In general, thermostats as a device class are popular in North America. Historically, this device is present in every house there. And no wonder, since this device sets the temperature almost without your interference. In winter, it will turn on the heating, and in summer, when it is hot – air conditioning or ventilation. Thirty years ago, mechanical thermostats controlled most of the climate systems in the USA.

But before you learn about the benefits of such devices, meet the company Nest, which manufactures thermostats for your smart home.

History of Nest

Nest dates back to 2010. It was then that former Apple employees Tony Fadel and Matt Rogers created a startup called Nest Labs. A year later, the company introduced its first version of the thermostat. The device became very popular, and the company’s business went up. Next year, in the wake of its success, Nest Labs will release a second version of the thermostat with an updated design and functionality. The company will later take the second version as a basis for the next generation after Google buys Nest Labs.

So, in 2014, Nest Labs was bought by Google for a whopping (for that time) 3.2 billion dollars without changing the name, is now a subsidiary. In the same year, Dropcam, a company engaged in the production of video cameras, came under the wing of Nest. We will hear about Nest Cam smart security cameras later. The company is also starting to develop a new wireless communication protocol. We will talk later about the protocol.

And so, at the end of 2016, Nest presents the third version of its smart thermostat, which is still relevant to this day.

American version of Nest Learning Thermostat (3rd Gen)

I want to say that a 24V interchanging current powers the climate systems of North America. That is not common in European countries. It can also be a problem in our country for those who bought their thermostat in the USA market and wants to mount it manually. But everything is possible. Read on if you need to learn how to do it.

The device has hardly changed, but the thermostat screen and its resolution have increased, so the operating mode and current temperature can be seen from the other end of the room. You don’t have to be close to see the thermostat. Compared to the 2nd Gen, the main changes are inside and in the software.

As for the inside, there is a presence sensor. With the help of this sensor, it “knows” whether someone is at home and adjusts the temperature accordingly. Of course, the device also has a temperature sensor. That means that the thermostat measures the temperature in the room in which it is. But it is also possible to buy remote temperature sensors and put them on the shelf or wall of the room where you want to monitor the temperature.

I stated above that Nest began developing a new wireless standard for their devices. The new thermostat already uses it. This new standard works on the 802.15.4 protocol. Are the numbers familiar? It runs at 2.4 GHz, just like ZigBee, but is a different energy-efficient standard. It is called Weave. It will later become the basis for an open communication protocol for Thread devices. But for now, Nest only uses Weave to connect their own devices. With this standard, the thermostat gets connected to the Nest temperature sensor.

There are more devices in the Nest ecosystem that use the Weave protocol. For example – a smoke and gas sensor Nest Protect. Nest Protect also has a presence sensor, just like the thermostat. Nest Connect is a device that increases the coverage area. All these devices work with a compatible smart lock – Yale Lock.

The box with the US version of the thermostat shows the device itself with the number 75. It is a comfortable temperature in Fahrenheit. The previous version (2nd Gen) displays the number 70 instead.

Let’s see what comes with the Nest Learning Thermostat. In addition to the thermostat in the box, there is a set of screws, a contact disk with ten terminals, a metal mounting plate, and a white plastic protective plate. As a bonus, Nest put a branded screwdriver in the box that is supposed to help you mount the device. You don’t need to use the white plate. It’s usually there to hide the defects on the wall after demounting the previous thermostat.

After mounting and connecting the wires to the disk, the thermostat gets connected to the appropriate connector. After that, it gets attached to its position. But, before we mount the disk to the wall, let’s check out its pinning.

As you know, a 24V interchanging current is powering the thermostat. Connect these wires to Rh and C (Comon) terminals. In the picture, the wires are red and black. C-wire will be “common” to all climate devices. W1 and W2 terminals are responsible for heating. If your home has, for example, a single-stage heater, then only the W1 terminal can be connected to it. Then, you can connect an additional heater to the W2 terminal.

So, when the thermostat decides to heat the room quickly, it gives voltage to both W1 and W2 terminals. But usually, the temperature is raised smoothly and in one circuit to save energy. The room cools down by the same logic. Terminals Y1 and Y2 are responsible for cooling, or, rather, the degree of cooling. If you set a central air conditioner in the room, then the contact of the Y1 terminal sends a signal to the relay. It will then open the ventilation latch with cold air. Meanwhile, the Y2 terminal controls an additional air conditioner.

The G terminal is usually responsible for powering the fan. O/B is rarely used, and only to control a special heating valve. You can take it as third-degree heating. The Rc terminal is used instead of Rh if you will only connect cooling (it connects to the left side). You can set up the “*” terminal in the thermostat settings. It can manage a humidifier, dehumidifier. You can even connect a third heating circuit.

