Thermostat compatibility

[Mike006]

wondering if my two wire Honeywell system is compatible for the 4th gen learning thermostat. No idea how to post a picture of the wiring, but it’s a red wire to the R and a blue wire to the C and that’s all. Also connects to the system in the attic through a WiFi enabled port Honeywell system 

[CoolingWizard]

@Mike006 

it does not appear that you have enough wires in your thermostat cable to run a conventional system. your current wiring only Supplies power for the thermostat and the thermostat uses either long range Bluetooth or it uses Wi-Fi to communicate to receiver that’s attached to your conventional system.

AC Cooling Wizard

[Biffo]

You cannot make a direct replacement because your existing wires are carrying mains voltage. The thermostat is basically just an on/off switch. Mains goes into it and when the thermostat completes the circuit then mains goes through to the Heat Demand side of your system.

However you should be able to re-purpose those two wires to connect the Nest thermostat to the Nest Heatlink box which you would install in the attic. I did this in a 1980’s house in the U.K. using a Nest 3. But it was not straightforward and required a lot of planning. I seem to remember having a spreadsheet showing some 13 electrical connections covering central heating and domestic hot water.

In summary those two wires are going to be very useful for carrying the 12v power supply from the attic but a lot of re-wiring may be required upstairs.