Wiring guide
5-Wire Thermostat Wiring (With C Wire)
Five wires with a C (common) wire is the easy case: gas or electric furnace, central AC, fan and constant power. Every major smart thermostat works; the only question is which letter each wire lands on.
Detected system: 1-stage heat, 1-stage cooling, fan, C wire present · 5 wires
Smart thermostat compatibility
| Thermostat | Verdict | What to know |
|---|---|---|
| Nest Learning (4th gen) | Works: direct swap | Direct swap: every wire has a matching terminal. |
| ecobee Premium | Works: direct swap | Direct swap: every wire has a matching terminal. |
| ecobee Enhanced | Works: direct swap | Direct swap: every wire has a matching terminal. |
| Honeywell T9 | Works: direct swap | Direct swap: every wire has a matching terminal. |
| Amazon Smart Thermostat | Works: direct swap | Direct swap: every wire has a matching terminal. |
Where each wire goes, thermostat by thermostat
| Old wire | Nest Learning (4th gen) | ecobee Premium | ecobee Enhanced | Honeywell T9 | Amazon Smart Thermostat |
|---|---|---|---|---|---|
| R (red) | Rc or Rh | Rc | Rc | R | R |
| W (white) | W | W1 | W1 | W | W |
| Y (yellow) | Y | Y1 | Y1 | Y | Y |
| G (green) | G | G | G | G | G |
| C (blue) | C | C | C | C | C |
Colors are typical, not a rule: always go by the letter the wire was connected to. Click a thermostat for its full diagram, parts and app settings.
How to confirm this is your setup
Five wires on R, C, W, Y and G. The C wire is often blue or black, but color means nothing: what matters is that at the furnace, the same wire lands on the terminal marked C or COM. Check that end before you trust it.
Mistakes to avoid
- Assuming a blue wire is C because it is blue. Some installers use blue for other jobs.
- Forgetting to connect C at the furnace end. A wire that is connected at the thermostat but folded back at the furnace does nothing.
- Leaving a jumper between Rh and Rc on the new thermostat. Most smart thermostats handle this internally and don’t need the old jumper.
Our advice
This is the simplest setup to upgrade. Every thermostat on this site takes it directly, so choose on features and price rather than wiring.