ecobee

What do my thermostat's wire labels mean?

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This article applies to all ecobee thermostats except Smart, Smart SI, EMS and EMS SI.

What do all the thermostat terminal letters/wiring labels mean?

Here are some letters you may see on your thermostat’s terminals and wire labels and what they mean. Use the Thermostat Compatibility Checker to see if an ecobee thermostat will work with your system.

Common thermostat wires: 

Label

Description

C

Also known as the common wire, the C wire enables the continuous flow of 24VAC power that ecobee thermostats need to operate.

Don’t see a C wire? There might be an extra wire tucked in the wall behind your thermostat’s backplate that you can utilize as the C wire. That is, provided it’s connected to the C terminal on your furnace/air handler control board. The C wire might also be labelled as the X or B wire. You’ll have the opportunity to safely check for a C wire during installation when your system is powered off.

Still no C wire? You can probably still install an ecobee with the Power Extender Kit (included with ecobee thermostats), or in other less common setups with other customizations we can walk you through at the time.

R

Heating and cooling system power wire.

If you only have one R wire (That includes R, Rc, and Rh), you’ll insert it into the Rc terminal on your ecobee.

Do not jumper any R wires!

Rh

If you don’t have an Rc wire, Rh serves as both the heating and cooling power wire.

With dual-transformer systems you’ll have two R wires—one from the cooling transformer (Rc) and one from the heating transformer (Rh). Learn how to install an ecobee thermostat in a dual-transformer system.

Rc

If you don’t have an Rh wire, Rc serves as both the cooling and heating power wire.

With dual-transformer systems you’ll have two R wires—one from the cooling transformer (Rc) and one from the heating transformer (Rh). Learn how to install an ecobee thermostat in a dual-transformer system.

W/W1 and W2

In a conventional system, W/W1 controls your heating system and, where applicable, W2 controls your heating system’s second stage, which helps warm the home faster.

If you have a heat pump system with auxiliary heating, you’ll normally connect the AUX/AUX1 or W2 wire to the ecobee’s W1 terminal. If you have two stages of AUX heat, you will connect AUX2 to W2 on your ecobee.

Y/Y1 and Y2

In conventional cooling systems, Y/Y1 controls the first stage of cooling and Y2 controls the second stage, which helps cool down the home faster.

In heat pump systems, Y1 controls your compressor, which heats and cools your home. If you have a two-stage compressor, Y2 controls your compressor’s second stage, allowing for different levels of heating and cooling.

G or G1

G or G1 controls your HVAC fan.

O/B

On heat pump systems, O/B controls the reversing valve, which tells your compressor to switch between heating and cooling.

E

Some thermostats for heat pumps have an E terminal, which toggles emergency heat on or off. Emergency heat should only be used on very cold days when the heat pump is unable to keep the house warm. The E wire normally connects to the ecobee’s W1 terminal.

AUX/AUX1 and AUX2

Heat pumps systems sometimes have a second, auxiliary heat source that helps warm your home quicker and keeps the home warm in frigid weather conditions when the heat pump cannot. Some auxiliary heat systems for heat pumps have two stages, hence AUX2.

If you have a heat pump system with auxiliary heating, you will normally connect the wire labelled AUX/AUX1 or W2 to the ecobee’s W1 terminal. If you have two stages of AUX heat, connect the AUX2 wire to the ecobee’s W2 terminal.

 

Less common thermostat wires:

When installing an ecobee thermostat, any unnecessary or spare wires can be safely taped off or wrapped around the wiring bundle and tucked back into the wall.

Label Description
S, S1, or S2

S terminals are for outdoor temperature sensors. ecobee thermostats obtain weather data over Wi-Fi so S wires aren’t necessary.

L

The L wire can be used to power indicator lights on older thermostats. ecobee thermostats feature an LCD display so the L wire isn’t necessary.

G2, G3, GL, GM, GH

Most HVAC systems feature a single fan speed. In multi-speed systems, fan speed is either controlled by the furnace control board or the thermostat.

I have a multi-speed system. How can I tell if it’s controlled by the furnace control board or by my thermostat?

