Thermostat Red and White and Green Connect to Blue and Brown Wires

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If you've ever had to set up a Thermostat, you know exactly what a hassle it can be.

There isn't any standardization in place, so you're at the mercy of the manufacturer when it comes to how they color-code their wires for terminals.

You're in for double the trouble if you're trying to swap one thermostat out for another 'cause now you have to deal with two different companies' systems for color-coding.

I know of your woes, and that's exactly why I wrote this article.

I've spent a lot of time reviewing many different smart thermostats in my quest to build the best, most convenient Smart Home possible, like the Nest Thermostat, EcoBee Thermostat, and Sensi Thermostat.

Being a Smart Home nerd has its perks, but having to constantly switch between different Thermostats developed by different companies is not one of them.

Over time, however, I've managed to crack the code, so to speak, and now I understand how certain manufacturers like to color-code their terminal wires.

In this article, I'll share what I've learned so that you can save yourself the time and effort to research wiring diagrams and the hassle usually involved when setting up Thermostat Wiring.

In general, the thermostat wire colors match the first letter of terminal names such as Red Wires for R terminals (for Power), Yellow Wires for the Y terminal (for Cooling), White for the W terminal (for Heating), Green Wires for the G terminal (for the Fan).

A few exceptions are blue (or sometimes black) wires for the C terminal (Common Terminal), light blue wires for Y2 (Second-stage Cooling), and brown wires for W2 (Second-stage Heating)

But these color codes can vary for different manufacturers. After reading this article, you'll know the color codes for the major Smart Thermostats out there, as well as how to identify the wires for non-standard connections.

Take necessary precautions before you set to work on any DIY tasks involving Thermostats.

Ensure that all the transformers and systems are turned off before doing any wiring.

Also, ensure that there's no power running through the air blower and condenser.

If there is a pre-existing Thermostat that you plan to swap out, then ensure that you snap a photograph of its wiring for reference purposes.

General Thermostat Wiring Color Code

Terminal	Wire Color	Description
R	Red	The R terminal is reserved for Power. For split systems, It is usually a red wire that runs from the main transformer, which is usually located in the air handler. But in some systems, you may find the transformer in the condensing unit. For this reason, to avoid injury or damage to the components cut off the power to the condenser and the air handler before attempting any wiring work on the thermostat.
Rc	Red	The Rc terminal is reserved for the power of the cooling unit. If your HVAC system uses a separate transformer for cooling and a separate one for heating, then the wire from the air conditioning system runs through to the Rc Terminal. If there is only a single transformer powering the Heating and Cooling Systems, then a jumper can be connected between Rc and Rh.
Rh	Red	The heating counterpart to Rc, the Rh terminal is reserved for the power of the heating unit. They are jumpered together in a single-stage heat system.
Y	Yellow	The Y terminal is reserved for Cooling. A yellow wire runs to the Compressor and controls the Air Conditioning system.
Y2	Light Blue	The Y2 terminal is rare and is used for second-stage cooling. If you have a two-stage cooling system (two settings – high and low) and need them controlled by a single thermostat, then a wire runs to this terminal from the second compressor.
W	White	The W terminal is used for Heating. A white wire is run from the heating source, which can be anything from a traditional oil or gas furnace to a more modern boiler or electric furnace.
W2	Brown	The heating counterpart to Y2, used for two-stage heating systems. A brown wire is run from the second heat source to this terminal.
G	Green	The terminal is used to power the Fan. A green wire is run from the Indoor Blower Fan to this terminal.
C	Blue/Black	This the Common Terminal, and usually, a blue or black wire is run to the transformer from this terminal to complete the circuit, and in some cases, provide power to the Thermostat.
O/B	Orange/Dark Blue	This terminal is found on thermostats designed to work with Heating Pumps and is used to power the defrost cycle on the heat pumps. An orange or dark blue wire is usually run from the heat pump to this terminal.
E	Any Color	This terminal is meant for Emergency heating in a scenario where the heat pump compressor is damaged, and some form of heating is essential. Manufacturers take liberties to assign whatever color they wish for the wire that runs from this terminal to the backup heat source, and it activates it in case of emergency.
X	Any Color	This terminal is meant for Auxiliary Power for heat pumps. While the E terminal activates the backup heat source, this terminal actually powers the backup heat source, and similar to the E terminal, the wires for this can be of any color.
S1 and S2	Shielded Wires	These terminals are used to run Outdoor Temperature Sensors and are sometimes labeled as T terminals. They run completely separate shielded wires that are immediately distinguishable from other wires. They are shielded to prevent electromagnetic interference from affecting the reading of the temperature sensors.

Thermostat Wiring Color Code for Nest Thermostat

The Nest Thermostat has the expected Rh, Rc, Y1, Y2, W1, W2, G, O/B, and C terminals on the back.

