If you have recently upgraded to an Ecobee smart thermostat, you may have noticed that it comes with a Power Extender Kit (PEK) in the box. But what exactly is the PEK, and how does it work?

The Ecobee Power Extender Kit works by connecting to your home’s existing thermostat wires to create a complete circuit; this provides continuous 24-volt AC power to your thermostat for homes that don’t have a C wire. Install the PEK on the HVAC system’s control board.

Ecobee smart thermostats come with a Power Extender Kit included free of cost, but not everyone needs to use the kit. That’s why we have provided additional information to help you determine if you need to use the PEK and how to install it if you do.

About the Ecobee Power Extender Kit

Ecobee thermostats are easy to install by yourself if your home has a C wire, or “common wire.” Smart thermostats require a C wire to provide constant electricity to the thermostat. Even when the thermostat is off, it needs power to run the display screen and other essential functions.

The C wire creates a complete circuit that allows 24V AC power from the R wire to flow continuously through it 24/7. Many homes’ existing thermostats already have a C wire, but if yours doesn’t, you can use the Power Extender Kit instead. The PEK works like a C wire, providing constant power to your Ecobee thermostat.

Do I Need to Use the Power Extender Kit?

If there is already a C wire attached to your HVAC system’s control board, then don’t worry about installing the PEK. You won’t need it.

To check which wires you have, remove your old thermostat from the wall. Check for a wire labeled C or one that’s plugged into the C terminal on the thermostat. Generally, the C wire is blue or black, but it can be any color.

Your home may already have a C wire even if it wasn’t connected to your old thermostat. It might be tucked inside your wall if it wasn’t being used.

If you still aren’t positive if there’s a C wire present, you can check to see if there is one attached to the HVAC control board.

Power Extender Kit Requirements

To use an Ecobee Power Extender Kit, your HVAC control board must have four wires: the G, R, W, and Y wires.

WireTypical Wire Color*Purpose
GGreenFan
R, RC, or RHRed24V power
WWhiteHeat
Y or Y1YellowAir conditioner
*Note that wire colors may vary, but these are the most commonly used colors.

If your current thermostat only has two wires, you are not able to use the Ecobee PEK. Check out this Ecobee support page for guidance on alternative options for homes that aren’t compatible with the PEK.

Installing the Ecobee PEK

You will install the Power Extender Kit before installing the Ecobee thermostat. Make sure power to your HVAC system is switched off at the breaker box before starting any installation.

The Power Extender Kit connects your home’s HVAC or furnace control board. Follow the steps below:

  1. Remove the cover from your HVAC system or furnace.
  2. Take a picture of the wires connected to the control board in case you need to reference it later to remember which is which.
  3. Label the G, R, W, and Y wires that are going to your thermostat. There may be other wires that are going to your A/C unit. Leave those as they are.
  4. Disconnect the four wires you labeled from the control board.
  5. Press the buttons on top of the Power Extender Kit and connect the wires.
  6. Connect the five white wires on the PEK to the control board.

If you’d rather not handle live wires by yourself, you can always hire an electrician or use Ecobee’s professional installation.

Ecobee Power Extender Kit Compatibility

Unfortunately, the Ecobee PEK isn’t compatible with other brands of thermostats.

If you are looking for a universal option for continuous power, you can use a 24V transformer instead of the PEK. The transformer plugs into a standard wall outlet and acts as the C wire providing constant power to the thermostat.

An external 24V transformer is easy to install. The transformer has two wires: Attach one to the C wire terminal on the thermostat and one to the R wire terminals.

24V external transformers are compatible with many smart thermostats and video doorbells.

Final Thoughts

If you aren’t a trained electrician, it may be difficult to understand how the Ecobee thermostat’s Power Extender Kit works. After reading this post, we hope you feel confident knowing how to determine whether you need to use the PEK and install it safely.