Getting a Nest thermostat can be a true investment for your house. If you switch from a manual thermostat to a smart wifi thermostat, you will increase the comfort in your home and reduce a lot of the hassle of maintaining the proper temperature. But one of the most common issues that people encounter is whether or not they need a common wire to install a Nest thermostat. If you are wondering the same thing, you came to the right place!

The short answer is that you don’t need a common wire to install your Nest thermostat. You can just as well use a C-adapter and your device will function just as well. However, experts will tell you that it is recommended to use your NEST thermostat with a C-wire. 

But in order to complete the installation process by yourself, there are certain aspects you need to consider. You will find out everything you need to know to install a Nest thermostat without a common wire by yourself.

What is a common wire

Common wires are extremely useful as they offer your thermostat a continuous supply of power. These wires get the power from your heating system, cooling system, or your furnace, and make sure that your thermostat doesn’t need to be recharged. 

According to the Nest website, your Nest thermostat will work without a C-wire but specialists still recommend using an adapter if you can’t get a C-wire installed. If your Best thermostat will not receive a constant flow of power, it might not work properly and it runs out of power it will not work at all. Such issues will affect the learning function of your thermostat and you will not be able to enjoy all its features. 

What do you need to install a Nest thermostat without a common wire 

If you don’t have a common wire you can use a C-wire adapter that will fulfill the same function as the common wire. C-wires adapters are fairly popular in such situations since they will save you the hassle of having a common wire connecting your HVAC system to your thermostat. 

You can find a C-wire adapter on the market for $50 and they are all performing the same tasks. So, get the C-wire adapter that is within your budget and you will be able to install your thermostat in minutes.

24 volts c wire transformer
Fyve – C wire transformer – Source

You can also install your Nest thermostat without the C-wire adapter, case in which all you will need will be the instructions of your product and a screwdriver. If you do that, make sure you follow the steps required by the manufacturer and the thermostat is compatible with your home heating and cooling system. 

How to install a Nest thermostat with a C-wire adapter

Once you got your Nest thermostat and your C-wire adapter, you can follow these steps to install it by yourself! Make sure you have your screwdriver handy as you will definitely need it in the process! 

Check the terminals of your Nest thermostat 

You will need to use a screwdriver to unscrew the top cover of your thermostat. After you do that, you will find four different terminals. The terminals are Rh terminal for power, G terminal for the fan control, Y1 terminal that controls cooling pools and W1 terminal that controls the heating loop. Also, while you are at this step, you will want to turn the power off so you can move forward with safety. Make sure you still have natural light or a flashlight to proceed with the following steps, though. 

Connect the Nest thermostat

If you had a previous thermostat that you are replacing with your Nest thermostat, it will help you to snap a picture or write down the correct connections as they will most likely remain the same. You will have to connect each wire to the correspondent terminal on your thermostat. For instance, you will need to connect the right wire to your heating W1 terminal so that the furnace can deliver the heat you need. Consequently, you will connect a wire to Y1 terminal for the cooling system and one to the G terminal for your fan system. Without the example of a previous thermostat, you can find clear indications on the instructions of your new thermostat so make sure to check those as well. 

Install the adapter 

Once your wire connections are made correctly, you can add the C-wire adapter. You will connect one wire of the adapter to the Rh terminal and the second wire of the adapter to the C terminal. Such C-wires adapters come with only two wires and it doesn’t matter which wire you connect to these two terminals. It is important to connect your wires in such a way that only the insulation can be seen from the outside of the terminal. 

If you complete this step correctly, there will always be power between the Rh and C terminals, allowing your Nest thermostat to run smoothly and without shortcomings. 

Assemble the thermostat back 

Now that your C-wire adapter is installed, you will add the case of the thermostat back on and make sure you screw it in tightly. It is important to leave the power off until you are sure that your thermostat is put together securely. Once you installed the Nest thermostat it is safe to turn the power back on and enjoy the new comfort of your home! Give your thermostat a few hours to adjust to your home system and start learning the needs you have before you decide if you are satisfied of it or not. These thermostats adjust to each home over time and eventually, you will have the perfect temperature with no effort on your part! 

Extra step: Check the current that your Nest thermostat receives

With a C-wire adapter, the amount of current that will get to your thermostat should be a minimum of 20 mA so if you get this value, everything works properly. If you don’t have a constant power getting to your thermostat, it means that the adapter was not connected the right way. For Nest thermostats that are installed without a C-wire adapter, there is a charging port that you can use to recharge your thermostat as needed.

Can I install a Nest thermostat with no C-wire and no C-wire adapter?

Yes, you also have the option to setup your Nest thermostat without any common wire or adapter, as the company also states on their website. If you do that, you will have to follow the installation steps indicated on your Nest thermostat instructions as these steps are explained for each model in particular. 

Nest thermostats that work without a C-wire or an adapter will need to be charged through their charging port. You can expect to charge your thermostat for a couple of hours and use it for 24 to 48 hours until you need to charge it again, depending on the system you have in your home. 

Final thoughts 

You can follow the steps in this guide to install your Nest thermostat by yourself, with no hassle, even if you don’t have experience in the matter. However, if you have any doubts regarding the safety aspect in your home, it is important to work with a professional electrician when you install your thermostat. Make sure to also check the information that comes with your Nest thermostat as the instructions of your device will be very valuable in the process. 


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