Plumbing – How to wire a smart thermostat with dual Transformer system? R , Rc, W , Y , G. No C wire. No Jumper

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Is this system considered a Dual Transformer system? According to Nest since there is a R and RC cable it must be a dual transformer. But they were unsure and I don't know what that means! I don't have a C wire. Trying to figure out which smart thermostat is best suited for such a setup and hook it up without tearing up much or pulling new wires!

Hope the picture makes sense. I currently have a Honeywell Thermostat with the following wires hooked up.

R, RC, G, Y , W. No jumpers. I have a FirstCO Air Handler, Burnham Heat, and AC unit outside the house.

  • Current Thermostat: Honeywell TH6220D1002
  • FirstCo Air Handler: 30MBX-3HW 120V-1PH-60HZ

Google did not help me much with the installation or ideas. They said "learning system may work".

Any help would be much appreciated. Thanks

enter image description here

Current System

Wiring Diagram Air Handler

wires from Air Handler - three cables boiler, condenser, thermostat

Best Answer

You have a two-transformer system most likely

From the way your existing thermostat is wired, you most likely indeed have a two-transformer system. This means that you will need a 3rd gen Nest, since the Nest E dropped two-transformer support, and the 2020 edition Nest supports the same physical connections as the Nest E.

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