How To Install Nest Thermostat E With 2 Wires

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With the current trend of purchasing smart home equipment, replacing your old thermostat with a new Wi-Fi thermostat is an excellent idea.

Suppose you ordered a Nest Thermostat, and you have taken down the old thermostat to replace it, and you hit a snag: there is no C-wire.

You don't want to waste the hundreds of dollars you spent on this really sweet equipment to go to waste, or worse, having to settle for a bad thermostat.

You can install a Nest Thermostat without a C-wire by using a C-wire adapter, that mimics a traditional C-Wire without you having to wire it.

If you are not a handyman, it saves a lot of money that you would otherwise have to spend on a professional installer too.

In this article, I will take you through a step-by-step procedure on how to install your Nest thermostat when you don't have a c wire by using a c-wire adapter.

However, if you are in a hurry and you just want to know which C Wire adapter I would recommend, it is the Ohmkat C Wire Adapter.

Do You Need a C-Wire For Your Thermostat?

A C-wire also called a Common wire, is used to provide continuous power to your thermostat, drawing power from the furnace or any heating or cooling system.

But is this necessary for your thermostat to work?

Nest claims that you can use the Nest Thermostat without a C-wire. While this is true, it would be advisable to have a C-wire.

A lot of Nest users have had problems when they use the thermostat without a C-wire.

In the absence of a C wire, your thermostat battery charges itself by using the power from your HVAC system. If your Nest Thermostat Battery won't charge, first to check is usually the C-Wire.

Now, if you have a C-wire, your thermostat will draw current from the C-wire to power the battery.

It ensures a return path to the thermostat so that it can power it without interrupting other wires which are used to switch the thermostat on and off.

This is all the more essential because maintaining a Wi-Fi connection to the thermostat can quickly drain the battery.

So, in a nutshell, even though it is not a necessity, the C-wire is needed for your thermostat to function better.

In fact, a common issue that is noticed is the Nest Thermostat delayed message when it is installed without a C Wire.

The delayed message indicates that the Nest Thermostat is not functioning properly.

How To Install Your Nest Thermostat With a C-Wire Adapter

The steps involved in the installation of the thermostat are reasonably straightforward, and they can be done in under 5 minutes.

The steps to install your thermostat are :

Step 1 – Get the C-Wire Adapter
Step 2 – Check the Thermostat Terminals
Step 3 – Make Necessary Connections to the Thermostat
Step 4 – Connect the Adapter to the Thermostat
Step 5 – Put the Thermostat Back On
Step 6 – Power ON Your Thermostat

All six steps are very easy, and I shall walk through each step in detail.

Step 1 – Get the C-Wire Adapter

As I mentioned before, the best way to connect the C-wire to your thermostat is to use a C-wire adapter.

As an HVAC expert, I would recommend the C Wire adapter made by Ohmkat for this purpose.

Why do I recommend it?

I have been using it myself for months.
It comes with a lifetime guarantee.
It was made specifically keeping in mind the Nest Thermostat.
It is made in the USA.

However, before you take my word, I want you to know why they are able to guarantee it for a lifetime.

It is next to impossible to wreck this thing. It has this called One-Touch Power Test, which enables us to check whether it is supplying power or not without the need for special tools.

Moreover, it is also short-circuiting proof making it a very safe device.

Safety is important because it is externally wired and connected to your outlet.

Step 2 – Check the Nest Thermostat Terminals

After unscrewing the top of your Nest thermostat, you can see the different terminals.

These may vary depending on which thermostat you use, but the basic layout is more or less the same.

The main terminals that we need to concern ourselves with are:

Rh terminal – This is what is used for power
G terminal – This is the fan control
Y1 terminal – This is the terminal that controls your cooling loop
W1 terminal – This is the terminal that controls your heating loop

The Rh terminal is solely used for powering the thermostat and thus completes the circuit for the thermostat.

Step 3 – Make Necessary Connections to the Nest Thermostat

Now we can start installing our Nest thermostat. Before you do any wiring, make sure you have turned off the power from your HVAC system for safety.

Before you remove your old thermostat, make sure to take note of the wiring that is already in place.

This step is crucial because you will have to make sure the same wires are connected to the corresponding terminals on your new Nest thermostat.

So it is a good idea to take a picture of your previous thermostat wiring before removing it.

If you have a heating system, you would need to connect the corresponding wire to W1, which establishes a connection to your furnace.

