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Duplicant
This article has not been revised for the current version (U51-596666). It was last updated for U47-562984. It may contain inaccuracies.
This article has not been revised for the current version (U51-596666). It was last updated for U47-562984. It may contain inaccuracies.

Thermal Conductivity is the property of a material that determines how quickly it heats or cools as it comes into contact with objects of different temperatures. Although the game states that between two objects, the lowest thermal conductivity is used, this is not true for all cases.

Equations[ | ]

The calculation of Heat Transfer in is mainly a product of:

  • the Temperature difference in °C
  • the passing time, which is always one tick,
  • the applicable thermal conductivity in
    • is the lower of the two
    • is the geometric mean of the two:
    • the arithmetic average of the two:
    • the two multiplied together:

For heat transfer with buildings, there is an additional factor:

  • the thermal mass per area of the hotter object: where is mass, is specific heat capacity (SHC), is the area of the building/cell (1 for cells), and divide by 5 if the hotter object is a building.
Equations [1]
Scenario Formula
Cell ↔ adjacent Cell
Solid ↔ Solid
Solid ↔ Liquid
Gas ↔ Liquid
Gas ↔ Gas
Solid ↔ Gas
Liquid ↔ Liquid
Entity lying on a Solid
Building ↔ Solid tile below it
pipe ↔ adjacent pipe
Inside a Cell
Entity ↔ Cell
Building ↔ Cell
Building ↔ Building
Building ↔ Conduction Panel Use Building ↔ Cell but treat panel as a 100 kg cell and divide result by 11
Building ↔ Entity
Building's Contents
pipe ↔ pipe contents
Insulated pipe ↔ contents
pipe contents ↔ conduction panel (as the packet teleports across the panel)
Cell ↔ pipe contents : transfers through the pipe instead
pipe bridge ↔ bridge contents : bridges teleport elements, NO contents
Building ↔ building contents
Building's Cell of Interest ↔ building contents see Cell↔Entity


Thermal Element Categories
Category Examples
Cell Gas, Liquid, Solid Block, Tiles, closed Doors, Joint Plate (middle), Tube Crossing (middle), etc
Entity Dupes, Creatures, Plants, Debris, Mesh Tile, Airflow Tile, etc
Building pipes, bridges, background buildings, geysers, generators, open Doors, Pneumatic doors (open/closed), etc
Pipe Liquid Pipe, Gas Pipe, Conveyor Rail, Wires (all kinds), Automation Wire, and Automation Ribbons
Bridge Liquid, Gas, Conveyor Wire, Automation, and Automation Ribbons
Contents Building Production Storage (Input/Output), Reservoirs, Fridges, Compactors, etc
Special Tempshift Plate, Conduction panel, Refrigerator, Compost

Certain buildings apply a modifier to their material thermal conductivity:

  • Insulated Tiles: divide by (not correctly reflected under Properties)
  • Insulated Liquid Pipe and Insulated Gas Pipe: divide by 32
  • Wires of any kind: divide by 20 (this may be a legacy of a ditched feature making wires truly overheat)
  • Radiant Pipes, Radiant Gas Pipes and Conduction Panel: multiply by 2

a Tempshift Plate conducts as a building, and also conducts to all Cells in a 3x3 (centered on it)

a Conduction Panel is a (long) pipe

  • conducts as a building in its cells
  • specially conducts building ↔ building in its MIDDLE tile
  • conducts any elements passing through it via pipe ↔ pipe contents

A building's contents act like they are in the building's Cell of Interest, and exchange heat through the Cell↔Entity Equation.

  • Powered Refrigerator, or Compost act as a normal building. BUT the contents will only interact with an imagined 277.15K (fridge) or 348.15K (compost) source at a locked conductivity of 1000 regardless of their material.

Bridges act as a long building, conducting along its length.

  • You can stack multiple bridges to increase heat transfer along the cells
  • You can use bridges to help stabilize a Guide/Liquid Airlock from evaporation or sublimation.

Joint Plates, & Tube Crossings act as a Cell, the connection points on the sides are cosmetic (for thermal conductivity)

Insulated Tiles reduce the thermal conductivity of their building material by (2/255)² (or 16 256) instead of 100 as stated in the game. It also uses instead of for the purpose of cell to cell conductivity, which is mostly going to be the insulated tile conductivity. Solid to gas multiplier still applies.

Note: in real life, the units would cancel out, but surface area plays no role in ONI's calculation. Therefore, an additional meter needs to be multiplied to the product to have the equation result in DTU. (Not just meter, but a large string of units when calculating buildings.)

