Fitting a new Nest Smart Thermostat need not be a daunting project. Here we will guide you through the process in simple, easy-to-follow steps that will have your new Nest up and running in no time. 

The first question to answer is why you would want to replace your current system with a Nest Thermostat. Here are some issues to consider before making the change.

The differences between Trane and Nest

Here we will focus on the features of the Trane ComfortLink II and the Nest system.

  • The essential difference is that the Nest system simplifies the operations of the Thermostat while the Trane ComfortLink II focuses on streamlining the complete home HVAC system.
  • The design of the two systems couldn’t be more different. The Nest system has a round stainless steel design, which is small and unobtrusive, while the Trane keypad is a seven-inch screen that you can color code to suit the interior of your home.
  • The Nest Thermostat is very simple to use. Follow a few easy-to-follow instructions, and your system will be up and running. You need only to adjust the temperatures to suit your personal requirements, and Nest will learn your habits and preferences.
  • The Nest system is super connective with almost all web-enabled devices.
  • Nest struggles a little with its inability to control variable-speed blower furnaces. These furnaces are becoming more popular because of their energy-efficient operation, and this is of concern if you are considering installing a Nest system.
  • Popular Mechanics awarded the Trane ComfortLink II the Breakthrough Award 2022, so there is a fair bit of innovation in the design and capability.
  • The advantage of having the seven-inch screen is that you can easily control all HVAC functions. The dehumidifier, heater, and air conditioner are all programable on the Trane ComfortLink II. It is also possible to add additional features, such as weather forecasts and indoor and outdoor thermometers.
  • As a smart thermostat, you can manage and monitor your thermostat using your smartphone.

Having gone through all the details of both systems, let’s get into installing the Nest Thermostat.

Steps to replace Trane with Nest

Step1. Check that your thermostat is compatible with Nest.

You will need to download the Google Home or Nest app to check for Compatibility. Alternatively, you can also make use of the Compatibility Checker.

The Compatibility Checker guides you through a series of questions about the wiring in your present Thermostat.

Some Additional Issues to Check;

There are some other issues that you need to consider before deciding that your present system is compatible with Nest.

  • If your heating system works with solid fuels such as coal, wood, or other biomass materials, you will have serious compatibility issues with Nest.
  • Wired remote sensors are not going to work with Nest monitors because Nest monitors outside temperatures through their Wi-Fi connection.
  • Nest systems can only handle one or two stages of cooling. The Nest ‘E’ Thermostat can control one stage of heating and one stage of cooling plus one extra stage of heating or cooling.
  • Heat pumps with an ‘L’ wire can be used with Nest Thermostats, but you don’t need to connect the ‘L’ wire because the Nest system monitors the system status information without the ‘L’ wire.
  • Remember to switch off your system at the fuse box before removing your Thermostat’s cover.

Once you have answered the questions about your current wiring, the Compatibility Checker will provide you with a list of Nest Thermostats that will be compatible with your thermostat. 

The app also provides a step-by-step guide installation guide and a wiring guide. It is very helpful, and I would suggest you refer to it during the installation process.

Once you have confirmed which Nest thermostat is compatible with your thermostat, it’s time to get to work.

A handy addition to your Nest Thermostat is the backing plate which will neatly cover the area on the wall left by your old thermostat. 

Step 2. After you have removed the cover of your old thermostat, take a picture of the wires. 

The Nest Thermostat comes complete with stickers you can attach to the individual wires, and it’s a good idea to stick them to the wires before disconnecting. 

A small word of caution regarding the stickers. They don’t seem to stick that well, so ensure you have them securely attached to the respective wires. Please check the chart below in case you lose a sticker or two.

I like the idea of making a note of the label on the wire and the letter of the connection board to be sure no mistakes are made. Remember that the Nest system has an internal link between the Rh and Rc connectors, so you don’t need to install an external link.

Wiring Color Codes

Wire Color              Connection
Red24V AC Power
GreenIndoor Fan
Black24V AC Common
OrangeRV on in Cool
BlueRV on in Heat
VariousSecond stage heat, or cool, or emergency
Thermostat wire color guide

Step 3. Disconnect all the wires after you have fitted the labels to them. Carefully remove the base plate from the wall.

Make sure the wires cannot slip back through the hole in the wall because if they do, it could be a big problem to fish them out again. 

Step 4. Fit the base plate to the wall

Fit the base plate to the wall using the screws provided if you are fitting the thermostat to a drywall and bring the wires through the center hole. If you are fitting the base plate to a masonry wall, you will need to use plastic anchors and corresponding screws.

With the base plate attached to the wall, you can now fit the plate with the connectors onto the base plate. Take note of the little level mounted at the top of the plate, and only tighten the screws once the bubble is between the lines.

Attaching the wires is easy; you must depress the little tab at each fitting, insert the appropriate wire, and then release the tab. Please give a little tug on the wire to ensure that it is firmly connected. 

Step 5. Fit the thermostat on its base

Once all the wires are correctly connected, it is time to fit the thermostat.  Be sure to remove the little insulation tabs from the batteries before you fit the thermostat.

Step 6. Turn on the Nest thermostat

Now is the time to switch the power back on at the fuse box. The screen on the Nest will light up, and you will need to scroll through the different language options to select the language of your choice and follow the easy setup instructions.

Replace existing thermostat with Nest

Frequently Asked Questions

Do Nest Thermostats work with older HVAC systems?

Yes, Nest Thermostats can work with almost all 24 V systems.

Do Nest Thermostats require a C wire?

No, they are designed to work without a C wire, but you may need to install a Nest Power Connector for some systems. The ‘C’ wire became essential when old thermostats, which were simply an ‘on-off’ system, were replaced with more modern thermostats that required a continuous 24 V ac supply.

How to check if there is a ‘C’ Wire 

To check if your thermostat wiring contains a ‘C’ wire, you will need to remove the cover plate of your Thermostat. If you find a wire connected to the ‘C’ terminal, you have a ‘C’ wire, and your installation can move ahead.

If there is no ‘C’ wire at the thermostat, look at the furnace by removing the cover of the furnace. Remember to switch the power supply off first. See if you can find a cable connected to the ‘C’ connection, and if there is one, then the other end is probably stuffed behind the backing plate of the thermostat.

Remember that the Nest Thermostat does not require a ‘C’ wire. The Nest Power Connector is the alternative to the ‘C’ wire and is far cheaper to install.

Does the Nest system charge itself?

Yes, the batteries are automatically charged as required by the power supply.


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