Conduction can be felt by touching the exterior wall of a boiler. The heat from the internal water is transferred to the solid boiler wall, where conduction begins. Individual molecules within the boiler wall material transfer heat energy from hot to cold areas, in this case, the boiler interior to the exterior. By touching the exterior boiler wall, the result of the conduction through the boiler wall, as well as the conductive heat transfer occurring between the wall and hand, can be felt.