Another way to interpret this is that the units of Thermal Conductivity are given in-game as while the unit is actually interpreted as .

Recap of Cell to Cell multipliers
Gas Liquid Solid
Gas 1 1 25
Liquid 1 625 1
Solid 25 1 1

Because of the Gas to Solid x25 multiplier, it's recommended to add a double tiles layer or a thin liquid layer when trying to insulate two rooms, to instead get a x1 multiplier.

Limits of Heat Transfer[ | ]

Lower Limits[ | ]

Heat Transfer will not occur if:

  • the temperature difference is less than 1 °C
  • the calculated thermal flow is less than 0.1 DTU
  • either of the masses is less than 1g

Upper limits[ | ]

Heat Transfer between cells has the following cap:

  • If the calculated heat transfer would result in a temperature jump of more than a fourth of their temperature difference in either material.

    Simply said: if the temperature difference is 40 °C, a materials temperature can change at most 10 °C per tick

Building Limits[ | ]

Heat transfer between a building and a cell has different limits, the lower limits which are applied to cells do not apply to buildings, but the upper limit is conceptually similar.

A building exchanges heat with all cells it covers simultaneously. In order to ensure that thermodynamics will not be violated the game limits heat transfer per cell such that at most the final temperature of the building would be the equilibrium temperature, assuming that the building completely covers such cells:

The maximum permitted heat transfer per cell is the difference between the building's temperature and the equilibrium temperature divided by the Area of the building.

If the thermal mass of the cell is very large relative to the building, then the maximum temperature change can be approximated as simply

Floating Point Calculation Limits[ | ]

While the above limits are deliberately implemented, it is also possible for heat exchange to fail to happen due to limitations of the floating point calculations used to calculate temperature changes.

Internally ONI uses 32 bit floating point numbers to represent temperatures, and due to the limited precision of floating point numbers it is possible for the result of a floating point calculation to be the same number. For example with 32 bit floats, the calculation: 300.0 + 0.00001 = 300.0

The game has a rule that if either tile fails to change temperature, then no heat exchange is allowed to take place, this prevents an exploit where a large tile, especially an unnaturally large tile, infinitely dumps heat/cooling into a smaller tile without itself changing temperature.

In real games this limit comes up all the time when the temperature difference between an Insulated Tile and a solid or liquid tile is relatively small. For example an Igneous Rock Insulated Tile which is itself at 20 C, will not exchange heat with a solid or liquid tile unless the temperature delta is at least 248.05 C, and won't exchange heat with a gas tile unless the temperature delta is at least 9.92 C. This makes it quite easy to achieve actually zero heat transfer without resorting to the Insulation material or vacuum. The exact formulas governing this are: and , where , , and are for the cell holding everything constant, and is the heat-exchange formula relevant between the two cells, which can be reversed to find .

It is also readily observed with liquid tiles, Magma and Water can have immense thermal mass which means relatively large DTU inputs are required to cause a temperature change. This results in the paradoxical outcome where full magma tiles don't exchange heat with insulated tiles, but partial magma tiles can exchange heat if they are sufficiently low mass. Using the above formula but applied to the Magma tile instead of the insulated tile, we can see that a cell with 715.6 kg or more magma will be unable to exchange temperature with an Igneous Rock Insulated Tile at 0C or higher, regardless of the magma temperature. For Mafic Rock, which has half the conductivity, only 357.8 kg of magma are needed.

Suffice to say that while floating point imprecision sometimes causes heat exchange to not happen at all, when temperature changes are small it also causes the actual temperature change to deviate quite significantly from what higher precision calculations would suggest.

Thermal descriptors[ | ]

There are 4 thermal descriptors in the game, and they get attached to elements when their thermal characteristic reach a certain threshold. These descriptor does not affect the element any further.

