G (sometimes F) turns on the indoor blower by itself, which lets you use the thermostat’s "Fan On" setting. It is usually green.
If you install a C-wire adapter (ecobee PEK, Honeywell wire saver, or Amazon’s adapter), the G wire at the thermostat typically becomes the new C wire, and the adapter sends fan and cooling signals over the Y wire.
Wires: R, W, Y, G, C · open in the tool
| Thermostat | G goes to | Whole setup |
|---|---|---|
| Nest Learning (4th gen) | G | Works: direct swap |
| ecobee Premium | G | Works: direct swap |
| ecobee Enhanced | G | Works: direct swap |
| Honeywell T9 | G | Works: direct swap |
| Amazon Smart Thermostat | G | Works: direct swap |
Wires: R, W, Y, G · open in the tool
| Thermostat | G goes to | Whole setup |
|---|---|---|
| Nest Learning (4th gen) | G | Works: direct swap |
| ecobee Premium | C | Works with an adapter |
| ecobee Enhanced | C | Works with an adapter |
| Honeywell T9 | C | Works with an adapter |
| Amazon Smart Thermostat | C | Works with an adapter |
Wire My Thermostat