Thermostat Wiring Colors – What Goes Where

By Max Anthony •  Updated: 11/25/22 •  6 min read

Thermostat Wiring Colors

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Having a good thermostat is one that is extremely important in any home. That you can adjust the thermostat to set a specific temperature throughout the year is essential to making your house comfortable, even in warm weather.

12% of homes in the United States have a central air-conditioning unit that controls the temperature of their home. North America is one of the most energy efficient countries in the world, so many households are equipped with intelligent thermostats that allow them to effectively control the temperature.

Smart appliances allow users to save energy by controlling and monitoring their usage. They also allow us to restrict the use and reduce the need to perform routine maintenance. Using smart thermostats will help you save energy by allowing you to limit the number of things that you use and reduce the need for you to constantly do things to maintain the system. It will be easy for you to conserve energy. Study after study has shown that homeowners who use energy-efficient thermostats can save 50% on heating and cooling costs.

With smart homes, more Americans can control the HVAC systems in the homes that they live in. To properly wire a thermostat is important for every homeowner. If the battery in your home thermostat stops working, you may fix it by doing some simple electrical repairs. This will save you time and money. If it is unnecessary to have a qualified person do all the work for you, then this will help you be familiar with the wiring process.

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In most cases, the wire color on a thermostat corresponds with the letter on a terminal such as red for Power (for turning on the power source), yellow for Cooling, white for Heating and green for the G terminal (for the fan).

Some exceptions to this rule are wires that are colored blue for the C terminal (Common Terminal), and white for the W2 terminal (second step heating).

But the colors can vary from one thermostat manufacturer to another. After you read this, you’re going to understand what color codes are on the most popular Smart Thermostats, as well as how to find wires that connect to other devices that use different colors.

Thermostat Wiring Colors

Red (R)

The R terminal is for power. If you have a split system, the R-terminal is a red wire that runs from the main transformer, that is normally in the air handler. You may also locate the transformer in the condensing unit. By cutting off the power to the air handler and the condenser units, you will prevent damage to the components.

Red (Rc)

Rc is the power cord that connects the heating and cooling unit to the power box. If you have a system that uses two transformers for cooling and heating, then the wire that comes out of your air conditioning system goes to one of the Rc terminals. If only one transformer powers the Heating and Cooling Systems, then a jumper can be placed in the line that passes from Rc to Rh

Red (Rh)

Similar to the electrical terminals on the power supply, the power supply at the Rc terminal is for the power supply to the central heat pump. The Rc terminal is for cooling. The Rh terminal is for heating.

Yellow (Y)

The Y terminal is used for cooling. A green wire carries power to the compressor and drives the control of the air conditioner.

Light Blue (Y2)

It is rare to find a Y2 terminal, but it is commonly needed for cooling units that are running in two stages. If your air conditioning has two stages (high and low) and you only need one thermostat for each stage, then a wire is run to this terminal on the compressor side.

White (W)

W terminal is placed near the power supply and connected to a wire that runs to the heating system. Wires of various colors run from any heating source (which can be anything from an old-fashioned oil or gas furnace to a more advanced boiler or furnace).

Brown (W2)

This is a very similar product to Y2, but for heating systems with two heating stages. A wire runs from the heat source to the terminal on the top of the fan.

Green (G)

This terminal supplies electrical current to a fan that runs on this terminal; the wires from the fan that runs on this terminal are connected to the common terminal. It is not uncommon for a wire to be run via an indoor fan to this terminal.

Blue/Black (C)

This terminal supplies the power that heat pumps need in order to turn the heat pump on. Sometimes, the thermostat will also need power from this terminal to turn the heat pump on.

Orang/Dark Blue (O/B)

This is a common terminal that is often used on thermostat systems that work with heat pumps. It powers the defrost cycle on the heat pumps. When heat is turned on in a heat pump, a wire that is normally red or blue is run from the heat pump to this terminal.

Any Color (E)

This is what is needed to allow the heat pump to restart when it is necessary to turn off the heat. Manufacturers usually allow people to specify any wire that runs from this terminal to the heat source that is used in case of emergency.

Any Color (X)

This is a terminal that allows heat pumps to power themselves. It uses a separate wire from the other terminals to power the heat source. It is possible that a terminal that looks like an E will turn on the heat source, but the fact is that the wires that run from the terminal to the heat source are not controlled by the unit, and if this terminal is not used, the power to the heat source will be switched off.

Shielded Wires (S1 and S2)

These terminal boxes are typically used to connect temperature sensors that are plugged into a wall. They are also called T terminals. They have completely shielded wires that are easily distinguished from other wires. The shielding protects the temperature sensor from interference from outside forces.

When you have learned the color codes of thermostat wires, you can try your hand at installing or changing your own HVAC system to your liking. Some manufacturers may not use a color code for the wiring, but you can easily recognize the wires by identifying the components to which they connect.

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Max Anthony

Mainly Max Anthony is an athletics tutor & lives in Texas but that's not it. He's is also a music producer, content creator, record producer, writer, and session musician. He has been producing music and engineering at a lower level for over 5 years. His passions include quality music gear and that's what he loves to write about on HifiBeast. ( Shoot him an email now )