Nest Thermostat 3rd Generation Installation Guide


Based on Nest’s online compatibility checker data, the Nest Thermostat works with most 24V systems, including gas, electric, oil, forced air, variable speed, heat pump, and radiant. It can control:

• Heating: one, two, and three stages (W1, W2, W3)
• Cooling: one and two stages (Y1, Y2)
• Heat pump: with auxiliary and emergency heat (O/B, AUX, E) • Fan (G, G2, G3)
• Power (C, RH, RC)
• Humidifier or dehumidifier (HUM, DEHUM)

The Nest Thermostat’s * connector can accept only one of these wires: W3, E, HUM or DEHUM.

The Nest Thermostat is designed to work even if your home doesn’t have a common (C) wire. Rarely, installing a new C wire may be required.

Professional installation recommended for:

• Dual fuel systems (heat pump with furnace) • Whole-home humidifiers and dehumidifiers

In the Box

Installation Steps

1. Switch off the power

This protects you and avoids blowing a fuse in your equipment. Adjust the temperature on your old thermostat to make sure your system is off.

Nest Thermostat 3rd Generation Installation Guide power off

2. Remove cover

Some covers pop off, while others need to be unscrewed.

Nest Thermostat 3rd Generation Installation Guide removing old cover

3. Check your system

If your old thermostat is labeled 120V or 240V or has thick wires with wire nuts, your system is high voltage. Not sure? Contact support.

Nest Thermostat 3rd Generation high voltage compatibility

CAUTION: Do not connect Nest to high-voltage wires.

4. Remove any jumper wires

Jumper wires are short wires between two connectors. You won’t need them. An R wire can go into either RC or RH.

Nest Thermostat 3rd Generation Installation Guide jumper wire removal

5. Label wires

Peel off the labels below and attach them to the thermostat’s matching wires.

Use the white labels for any W3, E, HUM or DEHUM wires. The * connector can only connect to one of these wires.

See two names for each connector on your old thermostat’s backplate?

Nest Thermostat 3rd Generation Installation Guide labeling wires

Tip: Take a picture of the wires on your old thermostat to help you remember.

6. Disconnect wires and remove the base

After removing the base, we recommend gently wrapping the wires around a pen or pencil to ensure they don’t fall back into the hole in the wall.

Nest Thermostat 3rd Generation Installation Guide removing old base

Remember, the power to your HVAC system must be off to avoid blowing a fuse in your equipment.

7. Mark where screws will go

Use the bubble level to make sure the Nest Thermostat is level.

Nest Thermostat 3rd Generation marking new screw holes

Use trim plate if needed

You can cover up holes or marks left by your old thermostat with the optional trim plate.

Snap the base and trim plate together, then screw them to the wall.

You’ll find the trim plate in the bottom of the box.

Nest Thermostat 3rd Generation trim plate Installation

Mounting on an electrical box

Electrical boxes aren’t common, but if you have one, secure the steel plate to the electrical box with two of the short steel plate screws. Insert the screws into the long slots on the steel plate.

Use the other two short screws to attach the Nest base and trim plate to the steel plate.

Nest Thermostat 3rd Generation steel plate Installation

8. Attach the Nest base

Pull the wires through the center of the base, then attach it to the wall with the screws.

Nest Thermostat 3rd Generation base plate Installation

9. Connect wires

After all the wires are securely connected, push them down to make sure they’re flush with the base.

Nest Thermostat 3rd Generation wires Installation

The exposed wire should be straight.

10. Attach the display

Press the display onto the base until it clicks.

Nest Thermostat 3rd Generation display Installation

11. Switch the power back on

Nest Thermostat 3rd Generation Installation Guide power back on

12. Setup and Nest Account

The Nest Thermostat will turn on and walk you through setup. Just turn the ring and press to select. During setup, you can connect the thermostat to Wi-Fi.

Go to or download the Nest app to create a Nest Account.
The app will show you how to connect your Nest Account and thermostat.

Nest Thermostat 3rd Generation app Installation

Remember, you can download the Nest app from the AppStore or GooglePlay.

Nest 3rd Generation Installation Guide