Tested by Alex Rivera
Set Aux Heat Lockout correctly to cut winter bills without sacrificing comfort. Brand-specific steps for Ecobee, Nest, and Honeywell.
Aux Heat Lockout (2025): How to Set It Right for Your Thermostat
Auxiliary heat can silently spike your bills. With the right lockout temperature, your heat pump or dual-fuel system stays efficient while keeping rooms comfortable.
What Aux Heat Lockout Means
“Aux heat” is your backup heating stage (electric resistance or gas). A lockout temperature tells the thermostat: don’t use auxiliary heat until outdoor temperature falls below this point. Correct lockout keeps your primary heat pump working where it’s efficient and prevents expensive backup runs.
Heat Pumps: Balance Point & Best Practices
Most air-source heat pumps are cost-effective down to about 30–40 °F (–1 to 4 °C). Above your balance point, the heat pump alone is cheaper than resistance heat. Start with a 35 °F lockout, then fine-tune ±5 °F based on comfort and runtime.
- Send-a-test on a mild evening: raise setpoint by 2 °F and confirm the thermostat does not call aux above your lockout.
- Expect longer but cheaper cycles near the balance point. That’s normal and saves money.
Furnace & Dual-Fuel: Economic Balance Point
Dual-fuel pairs a heat pump with a gas furnace. Here, lockout governs fuel switching: run the heat pump until gas becomes cheaper or more comfortable. Typical switchovers land between 30–45 °F, but the right number depends on your gas/electric rates and house load.
Pro tip: Pair the thermostat with an outdoor sensor or verified local weather feed for accurate lockout and fewer nuisance switchovers.
Brand-Specific Settings
Ecobee (Premium & Enhanced)
Path: Settings → Installation → Thresholds → Aux Heat. Choose Automatic (uses weather + runtime data) or Manual (set a value, e.g., 35 °F). Ecobee plays nicely with occupancy-aware SmartSensors, so rooms that are actually in use get priority before aux is considered.
Buy Ecobee Smart Thermostat Premium
Nest Learning Thermostat (3rd-Gen)
Nest uses “Balance” strategies instead of a simple manual lockout on the device. In the app/web, set heat-pump cutoff (often 30–45 °F) or choose Max Savings to delay aux longer. Schedules and Nest Temp Sensors influence room priorities, but Nest sensors lack motion — they shift by time blocks, not live occupancy.
Buy Nest Learning Thermostat (3rd-Gen)
Honeywell Home T10 Pro
Installer Menu: Code 0350 → Aux Heat Lockout. You can set both compressor and aux lockouts (separate values) when an outdoor sensor is connected. T10’s room sensors include humidity and occupancy, helping staging decisions in shoulder seasons.
- Common starting points: Compressor lockout 15 °F, Aux lockout 35 °F.
Comparison Table (Lockout Controls)
| Feature | Ecobee Premium | Nest Learning (3rd-Gen) | Honeywell T10 Pro |
|---|---|---|---|
| Manual Aux Lockout | Yes (Thresholds) | Partial (web/app cutoff) | Yes (installer menu) |
| Automatic Optimization | Yes (runtime + weather) | Yes (Balance modes) | Limited |
| Outdoor Temp Source | API or external sensor | Weather API | Wired/Wireless sensor |
| Sensor Influence | SmartSensor with motion | Temp Sensor (no motion) | T10 Sensor: temp + humidity + motion |
| Good Starting Lockout | 35 °F | 35–40 °F (Max Savings) | 35 °F aux, 15 °F compressor |
Values are starting points; fine-tune for your climate, envelope, and utility rates.
Step-by-Step: Set Aux Heat Lockout
- Confirm outdoor temperature source (sensor or weather feed). If using a wired sensor (Honeywell), verify placement is shaded and ventilated.
- Enter brand-specific settings: Ecobee Thresholds; Nest Balance/Heat Pump; Honeywell installer code 0350.
- Choose starting lockout (typically 35 °F for aux on air-source pumps; dual-fuel may differ).
- Test staging: raise heating setpoint by 2 °F above ambient — confirm the system honors lockout and only uses aux below your threshold.
- Tune after 48–72 hours based on comfort and runtime; adjust ±5 °F as needed.
Optimization: Sensors, Occupancy & Schedules
- Occupancy matters: With Ecobee SmartSensors or Honeywell T10 sensors, occupied rooms weigh more, reducing unnecessary aux calls. Nest sensors follow time blocks, so align schedules with real usage.
- Thermostat placement: Avoid cold drafts or sun-exposed walls; see our placement guide.
- Away/Vacation modes: Larger setbacks can trigger aux on recovery. Use gradual ramps or pre-heat windows to avoid hitting aux as you return.
- Utility programs: Pair with rebates and DR programs — many reward reduced aux runtime during peak events.
FAQ
Will a strict lockout make my home feel colder?
Near the balance point, expect longer heat-pump cycles and gentler temperature rises. If recovery feels sluggish, nudge lockout up by 3–5 °F or enable a small pre-heat before wake-up.
Do I need a physical outdoor sensor?
Ecobee and Nest can use weather services; Honeywell T10 benefits from a dedicated sensor for precise staging and dual thresholds.
What’s the difference between compressor and aux lockout?
Compressor lockout stops the heat pump when it’s too cold to run efficiently; aux lockout prevents backup heat from engaging too early. Dual-fuel systems often use both.
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