In a world covered in ice, keeping a high temperature is rather important. It has an impact on morale and health of your dwellers. Also, some of the buildings functions only when they have heating. A heat zone is created around a main reactor. With new researches you can modify the size of that zone and its heating power. You can also unlock smaller steam hubs which creates smaller heat zones without being connected to the main reactor. A hub like that is used for providing heat for excavating buildings that are farther from the main reactor but you can also use it to create smaller agglomerations of houses.
By clicking on a reactor you bring up a map with a temperature indicator for a given house. Each of buildings are marked by one of the six colors that refer to their assigned temperature:
- Ice-cold - purple
- Very cold - dark blue
- Cold - light blue
- Cool - green
- Liveable - orange
- Comfortable - red
Avoid stopping your reactor's work at all cost. A drop in temperature can have an impact on a probability of sickness. The total of temperature in work place and house determines a chance of getting sick by your citizens. You can check this information by clicking on a given dweller. Those, that have the highest chance of getting sick are homeless people so you should keep building houses to get rid of homelessness.
A proper placement of your buildings is also important. Only some of them have a construction that is not resistant to cold and must be placed in a heat zone. You should only place those buildings in that zone. Placing them outside of it means that they won't be functional. Other buildings can be placed anywhere. If you want to increase temperature in the buildings outside of heat zone you can safe some space and place additional steam hubs when you get enough coal.