Temperature

Temperature management is an important part of a productive colony. Temperature mostly affects pawn mood, food and corpse spoilage, and plant growth. In some biomes outdoor temperature can reach deadly highs, lows, or both depending on the season - pawns must wear appropriate clothing to survive long periods of time outdoors. Temperature also plays a major role and is affected by many things in world generation. Extreme cold or heat can even kill animals, and extreme heat can cause and sustain fires.

Celsius vs. Farenheit display

Under Options, players can choose the in-game display to show Celsius (°C) or Farenheit (°F) (or Kelvin (°K), if they prefer), and the game will display the current temperature as an integer (a "whole number") in your chosen temperature scale. However, the game code uses Celsius for all temperatures and trigger points, and will round the Celsius reading to give you a "non fractional" temperature reading in Farenheit (Kelvin is 1:1 re Celsius so has no unpredictable rounding problems). Thresholds for such things as thoughts for "too hot" or "too cold", for hypothermia or heatstroke, for the allowed temperatures for brewing beer, all are set in the game code in Celsius, and Celsius does not usually translate to a neat integer in Farenheit, despite being displayed as such.

This Wiki will list values in both Celsius and Farenheit, with the latter often showing a "tenths" decimal place that is not displayed in-game.* Understand that if you are using Farenheit and are paying very close attention, you might see some small apparent hiccups, as the value that appears in your display potentially has a very small (less than .3°F) error in it from that rounding. If you are close to a dangerous cutpoint, keep that in mind; if you want reliable temperature values (and especially if you are modding!), use Celsius.

(* Kelvin users can add +273.15° to the listed Celsius value and go from there; if you're using Kelvin, you probably don't need our help for that.)

Basics

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.

Extreme temperature has three potential effects that can harm or help a colony. The first, and often the one first observed, is on food, either preserving it (with cool/cold weather) or causing it to spoil faster (with warm/hot weather). The second is on living creatures. Each species has a "comfortable temperature range" (listed on its information page), including humans (16°C – 26°C / 60.8°F – 78.8°F). Any hotter or colder, and they will complain and get a bad mood, and visiting (or raiding) humans may decide to leave if temperatures grow too hot or cold. With extremes most any creature can suffer from heat stroke, or hypothermia or even frostbite, as appropriate. Animals can die as well, although they are hardier, but wild animals will tend to leave the map if temperatures move too far outside their "comfortable" range. The third is on plants, which will slow their growing in cold weather, and will die in extremely hot or freezing weather.

Food

Warm temperatures rot food and corpses, the hotter the faster, and even "durable" foods like corn and rice can eventually rot away. Cooler temperatures preserve food and corpses by slowing spoilage. Freezing temperatures stop spoilage entirely and preserve these items indefinitely.

One of the first short term projects that many players set for themselves is to construct a small dedicated freezer room (or a cool-temperature room if Tribal), and one of the important long-term projects for Tribal starts is electricity, for the ability to cool foods to avoid spoilage and avoid living hand to mouth.

Creatures

Clothing modifies the temperatures that cause heatstroke or hypothermia on humans, and can avoid various mood debuffs from uncomfortable temperatures. Clothing subtracts/adds directly to the coldest/hottest "comfortable temperature" that a colonist can tolerate (and these values are listed in tables under any specific clothing item). For example, items like cowboy hats and dusters can help keep a colonist cool by increasing their maximum comfortable heat limit, so they can tolerate brutal summer heat. When faced with temperature extremes, colonists automatically search for and equip any suitable clothing they can find in storage.

However, colonists' moods ignore clothing when sleeping, becoming unhappy in a mildly cold or hot bedroom. So, piling on the warmest clothing doesn't avoid a "slept in the cold" bad thought if a bedroom is not adequately heated.

See heat stroke, hypothermia amd frostbite for a full discussion on the mechanics of those ailments.

Extreme temperatures can have an effect on visitors as well. Trade caravans and raiders alike will leave if temperatures are too extreme, and allies will refuse requests to send troops. Similarly, wild animals may simply exit the map, and new ones will only migrate back slowly once temperatures return to within the comfortable range for their species.

If 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.

