I ran the compatibility checker with a wiring configuration and the tool reported that ecobee needs to take a closer look. Can you please let me know if my system configuration is supported?
My thermostat has the following wires: R, G, Y, W
It seems you have only 4-wires so in this case you'll use the included PEK module. The purpose of the PEK is to multiplex 2 wires (Y&G) to free up one wire so it can be used as a C (Common) wire. Therefore you do not have to run a new thermostat cable. Here are links to wiring the ecobee3 and installation videos: