Learn more about thermostat wire labels

When you’re checking to see if your system is compatible with a Google Nest thermostat, look for labels on your old thermostat’s wire connectors. In most cases, you’ll connect your wires to the Nest thermostat in the same connectors your old thermostat used. There are some exceptions and special cases. For example, the Nest thermostat uses a * connector for some wires. Here are some of the labels you might run into and what they mean.

Thermostat wire labels

Here are some of the labels you might see on your thermostat and what they do. After you know what wires you have, use our compatibility checker to see if the Nest thermostat will work with your system.

If your system is Nest thermostat compatible, use the Nest app to get a wiring diagram. See the following article for step-by-step installation instructions.

              How to install your Nest thermostat >

Common thermostat labels 

Label Description
R

The R wire is the power wire for your heating and cooling system.

If you only have one R wire (no Rh or Rc), you can connect your R wire to
either Rc or Rh on the Nest thermostat.

Do not connect any Jumper wires to the Nest thermostat.

Rh

If you don’t have an Rc wire, the Rh wire is the power wire for both your
heating and cooling systems.

If you have an Rh and an Rc wire, the Rh wire is the power wire for your
heating system.

Some HVAC systems, called dual transformer systems, use separate power sources for heating and cooling (Rc and Rh). If you have both an Rh and an Rc wire you have a Dual Transformer system.

We strongly recommend a Nest Pro installation to prevent damage to your system.

Rc

If you don’t have an Rh wire, the Rc wire is the power wire for both your
heating and cooling systems.

If you have an Rc and an Rh wire, the Rc wire is the power wire for your
cooling system.

Some HVAC systems, called dual transformer systems, use separate
power sources for heating and cooling (Rc and Rh). If you have both an
Rh and an Rc wire you have a Dual Transformer system.

We strongly recommend a Nest Pro installation to prevent damage to your system.

W or W1 The W or W1 wire controls your heating system.
Y or Y1

In most systems, the Y or Y1 wire controls your cooling system.

If you have a heat pump, your Y or Y1 wire controls your compressor. Your
compressor is responsible for heating and cooling your home.

         Determine if you have a conventional or heat pump system >

G or G1 The G or G1 wire controls your fan. Your fan pushes the warm or cool air
through your vents into the rooms of your home.
O/B

Heat pump systems use a changeover valve controlled by the O/B wire.
Your changeover valve tells your system when to switch between heating
and cooling.

          My system is heating when it should cool >

Note: O/B wires are typically orange, but you should not rely on Orange wire label
color alone to determine the function of a wire.

Some systems have separate O and B wires. Read below for information on additional wires.

E

On some thermostats, you’ll see an E connector. The E wire turns your
emergency heat on or off. Emergency heat is usually used when it’s too
cold outside for your regular heater to keep your home warm.

          Learn more about emergency heat >

Y2

The Y2 wire controls the second stage of cooling in conventional
systems, which can help cool your home faster.

In heat pump systems, the Y2 wire controls the second stage of your
compressor, which can help heat or cool your home faster.

AUX

Heat pump systems sometimes have auxiliary heat to help heat your
home more quickly or to help heat your home when it’s too cold outside
for your heat pump to run.

          Learn more about auxiliary heat >

C

The C wire is also known as the common wire. This wire connects your
system to the common ground and can help provide power to your
thermostat.

Don’t worry if you don’t have a C wire. The Nest thermostat doesn’t
require this wire for most installations.

          Learn more about common wires >

Tip: Common wires are typically blue, but you should not blue
rely on color alone to determine the function of a wire.

W2

The W2 wire can control different types of heat based on the type of
system you have.

          How to tell if you have a conventional or heat pump system >

If you have a conventional system

In some cold areas, you might have a furnace with different stages of
heat, low and high, to help heat your home quickly when it’s very cold
outside. The wire in the W2 connector controls the second stage of heat.

          Learn more about multistage systems >

If you have a heat pump

If you have a heat pump, the W2 wire may control your auxiliary heat.
Auxiliary heat helps heat your home when it’s too cold outside outside
for your heat pump to work efficiently.

          Learn more about auxiliary heat >

In some heat pump systems, the W2 wire may control a separate furnace
to help heat your home. These types of systems are called dual fuel systems because the heat pump and the furnace use different heat sources.

