Learn About The Colors Of Thermostat Wires With This Color Guide

If you have a thermostat that needs to be fixed, or you’re installing a new smart thermostat, we put together this thermostat wire color code to help you avoid DIY wiring problems. This is a list of common wire colors, but your thermostat may contain different colored wires therefore if you have any doubts, make sure to talk with our pros about a professional thermostat installation.  

Below are the most common thermostat wire colors with descriptions of each:  

  • White  
  • Yellow  
  • Green
  • Orange  
  • Red wires: Rc and Rh wires
  • Blue or C wires

White Wire

The white wire underneath your thermostat is the wire that connects to your heating system. It runs from your thermostat to your air handler or furnace. The white thermostat wire connects to terminal W in industry-standard thermostats. If your heater has multiple heating stages, you might find more than one white wire when you remove your thermostat.

Yellow Wire

The yellow wires that connect to your thermostat, connect to your compressor. They control your air conditioning system and terminate at your compressor contactor through an air handler. The yellow wires connect to the Y terminals on your thermostat.

Green Wire

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

Orange Wire

The orange wire connects to the heat pump if you have one. It terminates in your outdoor condenser and reverses the valve operation from hot to cold. The orange wire connects to terminal O on your thermostat.

The orange wire only applies if you have an air-source heat pump. Only air-source heat pumps connect to your outdoor condenser. Homeowners with geothermal heat pumps don’t need to connect to the orange wire.

Red Wire

Red wires indicate power. You may see an Rc and/or an Rh wire.  

The Rc Wire 

Rc wires are for air conditioning systems or dual transformer systems. Dual transformer systems refer to a setup with a cooling and heating transformer. Rc wires connect to the RC terminals on your thermostat.

The Rh Wire

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 Common wires. C wires are required for smart thermostats that need to be connected to a power source 24/7, regardless of the heat pump type. (It’s important to determine if your heat pump is compatible with your thermostat before you choose a thermostat.) 

Blue C wires belong to thermostats attached to a heat pump and connect to terminal B on your thermostat.

Still, Having Trouble?

With so many different configurations when it comes to thermostat wires, it can be daunting to do it alone. Avoid DIY wiring mistakes by booking an HVAC specialist through Pulled to help you get it right.

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