Crops

All biomes have a listed "growing season" - some are very short (or, in extreme cold, non-existent) and others are "year round". Many players pick their starting location based on this, seeking at least a long if not year-round location.

However, "year round" 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", and 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.

Buildings

All locations have their own temperature which can be seen in the right-hand margin of the screen by mousing over any area. By default, most* everything is "outdoors" temperature. A building must be completely walled to start to have a different temperature than "outdoors", and any missing roof will have a strong (but not necessarily absolute) effect as well.

(* Mining into mountains and finding "overhead mountain" can create areas with a stable, cool default temperature, but there are downsides to relying on such deep mountain rooms.)

Indoor temperature can be managed through structures found in the "Temperature" menu. Keep in mind that heat transfers between rooms and also the outside through roofs, walls, and doors. Large temperature differences, open doors, open roofs, and rooms with long walls adjacent to the outside or to "thin roof" solid mountain tiles can make temperature hard to regulate. Larger rooms have more thermal "mass", and their temperature changes more slowly than smaller rooms.

Temperature/heat transfer inside a room is instantaneous regardless of room size. This means long hallways can be used to transfer heat or cooling easily through a large base, using vents to share most of that temperature into side rooms.

Double thick walls and intermediate rooms act as an insulator and slow heat transfer - try using a hallway or storage room to protect bedrooms and work rooms from temperature extremes. Any room that borders an outdoors area transfers more heat, and will usually be closer to outdoor temperature, even if the room borders solid rock.

Try not to build long thin hallways connecting with the outdoors, or leave large solid rock clusters inside your base. This will increase your surface area to outdoor temperature and make indoor temperature more difficult to manage. Cut off outside hallways using doors and mine rock until all traces of outdoor area are gone.

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.

Note: When adding coolers/heaters, it's important to know that a structure will always share the "outside" temperature until it is fully "indoors" (which usually means walls and/or doors). Adding coolers/heaters before this is fine, but they will not start to change the temperature until the area is defined as "indoors".

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 to not inconvenience your colony.

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. Example: In a realistic setup, this means it can cool 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 60 °C (140 °F) can be cooled down to comfortable 24 °C (75.2 °F) or something near that with a single cooler.

Freezer

A freezer is the most straightforward use of coolers for a starting colony. 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. Select the cooler temperature settings and reduce their target temperature so that they continue running 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 32, and the other at 30. 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.

Also, put a battery (or three) nearby on a power switch, close enough to connect to your coolers (6 tiles), but kept off your power grid once charged, on standby. If you have a power problem, you can immediately click "reconnect" on your coolers, which will take power directly from the batter (no power conduit needed), keeping your freezer frosty until you can fix the power problem.

Freezer Tips

Building freezers that can tolerate extreme heat, due to the biome or heat waves, can be challenging. The type of material used to build the walls does not matter because they all have the same insulation values. However, increasing the walls from 1-thick to 2-thick dramatically improves the insulation, but thickness beyond 2-thick does not have a noticeable effect. Never block a cooler's intake or exhaust port or else it won't function.

Freezers lose a great deal of cooling through doors as pawns open them. 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.

The hot end of the Cooler is useful for climates where the temperature rarely gets above 20 °C (68 °F) and almost never above 30 °C (86 °F). Instead of pointing the freezer's hot end outside, point it directly into your base. This will increase your energy efficiency and may save a few components on Heaters.

Adding coolers

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.

Passive cooler

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The passive cooler is a very low-tech option automatically unlocked for tribal starts. They operate at the same strength as a Cooler and will cool rooms to a very comfortable 15 °C (59 °F) for 5 days. It needs to be fueled when it runs out of fuel.

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.

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.

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).

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.

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 flicking.

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.

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 outdoors for exterior doors. Equalization through open doors is less potent than vents.

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.

Extreme Temperature Effects

A heat wave near the equator in a hot season (and equators have two of those) can top 60^oC / 140^oF, which is bad enough. But things can get much, much worse...

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. The gear tab also shows aggregate stats about comfy temperatures.

There is an orange glow when hovering over very hot areas to help you identify them. In these areas, it is so hot that flammable objects will spontaneously catch fire, and pawns will be burnt by superheated air.

