Installing your ecobee with a boiler and AC (dual transformer system)

If you have a boiler as well as an air conditioner, you have a dual transformer system. The installation process for a dual transformer system is different from a standard installation, so please refer to the information below.


With dual transformer setups, you will have two R wires—one from the cooling transformer (RC) and one from the heating transformer (RH).

It’s also important to note that your C wire must come from the cooling side. If your current thermostat has a C wire that’s coming from your boiler, this will not work with the ecobee. Since the PEK isn’t compatible with dual transformer systems, if you don’t already have a C wire coming from your air handler, you have two options:


1) Run an additional wire from the air handler to the ecobee to use as a C

2) Re-purpose your G wire as the C, connecting it to the C terminal on the air handler and the C terminal on your ecobee. With this option, you will have to install a jumper wire between G and Y at the air handler control board—this will ensure that every time the air conditioning turns on, the fan will also engage. Without this jumper wire installed, the fan will not run when calling for cooling. You will also lose independent fan control with this option since you are re-purposing your fan (G) wire.


Option 2: Wiring with G re-purposed as C, jumper installed




If you require further assistance with your installation, reach out to our Support team. To ensure prompt service, please have wiring pictures at the thermostat, boiler, and air handler control board handy.




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