So the idea is that this little gadget sits on top of the wood burner and circul ates warm air around the room - and it certainly works! No batteries, no power supply, it powers itself from the heat via the Peltier de vice. A Peltier is more commonly found in those 12v cooler boxes. If you send power to the device, one side gets cold while the other side warms up. The great thing i s, if you heat up the warm side, you get power! One Peliter will produce about 3.5 volts. On the top is a Pentium 4 CPU heat sink. This is there to keep the cool side coo l (aided by the fan). Sandwiched between the hot plate at the bottom (which is just a piece of scrap 5 mm steel) is the Peltier. The motor is from an RC car servo - these work well from about .8 volts. The fan is made from an old biscuit tin, soldered onto the servos original brass pinion gear. The original plastic wire sheath (snigger) from the Peltier was stripped back an d replaced with high temp silicone. The LED above the motor lights up at full temperature (over approx 2 volts). The whole lot screws together through countersunk holes in the base plate to the original threads in the heatsink. The fan blows the air over the heat sink, so the Eco fan is best placed at the b ack of the stove. You can buy these on eBay but cost around 60. That's a lot of money considering t he Pelitier only costs a couple of quid