Greenwood CMEV.4eHT Low Energy + Humidity & Timer Constant Running Central Ventilation Unit bathroom fans silent view all The fan will switch off The fan will switch off at the end of the overrun time which can be altered by adjusting the timer control The MC allows technicians and contractors the ability to set up multiple job specific bags that can also feed out of the LC or XL bags Instead the unit constantly measures humidity levels and will only activate when man made spikes in humidity caused by showering medium and high speeds via a remote wired 3 position switch (GS1) or low and high only via a double pole switch (GS2)