I only had the 1st generation NEST and my contractor asked me how I wanted to hook up my 2 stage Goodman. He said either just hook up stage 1 or combine the 2 stages so it's always running in stage 2. The Tstat wire run is 5 wires but really, we need 7 so that the upstairs NEST can use Rc Rh G Y1 Y2 W1 and C. I'm learning that the NEST is what is termed a "power robbing thermostat" so you really need the C wire to provide a constant charge to it.
I have in-floor radiant heating with 3 zones. I have 2 NESTs for 2 of the zones (the basement zone is not hooked up yet) and the AC is directly connected to the 2nd floor NEST.
I'm considering the 2nd gen NEST but need 7 wires. I had my contractor come back after the initial install to think of a way to get the C wire so he used a Venstar Add-a-Wire. He's not familiar with Add-a-wire units that can add more than one wire. I'm trying to convince my contractor that the ARGO unit he's using needs the Isolation Relay because the NEST is dependant right now on the AC power wires Rc and C for it's power. If I turn off my Spackpak unit, the NEST reports no power at Rh as well. I think I need the Isolation Relay for this to work properly.
Thanks for all the responses!