The CT-DH-4 and 4P are designed to be used with CO2 equipment, dehumidifiers, and exhaust fans. While it is similar to the CT-DH-3 it has the added feature of independent outlets for temperature and humidity control. It is ideally suited for use with dehumidifiers. Temperature above your set point will activate the right hand outlets and deactivate the bottom left "CO2" outlet. Humidity will activate the top left "Dehumidify" outlet. Internal sensors will allow a 7 temperature comfort zone and a 5% humidity (differential) between the time the equipment comes "On" and goes back "Off" again. Set the temperature and humidity to the desired settings. The CO2 outlet is normally in the "On" position and is able to activate CO2 equipment as needed. An optional photosensor will defeat CO2 enrichment during darkness hours. Intended for indoor use only. The CT-DH-4 operates on 120 Volts AC with 15 Amp max switching capacity.