How to tell if your system is Nest thermostat compatible and get a wiring diagram

The Nest app now includes steps to check thermostat compatibility and give you a custom wiring diagram for your system. If you don’t have the app, you can follow these instructions to see if your system will work with Nest and how to connect the wires.

Complete all the steps below to set up and install your Google Nest thermostat.

1. Check Nest compatibility and get a wiring diagram - You are here
2. Install your thermostat on the wall
3. Set up your thermostat
4. Connect your thermostat to the Nest app
5. Get started using your Nest thermostat

There are two ways to check your system’s Nest compatibility and get a wiring diagram:

With the Nest app

  1. Tap Settings Nest settings icon on the app home screen.
  2. Scroll down and select Add product Nest add product icon.  to start the setup instructions.
  3. The app will ask you some questions about your thermostat wires. Answer them as accurately as possible.
  4. You’ll see a Nest wiring diagram when after you’ve installed the Nest thermostat base.

With this article

  1. Use a computer’s web browser to use our online Compatibility Checker. It’s basically the same as the one built into the app.
  2. Refer to this article for detailed instructions, tips and more information about compatibility.

1. Check your system's wiring 

1. Turn off power to your system

This protects you and avoids blowing a fuse in your
equipment.

There may be a switch on your system or near your system
that looks like a regular light switch. If your
system doesn’t have a switch, turn off power to it at the breaker or fuse box.

Turn off power through breaker box or switch

2. Test that you’ve correctly turned off power

Change the temperature on your thermostat by at least 5 degrees.

  • If it’s winter, turn up the temperature to turn on heating.
  • If it’s summer and you have system cooling, turn down the temperature.
  • Wait at least 5 minutes to see if your system turns on (you’ll need to wait because many systems have a built-in delay).

Tip: You can listen for your system to turn on, or put your hand near a vent to feel if there’s warm or cool air coming through.

3. Remove your thermostat’s cover

Some covers simply pull off, while others need to be
unscrewed.

If you have an older thermostat there may be a mid-plate
that also needs to be removed to expose the wires.

          Learn about thermostat mid-plates >

Remove thermostat cover

4. Look closely at your thermostat’s wires

Check that you don’t see any of the three characteristics listed below:

Thick wires or a high voltage label

high voltage text high voltage wire nut

High voltage systems typically have a thermostat that is labeled 120V or 240V, and has two thick wires with wire nuts. High voltage systems, such as electric baseboard heaters, aren’t compatible with the Nest thermostat.

Stranded thermostat wires

Look closely at the end of one of the thermostat wires. You
may need to pull one out of the connector to check. If there
is more than one large strand, the wiring isn’t Nest
compatible. When you’re done, reinsert it into the correct connector.

Note: If your wires are stranded, you may be able to have a 
local Nest Pro installer cap, solder or replace stranded wires
with a solid core wire, which will work with the Nest
thermostat. The method may depend on your local electrical code
requirements.

Stranded wires

 

Proprietary wires

  • If you see wires in your thermostat’s connector that have
    non-standard labels (for instance 1,2,3, or A, B, C) your
    system is proprietary.
     
  • If your system only has two wires, but you have both
    heating and cooling, your system is likely proprietary.

Proprietary systems aren’t compatible with the Nest
thermostat. However, some proprietary systems can be
rewired by a Nest pro installer to be compatible with the Nest thermostat.

Proprietary wires

 

2. Use the Compatibility Checker and get a wiring diagram 

Now that you’ve done some basic wiring checks on your thermostat, you’ll enter your system’s wires into Nest’s online Compatibility Checker.

1. Take a picture of your thermostat’s wires

Make sure that the connector labels are readable.

If you’re having trouble identifying a wire, or want to learn
about what it controls, see the following article for details.

         Learn more about identifying thermostat wires >

Phone taking a picture of thermostat wires

 

2. Go to the Nest Compatibility Checker

Use the Compatibility Checker to enter the connectors that
have wires on your current thermostat.

Be sure to read the tips below to help ensure you enter the
wires correctly.

compatibility widget

If your thermostat’s connectors have two labels

It can be hard to determine which set of labels to use in the
compatibility checker. Read the following article for more
information:

What to do if your thermostat’s wire connectors have
two labels >

Thermostat labels

 

What to do if your thermostat’s wire connectors have two labels >

Don’t use the wire colors as a guide

Simply enter which connectors have a wire and ignore the color of the wires. This is because not all systems are connected to the thermostat with the same wire colors.

