Heat

Heat, or temperature, will be a core game mechanic that will greatly affect how the player constructs their base and uses their units.

Heat transfer
Every block in the world (including air) has a temperature value. Hot areas will transfer their heat to colder areas. Heat also tends to move upwards, and the transfer of heat is obstructed by insulators, such as dirt.

Some areas, like the surface of the island, are designated to be "outside". If an area is outside, it's temperature will vary with the time of day and season. Additionally, outside spaces cannot have their temperature changed - they will merely absorb heat. This means that a good strategy during winter would be to keep your units in small, enclosed rooms with a heat source such as a fire.

Heat sources
Heat can be generated in many ways. Units give off a very small amount of heat, meaning that packing them close together in a room can save them from freezing in emergencies. A more practical source is a fire, which requires wood to keep burning. Lava, found at the center of the world, gives off a huge amount of heat (enough to be dangerous), and will instantly kill any unit that touches it. It could be useful for heating large spaces.