  • Thermally Reactive: Elements have a specific Heat Capacity of less than or equal to 0.2
  • Slow heating: Elements have a specific Heat Capacity of greater than or equal to 1.0
  • Insulator: Elements have a thermal conductivity of less than or equal to 1.0
  • High Thermal Conductivity: Elements have a thermal conductivity of greater than or equal to 10.0

Pipes list[ | ]

Liquid Pipes[ | ]

Liquid Pipes
Pipe Material Thermal Conductivity
Insulated Liquid Pipe Insulated Liquid Pipe Insulation Insulation 0.0000003125
Liquid Pipe Liquid Pipe Insulation Insulation 0.00001
Insulated Liquid Pipe Insulated Liquid Pipe Ceramic Ceramic 0.019375
Insulated Liquid Pipe Insulated Liquid Pipe Obsidian Obsidian 0.0625
Insulated Liquid Pipe Insulated Liquid Pipe Igneous Rock Igneous Rock 0.0625
Insulated Liquid Pipe Insulated Liquid Pipe Sedimentary Rock Sedimentary Rock 0.0625
Insulated Liquid Pipe Insulated Liquid Pipe Sandstone Sandstone 0.090625
Insulated Liquid Pipe Insulated Liquid Pipe Granite Granite 0.1059375
Insulated Liquid Pipe Insulated Liquid Pipe Wolframite Wolframite 0.46875
Insulated Liquid Pipe Insulated Liquid Pipe Tungsten Tungsten 0.46875
Liquid Pipe Liquid Pipe Ceramic Ceramic 0.62
Liquid Pipe Liquid Pipe Obsidian Obsidian 2
Liquid Pipe Liquid Pipe Igneous Rock Igneous Rock 2
Liquid Pipe Liquid Pipe Sedimentary Rock Sedimentary Rock 2
Liquid Pipe Liquid Pipe Sandstone Sandstone 2.9
Liquid Pipe Liquid Pipe Granite Granite 3.39
Insulated Liquid Pipe Insulated Liquid Pipe Thermium Thermium 6.875
Liquid Pipe Liquid Pipe Wolframite Wolframite 15
Liquid Pipe Liquid Pipe Tungsten Tungsten 60
Radiant Liquid Pipe Radiant Liquid Pipe Lead Lead 70
Radiant Liquid Pipe Radiant Liquid Pipe Niobium Niobium 108
Radiant Liquid Pipe Radiant Liquid Pipe Steel Steel 108
Radiant Liquid Pipe Radiant Liquid Pipe Iron Iron 110
Radiant Liquid Pipe Radiant Liquid Pipe Copper Copper 120
Radiant Liquid Pipe Radiant Liquid Pipe Tungsten Tungsten 120
Radiant Liquid Pipe Radiant Liquid Pipe Gold Gold 120
Radiant Liquid Pipe Radiant Liquid Pipe Cobalt Cobalt This content is available in Spaced Out (DLC) 200
Liquid Pipe Liquid Pipe Thermium Thermium 220
Radiant Liquid Pipe Radiant Liquid Pipe Aluminum Aluminum 410
Radiant Liquid Pipe Radiant Liquid Pipe Thermium Thermium 440

Gas Pipes[ | ]

Gas Pipes
Pipe Material Thermal Conductivity
Insulated Gas Pipe Insulated Gas Pipe Insulation Insulation 0.0000003125
Gas Pipe Gas Pipe Insulation Insulation 0.00001
Insulated Gas Pipe Insulated Gas Pipe Ceramic Ceramic 0.019375
Insulated Gas Pipe Insulated Gas Pipe Mafic Rock Mafic Rock 0.03125
Insulated Gas Pipe Insulated Gas Pipe Obsidian Obsidian 0.0625
Insulated Gas Pipe Insulated Gas Pipe Igneous Rock Igneous Rock 0.0625
Insulated Gas Pipe Insulated Gas Pipe Sedimentary Rock Sedimentary Rock 0.0625
Insulated Gas Pipe Insulated Gas Pipe Sandstone Sandstone 0.090625
Insulated Gas Pipe Insulated Gas Pipe Granite Granite 0.1059375
Gas Pipe Gas Pipe Ceramic Ceramic 0.62
Gas Pipe Gas Pipe Mafic Rock Mafic Rock 1
Gas Pipe Gas Pipe Obsidian Obsidian 2
Gas Pipe Gas Pipe Igneous Rock Igneous Rock 2
Gas Pipe Gas Pipe Sedimentary Rock Sedimentary Rock 2
Gas Pipe Gas Pipe Sandstone Sandstone 2.9
Gas Pipe Gas Pipe Granite Granite 3.39
Radiant Gas Pipe Radiant Gas Pipe Gold Amalgam Gold Amalgam 4
Radiant Gas Pipe Radiant Gas Pipe Iron Ore Iron Ore 8
Radiant Gas Pipe Radiant Gas Pipe Cobalt Ore Cobalt OreThis content is available in Spaced Out (DLC) 8
Radiant Gas Pipe Radiant Gas Pipe Copper Ore Copper Ore 9
Radiant Gas Pipe Radiant Gas Pipe Pyrite Pyrite 9
Radiant Gas Pipe Radiant Gas Pipe Wolframite Wolframite 30
Radiant Gas Pipe Radiant Gas Pipe Aluminum Ore Aluminum Ore 41
Radiant Gas Pipe Radiant Gas Pipe Niobium Niobium 108
Radiant Gas Pipe Radiant Gas Pipe Steel Steel 108
Radiant Gas Pipe Radiant Gas Pipe Thermium Thermium 440

Solid Tiles list[ | ]

Important: For Insulated Tiles, these numbers will not match what is seen in-game. This is because the value displayed in-game is , but the actual value used by calculations (and shown here) is .

