I just moved to North America from Europe (hence why furnaces, HRV systems etc are totally alien to me) and I'm having trouble understanding how to wire up an ecobee3 lite to replace my Honeywell thermostat. I have contacted ecobee support but they are taking days to respond and replying with template emails that don't address my specific questions. My house has a furnace and a HRV unit.

For simplicity I'll list my questions out individually.

1. Two wires going into the Rh terminal

From looking at my thermostat wiring, I have one wire going into Rc and two wires going into Rh (not a jumper, two individual wires). I can't find anything online that shows two wires going into Rh. Could it be for the HRV unit? Do I wire both of the Rh wires into the Rh terminal on the ecobee?

2. Lack of a C wire, but G is already wired in.

I don't have a C wire in which to power the ecobee (my current thermostat uses AA batteries). I know ecobee's PEK repurposes the G wire in order to create a C wire, but my G wire is already wired into my thermostat. I assume it's already serving a purpose (otherwise why would it be wired?) so I don't think I can use ecobee's PEK to piggyback of this wire? I know G is for the furnace fan - what are the consequences if I do use this wire as C instead of G?

Any help greatly appreciated!

Photo of thermostat wiring

  • Can you post photos of the wiring at the furnace/air-ahndler end of the system? – ThreePhaseEel Jul 19 '19 at 2:24

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