °F – 60.8 °F), but in practical terms, you should point the heat side at the colony when the outdoors temperature rarely goes above 20 °C (68 °F). Never block a cooler's intake or exhaust port, or else it won't function.

A cooler is theoretically able to cool a single square by about 1800 kelvin [K]. But this is not a linear relation, as a room always exchanges heat with adjacent rooms and/or the outside.

Analysis

Electric coolers are the only way to create freezers. Building one is as simple as making a room and replacing some wall tiles with coolers. Direct the cold "blue" zone of the cooler inside the room and the hot "red" tile to an outdoor area. Reduce the cooler's target temperature to below 0 °C (32 °F). As the room cools down any food left inside will decay more slowly until it freezes. Frozen food will stay fresh indefinitely and incurs no other benefit or penalty when eaten.

If your freezer area is more than about 50 squares, and/or you are living in an area with a hot summer, you will want 2 coolers (and perhaps more, see "adding coolers", below). Put one at 0, and the other at -2. With double walls, this will let one cooler "idle" at 20 W of power in cooler weather while the other easily keeps things frozen, but be available to help when needed for warmer weather. Batteries are useful for power outages; you may want to keep charged batteries disconnected via power switch for these situations.

Freezers lose heat through walls and doors. The material of a wall doesn't matter, but for maximum insultation, you should put a double layer of them. Doors will cause heat loss when opened. This loss can be offset by having doors arranged in sequence, one after another, at points of egress, in an "airlock" like fashion. The loss can be examined by mousing over the sections of the airlock to see the temperature. Using doors rather than autodoors can help reduce the cooling lost, though this slows down colonists.

Adding Heat

There may come a moment when you realize "I don't have enough coolers for this area...". If the weather is cool, that's not a big problem, but it's more likely that the weather will be brutally hot when you realize this. And it's also likely that it's your freezer that's not at "freezing" (since colonists can tough it out). If you open a wall to put in an additional cooler, your freezer immediately rockets to "outside" temperatures - which is probably a dealbreaker, rotting all your frozen items. So here's what you do...

Decide where in the current wall you will put your new cooler, and build a door outside where you will tear the existing wall down (you don't need "side walls" to support it). (A wall would "block" the cooler exhaust and prohibit construction, but a door will not!) Then, [f]orbid the door (so it doesn't get opened), and deconstruct your wall; the new door will maintain the area as "inside". Then build your cooler (remembering the orientation, warm side "out"). Once the new cooler has been installed, deconstruct the door, and you're done.

Heating Buildings

Campfire

Campfires are a quick and dirty solution to produce heat in a hurry. They require no energy, but are temporary structures and must be refreshed with wood every few days. Otherwise, they produce the same amount of heat as an electrical heater. They cannot raise the temperature to over 30 °C (86 °F). They can't be controlled, so may make pawns uncomfortably hot - open doors or roofs to lower heat..

Heater

The heater is used to raise the temperature of a room. It has two states of power consumption: low and high. In its low state, the heater produces no heat but still requires 18 W. It can be used to raise the temperature of a room to a likable 20 °C (68 °F) (room temperature) in the winter or create a walk-in heat trap for your foes. In any cold biome, such as the Tundra, the heater is a necessity for any base.

A heater (in theory) is able to heat a single square by about 1800 kelvin [K]. But this is not a linear relation as a room always exchanges heat with adjacent rooms and/or the outside. This heat conduction effect can be pretty noticeable in extremely cold or hot environments. Example: In a realistic setup, this means it can heat a room with 50 squares by an average of about 36 K per square. So a room with 50 squares and an outside temperature of -10 °C (14 °F) can be heated up to comfortable 26 °C (78.8 °F) or something near that with a single heater.

Incidental Heat

Generators

Generators produce a non-negligible amount of heat for the room they occupy, especially when placed in numbers. If placed strategically, you can reduce the number of heaters and coolers necessary to manage the temperature in your base.

It's also worth noting that generators will continue to produce heat (and burn fuel) during solar flare events. If your colony is in a very cold climate, this can be used to ensure that critical sections such as hydroponics or barns for sensitive animals don't lose all their heat in a power outage.

