An Endothermic Fire provides light and cools the player. It can be fueled with the same items as a regular fire (see Fuel), in addition to Nitre. An Endothermic Fire is unable to cook food. When burnt out, it drops Ashes.
Endothermic Fire Pit is more fuel efficient than the Endothermic Fire. Each fuel item burns as long as they would in a Fire Pit, which is twice as long as the burn time in a Campfire or Endothermic Fire.
Endothermic Fires and Endothermic Fire Pits are also included in the Shipwrecked DLC, where they are required to deal with Overheating during the Dry Season. They work exactly as they do in the Reign of Giants DLC.
In thermodynamics, the term endothermic describes a process that absorbs heat energy from its surroundings, while the term exothermic is the opposite.
The Endothermic fire is blue, meant to represent a lack of heat, but in reality blue flames are hotter than yellow flames. Therefore, if the "fire" in the Endothermic Fire Pit weren't merely a representation of a magical anti-heat phenomenon, it would actually be hotter than a regular fire pit.