The video below shows a wood stove fan. These fans function with no outside input of electricity. They use the heat gradient between the bottom of the fan in contact with the stove and the top of the fan, which is designed to radiate heat. The bottom to top flow of heat goes through an array of semiconductors. Semiconductors are used in most electronic devices today ranging from smartphones to computers. Semiconductors contain elements such as germanium or compounds such as cadmium selenide combined with specific impurities that alter their physical properties.
In the case of the fan, the elements of the semiconductor sandwiched between the hot and cooler areas of the gradient produce an electric current (Seebeck Effect) that is used to drive a small motor which rotates the blades of the fan. The rotating of the blades propels heat from the stove into the room and helps further cool the top of the fan enhancing the bottom to top heat gradient.