Air movement is an essential component of any controlled environment. Fans have numerous roles, for internal air movement and circulation. Air movers are used to ensure uniform distribution of air within internal spaces (and to ensure better consistency and distribution of factors such as heat, CO2, etc.), and extractor fans are used to remove (and introduce) air into grow environments, venting hot air, and introducing fresh, CO2 rich air.
Other fans can also be utilised to improve grow environment efficiency, such as floor drying fans. These can help to manage ground-level moisture whilst also contributing to the overall air circulation and distribution within a grow environment.