5 wire thermostat

Temperatures controlled by thermostats with five wires are usually used with systems with an air conditioner and a heating element. These systems are likely to use gas or electric heaters. Unlike analog thermostats, digital thermostats draw their power from the C-Wire. Older thermostats probably didn’t require power, but many newer thermostats do.

This is a mercury switch thermostat that is mechanical. Today, digital thermostats are available, but this one is mechanical. The older mechanical thermostat, typically a 4-wire thermostat that controls the type of system described above, is still installed in some older systems.

 Wiring a gas furnace and air conditioner with 5 wires

There is a new Honeywell VisionPRO Wi-Fi Programmable Thermostat model TH8320WF for installation. You can plan to use conventional wiring since you don’t use a heat pump. On the old thermostat, the jumper was for connecting two wires, so it would seem that there is only one wire missing.

5 wire thermostat wiring color code

The wiring color code for a wired thermostat is a standardized system used to indicate the function of each wire in the thermostat. The color code helps ensure that the thermostat is wired correctly and safely. The most common wire color code in the United States includes red for the 24VAC power supply wire, white for the heating wire, green for the cooling wire, yellow for the compressor wire, and blue for the common wire.

Some systems may also include wires for special functions such as a fan or a humidifier. It is important to follow the specific wire color code for your thermostat model and consult the manufacturer’s instructions or a professional electrician if needed to avoid any potential safety hazards or incorrect wiring.

Wire colors and code descriptions are the first things we need to use to identify and locate the wires. Once you know where the wires are and what they do, you will be able to locate them. Most thermostat installations, however, depending on the color code used by the installer.

What color goes where on a 5 wire thermostat?

Unless you refer to another jumper, I assume it is unused. This will not be a problem with your new thermostat. Please follow the instruction booklet that came with your new thermostat. That’s excellent news. Here’s some not-so-great information. Because your new thermostat will require an additional wire, you didn’t mention whether you had any extra wires in the thermostat bundle.

Unlike your old thermostat, your old thermostat is mechanical and doesn’t have a standard wire. Because the new thermostat is a state-of-the-art digital programmable wi-fi thermostat, it needs 24 volts of power to function efficiently. It requires the common wire to be 24 volts with the hot wire as the 24-volt power supply. This means you need a 24-volt hot wire and a 24-volt grounding wire. There is already the red wire for 24-volt seductive power, so either that wire needs to be replaced, or the all-new thermostat wire must be run to ensure you have enough wires for the job.

5 Wire Thermostat Wiring Problem: Old Wiring Additional Resources

White Wire

Under your thermostat is the wire that connects your heating system to the thermostat. This runs to your central air handler or furnace. On industry-standard thermostats, the white wire attaches to terminal W. Your HVAC system may have more than one white wire if it has multiple heating stages.

Yellow Wires

This wire connects to your compressor under your thermostat. Air conditioners are controlled by this wire. An air handler connects yellow wires to the compressor contactor. Your thermostat’s Y terminals are connected to the yellow wires on the air handler.

Green wire

Your furnace or air handler’s fan is connected to the green wire under your thermostat. The wire terminates at either your furnace or air handler. Terminal G on your thermostat is connected to the green wire.

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Orange Wire

If you have one, your heat pump is connected to the orange thermostat wire. It terminates in your outdoor condenser to reverse valve operation from hot to cold. Your thermostat’s O terminal connects the orange wire. Heat pumps with an air source are the only ones that use the orange wire. Your outdoor condenser can only connect to heat pumps with an air source. The orange wire is not necessary for homeowners with geothermal heat pumps.

Red Wires

Power is indicated by red wires. RC or Rh wires may be seen. 

  • RC Wire: RC Wire indicates an air conditioning system or a dual transformer system. The cooling and heating transformer system are called a dual transformer system. Your thermostat is equipped with RC terminals that connect to the RC wires.
  • Rh Wire: Rh wires are connected to your heating system rather than your cooling system. Depending on if you’re using dual transformers, this wire may be read without the H. RH is the wire that connects to your thermostat’s RH terminal.

Blue or C Wire

Because they are standard wires, blue wires are also referred to as C wires. Smart thermostats that need to be plugged into a power source 24/7 must have C wires, no matter what type of heat pump they are. (Before making any decisions, ensure your heat pump and thermostat are compatible). Any thermostat can have a C wire or a wire of various colors, but thermostats connected to heat pumps will have blue C wires. Heat pumps use blue cables. Your C wire connects to your thermostat’s B terminal.


If you’re installing a new smart thermostat or trying to fix your thermostat, this thermostat wire color code will make your life a whole lot easier. Most thermostat wiring styles are based on this, which applies to heating and cooling systems.

In a typical wiring diagram, there are four colors: red for 24-volt hot, white for heat, yellow for cooling, green for fan, and blue for common (although the colors may change every day).


  • Is there a color code for thermostat wires?

Temperature control systems that regulate heat and air conditioning usually use this wiring style.

  • What do 5 wire thermostats do?

An air conditioner with a heating system typically uses a thermostat with five wires.

  • Can cat5 be used for thermostat wire?

Ethernet cables should work fine since thermostats operate at low voltages and low currents. For simplicity’s sake, you might find it easier to treat each pair as a single wire.

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