Wiring guide
Honeywell Home T9 Smart Thermostat wiring for heat pump + emergency heat
Good news: the Honeywell Home T9 Smart Thermostat is a direct swap for this setup. Every wire has a matching terminal.
Separate AUX and E wires are common on older heat pumps. Many smart thermostats have no E terminal, so what happens to that wire decides whether you have a direct swap. Read the full heat pump + emergency heat guide for how to confirm your setup and mistakes to avoid.
Wiring diagram
Detected system: Heat pump, 1-stage compressor, 1-stage aux heat, emergency heat, fan, C wire present · 7 wires
Honeywell Home T9 Smart Thermostat
Works: direct swap| Wire | Color | Job | Connect to | Note |
|---|---|---|---|---|
| R | red | 24 V power | R | |
| C | blue | Common (C wire) | C | |
| Y | yellow | Cooling, stage 1 | Y | |
| G | green | Fan | G | |
| O | orange | Reversing valve (O/B) | O/B | |
| AUX | white | Auxiliary heat | W2 / Aux | |
| E | brown | Emergency heat | E |
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 Honeywell T9 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
- Reversing valve (O/B): set to O.
- 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; O → O/B; AUX → W2 / Aux; E → E.
Do I need a C wire for the Honeywell T9?
You already have a C wire, so no adapter is needed.