The Thermostat Wire Color Code You Need to Know

Image of different color wires
Your thermostat is an important part of your home. Whether you’re consulting it to decide what to wear or what to do (or not to do!), your thermostat prepares you for the day. It’s important to know how your thermostat is wired in the event it stops working. Each thermostat wire has a different color which signals its function.

This thermostat wire color code will help homeowners understand the anatomy of their thermostat:

  • White wires
  • Yellow wires
  • Green wires
  • Orange wires
  • Red or “Rc” wires: Industry standard for geothermal heat pumps
  • Rh wires: Industry standard for geothermal heat pumps
  • Blue or “C” wires

Make sure you know what’s happening underneath your thermostat! Read on for information about all possible thermostat wires.

How to Wire a Thermostat

To install a new thermostat or repair an existing device, you’ll need to understand the different colors of wires. Each wire connects to a different terminal and is responsible for a different function.

Below is an industry-standard thermostat wire color code complete with each wire’s function. Keep the following list handy whenever you decide to peak behind your thermostat.

The White Wire

The white wire underneath your thermostat connects to your heating system. It terminates at your air handler or furnace. The white wire connects to terminal W in industry-standard thermostats.

Yellow Wires

The yellow wires underneath your thermostat connect to your compressor. They control your air conditioning system. The yellow wires terminate at your compressor contactor via an air handler. The yellow wires connect to the Y terminals on your thermostat.

The Green Wire

The green wire underneath your thermostat connects to the fan of your furnace or air handler. It terminates at the air handler or furnace. The green wire connects to terminal G on your thermostat.

The Orange Wire

The orange thermostat wire links to your heat pump, if you have one. It terminates in your outdoor condenser for reversing valve operation from hot to cold. The orange wire connects to terminal O on your thermostat.

The orange wire only applies to homeowners with an air-source heat pump. Only air-source heat pumps connect to your outdoor condenser. Homeowners with geothermal heat pumps have no use for the orange wire.

Red or “Rc” Wires

Red wires, specifically Rc wires, are responsible for 24-hour volt AC power from your transformer. Rc wires are only for air conditioning systems or dual transformer systems. Dual transformer systems refer to a setup with a cooling and heating transformer. These wires only connect to your cooling system. Rc wires connect to the RC terminals on your thermostat.

The Rh Wire

The Rh wire, another type of red wire, is also responsible for 24-hour volt power from your transformer. The Rh wire connects to your heating system as opposed to your cooling system. This wire may be red without an “H” attached to it, depending on if you have a dual transformer setup. The Rh wire connects to the RH terminal on your thermostat.

The Blue or “C” Wire

Blue wires are also called “C” wires because they are the Common wire. C wires are necessary for any “smart” thermostat that needs to be connected to a power source 24/7, regardless of your heat pump type. (It’s important to determine that your heat pump is compatible with your thermostat before you decide.)

C wires or varying colors apply to every thermostat, but blue C wires belong to thermostats attached to a heat pump. Blue wires are for heat pumps, like orange wires. This wire connects to terminal B on your thermostat.

Got Your Wires Crossed?

There’s a lot to keep track of when it comes to thermostat wires! If you need help installing your new thermostat, Aire Serv® is here to help you get it right. Aire Serv can help homeowners with all thermostat and HVAC needs. Call (855) 512-2886 or request an appointment online to get started.