Tiles
Tile Material Thermal Conductivity
Insulated Tile Insulated Tile Insulation Insulation 6.15e-10
Tile Tile
Carpeted Tile Carpeted Tile
Insulation Insulation 0.00001
Insulated Tile Insulated Tile Ceramic Ceramic 0.0000381
Insulated Tile Insulated Tile Mafic Rock Mafic Rock 0.0000615
Insulated Tile Insulated Tile Fossil Fossil 0.000123
Insulated Tile Insulated Tile Igneous Rock Igneous Rock 0.000123
Insulated Tile Insulated Tile Obsidian Obsidian 0.000123
Insulated Tile Insulated Tile Sedimentary Rock Sedimentary Rock 0.000123
Insulated Tile Insulated Tile Sandstone Sandstone 0.000178
Insulated Tile Insulated Tile Granite Granite 0.000209
Plastic Tile Plastic Tile Plastic Plastic 0.150
Plastic Tile Plastic Tile Solid Visco-Gel Solid Visco-Gel 0.450
Tile Tile
Carpeted Tile Carpeted Tile
Ceramic Ceramic 0.620
Window Tile Window Tile Glass Glass 1.110
Tile Tile
Carpeted Tile Carpeted Tile
Mafic Rock Mafic Rock 1.000
Tile Tile
Carpeted Tile Carpeted Tile
Fossil Fossil 2.000
Tile Tile
Carpeted Tile Carpeted Tile
Igneous Rock Igneous Rock 2.000
Tile Tile
Carpeted Tile Carpeted Tile
Obsidian Obsidian 2.000
Tile Tile
Carpeted Tile Carpeted Tile
Sedimentary Rock Sedimentary Rock 2.000
Tile Tile
Carpeted Tile Carpeted Tile
Sandstone Sandstone 2.900
Tile Tile
Carpeted Tile Carpeted Tile
Granite Granite 3.390
Metal Tile Metal Tile Depleted Uranium Depleted Uranium This content is available in Spaced Out (DLC) 20.000
Metal Tile Metal Tile Lead Lead 35.000
Metal Tile Metal Tile
Bunker Tile Bunker Tile
Steel Steel 54.000
Metal Tile Metal Tile Niobium Niobium 54.000
Metal Tile Metal Tile Iron Iron 55.000
Metal Tile Metal Tile Copper Copper 60.000
Metal Tile Metal Tile Gold Gold 60.000
Metal Tile Metal Tile Tungsten Tungsten 60.000
Window Tile Window Tile Diamond Diamond 80.000
Metal Tile Metal Tile Cobalt Cobalt This content is available in Spaced Out (DLC) 100.000
Metal Tile Metal Tile Aluminum Aluminum 205.000
Metal Tile Metal Tile Thermium Thermium 220.000

Tips[ | ]

  • When cooling or heating an area it's better to run pipes through tiles than through atmosphere. In both cases the equation for "Building and the cells it occupies" is used which multiplies both Thermal conductivities, and in general, gases have a much lower thermal conductivity than liquids, which have lower conductivity than solids.
    • However, if drastic cooling is desired, then Steam Turbines and Aquatuners will have to be involved, which means a cavity filled with Steam will have to be used.
  • Since Insulated Tiles have a factor of 1/16256, and pipes a factor of 1/32, much less heat is transferred if a regular pipe goes through an insulated tile than when an insulated pipe goes through a regular Tile. Though, of course, insulating both has an even better insulating effect.
  • Even though Insulation has a lower thermal conductivity than any Insulated Tile, the change in formula from to makes insulated tiles much more practical insulators than a regular Tile made from insulation. Indeed, they are so good that even using regular rock is often sufficient to shut down heat transfer completely, or to practically unnoticeable levels.

References[ | ]

https://forums.kleientertainment.com/forums/topic/84275-decrypting-heat-transfer/

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