Honeywell Home T9 Smart Thermostat wiring for heat pump with b valve wire

Good news: the Honeywell Home T9 Smart Thermostat is a direct swap for this setup. Every wire has a matching terminal.

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.

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?

Honeywell Home T9 Smart Thermostat

Works: direct swap
Wires from the wallHoneywell T9Rred · 24 V powerRCblack · Common (C wire)CYyellow · Cooling, stage 1YGgreen · FanGBorange · Reversing valve (O/B)O/BW2white · Auxiliary heatW2 / Aux
WireColorJobConnect toNote
Rred24 V powerR
CblackCommon (C wire)C
YyellowCooling, stage 1Y
GgreenFanG
BorangeReversing valve (O/B)O/B
W2whiteAuxiliary heatW2 / Aux

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 Honeywell T9 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.

What you need

  • Honeywell Home T9 Smart ThermostatThe thermostat itselfCheck price

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Confirm against the official Honeywell Home install guide. The app also checks your wiring during setup.

Frequently asked questions

Where does each wire go on the Honeywell T9?

R → R; C → C; Y → Y; G → G; B → O/B; W2 → W2 / Aux.

Do I need a C wire for the Honeywell T9?

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

Other thermostats for this setup

Honeywell T9: other setups