A Nest thermostat installation is a low-voltage wire swap: you turn off the power, move each wire from your old thermostat to the matching connector on the Nest base, and finish setup in an app. Google says installing its Nest Thermostat usually takes 30 minutes or less. What changes between models is which app you use, what’s in the box and how many connectors the base has, so this guide covers how to install Nest thermostat models step by step, then the differences between them.
If you’re still choosing one, our guide to the best smart thermostats for Google Home compares the current Nest models with the alternatives.
The quick version
Here’s how to install a Nest thermostat, start to finish:
- Check that your system is compatible and see which app your model uses.
- Start setup in the app (the Google Home app for current models) and scan the QR code.
- Turn off the power at the breaker and check the system won’t turn on.
- Take a photo of the old wiring, remove any jumper wires and label each wire.
- Screw the Nest base to the wall, using its built-in level.
- Push each wire into its matching connector until the button stays down.
- Attach the display and turn the power back on.
- Finish setup in the app, then test heating, cooling and the fan.
Before you start
Know your model. Google sells two Nest thermostats today, and two older ones are still in many homes:
| Model | Setup app | Connectors on the base | Trim and steel plate |
|---|---|---|---|
| Nest Thermostat (2020) | Google Home | 6: W, Y, G, C, R, */OB | Sold separately (Trim Kit) |
| Nest Learning Thermostat (4th gen) | Google Home | 12, including Rh, Rc, star and AQ | Both included |
| Nest Learning Thermostat (3rd gen) | Nest app | 10, including Rh, Rc and star | Both included |
| Nest Thermostat E | Nest app | 6, with a combined */OB | Trim plate included |
Google ended app support for the 1st and 2nd gen Learning Thermostats in October 2025, so don’t reinstall one of those as a smart thermostat.
Check compatibility. Nest thermostats work with most 24 V heating and cooling systems, and Google’s Nest thermostat compatibility page links to its online checker. Enter the letters printed next to each connector, not the wire colors. Take the cover off your old thermostat and look for these signs that your system won’t work:
- It’s labeled 120 V or 240 V, or it has thick wires joined with wire nuts. That’s a high-voltage system, usually electric baseboard heat. For those, see our guide to the best smart thermostats for baseboard heaters.
- The wires are stranded (several thin strands, not one solid copper core).
- The connectors are labeled with numbers or letters like 1, 2, 3 or A, B, C, which means a proprietary system.
- It’s a millivolt system, usually a wall or floor heater.
Gather your tools. Google lists a Phillips #1 screwdriver and a flathead. A drill with a 3/32 inch bit helps for paneling, plaster or a stud behind the wall (use a masonry bit for brick or stone), and a flashlight and wire strippers can help. Use a screwdriver, not a power drill, on the base screws: over-tightening can crack the base.
Know when to call a pro. Google recommends professional installation for dual fuel systems (a heat pump with a furnace) and strongly recommends it for dual transformer systems (separate Rh and Rc wires), whole-home humidifiers and dehumidifiers, and multi-speed fans. If you’d rather have a pro do it, our guide to smart thermostat installation cost covers what pros charge.
How to install a Nest thermostat, step by step
These steps follow Google’s instructions for the Nest Thermostat (2020) and the Nest Learning Thermostat (4th gen). The older models follow the same physical steps with a different app (see the model section below). For the same job on other brands, see our guide on how to install a smart thermostat, or our guide to ecobee thermostat installation for an ecobee.
1. Add it in the app first
Before you touch any wires, check that your heating and cooling both work with the old thermostat, so you know about any existing problem. Then open the Google Home app, tap Add, then Device, and scan the QR code on the thermostat. Google says you have to be at the thermostat to add it. If the thermostat was used before, factory reset it first. From here, the app walks you through each step and builds a wiring diagram from the wires you tell it you have.
2. Turn off the power and check it’s off
Turn off the breaker (or breakers) for your heating and cooling system. To check, turn the temperature on your old thermostat up at least 5 degrees and wait at least 5 minutes, because many systems have a built-in delay. Do the same for cooling. If nothing turns on, the power is off. Working with the power on can blow a fuse in your equipment.
3. Photograph, check and label the wires
Take the cover off the old thermostat and take a clear photo of the wiring. It’s your reference if anything goes wrong. Then:
- Remove any jumper wires (short wires between two connectors on the old thermostat, often Rh and Rc). Nest thermostats don’t use them, so keep them with the old thermostat.