          Learn more about dual fuel >

Additional thermostat labels 

If you see these wires attached to your thermostat, you may need to contact a Nest Pro to
help verify the function of your thermostat’s wiring. If installed incorrectly, these types of
wires can damage your thermostat or your system.

           Find a Nest Pro >

Wire Label Description
SS1, or S2

The Nest thermostat does not need these wires. Install your Nest thermostat without these wire.

Wires labeled S or S1 can be indicator lights or sensor wires. The Nest thermostat uses its LCD display instead of an indicator light and gets sensor information, like outdoor weather conditions, over Wi-Fi.

L

The Nest thermostat does not need this wire.

Wires labeled L can be indicator lights. The Nest thermostat uses its LCD display instead of an indicator light.

G2 or GM

Requires Nest Pro installation.

Some heating and cooling systems have fans with multiple speeds. A G2
or GM wire will control the second speed of your system’s fan.

      Learn more about multi-speed fans >

G3 or GH

Requires Nest Pro installation.

Some heating and cooling systems have fans with multiple speeds. A G3
or GH wire will control either the second or third speed of your system’s fan. Your Nest Pro will be able to tell which speed this wire controls.

       Learn more about multi-speed fans >

O

May require Nest Pro installation if you have both an O wire and a B wire.

O and B wires control when your heat pump cools or heats your home.

B

May require Nest Pro installation if you have both an O wire and a B wire.

O and B wires control when your heat pump cools or heats your home.

In some installations the common wire may be disguised as a B wire.

        How to tell if your B wire is a common wire >

        Learn more about common wires >

Tip: Common wires are typically blue, but you should not blue
rely on color alone to determine the function of a wire.

W3

May require Nest Pro installation.

In some systems, the wire in the W3 connector controls your third stage
of heat. This wire might also control your emergency heat. If you’re not sure what type of heating you have, contact a Nest Pro.

         Learn more about multistage systems >

         Learn more about emergency heat >

H or HUM or 
HUM1

Requires Nest Pro installation.

This wire will control your in-home humidifier. If your system has a humidifier wire, or more than one humidifier wire, you’ll need a
professional installation.

H2 or HUM2

Requires Nest Pro installation.

Some humidifiers use two wires to turn on or off. Only one humidifier
wire can be connected to your Nest thermostat. Your Nest Pro will determine how to install your humidifier.

D or DH or DHUM 
or DEHUM1

Requires Nest Pro installation.

This wire will control your in-home dehumidifier. If your system has a dehumidifier wire, or more than one dehumidifier wire, you’ll need a professional installation.

DH2 or DHUM2 
or DEHUM2

Requires Nest Pro installation.

Some dehumidifiers use two wires to turn on or off. Only one
dehumidifier wire can be connected to your Nest thermostat. Your Nest
Pro will determine how to install your dehumidifier.

Other

Requires Nest Pro installation.

If you see a wire label not listed here, or you see a wire labeled Other,
you’ll need to contact a Nest Pro to check compatibility and have your thermostat installed.

            Systems that are incompatible with the Nest thermostat >

 

Incompatible thermostat labels 

If you see these wires attached to your thermostat, your system is not compatible with the Nest thermostat.

Note: Not all wiring that is incompatible with the Nest thermostat is listed here.

           Systems that are incompatible with the Nest thermostat >

Wire Label Description
Y3 Y3 wires indicate a system that has three stages of cooling. The Nest
thermostat does not support three stages of cooling.
1 2 3 4

Wire labels such as 1 2 3 and 4 indicate a proprietary system.

Proprietary systems are designed by the manufacturer so that they will
not work with other thermostats.

         Learn more about proprietary systems >

A B C D

Wire labels such as A B C and D indicate a proprietary system.

Proprietary systems are designed by the manufacturer so that they will
not work with other thermostats.

         Learn more about proprietary systems >

V or VR These types of wires are not compatible with the Nest thermostat.
Water or H2O These types of wires are not compatible with the Nest thermostat.

 

I don’t see my wiring labels here

If you still need additional help to learn more about your thermostat wiring, contact a Nest
Pro
.

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