Amazon Smart Thermostat wiring for rh + rc dual transformer

The Amazon Smart Thermostat is not compatible with this setup. See the alternatives below.

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)

📷 Upload or take a photo

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?

YesNoNot sure

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? Thick wires joined with wire nuts, 120/240 V labels, or electric baseboard heaters (line voltage) Gas wall/floor heater or fireplace that runs without household power (millivolt) Numbered terminals (1, 2, 3, 4 or A, B, C, D), e.g. Carrier Infinity or Lennox iComfort

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?

Amazon Smart Thermostat

Not compatible

Separate Rh and Rc wires mean two transformers, which the Amazon Smart Thermostat doesn’t support.

Wire	Color	Job	Connect to	Note
RH	red	Heating power	Don’t connect	No matching terminal on the Amazon Smart Thermostat
W	white	Heat, stage 1	W
RC	black	Cooling power	Don’t connect	No matching terminal on the Amazon Smart Thermostat
Y	yellow	Cooling, stage 1	Y
G	green	Fan	G

Install steps

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

What you need

Amazon Smart ThermostatThe thermostat itselfCheck price

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

Frequently asked questions

Where does each wire go on the Amazon Smart Thermostat?

RH → not connected; W → W; RC → not connected; Y → Y; G → G.

Do I need a C wire for the Amazon Smart Thermostat?

Separate Rh and Rc wires mean two transformers, which the Amazon Smart Thermostat doesn’t support.

Other thermostats for this setup

Amazon Smart Thermostat: other setups