For instance, don’t enter R in the Compatibility Checker if you see a red wire or W if you see a white wire. The label on the wire connector is what you should enter. So check R if there’s a wire of ANY color in your thermostat’s R connector.

Don’t enter jumper wires

If your thermostat has a short “jumper” wire between two
connectors, don’t include that wire; only enter the labels for
wires coming from inside your wall that are attached to the
thermostat. For instance, in the illustration on the right, you
would only enter RhY1G and C wires into the checker. You
would not enter Rc in the checker, because it is only
connected by a jumper.

Nest thermostat wires from wall

3. Save your wiring diagram

 

When you’ve entered your thermostat’s wires, the
Compatibility Checker will let you know which thermostat
your system will work with. Many systems will work with
the Nest Thermostat E, but more complex systems may
require a Nest Learning Thermostat.

Nest thermostat wire guide

 

No matter which Nest thermostat your system is compatible with, the Compatibility Checker will show you a customized wiring diagram that you’ll need to use for thermostat installation. You can print it out or email a copy to yourself.

3. Install your thermostat 

Once you have your wiring diagram you’re ready to begin installing your thermostat.

          Install your thermostat on the wall >

If you need more help using the compatibility checker or you’re still not sure if your system is compatible with the Nest thermostat you can find more information below.

You can always contact a Nest Pro if you need additional help.

Learn more about compatibility 

Systems that are Nest compatible 

Compatibility

Nest Learning Thermostat

Nest Thermostat E

Natural Gas, Oil, Electric fuel types

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Single stage heating and/or cooling

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Single stage heating with two stages of cooling

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Two stages of heating with one stage of cooling

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Single stage heat pump with/without AUX heat

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Single speed fan

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Single stage heat pump with separate single stage furnace heating (Dual fuel)*

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Single stage heat pump with separate two stage furnace heating (Dual fuel)*

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Two stage heat pump with/without AUX heat

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Two stage heat pump with separate two stage furnace heating (Dual fuel)*

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Humidifier* or dehumidifier*

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Dual transformer systems*

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Two stages of cooling and two or three stage furnace heating

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Two or three speed fan*

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PTAC systems

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*Important: Professional installation is recommended for some systems since their wiring and setup can be complicated. These include:

  • Dual fuel systems (heat pump with furnace)
  • Dual transformer systems (Systems that have more than one R wire)
  • Whole-home humidifiers and dehumidifiers (compatible with Nest Learning Thermostat only)

If you have one of these systems, you can find a local Nest pro installer with our online Pro Finder.

Pro installation recommended for dual fuel systems

A dual fuel heat and cooling system (also called a hybrid or packaged system) is a combination of a heat pump for primary heating and cooling and a furnace (usually gas or oil) that provides a second and/or third stage of heating. The Nest thermostat is compatible with these systems and supports up to 2 alternate heat sources.

Note: It's important for a professional to assess the requirements for your specific dual fuel configuration since choosing incorrect options for a dual fuel system can result in damage to your system.

 

Compatibility with zoned systems

Nest thermostats are compatible with zoned systems, including zoned systems with dampers. However, there are some zoned systems that require a common wire to work with a Nest thermostat. For more details, please see the following article:

How the Nest thermostat works with zoned systems >

 

About the Nest thermostat’s star connector

Nest thermostats also have a star connector *  that offers
you some flexibility for installing specialized systems.

The Nest Learning Thermostat’s  *  connector lets you install
a humidifier, a dehumidifier, emergency heat, multiple fan
speeds, or a 3rd stage of heating.

The Nest Thermostat E’s  *  /OB connector lets you install a
heat pump, a second stage of heating, or a second stage
of cooling.

        Learn more about the star connector >

Nest thermostat star connector

 

About the C wire

The C wire doesn’t control heating or cooling. Instead, C wires deliver power from the system to the thermostat in case the other wires can’t provide enough power. Not all systems have a C wire installed, but Nest thermostats were engineered to use as little power as possible for their display and internal circuitry, so in the vast majority of cases, they don’t need a C wire. But if you find that you need a C wire with a Nest thermostat, you can contact a local Nest Pro installer to run one for you. Costs can vary depending on how difficult it is to route a new wire through your walls.

