Figure 3-15 shows the essential parts of the pan-type humidifier. The main part is a tank of water heated by low-pressure steam or forced hot water where a water temperature of 200°F (93°C) or higher is maintained. The evaporative-type humidifier is fully automatic, the water level being controlled by means of a float control. In operation, when the relative humidity drops below the humidity-control setting, the humidifier fan blows air over the surface of the heated water in the tank. The air picks up moisture. The air is blown to the space to be humidified. When the humidity control is satisfied, the humidifier fan stops.