Wiring guide
2-Stage Heat & 2-Stage Cool Thermostat Wiring
W2 and Y2 mean a two-stage furnace and a two-stage AC. They run on low most of the time and step up on extreme days. Budget thermostats can’t run the second stages.
Detected system: 2-stage heat, 2-stage cooling, fan, C wire present · 7 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 | Not compatible | You have 2 heat stages; the Amazon Smart Thermostat supports 1. |
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 |
| C (blue) | C | C | C | C | C |
| W1 (white) | W | W1 | W1 | W | W |
| W2 (brown) | W2 | W2 | W2 | W2 / Aux | None |
| Y1 (yellow) | Y | Y1 | Y1 | Y | Y |
| Y2 (orange) | Y2 | Y2 | Y2 | Y2 | None |
| G (green) | G | G | G | G | G |
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
Wires on W1 and W2 (two-stage furnace) and on Y1 and Y2 (two-stage AC), plus R, C and G. The furnace or condenser nameplate usually says “two-stage” or “2-stage”. If only one of W2 or Y2 is present, you have two stages on that side only.
Mistakes to avoid
- Buying a thermostat that only supports one stage and then capping W2 or Y2. Everything still runs, but on low stage only, and you lose the comfort and efficiency you paid for.
- Swapping Y2 and W2. They look alike on some old plates, so label every wire before you remove it.
- Leaving the stage timer settings at the default. Adjust them in the app if the system switches stages too quickly or too slowly.
Our advice
The Amazon Smart Thermostat runs one stage of heat and one of cool, so it is a poor fit here. Nest, ecobee and Honeywell T9 all run two stages of both.