Installing Your ecobee3 Lite

What You'll Need

• ecobee3 Lite
• ecobee app (iOS or Android)
• 2.4GHz Wi-Fi network
• Phillips head screwdriver
• Labels or tape for marking wires
• Optional: Power Extender Kit (sold separately for this model)

Before You Start

The ecobee3 Lite works with most 24V HVAC systems including conventional gas, electric, and oil furnaces, as well as single-stage heat pumps with auxiliary heat. It does not support high-voltage (120V/240V) systems, millivolt systems, or proprietary communicating systems. Before removing your old thermostat, snap a photo of the wiring so you have a reference.

C-Wire Requirement

The ecobee3 Lite requires a C-wire for continuous power. If your existing thermostat wiring does not include a C-wire (usually a blue wire, but color is not always reliable), you have a few options. You can purchase the ecobee Power Extender Kit separately, which repurposes one of your existing wires at the furnace control board. Alternatively, you can have an HVAC tech run a new thermostat cable with a C-wire included, or use a third-party add-a-wire kit. The ecobee app will tell you during setup if it detects a missing C-wire.

Step-by-Step Installation

1. Turn off your HVAC system at the breaker panel. Do not just switch the thermostat off -- cut power at the breaker to avoid any risk of shorting wires.
2. Remove the old thermostat faceplate and photograph the wiring. Label each wire with the terminal letter it is connected to (R, W, Y, G, C, O/B).
3. Disconnect wires and remove the old backplate. If a wire falls into the wall, wrap it around a pen to keep it accessible.
4. Install the ecobee3 Lite backplate using the included screws and anchors. Use the built-in bubble level to get it straight.
5. Connect your labeled wires to the matching terminals on the backplate. Push each wire into the screw terminal and tighten. Make sure no bare copper from one wire is touching another.
6. Snap the thermostat onto the backplate until you feel it click into position.
7. Restore power at the breaker.
8. Walk through the on-screen setup:
   • Select your language and region
   • Confirm detected wiring and system type
   • Connect to your 2.4GHz Wi-Fi network
   • Download the ecobee app, create an account, and register the thermostat

HVAC Compatibility Notes

The ecobee3 Lite supports 1 stage of heating and 1 stage of cooling for conventional systems, or 1 stage of heat pump operation with auxiliary heat. It does not support 2-stage systems, so if your furnace has a W2 wire, you may want to step up to the ecobee Smart Thermostat Enhanced. The ecobee3 Lite does include an accessory terminal for connecting a humidifier or dehumidifier.

Smart Home Integration

The ecobee3 Lite works with Amazon Alexa, Google Assistant, Apple HomeKit, and SmartThings. HomeKit setup uses the code printed on the thermostat or the included card. You can add SmartSensors (sold separately) to monitor temperature in other rooms and have the thermostat prioritize those readings on a schedule. IFTTT and Home Assistant integration are also supported.

Energy Saving Features

• Smart Home/Away uses the built-in occupancy sensor to detect whether anyone is home and adjusts the temperature accordingly
• 7-day scheduling lets you set different comfort and setback temperatures for each day of the week
• Monthly energy reports in the ecobee app break down your heating and cooling runtime with tips for improvement
• Smart Recovery learns how long your system takes to reach target temperatures and starts early so your home is comfortable when you need it

Troubleshooting

• No power after installation: The most likely cause is a missing or loose C-wire connection. Open the backplate and verify the C terminal has a wire firmly seated. If you do not have a C-wire, you will need a Power Extender Kit (sold separately for the ecobee3 Lite).
• Won't connect to Wi-Fi: The ecobee3 Lite supports 2.4GHz only. If you have a dual-band router, make sure you select the 2.4GHz network. If your network name contains special characters, try renaming it temporarily to something simple during setup.
• Blank screen after power restore: Pull the thermostat off the backplate and reattach it. If still blank, check the breaker and verify at least the R and C wires are connected properly.
• HVAC not responding: Use the built-in test equipment feature under Settings to test the fan, heat, and cooling individually. If the fan runs but heating or cooling does not kick in, check that W and Y wires are seated firmly.
• SmartSensor not pairing: Pull the battery tab on a new sensor, or remove and reinsert the battery on an existing one. In the ecobee app, go to Sensors and tap Add Sensor. Make sure the sensor is within 45 feet of the thermostat with no major obstructions.
• Factory reset: On the thermostat go to Main Menu, then Settings, then Reset. You can reset the schedule only or do a full reset to factory defaults.