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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.

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. Go to the troubleshooting section below for the correct settings.

Turn Emergency Heat on or off

You can manually turn on Emergency Heat on with your thermostat. This option will only appear if your system has Emergency Heat. The instructions depend on the thermostat model you have. Select your thermostat below.

Important: 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.

Nest Thermostat

With the Home app

  1. Open the Home app and tap your thermostat.
  2. Tap Settings Nest settings iconand then Thermostat and then Emergency Heat.
  3. Tap the switch to turn it on or off.

On your thermostat

  1. Go to Settings Nest settings iconand then Emergency Heat emergency heat.
  2. Select Continue and then Yes to turn it on. If Emergency Heat is already running, select Turn off or Leave on.

Nest Learning Thermostat and Thermostat E

Turn emergency heat on

  1. Press the thermostat ring to bring up the Quick View menu.
  2. Go to Settings Nest settings iconand then Equipment.
  3. Select Continue when the wire diagram appears.
  4. Select Continue a second time when you find 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.

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 there's no Emergency Heat option for your Nest thermostat:

  • Your system doesn’t have Emergency Heat. Go to the first section of this article for steps 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 your Nest thermostat model:
Select the thermostat you have:

Nest Thermostat

Nest Thermostat 3/4ths view

Nest Thermostat E

Nest thermostat e heating

Nest Learning Thermostat

Nest thermostat heating with silver ring

How to tell which thermostat you have

Nest Thermostat

  1. Pull off your thermostat’s display to check if there’s a wire in the Star Star connector icon OB connector.
  2. Next, open the Home app and tap on your thermostat.
  3. Go to Settings Nest settings iconand then Thermostat.
  4. Emergency Heat should be listed under Equipment. If it is, it will say Off or On. There should also be Emergency heat type and Emergency heat source listed under "System details."
  5. If Emergency Heat doesn't appear, tap on Wiring. The Star Star connector icon OB connector should say Heat pump next to it. If not either you don’t have a heat pump, your thermostat is wired incorrectly, or the wires aren’t configured.

Nest Learning Thermostat

  1. Go to Settings Nest settings iconand then Equipment for a diagram of the wires that are connected to your thermostat. You’ll also find which function they control.
  2. If there's a wire in the Star Star connector icon connector, make sure it says Emergency Heat in the thermostat’s Equipment menu.
  3. If you there are no wires in the Star Star connector icon connector or O/B connector, you either don’t have a heat pump system or your thermostat is wired incorrectly. Both of these wires are needed for emergency heat.
  4. If there are wires in the Star Star connector icon connector and O/B connector, pull of your thermostat display and make sure the wires are corrosion free, fully inserted into the connector, and that the connector button stays down.
  5. 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.

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

  1. Choose Settings Nest settings icon from the main menu.
  2. Turn to Equipment.
  3. Select Continue when the wire diagram appears.
  4. Select Continue a second time when you find 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 there's no 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 Nest settings iconand then Equipment. You’ll find a picture of which wires are connected to your Nest thermostat and which function they control.

  • If you there are no wires in the O/B connector or W1 connector, make sure they haven’t come unplugged. Both of these wires are needed for Emergency Heat.
  • If there's a wire in the W1 connector, make sure it says AUX heat.
    • Note: If Alt heat (not AUX heat) appearsyour Nest Thermostat E is configured to work with a dual fuel system. You won’t find an option to use Emergency Heat, but your thermostat will automatically use alternate heat when needed.
  • If there's a wire in the O/B connector, make sure it says Heat Pump.
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