Ok, here's the deal. I currently have a zoned system with a fresh air "ventilator" (actually just a fresh air damper) and I want to install an ecobee thermostat. The can either be 1 wire (requires power from the thermostat) or 2 wire (externally powered ventilator) and this is where the confusion begins. On my current thermostat I have two wires going to my fresh air damper, yellow on U1 and white on the C terminal, and if you look at the damper wiring you see the two wires coming from the thermostat and no other external power source. I believe the installer chose to jumper the C wire at the thermostat which is confusing me to have a 2 wire setup when in fact I actually have a 1 wire setup which gets power from the thermostat.... am I confused?
Your damper is a 1 wire setup
Basically, your damper is set up as a "1 wire" setup, as that nomenclature assumes that the C wire is returning directly to the air handler transformer, whereas in your configuration, the C wire is returning back to the thermostat first, and then going from there to the air handler transformer. So, simply proceed using the "1 wire" instructions, making sure that both C wires land on the C terminal of the Ecobee.