          When the Nest thermostat needs a C wire >

Systems that are incompatible with Nest 

While most 24V heating and cooling systems are compatible with Nest thermostats, there are some systems that aren’t compatible. You can quickly tell if you have one of these systems without having to use the Compatibility Checker or to look at your thermostat’s wiring.

If you have one of the system types below, it won’t work with a Nest thermostat.

Millivolt heaters that use fuels like natural gas or electricity Picture of a floor furnace and wall-mounted furnace
Solid fuel systems that use coal, wood chips, pellets, anthracite, or other biomass materials Solid fuel system
Baseboard electric heaters that are high voltage (120 or 240V) high voltage text

 

  • Wired remote sensors: Remote sensor wires are typically used to give your thermostat outside weather data. These wires can’t be connected to Nest thermostats. But Nest thermostats don’t need wired sensors since they get weather information over Wi-Fi. So even if your system has sensor wires it may still be Nest compatible.

  • Proprietary systems: Proprietary systems use a serial communications protocol to communicate between the system and the thermostat. Nest thermostats can’t communicate with serial protocols, though some proprietary systems can be re-wired by a professional installer with standard HVAC wires so they can work with a Nest thermostat. Proprietary systems typically have unconventional wire labels such as A, B, C and D or 1, 2, 3 and 4.

  • Some micro-controller based systems: Systems that use micro-controllers instead of relays are sometimes more sensitive to power sharing. If so, your Nest thermostat may need a common wire to be compatible with these systems.

  • Systems that can’t deliver enough power: Some systems can’t deliver enough power (at least 20 volts) over the existing system wires, so a Nest thermostat’s battery may slowly drain and eventually cause the thermostat to turn off. These systems are sometimes called high impedance systems.

  • Some system hardware such as gas valves and zone or relay panels require a common or C wire to work with Nest thermostats. If you would like to find out more information about installing a common wire, contact a local Nest Pro.

  • Gas valves: Some gas valves on systems vibrate or buzz when a Nest thermostat is installed. This can usually be fixed by connecting a common wire.

  • Zone relay or control panels: Some systems have control panels or equipment interface modules that require a common wire to be compatible with Nest thermostats. Here’s a list of some known panels that require a common wire. This list is not meant to be comprehensive, so your system may be incompatible even if it isn’t listed here.

  • Beutler ZTE2S
  • Bryant 548F036
  • Carrier HK42FZ011
  • Honeywell AQ25110B
  • Honeywell EMM-3
  • Honeywell HZ221
  • Honeywell HZ311
  • Honeywell HZ322
  • Honeywell HZ462
  • Honeywell Trol A Temp MABS EZ
  • Honeywell TZ-4
  • Lennox LZP-2
  • Nordyne 624631-A
  • Nordyne 903915A
  • Villara ZTE2S
  • Waterfurnace ATV045A 110CIT
  • White-Rogers 36C03-300
  • ZoneX DigiTract 4
  • Ztech ZTE2S

Incompatible system wiring

Too many stages of cooling or heating: Nest Learning Thermostats are only compatible with systems that have one or two stages of cooling.

The Nest Thermostat E is only compatible with one stage of heating, one stage of cooling, and an additional stage of either heating or cooling.

International systems: Some international systems, such as Buderus boilers, have dry contacts or other incompatible wiring. These systems may require relay panels in order to be installed with standard American thermostat wiring.

Heat pumps with L wires: L wires are typically used to show system status, like emergency heat being on. Nest thermostats can work with systems that use Service Light (L) wires. While L wires can't be connected to the Nest thermostat, they don’t need them. The Nest thermostat and Nest app will show you system status information without connecting L wires.

Thermostat wire labels 

If you need to know more about what the labels on your thermostat wires mean, read the following article for more information:

        Learn more about thermostat wire labels >

1. Check Nest compatibility and get a wiring diagram - You’ve just completed
2. Install your thermostat on the wall
3. Set up your thermostat
4. Connect your thermostat to the Nest app
5. Get started using your Nest thermostat 

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