Nest thermostat compatibility

The online Compatibility Checker has full instructions to check 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.
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 check 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 that comes 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

Incompatible thermostat wires

If your thermostat’s wires are high voltage or stranded, then your system isn’t compatible. But, it’s possible that a trained professional can make your system compatible.

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 professional 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.
High voltage wires High voltage systems typically have a thermostat that is labeled 120 V or 240 V, and has two thick wires with wire nuts. High voltage systems, such as electric baseboard heaters, aren’t compatible with Nest thermostats. In some cases, it’s possible that your system can be made Nest thermostat-compatible. Contact a local professional and have them install a step down transformer to 20 - 30 V.
Take a picture of the wires Save a picture of your current thermostat’s wires in case you need help later. Make sure that the connector labels are readable. Identify 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. Refer to the following article for more information: What to do if your thermostat’s wire connectors have two 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 find a red wire, or W if you find 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 Rh, Y1, G and C wires into the checker. You would not enter Rc in the checker, because it is only connected by a jumper.

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

Note: Use this table for reference only.

System types	Nest Learning Thermostat (3rd gen or earlier)	Nest Thermostat E	Nest Thermostat	Nest Learning Thermostat (4th gen)
Heat only, cool only, Heat+Cool			C wire or Nest Power Connector required
Natural Gas, Oil, or Electric fuel types
Single stage heating and/or cooling			Heat only or cool only C wire or Nest Power Connector required
Single stage heating with two stages of cooling
Two stages of heating with one stage of cooling
Single stage heat pump with or without AUX heat			C wire or Nest Power Connector required
Single speed fan
Single stage heat pump with separate single stage furnace heating (Dual fuel) 1			C wire or Nest Power Connector required
Single stage heat pump with separate two stage furnace heating (Dual fuel) 1
Two stage heat pump with or without AUX heat
Two stage heat pump with separate two stage furnace heating (Dual fuel) 1, 2
Humidifier* or dehumidifier 1, 2
Humidifier and dehumidifier1,3
Dual transformer systems 1, 2
Two stages of cooling and two or three stage furnace  heating 2
Two or three speed fan 1, 2
PTAC systems 2
Ventilation systems
HVAC power compatibility

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

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.

³ Nest Learning Thermostat (4th gen) can support humidifier, dehumidifier or ventilation on AQ+.

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 many cases, they don’t need a C wire.

But if you find that you need a C wire with a Nest thermostat, you can install the Nest Power Connector. Or you can contact a local professional to install the power connector or run a C wire 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 information, go to How the Nest thermostat works with zoned systems

About the Nest thermostat’s star connector

Nest thermostats also have a star terminal  that offers you some flexibility to install specialized systems. The 3rd or earlier generations of the Nest Learning Thermostat’s * terminal lets you install a humidifier, a dehumidifier, emergency heat, multiple fan speeds, or a 3rd stage of heating. The Nest Learning Thermostat (4th gen) has the AQ+ and AQ- * terminals which offer flexibility to install a humidifier, dehumidifier or ventilation system. If you have a 1-wire humidifier, dehumidifier or ventilation system, you can connect it solely to the AQ+ terminal with no wire in AQ-. This means that the thermostat provides power to the humidifier, dehumidifier or ventilation system by shorting R to AQ+. If you have a 2-wire humidifier, dehumidifier or ventilation system (also referred to as an externally powered humidifier, dehumidifier or ventilation system), you can connect 1 wire to AQ+ and the other to AQ-. In this case the thermostat does not provide power to the humidifier, dehumidifier or ventilation system. To turn it on, the thermostat simply shorts AQ+ to AQ-. The additional AQ terminals mean that the system can:  Have the humidifier on * and dehumidifier on AQ, or dehumidifier on * and humidifier on AQ Support a 2-wire humidifier, dehumidifier or ventilation system The Nest Thermostat E’s * or OB terminal lets you install a heat pump, a second stage of heating, or a second stage of cooling. Learn more about the star terminal

While most 24 V 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.

Proprietary systems If you find wires in your thermostat’s terminal that have non-standard labels (for instance 1,2,3, or A, B, C), your system is proprietary. If your system only has 2 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 provide an adapter you can use for it to be compatible with your Nest thermostat or you can have it rewired by a pro installer to be compatible.
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.
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 2 to 4 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 professional and have them install a step down transformer to 20 - 30 V. High voltage thermostats should only be installed or uninstalled by a professional due to the high voltage that they carry.
Solid fuel systems Systems that use coal, wood chips, pellets, anthracite, or other biomass materials are typically incompatible with Nest thermostats.

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 professional.

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 professional.

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. Below is 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

• Conventional systems: Nest Learning Thermostat (4th gen) can support up to 2 stages of cooling and up to 3 stages of heating.  
• Heat pump systems: Nest Learning Thermostat (4th gen) can support 4 stages of heating, consisting of 2 stages heat pump heating and 2 stages of alternate heating. Nest Learning Thermostat (4th gen) can support up to 2 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, it doesn't need them. The Nest thermostat and Nest app will show you system status information without connecting L wires.

Forced hot water or steam systems