If you have a single extractor fan and want a no-nonsense device for manually adjusting the speed setting then this controller from Variispeed is a great option! The product looks smart, does the desired job and costs under a tenner!
 
Simply plug your fan into the Variispeed Controller, then insert it into a mains socket and use the dial to dictate the rate of airflow. Talk about being hassle-free! Finally say goodbye to overly complicated, long-winded set ups!
 
During times of high temperatures you can change the Variispeed Controller settings to increase the fan speed so that warm air is pushed out of the room/tent with more urgency. Alternatively, when the colder months come around you are able to keep any heat present in the grow space for longer by using the unit to reduce the airflow or even put a stop to it altogether.     
 
The Variispeed Fan Controller measures 53mm x 63mm x 98mm and accommodates a maximum power load of 300W.
 
Note: a gentle humming sound may be produced during use