Wire My ThermostatAmazon Smart Thermostat wiring for 2 wires, heat only
The Amazon Smart Thermostat is not compatible with this setup. See the alternatives below.
Two wires almost always means a heat-only furnace or boiler: the thermostat just closes a circuit to call for heat. There is no fan wire, no cooling and no C wire, so power for a smart thermostat is the real problem.
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
4Your wiring
Which smart thermostats work with your wires?
Amazon Smart Thermostat
Not compatible| Wire | Color | Job | Connect to | Note |
|---|---|---|---|---|
| R | red | 24 V power | R | |
| W | white | Heat, stage 1 | W |
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
- 18/5 thermostat wireAdds the missing C wireCheck 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?
R → R; W → W.
Do I need a C wire for the Amazon Smart Thermostat?
No C wire and too few wires for an adapter. You’ll need a new 18/5 thermostat cable from the equipment to the wall.