Nest Learning compatible with existing wiring

[DavidBaron]

Hello, we moved into a house with two AC units and separate radiant heating floor.  There are two old thermostats, one for each AC unit/zone. Each thermo has a Red wire connected to RH, another Red wire connected to RC, a 'double' White wire, a single Yellow wire and a single Green wire. I've watched the Installation Video and it does not include what I would do with my available wires. I've not yet purchased the Nest units (2 of them). Should I, and if so, how would I re-wire it with my existing wires?

[CoolingWizard]

@DavidBaron , the good news is that all thermostats are colorblind. So just keep straight which wire is attached to which terminal. Inside the Nest Thermostat box are labels you can attach. Also take a photo of the thermostat showing the wires attached before removing the old thermostat. 

Since your system is two separate systems, this why you have Rh and Rc wires. Each system is supplying the two red wires.  Nest call this a duel fuel system.  Rh is your heating system and Rc is the air conditioner.  

You say you heating system is radiant? Would that be hydronic?

AC Cooling Wizard

[DavidBaron]

Hi CW, yes, our radiant heating is hydronic (closed loop heated water). In regards to your response, I am still not clear if what I have will work with Nest Learning units. Our two 'zones' are both AC. The radiant heating is its own system with its own boiler and its own thermostats/controllers. So, please, let me ask again: Will our current wiring simply 'work' with Nest Learning right out of the box? We have: RH (1), RC (1), W (1), Y (1) and G (1) wires. No C. If the answer is 'yes', then I would ask 'how do we do the wiring?' Is it as simple as inserting the existing wires into the matching slots, as seen on https://store.google.com/us/product/nest_learning_thermostat_3rd_gen?hl=en-US, roughly 30% down? Even with no C wire? Thank you again!

[CoolingWizard]

@DavidBaron ,

Since you say the hydronic heating system has its own thermostat, and you have two separate Air Conditioning units, the wires you have identified includes a separate heating system. The Rh is the control voltage for the heating system. When heat is called for, the Rh is internally connected to W.  This sends control voltage to the Integrated furnace controller and starts the heating cycle.  Once the desired heat temperature is met, the thermostat drops the connection to W and that causes the heating system to shutdown. 
In the case of the Air Conditioner, when cooling os called for, the thermostat internally connects Rc to Y and G. Y starts the outdoor compressor unit and G starts indoor blower fan. 

If your only heating source is the hydronic boiler and the radiators, Then their should not not be Rh or W in the AC thermostats. 

AC Cooling Wizard