my ecobee smartthermostat premium keeps using the auxiliary heat way too much, even when it's not that cold out. how do i stop it?

Diagnosis

This issue occurs when the ecobee SmartThermostat Premium perceives that the heat pump is unable to keep up with the heating demand, triggering the "Auxiliary Heat" (usually electric heat strips or a gas furnace) to bridge the gap. This is typically caused by a conflict between the "Auxiliary Heat Maximum" temperature setting and the "Compressor Minimum Outdoor Temperature" threshold. If the outdoor temperature drops even slightly below the set threshold, the ecobee will either disable the heat pump entirely or force the auxiliary heat to run simultaneously to maintain the set point. Furthermore, the "Heat Differential" setting may be too narrow. If the differential is set to 0.5°F or 1.0°F, the thermostat triggers a call for heat more frequently. When combined with a high "Aux Heat" staging temperature, the system enters a cycle where it relies on the expensive auxiliary strips because the heat pump cannot raise the indoor temperature quickly enough to satisfy the tight differential. You can confirm this by checking the "Equipment Status" on the thermostat screen; if you see "Aux Heat" active while the outdoor temperature is still relatively mild (e.g., 35°F to 45°F), your thresholds are misconfigured.

How to Fix It

To optimize your heat pump and minimize auxiliary heat usage, you must adjust the staging thresholds and the compressor lockout settings. Follow these precise steps on your ecobee SmartThermostat Premium:

1. Press the thermostat screen to wake it up and navigate to the Main Menu (three horizontal lines).
2. Select Settings, then scroll down and select Installation Settings.
3. Navigate to Thresholds. This is where the logic for your HVAC equipment is stored.
4. Find Compressor Min Outdoor Temp. If this is set to a high number (like 35°F), the heat pump will shut off completely at that temperature, forcing the system into 100% auxiliary heat. Change this to Disabled or lower it to 20°F-25°F depending on your heat pump's SEER rating and efficiency.
5. Next, locate Aux Heat Max OAT (Outdoor Air Temperature). This setting determines the maximum outdoor temperature at which the auxiliary heat is allowed to turn on. If this is set to 40°F, your heat strips will run even in mild weather. Lower this to 30°F or 25°F to ensure the heat pump does the heavy lifting until it truly cannot keep up.
6. Go back to the Thresholds menu and find Heat Differential Temp. Change this to 1.5°F or 2.0°F. This prevents the system from "short-cycling" and gives the heat pump more time to raise the temperature without the thermostat panic-triggering the auxiliary heat.
7. Save the settings and return to the home screen.

If That Didn't Work

• Check your "Heat Pump" vs "Furnace" configuration: Ensure your system is correctly identified in the Installation Settings. If the ecobee thinks you have a conventional furnace instead of a heat pump with auxiliary heat, it will trigger the heat strips incorrectly. Re-run the equipment setup and verify the "Heat Pump" option is selected.
• Adjust the "Aux Heat Stage 1" temperature: If you have multiple stages of auxiliary heat, check the staging temperatures. If Stage 1 is set too high, it will kick in far too early. Lower the Stage 1 threshold by 5 degrees to force the heat pump to work longer.
• Inspect the Outdoor Unit (Condenser): If the auxiliary heat is running despite correct settings, your heat pump may be physically unable to move heat. Check for frozen coils or a clogged outdoor unit. If the heat pump isn't producing heat, the ecobee's "Aux Heat" logic will kick in as a failsafe to prevent the house from freezing.
• Verify Outdoor Temperature Sensor accuracy: The ecobee relies on internet weather data or a remote sensor. If the local weather station providing data to ecobee is inaccurate, the thermostat will "think" it is colder outside than it actually is. Try installing a physical ecobee Remote Sensor outdoors to provide a more accurate local reading.

Heads Up

• Energy Costs: Auxiliary heat (electric strips) is significantly more expensive than heat pump heating. Always prioritize lowering the "Aux Heat Max OAT" to save on monthly utility bills.
• Filter Maintenance: A clogged air filter reduces airflow, making the heat pump less efficient. This can trick the thermostat into thinking the heat pump is failing, triggering the auxiliary heat. Change your filter every 30-90 days.
• Avoid "Recovery" Mode: If you use a schedule, avoid large temperature jumps (e.g., jumping from 62°F to 72°F at 7 AM). This "recovery" demand often triggers the auxiliary heat to reach the target temperature faster. Use a gradual ramp-up instead.