The SMS Fan Controller gives you much greater control over the humidity of your grow room. You can choose to manually set the airflow output from the fan or you can have this set automatically thanks to the attached thermostat. The automatic option is obviously a better option if you wish to control the ambient temperature in your absence. Just set your preferred temperature on the unit and switch your fan to a minimal setting. If the temperature should rise above your required setting, the fan will fan up and reduce the heat accordingly. The fan will then return to its minimal setting.
By controlling your fan better, you will not only create a more stable environment for your plants, but you will also prolong the life of your fan and reduce power consumption.
If you only wish to have full manual control over your grow room humidity, consider the SMS Fan Controller without Thermostat