W2 is a second heat stage: a two-stage furnace runs on low most of the time and uses W2 on cold days. On a heat pump, W2, AUX, or X2 on older Carrier/Trane thermostats runs backup electric heat strips.
The Amazon Smart Thermostat has one heat terminal, so it can’t run a second furnace stage.
Wires: R, C, W1, W2, Y1, G · open in the tool
| Thermostat | W2 goes to | Whole setup |
|---|---|---|
| Nest Learning (4th gen) | W2 | Works: direct swap |
| ecobee Premium | W2 | Works: direct swap |
| ecobee Enhanced | W2 | Works: direct swap |
| Honeywell T9 | W2 / Aux | Works: direct swap |
| Amazon Smart Thermostat | None | Not compatible |
Wires: R, C, Y, G, O/B, AUX · open in the tool
| Thermostat | AUX goes to | Whole setup |
|---|---|---|
| Nest Learning (4th gen) | AUX | Works: direct swap |
| ecobee Premium | W1 | Works: direct swap |
| ecobee Enhanced | W1 | Works: direct swap |
| Honeywell T9 | W2 / Aux | Works: direct swap |
| Amazon Smart Thermostat | W | Works: direct swap |
Wire My Thermostat