Can the Nest Learning Thermostat control a dual-fuel heat pump system with auxiliary emergency gas heating?

Yes, the Nest Learning Thermostat supports dual-fuel heat pump systems by managing the heat pump as primary heating and switching automatically to the auxiliary gas furnace using programmed outdoor temperature lockout thresholds.

Dual-fuel installations combine an electric heat pump with a gas furnace to optimize heating efficiency and manage utility costs across fluctuating outdoor temperatures. Systems installed in variable climates require specific control logic to switch heating sources when outdoor ambient temperatures drop below the heat pump's thermal balance point, typically between 30°F and 35°F.

If you only do one thing: Set the dual-fuel compressor lockout threshold between 30°F and 35°F in the Nest Equipment settings so your gas furnace takes over the full heating load during sub-freezing weather.

1. Terminal wiring assignment: Land the reversing valve conductor on the O/B terminal, compressor stage one on Y1, and the gas furnace call on W2/AUX using standard 18 AWG solid copper thermostat wiring.
2. Dedicated common wire connection: Connect a dedicated 24VAC common wire to the C terminal on both the furnace control board and the Nest baseplate to prevent power-stealing voltage drops and random system reboots.
3. Dual-fuel equipment configuration: Select the "Dual Fuel" system type in the Nest Pro setup menu, designating the heat pump as primary electric heating and the gas furnace as the fossil-fuel auxiliary and emergency heat source.
4. Lockout threshold calibration: Program the compressor lockout point between 30°F and 40°F based on equipment sizing and regional utility rates, allowing the thermostat to use local Wi-Fi weather data to alternate heat sources.
5. Reversing valve logic verification: Test heating and cooling calls during setup to verify the O/B terminal orientation matches manufacturer specifications, energizing on cooling (O) for most brands or heating (B) for Rheem and Ruud units.

• Watch out for: Power sharing without a dedicated 24VAC C wire, which can pulse phantom voltage through the gas valve circuit and trigger furnace control board lockouts or burner relay chatter.
• Watch out for: Configuring the equipment as single-source electric auxiliary heat rather than dual fuel, which runs the heat pump compressor and gas furnace burners simultaneously and risks rupturing the refrigerant coil from extreme high-side pressure.
• Watch out for: Incorrect O/B reversing valve orientation during initial commissioning, which causes the heat pump to blow air-conditioned 55°F air when calling for 70°F indoor heat.

Verify that your thermostat cable contains at least six dedicated conductors (18/6 gauge) between the furnace board and the wall subbase, or arrange professional dual-fuel configuration backed by the ARS/Rescue Rooter Exceptional Service Guarantee by calling 866-399-2885.