On pawns

Temperatures below a pawn's minimum comfortable temperature or above their maximum comfortable temperature will cause them discomfort with mood debuffs and in extreme cases can cause ailments and even death. A pawn will be happy within the range set by their minimum and maximum comfortable temperatures, and safe within 10°C of them. Beyond that, there is a risk of heatstroke or hypothermia. Insectoids do not suffer from hypothermia, and instead get hypothermic slowdown. At very extreme temperatures^{How extreme?}, there is the risk of spontaneous burns and frostbite.

Note that human pawns will also get a mood debuff for "Slept in the Cold/Heat" any time they sleep in an area outside their natural, i.e. before clothing, range of 16 °C (60.8 °F) to 26 °C (78.8 °F) - this occurs regardless of the apparel they wear.

The simple cure for any afflicted colonist is to return them to a normal temperature environment. This process can be sped up by forcing the colonist into the opposite extreme, such as putting heatstroke victims in a freezer to cool off.

Ailments include:

Heatstroke - caused by prolonged exposure to heat.
Burns - caused by exposure to extreme heat or contact with fire.
Hypothermia - caused by prolonged exposure to cold.
Frostbite - injury to extremities caused by prolonged exposure to cold.

On objects

Objects such as wooden structures and furniture will ignite once they reach a high enough temperature, 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.

Extreme cold has no negative effect on objects; most food and plant matter items spoil depending on temperature, and become refrigerated at temperatures below 10 °C (50 °F), slowing down the spoiling process. When temperature reaches freezing (0 °C (32 °F)), they become frozen and completely stop spoiling.

Fertilized eggs can become "ruined by temperature" in either moderately hot or cold environments. They are still usable as food, however no animal will hatch from them.

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.

For example, the highest and lowest temperature pawns can survive is way above and below the temperature for plant growth and the temperature range of most workbenches. In extreme heat, even the spontaneous Combustion of Building Material becomes an issue.

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 multiplied by a factor equal to 10 divided by the temperature in Celsius
9 °C (48.2 °F)	Food spoiling rate divided by a factor of 1.11.
8 °C (46.4 °F)	Food spoiling rate divided by a factor of 1.25.
7 °C (44.6 °F)	Food spoiling rate divided by a factor of 1.43.
6 °C (42.8 °F)	Food spoiling rate divided by a factor of 1.66.
5 °C (41 °F)	Food spoiling rate divided by a factor of 2. Bad temperature bench modifier
4 °C (39.2 °F)	Food spoiling rate divided by a factor of 2.5.
3 °C (37.4 °F)	Food spoiling rate divided by a factor of 3.33.
2 °C (35.6 °F)	Food spoiling rate divided by a factor of 5.
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.
-273 °C (-459.4 °F)	Minimum value.

Room Temperature Mechanics

Temperature mechanics

Equalisation calculations happens once every 120 game ticks.

All internal calculations are done in celsius. Fahrenheit is simply a different way to display the same absolute value.

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

Outside

Spaces that are not enclosed are simply considered "outside". The outside temperature is defined entirely by the climate and storyteller. No amount of heat adding/removing can change it, not even the Mod Tools can change it by simply adding/removing heat to the outdoor "room" - unless they set it for the entire map, nothing will happen. Proximity to heatsources does not matter. Instead the "outside" value is used.

Despite this "outdoor" is still used like any other neighbouring room for wall equalisation. And often the most important room for that matter.

Rooms can be in one of 3 states:

Unroofed (not a single roof tile). This means it will simply use outdoor temperatures. It does still count as a "room" for most game mechanics, but for temperature mechanics every active tick it will set to outdoors temperature regardless of difference.
fully roofed (all tiles in the room have a roof tile). These rooms are entirely subject to heating, cooling and temperature equalisation
partially roofed (uses outdoor temperature) while this room seems to maintain temperature while paused, the next equalisation tick will simply set it to outdoor temperature as a fully unroof one
partially roofed (not use outdoor temperature) While there will be significant equalisation via the (lack of) roof, the room still has its own temperature calculation. The exact flipover point between this and "uses outdoor" is not static and seems to change with roomsizes. Possibly something based on the summed "no roof equalisation" value. < 1/4 of all roof tiles seems to be the limit.

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