This controller makes it easy to coordinate your exhaust and CO2 production. The CO2-4e Controller has the same features as the CO2-2e, but includes 2 extra timers. This controller features an Overall Cycle Timer that controls the maximum time between exhaust cycles. It also has an Exhaust Cycle Timer to control how long the exhaust fans will run. May be upgraded to PPM level control with the addition of the PPM-1c. Rated for 15 amps @ 120 volts. 3 year no hassle warranty.