· If your multi-speed system is connected to your current thermostat by a single G wire, fan speed is set by the furnace control board.

· If multiple G wires connect to your thermostat, your thermostat manages fan speed.

ecobee thermostats support the former type but not the latter.

If you’re installing an ecobee thermostat in a multi-speed system with multiple G wires running to your old thermostat, use the table below to match your preferred fan speed with the correct wire:

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O and B

On heat pump systems, the O and B wires tell the compressor when to switch between heating and cooling your home.

If you have a wire labelled B but do not have a separate wire labelled O, connect it to the ecobee thermostat’s O/B terminal.

If you see O and B as separate wires in your current setup, we recommend booking a pro near you to install your ecobee.

Worth a look: Occasionally, the wire labelled B may in fact be the common wire (C), which is needed to power an ecobee thermostat. Not sure? We’re here to help. Reach out to our friendly support team at 1-877-932-6233 or via live chat.

W3

A wire connected to the W3 terminal on your current thermostat indicates that you have a three-stage furnace. ecobee thermostats do not support three-stage furnaces. One work-around is to place a jumper between the W2 and W3 terminals on your furnace’s control board.

Caution: Always ensure that your system is powered off before performing any modifications to your system!

If you see a wire connected to your current thermostat’s W3 terminal, we recommend booking a pro near you to install your ecobee.

Y3

A wire connected to the Y3 terminal on your current thermostat indicates that you have a three-stage cooling system. ecobee thermostats do not support three stages of cooling. One work-around is to place a jumper between the Y2 and Y3 terminals on your furnace’s control board.

Caution: Always ensure that your system is powered off before performing any modifications to your system!

If you see a wire connected to your current thermostat’s Y3 terminal, we recommend booking a pro near you to install your ecobee

H or HUM or HUM1 and H2 or HUM2

This wire or pair of wires controls your whole-home humidification system.

ecobee SmartThermostat with voice control, ecobee4 and ecobee3 are compatible with accessories, including humidification equipment. When you are setting up your thermostat for the first time, you can add one compatible 1- or 2-wire accessory such as a humidifier, dehumidifier or HRV/ERV.

View the wiring diagrams for your ecobee to learn how to wire an indoor air-quality accessory.

Have questions? We’re here to help. Reach out to our friendly support team at 1-877-932-6233 or via live chat.

D or DH or DHUM or DEHUM1 and DH2 or DHUM2 or DEHUM2

This wire or pair of wires controls your whole-home dehumidification system.

ecobee SmartThermostat with voice control, ecobee4 and ecobee3 are compatible with accessories, including dehumidification equipment. When you are setting up your thermostat for the first time, you can add one compatible 1- or 2-wire accessory such as a humidifier, dehumidifier or HRV/ERV.

View the wiring diagrams for your ecobee to learn how to wire an indoor air-quality accessory.

Have questions? We’re here to help. Reach out to our friendly support team at 1-877-932-6233 or via live chat.

V, VR, Vg, V+

If you see a wire(s) labelled V or VR (or both) or Vg and V+ plugged into your current thermostat, we’ll need to take a closer look to ensure your system is compatible with ecobee thermostats.

Please reach out our friendly support team at 1-877-932-6233 or via live chat to see if your wiring is compatible with ecobee.

Other

If you see a wire labelled Other, or wire labels that aren’t listed here or in the below list of incompatible thermostat wires, please reach out to our friendly support team at 1-877-932-6233 or via live chat to see if your setup is compatible with ecobee. If it is, we recommend booking a pro near you to install your ecobee.

 

Incompatible thermostat wires:

Unfortunately, if you see any of the following wires attached to your current thermostat, your system is not compatible with ecobee.

Label Description

1 2 3 4

These wire labels indicate a proprietary system that isn’t compatible with ecobee thermostats.

A B C D

These wire labels indicate a proprietary system that isn’t compatible with ecobee thermostats.

Water or H20

ecobee thermostats are not compatible with these types of wires.

L1 and L2, or 110, 120 or 240 volts

These wire labels and terminal blocks indicate a high-voltage system and are accompanied by a Danger, Warning or Caution symbol. ecobee thermostats are not compatible with high-voltage systems.

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