Nest thermostat star terminal

A Nest thermostat’s star terminal or O/B terminal can be used to control several different system functions, depending on what type of system you have. For example, you can use the star terminal to connect a wire that controls a humidifier or dehumidifier, or emergency heat. 

• During setup, the app will give you a custom wiring diagram to install your Nest thermostat. You should only insert a wire into the thermostat’s star terminal if the wiring diagram tells you to.
• If the app tells you to put a wire into the star terminal during setup, your thermostat will ask you to tell it which wire it is, and what it controls. 
• No matter which Nest thermostat you have, you can only put one wire into the star terminal, so only one function is supported at a time.
• If you upgrade to a new thermostat, you'll be asked what equipment is connected to the  terminal. If you're unsure, exit the setup flow and check your previous thermostat's wiring by going to Devices  your device's tile  Settings   Thermostat  Wiring.
  • You can also check the wiring from the thermostat by going to Settings Equipment.

Important: If you’ve connected a humidifier, dehumidifier, or multi-speed fan wire to the star terminal, we strongly recommend that you get help from a pro. Make an appointment with our installation partner OnTech to have a trained pro come to your home to install and set up your Nest products.