ecobee Smart Thermostat Premium wiring for b wire used as common

Good news: the ecobee Smart Thermostat Premium is a direct swap for this setup. Every wire has a matching terminal.

On many Trane, American Standard and Carrier furnaces, the B terminal on the old thermostat is actually the common wire. Put it on O/B and you can blow a fuse or damage the thermostat.

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

Do you have a heat pump?

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?

4Your wiring

Your system: 1-stage heat, 1-stage cooling, fan, C wire present · 5 wires
Your B wire is treated as the common (C) wire. That is normal on many Trane, American Standard and Carrier systems. If it lands on a B or O terminal at the equipment, stop and recheck.

Which smart thermostats work with your wires?

ecobee Smart Thermostat Premium

Works: direct swap
Wires from the wallecobee PremiumRred · 24 V powerRcBblue · Common (C wire)CWwhite · Heat, stage 1W1Yyellow · Cooling, stage 1Y1Ggreen · FanG
WireColorJobConnect toNote
Rred24 V powerRc
BblueCommon (C wire)C
WwhiteHeat, stage 1W1
YyellowCooling, stage 1Y1
GgreenFanG

Install steps

  1. Turn off power to the furnace/air handler (switch or breaker) and the AC condenser. Confirm the old thermostat is dead.
  2. Photograph the old wiring, then label each wire with the letter it came off. Ignore short jumpers.
  3. Connect each wire to the ecobee Premium terminal shown above. Cap unused wires one at a time.
  4. Restore power and finish setup in the app.
  5. 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; B → C; W → W1; Y → Y1; G → G.

Do I need a C wire for the ecobee Premium?

You already have a C wire, so no adapter is needed.

Other thermostats for this setup

ecobee Premium: other setups