Stove fans are small fans that are usually set on top of a wood-burning stove, although they can be put on top of anything warm, like an oven. A stove will slowly radiate heat into the surrounding room, but it can take a long time for this to warm up a room. A fan will make air move past the stove and into the room, which will make the room warm up much faster. (This type of heat is called "convection.")
Although any kind of fan can help warm move air around a room, this type of stove fan is placed directly on the top of the stove. You don't plug it in, and it doesn't have any batteries. Instead, the heat from the stove itself causes the fan to move.
There are two main ways a stove fan can work:
- a thermoelectric generator, where a large-enough difference in temperature between the base of the fan (which sits on the stove) and the top of fan (which is cooled by a heat sink) causes a thermoelectric generator (which has a set of doped semiconductor elements, one being a P-type element and the other being an N-type element) to make a small electric current. This small current drives a small, low-torque motor.
- a Stirling engine, where the heat makes the gas in a cylinder expand, which pushes a piston. The air cools down as the piston reaches the top of the cylinder, and the air contracts. The piston's movement causes the fan to move via a crank.