Furnaces function identically to other fires, such as stoves, fire places, or campfires. The furnace provides no advantage over campfires beyond protection against wind. Furnaces have one cooking slot.
In addition, a furnace has an attached forge that can be used for crafting items. Furnaces have a maximum temperature of 200°C; any temperature above 100°C can only be reached by adding Coal to the furnace.
Furnaces have fixed locations that do not change between games. Notable furnaces are listed here.