The Hydor InLine 300W aquarium heater connects to flexible hose coming from an external pump or filter.Completely safe. No danger of damage if the equipment is left running without water for a short period of timePatented heating element made with the exclusive PTC system. The traditional metal resistor coils have been replaced by a special polymer sheet, silk-screened with heating inkSetting of temperature controlled by an electronic circuit with indicator lightTemperature range: 64-92 degrees Fahrenheit