Wiring guide
Amazon 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. Read the full 2 wires, heat only guide for how to confirm your setup and mistakes to avoid.
Wiring diagram
Detected system: 1-stage heat, no C wire · 2 wires
Amazon Smart Thermostat
Not compatibleNo C wire and too few wires for an adapter. You’ll need a new 18/5 thermostat cable from the equipment to the wall.
| 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.