If you have a cooling system, connect a wire to Y1. If you have a fan, then connect it using the G terminal.

Step 4 – Connect the Adapter to the Nest Thermostat

As mentioned in the previous step, you need to make sure that the connections are exactly the same as how it was in the thermostat that you took off, except for two:

You have to disconnect the Rh wire that you had before. Now take one wire from the adapter and connect it to the Rh terminal instead.
You have to take the second wire from the adapter and connect it to the C terminal.

It does not matter which of the two wires you connect to the Rh or C terminal.

Make sure all the wires are properly and tightly connected to the respective terminals.

It is a better practice to ensure that the copper part of the wire is not exposed outside the terminal.

Ensure that only the insulation of all the wires is visible outside the terminal.

Basically, what we have done is establish a completed circuit where power can run from the Rh to the C wire and can power the thermostat uninterrupted. Your Nest thermostat wouldn't work if there was no power to the Rh wire.

So now the C wire is powering your thermostat, whereas previously it was your HVAC system.

Step 5 – Put the Thermostat Back On

After you have made all the necessary connections, you can put the thermostat back on.

Make sure that the power is still off until you have completed putting the thermostat back on.

This is to ensure that no short-circuiting takes place and damages the device.

All the wiring done here is low voltage wiring so there isn't anything, in particular, to worry about.

But as a precaution, it is always better to keep the power off. Once the top of the thermostat is tightly placed back on, you are ready to power it on.

Step 6 – Power ON Your Thermostat

Now you can plug your thermostat into a standard power outlet and power ON your Nest thermostat.

If the thermostat starts to blink then that means that all the wiring has been done properly, and we are good to go and set it up.

All you need to do is use a C wire adapter to easily and quickly install your Nest thermostat.

If you want to hide the wires from your adapter you can run these through your wall. This will be easier if your walls or ceiling are partially finished.

Either way, if you are doing this make sure to check the local codes and ordinances in your area to make sure no violations are committed.

Once you power it on, check for the amount of current it is receiving. If it shows 20mA (Milli Amperes) of current or above 20mA of current then you are good to go.

When you face issues with a C-wire it usually shows a current of less than 20mA.

But if it shows anything above 20mA, then it means that your thermostat is working just fine.

Another point to note is that in case you don't have a C wire adapter currently, or you're waiting for it to arrive but need to use the thermostat, then Nest thermostats have a charging port on the back of the thermostat.

You could plug it in for a couple of hours and put it back on the wall and have it ready for use for 24 to 48 hours.

This can charge your thermostat and make sure you can use it until your C wire adapter arrives.

What happens If You Don't Install a C Wire For Your Nest Thermostat?

Nest thermostats run on a lithium-ion battery, which recharges itself from your home's HVAC system.

When your Nest Thermostat has low battery, it gets recharged once you power on your thermostat and use it for heating or cooling purposes by drawing a small amount of power to the battery.

The Nest Thermostat is one of the best smart thermostats without a C-Wire.

Now as you might have noticed, this is dependent on whether or not you power on your system for use.

So what happens if you don't? In this case, Nest tries to draw power from your HVAC system by itself.

This is a nominal amount of power and it only does this when your system is off.

But sometimes, if your system is highly sensitive, it detects the power drawn by the thermostat and turns the system on.

Once the system is turned on, the thermostat stops charging itself. But since charging is incomplete and the battery is still low, it turns itself off, which can lead to a constant fluctuation in your furnace or AC system, where your heating or cooling system keeps turning on and off repeatedly.

Some problems that people who use a Nest thermostat without a C wire have reported are:

Furnace or AC is turning off and on rapidly and making a lot of noise
The fan keeps getting stuck
Ineffective functioning of the heat pump

Final Thoughts about Nest Thermostats without C-Wire

In a nutshell, you do not need a C wire for using your thermostat, but it is always better to use one for more effective functioning.

It ensures that your thermostat gets a constant steady source of power to ensure that no faults happen.

If you don't have a C wire in your house, the easiest way to overcome this is to get a C wire adapter to connect it to your thermostat.

I would recommend using the OhmKat adapter as it works seamlessly with the Nest thermostat.

You can also install thermostats from other companies like Sensi, and Ecobee, without C-Wires.

Frequently Asked Questions

How to power a thermostat without a C-wire?

Thermostats can be powered either using an indoor adapter, or they can be powered off their internal battery.

However, in order to ensure no downtime, it would be better to get an indoor adapter.