But an unconventional yet welcome surprise is a Star(*) terminal, a versatile terminal that can be used as:

1. An E terminal
2. Y3/W3 terminal for three-stage cooling/heating, respectively
3. Humidification H Terminal
4. Dehumidification DH Terminal
5. An extra G terminal

The most common HVAC system is currently the Split system, which made up about 57% of all HVAC units sold in 2017 and is set to continue to grow.

A conventional Split System consists of a single-stage heating and single-stage cooling unit and can be easily wired up to the Nest Thermostat.

Once again, take the necessary precautions before starting any wiring work and disconnect the power from the major components in your HVAC systems, such as the transformers in the air handlers and compressors.

To wire up your Nest Thermostat, simply:

• Connect the Red wire from the transformer to either the Rc or Rh terminals (as they are connected internally)
• Run the White Wire from the furnace to the W terminal.
• Connect the Yellow Wire from the compressor to the Y Terminal
• Run the Green Wire from the Air blower to the G terminal
• Wire up the blue C-wire to the C terminal from the transformer. Or you can omit this and connect a power adapter.

Feel free to connect an additional heat source to the W2 terminal and an additional compressor to the Y2 terminal according to your HVAC system

There is no need to jumper the Rc and Rh terminals on the Nest Thermostat as this is already done internally within the thermostat.

Thermostat Wiring Color Code for Ecobee Thermostat

The Ecobee Thermostat comes with the expected  Rh, Rc, Y1, Y2, W1, W2, G, O/B, and C terminals on the back but also comes with ACC+ and ACC- terminals to connect accessories such as Humidifiers and Dehumidifiers. They must be wired accordingly to complete the circuit.

To wire up your EcoBee Thermostat, simply:

• Connect the Red wire from the transformer to either the Rc or Rh terminals (as they are connected internally)
• Run the White Wire from the furnace to the W terminal.
• Connect the Yellow Wire from the compressor to the Y Terminal
• Run the Green Wire from the Air blower to the G terminal
• Wire up the blue C-wire to the C terminal from the transformer. Or you can omit this and connect a power adapter.

Feel free to connect an additional heat source to the W2 terminal and an additional compressor to the Y2 terminal according to your HVAC system

It is not necessary to jumper the Rc and Rh terminals on the Ecobee Thermostat as they are already connected within the thermostat.

Thermostat Wiring Color Code for Sensi Thermostat

The Sensi Thermostat comes with the expected  Rh, Rc, Y, Y, W1, W2, G, O/B, and C terminals but also comes with an L terminal.

This terminal is for connecting the LCD display.

To wire up your Sensi Thermostat, simply:

• Connect the Red wire from the transformer to either the Rc or Rh terminals (as they are connected internally)
• Run the White Wire from the furnace to the W terminal.
• Connect the Yellow Wire from the compressor to the Y Terminal
• Run the Green Wire from the Air blower to the G terminal
• Wire up the blue C-wire to the C terminal from the transformer. Or you can omit this and connect a power adapter.

Feel free to connect an additional heat source to the W2 terminal and an additional compressor to the Y2 terminal according to your HVAC system

Do not jumper the Rc and Rh terminals on the Sensi Thermostat as there is a built-in jumper within the unit.

Conclusion

Now that you've gotten the general idea of the color code of Thermostat Wires, you can try your hand at setting up/modifying your own HVAC system to your liking.

Although not all manufacturers will use the same color code for the wiring, you can identify the wires by tracing which component they are connected to in your HVAC system.

You May Also Enjoy Reading:

• What Is The Y2 Wire On A Thermostat? [2021]
• Best Thermostat Lock Boxes You Can Buy Today [2021]
• Ecobee Thermostat Blank/Black Screen: How To Fix
• How To Fix Nest Thermostat Delayed Message Without A C Wire
• Ring Thermostat: Does It Exist?

Frequently Asked Questions

Do I need to turn off power to install a thermostat?

When installing a new electrical appliance in your electrical grid, it is always wise to turn off the power to avoid any potential harm to yourself and potential damage to your components.

Can thermostat wires cause fire?

Short-circuit between the thermostat wires and the household line voltage can damage the thermostat, and at times, even fire.

Does R go to RC or RH?

For smart thermostats and modern dumb thermostats, Rc and Rh are usually jumpered internally so the red wire can go in either, but in older thermostats, the general rule is for the power line from the heating side to go to Rh and the power line from the cooling side to go to Rc.

What happens if you wire a thermostat wrong?

Wiring a thermostat wrong can have potentially devastating effects, ranging from Electric shock, blowing a fuse, damaging the thermostat, or the HVAC components themselves. You could also cause a fire.

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Source: https://robotpoweredhome.com/thermostat-wiring-colors/

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