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What is the star connector on the 2nd generation Nest Learning Thermostat?

The Nest Learning Thermostat includes a connector that can be used for a few different functions: stage 3 heating, emergency heat, humidification, or dehumidification.

With the 2nd generation Nest Learning Thermostat, we’ve added support for the following heating and cooling system functions:

Connector Label Function

W3


Stage 3 heating


E


Emergency heat


HUM


Whole-home humidification


DEHUM


Whole-home dehumidification

Important note: The Nest Thermostat connector can only support one of these functions. As an example, if you have emergency heat and whole-home humidification, you’ll need to select one in order for your system to be compatible with the Nest Thermostat (in this case, we’d suggest humidification, as the Nest Thermostat does the equivalent of emergency heat differently, without wires).

When you put a wire in the connector, the Nest Thermostat will ask which of the above functions the wire supports. What we ask depends on what type of system you have.

If you have a conventional system, the Nest Thermostat will ask you if the wire in the connector controls humidification, dehumidification, or stage 3 heating. If you have a heat pump or dual fuel system, the Nest Thermostat will ask you if the wire in the connector controls humidification, dehumidification, or emergency heat.

Conventional heating and cooling Heat pump


For systems that have stage 3 heating or emergency heat, you’ll be able to configure the Nest Thermostat yourself. However, if you’ve connected a humidifier or dehumidifier to the connector, we strongly recommend that you get help from a professional installer.