HVAC Wiring Colors (Thermostat Wire Color Code)

HVAC wiring colors can be a little confusing. In this article, we’ll cover the different colors of hvac wiring and what they mean. We’ll also give you a guide to understanding the different types of hvac systems and how they work. So if you’re looking to learn more about hvac wiring colors, keep reading!

The thermostat is one of the most important things in your home. You can live in your house even on the hottest summer days and the coldest winter days if you can change the temperature.

Smart heating and cooling systems let people save energy by monitoring and controlling how much energy is used. They also make it easier to save energy because we can limit how much we use them and do less work ourselves. Research on the smart home market shows that people who use smart heating and cooling systems save 50% of the energy they use.

With the rise of “smart homes,” more and more Americans are able to control the HVAC system in their homes. Everyone who owns their own home needs to know how to wire a thermostat. If your thermostat stops working, you might be able to fix it yourself to save money and time. If you’d rather hire a pro, this information will help you understand how the wiring process works.

Standard HVAC Wiring Color Code

  • Red wire is the one that powers the thermostat. The red wire goes to the 24VAC (Rh for heating, Rc for cooling). If you don’t have two transformers, you can write “R” on the Rh wire.
  • Green wire connects to the fan. Connects to the air handler or furnace’s fan (and terminates there).
  • The white wire goes from the heating system to the furnace or air handler. If your HVAC system has more than one heating stage, your thermostat may have more than one white wire.
  • Yellow wire is responsible for the cooling system. These wires go through the air handler and end at the contactor for the compressor.
  • The common wire is blue or black. This is a wire that all heat pumps have in common. If your HVAC system needs to be connected to a power source at all times, it will need a common wire.

Blue common wires are usually found in homes with heat pumps (if there is no heat pump, then the color might be black).

The wire goes to the B terminal, which keeps the thermostat always connected to the source of power. This helps control the “smart” parts of the device.

hvac wiring diagram example 1
HVAC Wiring Colors (Thermostat Wire Color Code) 1

Wiring a thermostat is as easy as connecting the wires with the right colors to the right terminals. To finish the procedure successfully, you must know what each wire is for. If you don’t understand how the thermostat is wired, it’s best to call a professional.

Nest Thermostat Wire Colors

There are different colors of nest wires, but:

  • Usually, common wires are blue.
  • If you have a heat pump and there is an orange wire in the W and O/B connector, put it in the O/B connector on the thermostat.
  • If you don’t have a heat pump and there is a white wire in the W and O/B connector, put it in the W connector on the device.

How Can You Tell What Wires Are in a Thermostat?

  • Turn off the thermostat and the HVAC unit.
  • Find the HVAC control board. The thermostat wires connect to the heating and cooling system at this board.
  • Most likely, the wires will be marked by color. Also, they should have labels.

What do the letters on the thermostat wiring mean?

thermostat wiring letters mean
HVAC Wiring Colors (Thermostat Wire Color Code) 2

The R wire, which is often red, is the wire that gives power to the whole HVAC system. If you have both a Rh and a Rc wire, you can connect the R wire to either one.

If you only have the R wire, it will only have one R connector.

The Rc and Rh terminals are connected together in a single-stage heat pump system and a 4-wire heating and cooling system. But that isn’t the problem with a 5-wire system.

Different Kinds of Thermostat Wiring

Two Wires

2 wire thermostat wiring diagram
HVAC Wiring Colors (Thermostat Wire Color Code) 3

Almost certainly, if you have two wires, you have a digital thermostat that only provides heat (i.e. without air conditioning). The two wires are usually red and white. The thermostat is powered by the red wire, and the white wire heats the room.

Three Wires

3 wire thermostat wiring color code
HVAC Wiring Colors (Thermostat Wire Color Code) 4

This is the most common way to connect and control a boiler with a digital thermostat. There’s a hot wire with 24 volts, a common wire with 24 volts, and a white wire.

Four Wires

4 wire thermostat wiring color code
HVAC Wiring Colors (Thermostat Wire Color Code) 5

This is a common way to set up a thermostat that runs on batteries or a digital thermostat that only controls the heat. The standard set-up is made up of The thermostat is powered by the red wire, the heating unit is connected to the white wire, the blue wire is the common wire, and the fan is connected to the green wire.

Five Wires

This is the most common way to wire a thermostat, and it works for both wiring and cooling systems. Red is for 24-volt hot, white is for heat, yellow is for cooling, green is for the fan, and blue is for the common (although the common wire may be a different color).

hvac wiring colors
HVAC Wiring Colors (Thermostat Wire Color Code) 6

Six Wires

If your system has two levels of heat and one level of cooling, you have a 6-wire thermostat.

HVAC Wiring Color Video

What happens when you wire a thermostat wrong?

Electric shock is one thing that could happen if the installation is done wrong. A circuit breaker is tripped. The unit’s thermostat, electrical system, or even the AC/furnace unit itself could be damaged.

Does changing a thermostat require turning off the power?

Before you look at or work on a thermostat, you should always turn off the power to it at the service panel.

What circuit breaker do I turn off to turn off the thermostat?

You just turn off the “HVAC,” “Cooling,” or “Heating” circuit breaker. All power will be cut off to the HVAC system.

How do I turn the power off to my HVAC system?

Look for a switch on your furnace or near it. The switch can be in different places, so if you can’t find it right away, look on the sides, in the back, or even in the rafters. The switch will look like a regular light switch, and it should be turned to “off.”

Can the wires in a thermostat start a fire?

Yes. More than 135,000 thermostats are being taken back because a fire could start if the thermostat wires come in contact with household line voltage.

Can a broken thermostat stop a furnace from working?

Yes. A broken thermostat is one of the most common problems with a furnace. If your fan is always running, you know that your thermostat isn’t working right. This will make the battery in your thermostat run down and make your furnace work less well.

Can I turn off the HVAC?

It’s fine to turn off your air conditioner when you’re at work or when the weather is nice enough that your home doesn’t need cooling.

How does a thermostat catch on fire?

The safety commission says that if the wires of the thermostat touch the line voltage in the house, the thermostat can be damaged and a fire can start.