The Primair switches fans on & off according to room temperatures, you set the temperature dial to the ideal level and allow the Primair to bring your fans on to cool the room, and to switch the fans off when the ideal temperature is reached.

The Primair also has an added bonus feature, it allows you to set an idle spped so that when the room is at ideal temperature and the Primair has switched the fans off, they will revert to the idle speed. The idle speed can be set to anything from 0% - 100%