Learn about Emergency Heat

Some heat pump systems include a feature called Emergency Heat that can be manually turned on if the primary heating system isn’t working or keeping your home warm enough. You should rarely need to use Emergency Heat. But if you need to run it regularly, your system may need servicing from a qualified HVAC technician.

How to tell if your system has Emergency Heat

There are a few ways to tell if your system has Emergency Heat:

  • Your current thermostat has a switch or a button labeled “Emergency.”

  • Your current thermostat has a connector labeled E, and there’s a wire in it.

  • Your heat pump’s manual or manufacturer says your model has it.

  • Contact a local pro. They’ll be able to tell if your system has Emergency Heat, install your Google Nest thermostat, and set it up correctly.

Important: Emergency Heat and Auxiliary Heat are different types of backup heating and operate differently. Emergency Heat must be turned on manually while Nest thermostats can use Auxiliary Heat automatically as needed.

How to set up Emergency Heat

When you’re installing a Nest thermostat the app will guide you through installation and setup. The app will ask you to enter the wires on your current thermostat. Then it will give you a Nest thermostat wiring diagram that’s customized for your system. Always follow this diagram to connect the Emergency Heat wire to the right thermostat connector.

You’ll also need to tell your Nest thermostat which wire will be used for Emergency Heat. See the troubleshooting section below for the correct settings.

How to turn Emergency Heat on or off

You can manually turn on Emergency Heat on with your Nest thermostat.

Important: Running Emergency Heat is usually expensive and inefficient. If you find that you’re using it often, contact an HVAC technician for a system check up.

How to turn Emergency Heat on

  1. Press the thermostat ring to bring up the Quick View menu.

  2. Go to Settings and then Equipment.

  3. Select Continue when you see the wire diagram.

  4. Select Continue a second time when you see a summary of your system.

  5. Select Emer. Heat.

  6. Select Emer. Heat again (Nest Learning Thermostat) or Turn On (Nest Thermostat E) to confirm that you’d like to turn Emergency Heat on.

Your Nest thermostat will use Emergency Heat to reach your set temperature as needed until you manually turn it off.

How to turn Emergency Heat off

  1. Press the thermostat ring to bring up the Quick View menu.

  2. Select Thermostat Thermostat off icon .

  3. Then select Turn Off.

Your Nest thermostat will then resume heating normally.

Troubleshoot Emergency Heat

If Emergency Heat isn't working after you’ve finished installation, or you don’t see the Emer. Heat option in the Equipment menu on your Nest thermostat:

  • Your system doesn’t have Emergency Heat. Check the first section of this article on how to check.

  • The thermostat’s wires aren’t in the right connectors. Double check your wiring diagram and that the wires are in the correct connectors on your Nest thermostat.

  • Your Nest thermostat isn’t set up right. The correct settings depend on which Nest thermostat you have:

Nest Learning Thermostat

  1. Go to Settings and then Equipment to see a diagram of the wires that are connected to your thermostat. You’ll also see which function they control.

  2. If you see a wire in the Star Star connector icon connector, make sure it says Emergency Heat in the thermostat’s Equipment menu.

  3. If you don’t see wires in the Star Star connector icon  connector or O/B connector, make sure they are fully inserted and that the connector button stays down. Both of these wires are needed for Emergency Heat.

  4. If the Star Star connector icon connector is not set as Emergency Heat, and you’re not sure if you should have Emergency Heat, contact a local pro for help.

  5. If you’re sure your system has emergency heat, double check the Star Star connector icon connector’s setting.

  1. Choose Settings   from the main menu.
  2. Turn to Equipment.
  3. Select Continue when you see the wire diagram.
  4. Select Continue a second time when you see a summary of your system.
  5. Choose  Wire Type.
  6. Select E: Emergency.
  7. The Emer. Heat option will now be available in the Equipment menu.

If you don’t see the option for E: Emergency, the Nest thermostat does not detect an O/B wire. Emergency heat is only compatible with Heat Pump systems. Check to make sure that your O/B wire is fully inserted.

Nest Thermostat E

Check in Settings  and then Equipment. You’ll see a picture of which wires are connected to your Nest thermostat and which function they control.

  • If you don’t see wires in the /OB connector or W1 connector, make sure they haven’t come unplugged. Both of these wires are needed for Emergency Heat.
  • If you see a wire in the W1 connector, make sure it says AUX heat.
    • Note: If you see Alt heat (not AUX heat)your Nest Thermostat E is configured to work with a dual fuel system. You won’t see an option to use Emergency Heat, but your thermostat will automatically use alternate heat when needed.
  • If you see a wire in the /OB connector, make sure it says Heat Pump.
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