The iDevices Thermostat works with HVAC systems that have humidification & dehumidification features. The terminal labeled “HUM” serves as a multi-function relay to allow for Humidification, Dehumidification, W3 (3rd Stage Heat) or AUX heat (for heat pump systems) when supported by the HVAC system.
Humidification is applicable to Heat, Auto Heat, or Emergency Heat modes and can be set for dependent or independent use. When humidification is set to dependent, humidification will only occur when heating is active. When set to independent, humidification can occur when the system is in Heat, Auto Heat, or Emergency Heat Modes, but not actively heating.
Dehumidification works in Cool, Heat, or Auto modes. This feature kicks on when humidity rises above the dehumidification setpoint and remains active until the humidity drops below the dehumidification set point.
W3/AUX is an additional heat source that’s typically meant to supplement Heat Pump systems. Aux heat is usually triggered when the ambient temperature is 2-2.5° degrees below the set point.
To learn how to set configure the HUM relay, visit: Configuring the HUM Relay