A skyhearth is a black, rubbery mass ranging from the size of a fist to several feet around. It has a mass of thread-thin tendrils at one end, which float upwards like whisps of smoke. It essentially eats wind and light to produce heat. When wet, it produces electricity instead. The energy generated is proportional to its size.
Most families have a decent-sized skyhearth in the house, used for cooking and heating. Very large skyhearths can produce temperatures that rival a blast-furnace, but only in a small area. Wealthy villages use skyhearths to provide public lighting, and remote settlements sometimes use them to power electric defenses.
They reproduce by budding.