Steam Geysers

A steam geyser will heat up a roofed room even when covered with a geothermal generator. They are extremely useful for staying warm in frozen climates, but can overheat an indoors space in warmer biomes.

Fire Weapons

Weapons that generate fire such as Molotov cocktail and Incendiary launcher can be used to quickly generate heat inside your colony. Under normal conditions this is a bad idea because fires will quickly bring your base to intolerable temperatures. However in a bitter arctic climate with no wood and inadequate heaters, these weapons are your last defense against freezing to death. Draft your colonist and force them to open fire on an empty space, or burn spare corpses and rags to increase heat output.

Solar Pinhole

Solar pinhole is a psycast that creates heat and light. It lasts five days. It is useful for emergency situations, such as power shortages during cold snaps.

Heat Transfer

Vent

A vent allows transfer of temperature and gases from one room to another.

Vents can have any building in front of it, but no walls. Vents work best when connecting directly to a climate controlled room. Trying to chain vents across smaller rooms will lead to each successive room getting less effective climate control, and connecting to a hallway won't work well if the hallway is blocked with doors. A vent can be designated to be closed, an action carried out by colonists assigned to Basic.

Doors

Similar to double thick walls, double doors (not side-by-side, rather, both in the path of travel) improve insulation and reduce temperature equalization. A door can be left permanently open (mark the door to 'hold open' and have a pawn pass through) to help control temperature. Open doors allow temperature to more quickly equalize between rooms or the outdoors. Equalization through open doors is less potent than vents.

Temperature mechanics

Equalisation calculations happens once every 120 game ticks.

Temperature seems to be measured to an extreme precision. A outdoor of -9 °C (15.8 °F) and a room of 2,000 °C (3,632 °F) have a difference around -9555.292C

Passive Equalisation

This is equalisation via walls and roofs.

Walls will equalize towards the room on the other side. This can be another fully realized room or simply the outdoors. If the other side is not outdoors, that room will also equalize towards this room.

The material of the walls does not matter. Wood is as isolating as any stone or metal. And unmined rocks are equally effective.
The surface area does seem to matter. Basically, the game is using a 2D variant of the square-cube law, with walls taking the place of "surface area" and room size taking the place of "volume". As such square rooms are the most efficient at keeping temperatures.
A 2nd layer halves the temperature equalisation via walls. Adding more than a 2nd layer of wall does not seems to have any effect.
Furniture acts highly variable for this and even just the definition what is a room. Nutrient dispensers are one of the few items working fully like walls for equalisation purposes

Example wall equalisation values at -9555.208C difference:

1x1: -161.470°C
2x2: -81.235°C
3x3: -54.157°C
4x4: -40.618°C
5x5: -32.494°C
6x6: -27.078°C
7x7: -23.210°C

Example double wall equalisation values at -9555.208C difference:

1x1: -81.234°C
2x2: -40.617°C
3x3: -27.078°C
4x4: -20.309°C
5x5: -16.247°C
6x6: -13.539°C
7x7: -11.605°C

Roof is a major part with equalisation with the outdoor temperature. It will always equalize with the outdoor temperature, regardless what the room borders. However, the equalisation rate is also constant for all room sizes at the same temperature difference. There are 4 basic types of roof:

unroofed
Constructed (Thin Roof)
Thin Rock (Thin Roof)
Thick Rock

Thin Roof at a difference of -9555.208C it is -57.331°C.
unroofed tiles are looked at in relation to the total count of roofed tiles. With at least 1/4 unroofed the room will simply equalize to outdoor temperature on the next tick.
thick roof isolate the same as thin roof. However, they also add a cooling effect if indoor temperature is above about 15 °C (59 °F); this effect is extremely small compared to other sources, however

Active Equalisation

While Vents, Coolers and open doors still keep rooms separated, they also equalize temperature at a very high rate. This rate is unfortunately not shown on any tooltip.

Torches, Campfires, Heaters and Passive coolers will directly modify the room temperature instead, adding/removing heat every equalisation tick as appropriate for their settings/current state.

Architect

Temperature: Campfire • Heater • Cooler • Passive cooler • Vent