common wire on thermostat

In the past, thermostats were simple switch-on devices that didn’t require a power source. Modern thermostats with Wi-Fi and a backlit display, in contrast, require a continuous power supply. A C-wire, also known as the “common wire on the thermostat,” permits the constant supply of power 24 VAC for the thermostat.

Is the common wire the C wire?

To render your system compatible, however, you might occasionally need to attach a common (C) wire or a powered accessory, such as the Nest Power Connector. In contrast to other wires attached to your thermostat, a C wire does not manage heating and cooling operations. Your thermostat receives only steady power from it.

Need of common wire on the thermostat

In technical terms, power flows through an R (red) wire; however, it is not continuous (not by itself in any case). Ensuring it is continuous requires an ordinary wire to complete the circuit. Once the course is completed, the 24V power will flow continuously. If you’re purchasing an intelligent thermostat, you’re likely thinking about making the installation yourself. If you can change an outlet or light switch and are skilled enough, you’re qualified to be able to install the smart thermostat, assuming that your thermostat already is wired with a C. If your system is connected to C-wires, they could be active or hidden behind your thermostat.

If your thermostat doesn’t have C-wires, you’ll have to install a new wire between your heater and your thermostat to set up the majority of modern intelligent thermostats. If you have AC and heat AC, you’ll require 18/5. If you’re heating, the 18/3 should suffice; however, you might consider running 18/5 to ensure your future security.

Identifying Your Thermostat’s Wires

There are two methods to determine which wiring your HVAC system is using.

Method 1: Examine the wiring behind your thermostat.

Take your thermostat off the wall, and then look at the wires that connect to it. If you have a wire connected to the terminal marked “C,” that means you’re (probably) in good shape with installing a smart thermostat. If you do not find a C-wire in your thermostat, do not think you don’t have one. It could be tucked away in the wall, as some installers use if the C-wire is there but isn’t needed. If you spot C-wires in your furnace, the other end could be hidden in the wall behind the thermostat.

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Method 2: Examine the wiring inside your furnace

  • Switch off the power supply to your furnace, then remove the cover. (The difficulty of doing it is dependent on the stove and the installation).
  • Look for row screws labeled R, C, W G/Y/Y2, and the ones above.
  • This HVAC unit compatible with the intelligent thermostat will require either.
  • A new set of wires is connected between the thermostat and the furnace or the Venstar Connect-aWire the Venstar Add-a-Wire.
  • A smart thermostat like the ecobee3 includes the Energy Extender Kit for devices that do not have C-wires.

If you are worried that putting a probe within your furnace or thermostat isn’t your cup of tea, think about employing a professional to assist with installing your thermostat. There aren’t any standards regarding wire colors. Any wire can be employed to serve any use. The previous owner or handyman could be “creative,” and the wire you see behind your thermostat may differ from what you’ve read on the internet or here.

Here are the most common applications of wire color:

  • Blue or Black: C -Common wire could not be used by your current thermostat. Allows continuous flow of power from to the Red wire.
  • Red R 24VAC power source from the transformer in the furnace.
  • Red Rc 24VAC (dedicated to the heat call).
  • White: W – Heat.
  • Yellow: Yellow Air conditioner.

Nest Owners Not Exempt

The fad Nest thermostat operates without a C wire, but some conditions exist. The Nest draws power from your cooling or heating systems without an electrical connection. If it’s working, if it’s not, however, the Nest requires electricity. When it’s not running, the Nest can “pulse” the heating wire to turn on the furnace, pulling some energy to power itself. In specific systems, this may not be noticed however, in other systems, the furnace behaves in a manner that resembles being told to turn off and then shut off.

Nest’s maker updated its manual to inform consumers that the Nest might not be compatible with some single-cycle or no-C-wire systems. However, the reality is that old wiring will get more and more a hassle to manage.

Do not do “fan wire” tricks

You could use the fan wire as a power cable, but you (and the next homeowners in your house) aren’t able to turn the fan off. If you’re looking to invest a few hundred dollars in the thermostat, you should invest a bit more in an adapter or professional to complete the task correctly.

What do you do if you do not have a C-wire?

Employ a professional to wire new wires through your thermostat and furnace (or DIY it) Take the Ven star add-a-Wire to add wire to the 4-wire configuration. Find an intelligent thermostat designed to work with systems that don’t have the C-wire, such as ecobee3 (it includes an adapter to wireless systems that don’t require a C-wire) as well as the Emerson Sensi (in several methods, it doesn’t need any C-wire in any way).


Do thermostats require a unidirectional wire?

The thermostat should indeed be wired with a C wire if you’re updating your thermostat. Whether they are competent or not, most modern thermostats need a power source, and it’s unlikely to change anytime soon.

Which color will be the standard wire of a thermostat?

Blue wires are often referred to as “C” wires because they are standard wires. C wires are required to every “smart” thermostat, which requires continuous connection to a power source regardless of the heat pump model.

What is the most common wire that is used on thermostats?

C-wires or the standard wire are connected to your heating system that is low voltage (24v) and supplies uninterrupted power to your thermostat. Today, most newer heating and cooling systems in the electric market are equipped with C-wires that guarantee compatibility with most smart thermostats.

Apart from this if you are interested to know more about Electrical Checks You Must do Before Moving Into a New Home then visit our category.