You can find several connection options in the Nest Pro Installer Guide

The image below shows one of the options for connecting the thermostat to the heater using a dry contact relay. Other terminals and corresponding devices are connected similarly.

After connecting the wires to the contact ring and installing the thermostat in place, the power is turned on. The thermostat itself will “see” which wires are connected to the terminals. All you have to do is make basic settings and connect to Wi-Fi. By the way, in the settings, you can set the temperature not only in Fahrenheit but also in Celsius.

The European version of Nest Learning Thermostat (3rd Gen)

Following the acquisition of Nest Labs by Google, the company began to conquer other markets. Nest has appeared in European stores with the second Gen of the thermostat. But, as it turned out, not all functions in Europe were in demand. For example, in Europe, air conditioning or ventilation was very rarely part of a centralized climate system. The heating control also did not have 24V power as in the US.

That’s why Google decided to release a separate version of the thermostat for countries outside of North America. You will recognize the box of the European version by the number 20 on the thermostat, which is familiar to us, comfortable 20 degrees Celsius. The box with the “European” is a little bigger. The reason is that another device called Heat Link is in the kit.

Modern gas boilers often include thermostats of their brands. Such thermostats connect to the “motherboard” of the boiler with two wires. Once connected, the boiler and thermostat communicate using the OpenTherm protocol. This way, you can manage the heater remotely. OpenTherm has one significant advantage over relay control. During space heating, the boiler gradually increases the coolant temperature. So, the burner inside the boiler doesn’t get exposed to heat. Therefore it lasts longer. In addition, the gradual heating of the coolant reduces gas consumption and saves money.

The photo below shows a Heat Link with an open protective cover. Its inner part shows the scheme of connection to the corresponding contacts.

The first two contacts are the power supply terminals of the 220V device. We are interested in the last two groups of terminals. These are the contacts of the OpenTherm wires and the power contacts of the thermostat with a voltage of 12V.

By the way, you can supply the power to the thermostat via a standard USB connector. The thermostat will connect to the Heat Link device via the already familiar wireless Weave. The distance between the devices cannot exceed 30 meters. But it’s nice that you don’t have to drill the walls. So, you can install the Heat Link in the boiler room and the thermostat on the dresser on a stand.

The kit with the “European” also has a contact ring, but it differs significantly from the American version. There are only two power terminals on the contact ring marked as T1 and T2. The wires to these terminals connect to the corresponding Heat Link contacts. Do not confuse the polarity when connecting these contacts.

Let’s go back to the Heat Link. Just like I said, the advantage is support for the OpenTherm standard. But you are probably already asking the question: will a boiler without OpenTherm work with a thermostat? Jumping ahead, I would say yes, but only in the relay mode (on/off). Some boilers have two terminals on board to connect the so-called “dry” relay instead of an OpenTherm link. Usually, a jumper connects those terminals. If you disconnect the contacts – the boiler turns off, and once connected – it will turn back on. Below is a diagram connecting a dry pair of wires to the Heat Link.

Below is a diagram of the connection of the electric heater to the Heat Link. Note that the current flowing through terminals “1”, “2”, and “3” must not exceed 3A.

After installing all elements of the thermostat, it is possible to begin adjustment. After setting up and connecting to your home Wi-Fi network, you can start using your device.

Nest Learning Thermostat software

From the first day of using the thermostat, the device starts to learn about your habits. It checks how comfortable the room feels to you and remembers if you lower the temperature before sleep. In about a week, the thermostat begins to make adjustments to the climate of your house. It can be both temperature and humidity in the room. The device also turns on the “Auto Away” mode if no one is home. The thermostat will reduce the temperature to an acceptable level, saving you money. The thermostat adapts to your operating mode, and before you return from work, your home will be warm and cozy.

A stable connection to the Internet is required for the thermostat to work correctly. The device connects to the home router via Wi-Fi.

You can control your device in a few ways. The first way is physical interaction. You can always go to the thermostat and set a comfortable temperature by rotating the ring. The second way is through a web browser. You can go to the thermostat settings anywhere around the world and view device statistics or other climate information at home. The third way to control is using an application on your smartphone. Here you will see everything in the browser, but in a more convenient format. You need to log in to the account you created when you first set up the thermostat for the last method.

The fourth method is voice control using Google Nest speakers. Set up the integration once, and the thermostat will appear in the app. You can now control the thermostat using voice commands.