To give better insight into how our software is built, the temperature controller only activates heaters, A/Cs, or fans; as the humidity controller only activates dehumidifiers or humidifiers. The reason is that if a fan is used both for temperature and humidity control, the different targets of rH (relative humidity) and temperature can interfere with each other. This being said, if you don't have a humidifier or a dehumidifier plugged into your Grow Hub, you won't be able to have humidity control.