- Put a label from the box on each wire, matching the letter of the connector it’s in, and check off those wires in the app.
- Leave any wire that wasn’t connected to the old thermostat unconnected.
4. Remove the old thermostat and mount the base
Disconnect the wires and unscrew the old thermostat. Wrap the wires around a pencil so they can’t fall back into the wall. If the old thermostat left holes or unpainted patches, fit the trim plate behind the Nest base, and if your wires come out of an electrical box, mount the steel plate on the box first. Pull the wires through the middle of the base, line it up with the built-in level and screw it to the wall (Google recommends drywall anchors).
5. Connect the wires
This is the main Nest thermostat wiring step. For each wire, press the connector button, push the wire all the way in and let go: the button should stay down. Google says to strip about 10 mm (3/8 inch) of wire, and the bare end should be straight. Put one wire in each connector, then push the extra wire back into the wall so the display can sit flat. The app checks which connectors have a wire and flags anything that doesn’t match.
6. Attach the display and turn the power back on
On the Nest Thermostat (2020), pull out the battery tab on the display first. Line the display up with the base and press until it clicks, then turn the breaker back on. The Learning Thermostat (4th gen) turns on by itself once it’s on the base and the power is back.
7. Finish setup and test it
The app runs a power test and asks a few questions about your system, such as your heating type. Then you connect the thermostat to Wi-Fi, add your home address and room, and choose your temperature presets and schedule. Before you finish, run the heat, the cooling and the fan for a few minutes each to make sure every wire does what the app expects. To control a Nest Thermostat (2020) or Learning Thermostat (4th gen) from an iPhone too, here’s how to add a Nest thermostat to Apple Home.
Nest thermostat wiring: what goes where
Most installs are a straight letter-to-letter match: W to W, Y to Y, G to G, C to C. These are the wires that confuse people:
- R, Rh and Rc. With a single R wire, put it in Rh or Rc on a Learning Thermostat, or in R on the Nest Thermostat (2020). If you have both an Rh and an Rc wire, you have a dual transformer system, and Google strongly recommends a pro. The 2020 model has only one R connector.
- A “B” wire. On some systems the wire in the old B connector is really a common (C) wire. If your old thermostat had separate B and C connectors, the B wire goes in O/B. If you’re not sure, check your furnace’s control board or ask a pro: Google warns that a C wire in any other connector can blow a fuse or damage the thermostat.
- The star connector. On Learning Thermostats it takes one extra wire, such as W3, E (emergency heat), HUM or DEHUM. On the Nest Thermostat (2020) and Thermostat E it’s labeled */OB and takes one of O/B, W2 or Y2. Only use it if the app’s diagram tells you to.
- O/B on a heat pump. An orange wire in an O/B connector usually means a heat pump, and the app asks how it’s set up. Our guide to aux heat explains the heat pump terms.
- S and L wires. Nest thermostats don’t need them, so leave them unconnected.
For what every letter means, our thermostat wiring guide has diagrams for common systems.
What’s different on each model
Google Nest Thermostat (2020)
If you want to know how to install Google Nest Thermostat models with the mirrored display, the main differences are the batteries and the plates. It runs on your system’s wires with two AAA batteries as backup (they’re in the box, behind the pull tab). The base has six connectors, so it supports one stage of heating and cooling plus a second stage of either, or a heat pump with aux or emergency heat. If you’re still choosing a thermostat for a heat pump, our guide to the best thermostats for heat pumps compares how each model handles aux heat. The box has no trim plate or steel plate: if you need either, buy the Nest Thermostat Trim Kit, which includes both.
Nest Learning Thermostat (4th gen)
The Nest Learning Thermostat (4th gen) has a bigger base with 12 connectors, including separate Rh and Rc, a star connector and AQ+/AQ- for ventilation or a humidifier. The trim plate and steel plate are in the box. It has a built-in rechargeable battery, and an LED on the base lights up when the base is getting power from your system: if the display stays dark after you turn the breaker on, take it off and check that light. The box also includes a Nest Temperature Sensor (2nd gen), which you add in the Google Home app by scanning its QR code and pulling its battery tab.
