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How To Install Nest Thermostat Without A C-Wire (6 Easy Steps)

installing nest thermostat without c wire

I have been using the same Nest thermostat for a long time now. What I wanted was a change. For this I had to buy a newer model of my thermostat. So about a week before, I ordered the latest Nest thermostat for my home.

It was the time to replace my old thermostat with the new one. The replacement process was known by me so I didn’t face much trouble. But what I saw was that there was no C-wire, opps! Suddenly I started to think about the money which I had spent to make this purchase. However, I tried being calm and focused on finding the real solution of this problem.

You Can Install Nest Thermostat Without C-wire By Using A C-wire Adapter. It Compensates The Absence Of A C-wire And Is Much Cheaper Than The Professional Installers.


Now you must be thinking that how do I do all the wiring for Nest thermostat? Well, there isn’t much to worry about as I will guide you through all the steps in detail like I did when your Nest thermostat was showing delayed message and when it was not heating properly.

First of all, you should know about the C-wire adapter which you will be using in the process. If you take my suggestion then I would definitely recommend you to use Ohm Kat C-wire adapter.


It is very important to know about the contribution of a C-wire or common wire in the thermostat. So basically this wire draws power from furnace or sometimes from heating or cooling units in order to provide continuous power to your thermostat.

Yes, you can use Nest thermostat without a C-wire but it is recommended to use it with a C-wire. According to a survey, people who were using Nest without a C-wire faced multiple issues. If there isn’t a common wire then obviously your thermostat will draw power from your HVAC system to charge itself.

However, if you use a common wire then the charging will be done by drawing power from this wire. Like this other nest wires will not be disturbed at all. So if not compulsion but using your Nest thermostat with a C-wire is definitely a necessity. The thermostat will function much better in the presence of a C-wire.


If you want to install Nest thermostat without C-wire then you will have to follow the below mentioned steps. These steps are pretty much straight-forward and doesn’t involve any complexities so make sure you follow them correctly.


STEP 1 – Get the required C-wire adapter and make the necessary connections to the thermostat

STEP 2 – After this is done, connect the adapter to the thermostat

STEP 3 – Power ON your thermostat and you are good to go

These steps have been told to you briefly, but now I will tell you about each and every step in great detail so you don’t have to face further inconvenience.


In this section of the article, all the steps will be explained in a detailed manner.


As mentioned above, the best C-wire adapter has to be Ohm Kat adapter. The reason why I suggested you this adapter is because firstly I have been using it for a very long time and I didn’t face any inconvenience. Secondly, these adapters are specifically made for Nest thermostats so there aren’t any compatibility issues as well. Lastly, it provides lifetime guarantee and is made in USA.

The next best thing of this adapter is that it provides great safety to its users. As the connections have to be external so safety must be ensured properly.


For this process, you must have some initial knowledge about the terminals of your thermostat. However, terminals vary with the model but the basic layout of every model is somehow the same.

  1. Y1 Terminal: Cooling loop controller
  2. W1 Terminal: Heating loop controller
  3. G Terminal: Fan Controller
  4. Rh Terminal: Power Controller

The Rh terminal is the power controller which means it completes the circuit for your thermostat.


Now the grind starts, this is the time when you can actually start the installation process. But before performing any further steps, it is advised to turn OFF your thermostat from the main outlet for safety concerns and then take a picture of the wiring so it doesn’t get difficult for you to connect the wires. Depending upon your system, the corresponding wire will be connected to either W1, Y1 or G terminal.


All the wire connections will remain the same except for a few ones.

  • The Rh wire should be disconnected. Connect one wire of the adapter to the Rh terminal.
  • The other adapter wire should be connected to the C terminal.

While making connections, make sure that there aren’t any lose connections. Only the insulation part of the wires should be seen while the copper part must be hidden. By making these connections, we have established a circuit which will power your thermostat without getting power from the HVAC system.


After you have made all the relevant connections, it is now the time to put back the thermostat on. This is a step which is performed to ensure your safety. Although the work done here is with low-voltage wires but safety must always be your first priority.


Once you have done all the above mentioned work, now is the time to power ON the thermostat. For this you will have to turn ON the power from the main outlet and then proceed further. If you see blinking after powering ON your thermostat then it means the wiring has been done correctly.

Now it is time to check the amount of current flow. If it is 20mA or above then you are good to go. However, if you see current flowing less than 20mA then there should be an issue which needs your attention.

In the absence of a C-wire adapter, you can use the USB port present at the back of the thermostat for charging purpose.


Nest thermostats come with rechargeable backup batteries known as lithium-ion batteries. These batteries need a constant charge up and they do this by drawing power from your HVAC system.

If your thermostat has a low battery then it will automatically charge itself as soon as the thermostat gets ON for heating or cooling purpose. It means your thermostat requires the system to be turned ON in order to get itself charged up.

If you don’t do this then the thermostat will draw power from the HVAC system itself automatically. If you own a highly sensitive system then this activity will be detected within no time. If this detection is successful then the system will get ON and the charging of your thermostat will remain incomplete.

Suppose the system gets turned ON and your thermostat is experiencing low battery then what will happen is that it will get turned OFF automatically causing a malfunction. This malfunction can cause damage to the other components as well.


Following are the issues which have been reported by people who were using Nest thermostat without C-wire.

  1. AC and furnace is showing abnormal behaviors
  2. AC and furnace is making strange noises
  3. Improper heat pump functioning
  4. The fan keeps getting stuck


Q – How To Install A Nest Thermostat?
A – There are 2 ways to install a Nest thermostat; with a C-wire and without a C-wire. Both of these approaches are easy to follow so you can adopt the one which suits the best to you.

Q – What Happens To Nest Thermostat Without A C-wire?
A – If your system has a C-wire then the thermostat will do the charging by drawing power from it. However, if there isn’t any C-wire present then the thermostat will draw power from your HVAC system automatically. The latter case can cause damage to other components as well.

Q – How Do I Know If My Nest Needs A C-wire?
A – The biggest indication that your Nest needs a C-wire is the occurrence of delayed messages being shown on your thermostat. This is the biggest hint that your system is in the need of a C-wire.

Q – Which C-wire Adapter Is The Best?
A – The best C-wire adapter is Ohm Kat adapter. This adapter provides lifetime guarantee and also full safety to its users. It is a USA made product so there are other perks involved as well.

<strong>FINAL THOUGHTS</strong>
It is always advisable to use a C-wire in your thermostat, however if you are unable to do this then simply use a C-wire adapter as a replacement for it. The installation process of the adapter has been explained above so make sure you follow the instructions carefully.

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