- If you look at My ecobee V5 thread, I have a smartapp called MonitorAndSetEcobeeHumidity that uses
a target humidity level to trigger your humidifier/dehumidifier/HRV/ERV connected to ecobee.
- Otherwise, if you want to implement some custom rule, you may want to look into Core. My Ecobee device exposes all thermostat capabilities for Core processing.
Regards.