The stove pipe thermometer has a thermal expansion coil on the rear that expands and indicates on the front of the thermometer gauge when to reload your stove to keep it in the most efficient zone. Too low and creosote is building up in your stove pipe. Too high and you are losing energy from the stove. It’s more than a thermometer. It is specifically designed to be used with wood burning stoves. The heat is transferred via the magnet and coil and the readout gives you peace of mind that you are not wasting energy.