How to tell if your system is Nest thermostat compatible

  • Google Nest thermostats are designed to work with most 24V systems, even older systems. They work with all common fuel types including natural gas, oil, and electricity. 
  • Check your system’s compatibility before purchasing a Nest thermostat with our online Compatibility Checker. Your system may work with either the Nest Thermostat E or the Nest Learning Thermostat, or only one of them.

Use the Compatibility Checker 

The online Compatibility Checker has full instructions to see if your heating and cooling systems are compatible with Nest thermostats, but here is some additional information to help you as you use it.

How to turn your system's power off

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

How to test that system power is off

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.

How to 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

Incompatible thermostat wires

Stranded 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 contact a local pro to 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

                                                                                                                                                                                                               

Take a picture of the wires

Save a picture of your current thermostat’s wires in case you need help with Nest thermostat installation or another issue. 

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

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

Ignore the wire colors

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

Learn more about compatibility

Systems that are Nest compatible 

Use the Compatibility Checker to make sure your home’s system is compatible with a Nest thermostat.

There are some key differences between Nest thermostats and what systems will work with each.

Note: Use this table for reference only.

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) 1

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Single stage heat pump with separate two stage furnace heating (Dual fuel) 1 

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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) 1, 2

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Humidifier* or dehumidifier 1, 2

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Dual transformer systems 1, 2

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Two stages of cooling and two or three stage furnace heating 2

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Two or three speed fan 1, 2

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PTAC systems 2

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1 Your system requires advanced configuration and wiring. If you have one of these systems,  contact a local pro.

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

2 Nest thermostat can only support one of these systems at a time.

About the C wire

The common (C) wire doesn’t control heating or cooling. Instead, C wires help 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 pro 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

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 C 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

Systems that are incompatible with Nest thermostats 

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

Millivolt systems are typically wall heaters or floor heaters and use electricity or natural gas. These systems use much less electricity than low voltage systems and can't deliver the right amount of power to Nest thermostats.

 

 

Picture of a floor furnace and wall-mounted furnace

High voltage systems

  • High voltage systems are usually electric baseboard heating systems or other radiant systems powered by electricity. 
  • High voltage thermostats are often built into the wall and typically have two to four thick wires coming out of the thermostat. Wire nuts are often used to connect the thermostat to the system wires.
  • High voltage thermostats are usually labeled 110, 115, 120 or 240 VAC   Note: In some cases it is possible to make a high voltage system Nest compatible. Contact a local pro and have them install a step down transformer to 20-30V.
  • High voltage thermostats should only be installed or uninstalled by a professional due to the high voltage that they carry.

 

 

high voltage text

 

high voltage wire nut

Proprietary systems

  • 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 Google Nest thermostats. However, some proprietary systems can be rewired by a pro installer to be compatible.

 

 

Proprietary wires

Solid fuel systems 

Systems that use coal, wood chips, pellets, anthracite, or other biomass materials are typically incompatible with Nest thermostats.

 

 

Solid fuel system

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.  Even if your system has sensor wires, it may still be Nest compatible.

Some micro-controller based systems

Systems that use micro-controllers instead of relays are sometimes more sensitive to power sharing. If you have a micro-controller based system, your Nest thermostat may need a C 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. You may be able to install a C wire to make your system compatible with a Nest thermostat. Contact a local pro.

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

Zone relay or control panels.

Some systems have control panels or equipment interface modules that require a C wire to be compatible with Nest thermostats. Here’s a list of some known panels that require a C 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.

Get pro installation for a dual fuel system

A dual fuel heating 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. 

You have a dual fuel system if you have a furnace inside of your home, and a heat pump on the outside of your home. Heat pumps look similar to air conditioners, so check the label on your outdoor unit to make sure it’s a heat pump. If you’re still not sure which system you have,  contact a local pro.

If you have a dual fuel system, you will need to have a trained professional set up your thermostat. It’s important that 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. Contact a local pro.

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

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