Wire My Thermostatecobee Smart Thermostat Premium wiring for k wire (honeywell wire saver)
This setup is possible with the ecobee Smart Thermostat Premium, but a professional install is recommended.
A wire on K means a Honeywell wire saver module is installed at the furnace, combining fan and cooling on one wire to free up a C wire. Only some thermostats understand K.
1Snap a photo of your old thermostat’s wires (optional)
AI reads the terminal letters and wire colors, then you double-check them. Photos are not saved.
2Tick every terminal that has a wire
Pull the faceplate off your old thermostat. Use the letter printed next to each wire, not its color. Skip short jumper wires between two terminals.
More labels (W3, X, X2, K, PEK, L, S, T, U, HUM, DEHUM)
3A few quick questions
4Your wiring
Which smart thermostats work with your wires?
ecobee Smart Thermostat Premium
Pro install recommended| Wire | Color | Job | Connect to | Note |
|---|---|---|---|---|
| R | red | 24 V power | Rc | |
| C | green | Common (C wire) | C | |
| W | white | Heat, stage 1 | W1 | |
| K | yellow | Wire saver (fan + cool) | Don’t connect | No K terminal. A pro must remove the wire saver and restore G and Y. |
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 ecobee Premium 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
- ecobee Smart Thermostat PremiumThe thermostat itselfCheck price
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Confirm against the official ecobee install guide. The app also checks your wiring during setup.
Frequently asked questions
Where does each wire go on the ecobee Premium?
R → Rc; C → C; W → W1; K → not connected.
Do I need a C wire for the ecobee Premium?
You already have a C wire, so no adapter is needed.