How heat behaves
Conduction, thermal mass, and why the wall matters.
Not a task — the behaviour every task on this site rests on. If you understand this page, the smelting and coking pages stop being recipes to follow and start being obvious.
Every cell in the world carries a temperature, including air. Heat moves between neighbours, and what each material does at what temperature is on its own page.
Conduction is a property of the destination
Each material has a number for how readily heat crosses into it. It runs from 0 to 255 and it is the single most important number for anything you build around a fire.
Air is deliberately low, or a fire would flash-heat a whole room.
That table explains the single commonest failure in this game: what you build a wall out of decides whether the thing behind it ever gets hot. An iron wall cooks what is behind it. A refractory wall is designed not to — it is furnace lining, and its whole job is keeping heat away from what is on the other side. Line a retort with it and the retort sits cold while the fire roars.
Refractory is not a better wall. It is an opposite wall, and it is right when you want to contain heat and wrong when you want to transmit it.
Thermal mass is a separate axis
A second number says how much heat a material holds, as a doubling: 2×, 4×, 8×. It is not the same thing as conduction, and separating them is what lets lava heat everything it touches at full rate while staying molten for a long time.
Practically: something with high thermal mass stays hot long after you stop heating it. Coke holds 4×, which is part of why a coke bed is worth building.
Temperature decides what a material is
Materials change into other materials at thresholds. There are four kinds, and every material page lists whichever it has:
- Ignites at — it catches fire and becomes something burning
- Melts or boils at — it becomes a liquid or a gas
- Freezes or sets below — the reverse
- Decays — it falls apart over time, regardless of heat
The melting and setting points are deliberately not the same number. Molten iron appears at 190 °C and does not set until it drops below 160 °C, so it keeps flowing for a while after you stop heating it. Every chain like this is walkable by clicking, from any material page.
A fire is a material, not an effect
This is the thing that makes the simulation make sense. Fire, embers and lava are materials with temperatures, sitting in cells. That is why:
- burning different things gives different temperatures (130 °C to 215 °C)
- a fire spreads by heating its neighbours past their ignition points
- water quenches fire by touching it
- you can build a heat source the same way you build a wall
There is no "furnace" object doing the work. There is a hot material next to a cold one.
Where to go from here
- Making fire — starting one at all
- Ore into bars — the two tables that matter
- Coke, and the sealed retort — the process that needs all of this at once