Nest Learning Thermostat (3rd gen) and Nest Thermostat E
If you’re looking up how to install Nest Learning Thermostat (3rd gen) or Thermostat E units, follow the same wiring steps, but use the Nest app instead of the Google Home app. If you aren’t sure which model is on your wall, here’s how to tell which Nest thermostat you have from the front or the base. After you turn the power back on, the thermostat walks you through setup on its own screen: language, wiring check, heating type and Wi-Fi. Then you add it to your account in the Nest app with the entry key or QR code from the thermostat. A blinking red light after you turn the power on means the battery is charging.
If you need a C wire or the Nest Power Connector
Nest thermostats are designed to work without a C wire in most homes, but Google says some systems, including heating-only, cooling-only, zone-controlled and heat pump systems, need a C wire or a Nest Power Connector. On the current models, the app tells you after its power test. If you’re still choosing a thermostat for a home with no C wire, our best smart thermostats without a C wire guide compares the options.
If you have a spare wire in the bundle, a pro (or you, if you’re comfortable at the furnace) can connect it as a C wire at both ends. If there isn’t one, the Nest Power Connector installs at your furnace or air handler and works with every current Nest thermostat. It needs a 24 VAC system with a C terminal on the equipment. Without one, Google says to call a pro. Google also warns that some third-party C-wire adapters can cause problems or damage a Nest, so stick to its own connector. Our guide to C-wire adapters compares the options.
If it doesn’t work after installing
Most problems after a Nest thermostat installation are power or wiring problems:
- The display won’t turn on. Check that the breaker is fully on and the furnace panel is closed (some systems won’t run with the panel open). On a 4th gen, check the base LED.
- Power warnings. A battery that keeps draining, Wi-Fi that drops, a “Delayed” message or codes like E1, E297, N260 or N261 point to a power problem that a C wire or the Power Connector usually fixes. Our Nest thermostat battery guide explains what each low battery warning means.
- The system does the wrong thing. Compare the wiring with your photo and the app’s diagram, and check that each wire is fully inserted.
Our guide to Nest thermostat problems covers each fix, and our guide on how to reset a Nest thermostat helps when you need to start the setup over.
The bottom line
For most homes, a Nest thermostat installation is a half-hour job: power off at the breaker, photograph and label the wires, mount the base, match each wire to its connector, and finish in the app. Use the Google Home app for the Nest Thermostat (2020) and the Learning Thermostat (4th gen), and the Nest app for the 3rd gen and Thermostat E. Call a pro for high-voltage or proprietary wiring, separate Rh and Rc wires, dual fuel, or a system with no C terminal when the app asks for more power.
Can I install a Nest thermostat myself?
Yes, in most homes. Google says installation usually takes 30 minutes or less and the app guides you through it. Call a pro if your system is high voltage, has stranded or proprietary wiring, has separate Rh and Rc wires, or is a dual fuel system.
Does a Nest thermostat need a C wire?
Not usually. Nest thermostats are designed to work without one, but Google says some systems, including heating-only, cooling-only, zone-controlled and heat pump systems, need a C wire or the Nest Power Connector. The Google Home app tells you after its power test.
Which app do I use to set up a Nest thermostat?
The Nest Thermostat (2020) and the Nest Learning Thermostat (4th gen) can only be set up in the Google Home app. The Nest Learning Thermostat (3rd gen) and the Nest Thermostat E are set up on the thermostat and then added in the Nest app.
Where does the R wire go on a Nest thermostat?
With a single R wire, put it in Rh or Rc on a Learning Thermostat, or in R on the Nest Thermostat (2020). Don’t connect the old jumper wire. If you have both an Rh and an Rc wire, you have a dual transformer system and Google strongly recommends a pro.
Does the Nest Thermostat come with a trim plate?
The Nest Thermostat (2020) doesn’t: the trim plate and the steel plate for an electrical box come in the Nest Thermostat Trim Kit, sold separately. The Nest Learning Thermostat (4th gen) includes both.
Why won’t my Nest thermostat turn on after installation?
Check that the breaker is fully on, the furnace panel is closed and every wire is fully inserted. On the Nest Thermostat (2020), make sure you pulled the battery tab. On the Learning Thermostat (4th gen), take the display off and check that the LED on the base is lit.
Written by Evan Mercer
Founder & Lead Researcher, Smart Home Matrix
Evan digs through spec sheets, firmware changelogs, and thousands of owner reviews so you don’t have to. Every guide starts with a compatibility check and ends with picks he would install in his own home. Read more about Evan and this site, or see exactly how we choose products.