This CO2-4E Carbon Dioxide (CO2) Controller has two timers that allow for efficient control of CO2 levels - one controls how much CO2 is released, the other controls how long it is released. The 4 Timer Controller also features an Overall Cycle Timer that controls how long CO2 remains in the garden before it is exhausted and an Exhaust Cycle Timer controls how long exhaust fans run. This unit also features temperature and humidity controls that will stop CO2 production if levels rise above specified point and can also trigger ventilation equipment. A photosensor disables CO2 production when garden lights are off. Unit is rated for 15 amps at 120 volts and carries a three-year manufacturers warranty. Unit is designed to work with the CO2 PPM Monitor.