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.

Your wiring is pre-filled below. Change any terminal to match your wall exactly.

1Snap a photo of your old thermostat’s wires (optional)

📷 Upload or take a photo

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

Do you have a heat pump?

YesNoNot sure

A heat pump is an outdoor unit that both heats and cools. Heat pump thermostats usually have an “EM HEAT” or “AUX” setting.

Do any of these apply? Thick wires joined with wire nuts, 120/240 V labels, or electric baseboard heaters (line voltage) Gas wall/floor heater or fireplace that runs without household power (millivolt) Numbered terminals (1, 2, 3, 4 or A, B, C, D), e.g. Carrier Infinity or Lennox iComfort

4Your wiring

Your system: 1-stage heat, 1-stage cooling, fan, C wire present · 5 wires

Which smart thermostats work with your wires?

Google Nest Learning Thermostat (4th gen)

Works: direct swap

Wire	Color	Job	Connect to
R	red	24 V power	Rc or Rh
W	white	Heat, stage 1	W
Y	yellow	Cooling, stage 1	Y
G	green	Fan	G
C	blue	Common (C wire)	C

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 Nest Learning (4th gen) terminal shown above. Cap unused wires one at a time.
Restore power and finish setup in the app using the settings below.
Test heat, cool and fan. If a breaker trips or equipment runs nonstop, power off and call a pro.

App settings to choose

Single R wire: the Nest app tells you whether to use Rc or Rh.

What you need

Google Nest Learning Thermostat (4th gen)The thermostat itselfCheck price

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Confirm against the official Google Nest install guide. The app also checks your wiring during setup.

Frequently asked questions

Will the Nest Learning (4th gen) work with 5 wires with c wire?

Works: direct swap. Every wire has a matching terminal, so it’s a direct swap. See the Nest Learning (4th gen) wiring diagram.

Will the ecobee Premium work with 5 wires with c wire?

Works: direct swap. Every wire has a matching terminal, so it’s a direct swap. See the ecobee Premium wiring diagram.

Will the ecobee Enhanced work with 5 wires with c wire?

Works: direct swap. Every wire has a matching terminal, so it’s a direct swap. See the ecobee Enhanced wiring diagram.

Will the Honeywell T9 work with 5 wires with c wire?

Works: direct swap. Every wire has a matching terminal, so it’s a direct swap. See the Honeywell T9 wiring diagram.

Will the Amazon Smart Thermostat work with 5 wires with c wire?

Works: direct swap. Every wire has a matching terminal, so it’s a direct swap. See the Amazon Smart Thermostat wiring diagram.