Heat Pump With a B Wire (Rheem / Ruud Style)

Rheem, Ruud and a few other brands energize the reversing valve in heating mode and label it B. Put it on O/B and choose B in settings, or your heat and cool will be backwards.

Detected system: Heat pump, 1-stage compressor, 1-stage aux heat, fan, C wire present · 6 wires

Smart thermostat compatibility

ThermostatVerdictWhat to know
Nest Learning (4th gen)Works: direct swapDirect swap: every wire has a matching terminal.
ecobee PremiumWorks: direct swapDirect swap: every wire has a matching terminal.
ecobee EnhancedWorks: direct swapDirect swap: every wire has a matching terminal.
Honeywell T9Works: direct swapDirect swap: every wire has a matching terminal.
Amazon Smart ThermostatWorks: direct swapDirect 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)

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: Heat pump, 1-stage compressor, 1-stage aux heat, fan, C wire present · 6 wires
Your B wire is treated as the reversing valve (energized in heat), common on Rheem and Ruud heat pumps. Set the new thermostat’s O/B setting to B.

Which smart thermostats work with your wires?

Google Nest Learning Thermostat (4th gen)

Works: direct swap
Wires from the wallNest Learning (4th gen)Rred · 24 V powerRc or RhCblack · Common (C wire)CYyellow · Cooling, stage 1YGgreen · FanGBorange · Reversing valve (O/B)*OBW2white · Auxiliary heatW2
WireColorJobConnect toNote
Rred24 V powerRc or Rh
CblackCommon (C wire)C
YyellowCooling, stage 1Y
GgreenFanG
BorangeReversing valve (O/B)*OB
W2whiteAuxiliary heatW2

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

App settings to choose

  • Reversing valve (O/B): set to B.
  • Equipment type: heat pump with auxiliary (electric strip) heat.
  • 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 heat pump with b valve 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 heat pump with b valve 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 heat pump with b valve 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 heat pump with b valve 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 heat pump with b valve wire?

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

Other wiring setups