How heat behaves
Understand conduction, thermal mass, and temperature.
Every cell has a temperature, including air. Heat moves between neighboring cells. A material may ignite, melt, boil, or freeze when its temperature crosses a threshold. The material pages list those thresholds.
Moving heat through a wall
Conduction measures how readily heat enters a material. It ranges from 0 to 255.
Use iron or stone when you need a fire to heat something through a wall. Use refractory material when you need to keep heat from passing through. For example, a retort lined with refractory material will stay too cool while the fire burns outside it. Air also conducts poorly, so a fire does not heat an entire room at once.
Thermal mass
Thermal mass tells you how much heat a material holds. Some materials hold 2, 4, or 8 times as much. A material can conduct heat quickly and still take a long time to cool. Lava is one example. Coke holds 4 times as much heat, so a coke bed stays hot after you stop feeding it.
Material changes
The material pages list the temperatures at which a material ignites, melts, boils, freezes, or sets. They also show decay, which happens over time rather than at a temperature threshold.
Melting and setting do not always happen at the same temperature. Iron ore melts at 190 °C, but molten iron does not set until it falls below 160 °C. It can keep flowing after the heat source is gone.
Fire, embers, and lava are materials occupying cells. A fire spreads by heating nearby fuel past its ignition temperature. Water quenches fire when it touches it. The temperature of a fire depends on what is burning, so a change of fuel can change what you are able to melt.
For the practical steps, see Making fire, [Ore into bars](smelting.html), and Making coke. To heat something without a fire, see Electric heat.