The SMS 4.5 Amp Twin Pro Fan Speed Controller is a great choice of grow room climate controller for indoor gardeners who want the very best. The SMS PRO 4.5 Amp Twin Fan Speed Controller unit has two programs installed to optimise grow room conditions: the original programme from the SMS Twin Fan Controller, and an additional humidity control program. The original program will perform a 5 minute scan of the grow room and calculate the gradual increases and decreases of your fans. In the course of the scan it will automatically establish the capacity at which level to run your fans to maintain a controlled temperature. The second program activates when the grow room lights have been switched off. During the night period, the SMS PRO 4.5 Amp Twin Fan Speed Controller gets to work. The unit calculates the humidity in the grow room and any excess humidity is corrected by the PRO Twin Controller gently increasing the fan speeds for just the right amount of time.