Google Nest Learning Thermostat (4th gen) wiring for rh + rc dual transformer

This setup is possible with the Google Nest Learning Thermostat (4th gen), but a professional install is recommended.

Wires on both Rh and Rc (not a short jumper between them) mean separate heating and cooling transformers, common with a boiler plus a separate AC air handler. Bridging them can destroy equipment.

1Snap a photo of your old thermostat’s wires (optional)

AI reads the terminal letters and wire colors, then you double-check them. Photos are not saved.

2Tick every terminal that has a wire

Pull the faceplate off your old thermostat. Use the letter printed next to each wire, not its color. Skip short jumper wires between two terminals.

More labels (W3, X, X2, K, PEK, L, S, T, U, HUM, DEHUM)

3A few quick questions

Do you have a heat pump?

A heat pump is an outdoor unit that both heats and cools. Heat pump thermostats usually have an “EM HEAT” or “AUX” setting.

Do any of these apply?

4Your wiring

Your system: 1-stage heat, 1-stage cooling, fan, no C wire, dual transformer · 5 wires

Which smart thermostats work with your wires?

Google Nest Learning Thermostat (4th gen)

Pro install recommended
Google recommends a professional install for dual-transformer (Rh + Rc) systems.
Wires from the wallNest Learning (4th gen)RHred · Heating powerRhWwhite · Heat, stage 1WRCblack · Cooling powerRcYyellow · Cooling, stage 1YGgreen · FanG
WireColorJobConnect toNote
RHredHeating powerRh
WwhiteHeat, stage 1W
RCblackCooling powerRc
YyellowCooling, stage 1Y
GgreenFanG

Install steps

  1. Turn off power to the furnace/air handler (switch or breaker) and the AC condenser. Confirm the old thermostat is dead.
  2. Photograph the old wiring, then label each wire with the letter it came off. Ignore short jumpers.
  3. Connect each wire to the Nest Learning (4th gen) terminal shown above. Cap unused wires one at a time.
  4. Restore power and finish setup in the app.
  5. Test heat, cool and fan. If a breaker trips or equipment runs nonstop, power off and call a pro.

What you need

  • Google Nest Learning Thermostat (4th gen)The thermostat itselfCheck price

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Confirm against the official Google Nest install guide. The app also checks your wiring during setup.

Frequently asked questions

Where does each wire go on the Nest Learning (4th gen)?

RH → Rh; W → W; RC → Rc; Y → Y; G → G.

Do I need a C wire for the Nest Learning (4th gen)?

See the notes above for your power options.

Other thermostats for this setup

Nest Learning (4th gen): other setups