You’ve just spent several thousand dollars on a state-of-the-art cold-climate heat pump. You were promised lower carbon emissions and, more importantly, a significant drop in your monthly utility bills. But then January hits. You open your email to find a billing statement that looks more like a mortgage payment than a power bill. You look at your smart thermostat and see those dreaded words: “Auxiliary Heat Running.” It feels like a betrayal. You bought a precision-engineered machine, yet your house is currently heating itself with what is essentially a collection of giant, expensive toaster ovens hidden inside your ductwork. I’ve sat at kitchen tables with hundreds of homeowners facing this exact frustration. The anxiety is real—you worry that the system is broken, or worse, that you were sold a bill of goods. The truth is usually much simpler and, thankfully, much cheaper to fix. Your heat pump isn’t the problem; it’s the “brain” controlling it. Most installers, even the good ones, leave smart thermostats on their factory default settings. These defaults are designed for one thing: preventing “no-heat” service calls. They prioritize immediate comfort over efficiency, which means your 10-kilowatt electric backup strips are kicking in far more often than they need to. We’re going to stop that today.

Why does my auxiliary heat turn on when it isn’t even that cold outside?

The most common “costly trap” in the HVAC world is the default temperature differential setting. Most smart thermostats, like the ecobee or Honeywell Home series, come out of the box with a 2°F (1.1°C) differential rule. This means if you walk over to your thermostat and bump the temperature up by just two degrees, the thermostat assumes the heat pump is “struggling” and immediately engages the auxiliary heat strips to bridge the gap. Think about the physics of that for a second. Your heat pump might be drawing 2 or 3 kilowatts of power to move heat from the outside air into your home. Your auxiliary heat strips, however, are likely drawing 10, 15, or even 20 kilowatts. When that auxiliary light comes on, your meter starts spinning five times faster. In many cases, the heat pump could have reached that target temperature on its own in an extra ten or fifteen minutes, but the thermostat’s “impatience” cost you three dollars in electricity for a single heating cycle. Installers leave these settings wide open because they don’t want you calling them at 2:00 AM saying the house feels “chilly” while it slowly recovers from a set-back. They prioritize speed over your bank account. To truly optimize your system, we have to move away from “Automatic” settings and toward “Manual” lockout thresholds based on your specific climate and equipment.

What is the difference between the thermal balance point and the economic balance point?

Before we dive into the menus, you need to understand two concepts that will dictate your settings: the Thermal Balance Point and the Economic Balance Point. The Thermal Balance Point is the outdoor temperature at which your heat pump’s heating capacity exactly matches your home’s heat loss. Above this temperature, the heat pump can maintain your indoor setpoint all by itself. Below this temperature, the house is losing heat faster than the heat pump can pump it back in, and you need auxiliary help to keep the temperature stable. For a modern, well-insulated home with a cold-climate heat pump, this point is often as low as 5°F to 15°F (-15°C to -9°C). The Economic Balance Point is different. This is the temperature where it actually becomes cheaper to run your backup heat than your heat pump. If you have a gas furnace as your backup (a “dual-fuel” or “hybrid” system), this point depends on the current price of natural gas versus electricity. If your backup is electric resistance strips, the economic balance point essentially doesn’t exist—the heat pump is always more efficient than the strips, even at -15°F, provided it can still produce heat. The “nuance matrix” below shows how you should approach these settings based on your specific equipment type.

How do I find the hidden installer settings on my smart thermostat?

You won’t find these settings in the standard “Preferences” or “Schedule” menus. Manufacturers hide them because they don’t want casual users accidentally disabling their heat in the middle of a blizzard. But you aren’t a casual user; you’re the person paying the bill. For an ecobee, you need to go to the physical thermostat (not the app), tap the Menu icon, go to Settings, then Installation Settings, then Thresholds. You’ll see a warning that you’re entering the installer menu—proceed with confidence. For a Nest Learning Thermostat, these settings are under “Equipment” and then “Heat Pump.” Nest calls their lockout feature “Heat Pump Balance.” If you set it to “Max Savings,” it automatically tries to limit auxiliary heat, but for true control, you should look for the “Lockout” temperatures in the Pro Setup menu. For Honeywell Home (T-Series), you usually have to hold the “Menu” button for 5 seconds until the Advanced Menu appears. You’ll be looking for ISU (Installer Setup) numbers. For example, ISU 355 is often the Aux Heat Dropout temperature.

The 4-Step Thermostat Audit: Your Actionable Playbook

If you want to solve the high-bill problem today, follow this checklist. I recommend doing this on a Saturday morning when you can monitor the house for a few hours to ensure the comfort levels remain acceptable. 1. Identify Your Compressor’s Floor: Look up your heat pump’s model number. Is it a “cold-climate” unit (like a Mitsubishi HyperCore or a Daikin Fit)? If so, it can likely produce meaningful heat down to -13°F (-25°C). Set your Compressor Minimum Outdoor Temperature to at least 0°F (-18°C). If it’s a standard unit, 15°F (-9°C) is a safer floor. 2. Set the Aux Heat Lockout (The “Ceiling”): This is the most important step. Set your Auxiliary Heat Maximum Outdoor Temperature to 35°F (1.7°C). This ensures that if it is above freezing outside, your electric strips are physically incapable of turning on, no matter how much you wiggle the thermostat dial. 3. Adjust the “Aux Heat Differential”: In the same menu, look for “Aux Heat Max Temperature Differential.” Change this from the default 2°F to at least 5°F (2.8°C). This gives the heat pump more “room” to work. If you come home and the house is 65°F and you want it to be 68°F, the heat pump will now do that work solo. The strips will only kick in if the house drops significantly below your target. 4. Configure Minimum Compressor Run Time: Heat pumps are most efficient when they run for long periods. Short-cycling (turning on and off every 10 minutes) kills efficiency and wears out the hardware. Set your Minimum Compressor Run Time to 10 or 15 minutes. This forces the system to stay on long enough to reach peak operating efficiency.

Should I ever disable the lockout settings?

There is one scenario where you might need to relax these settings: the “Recovery” problem. If you are the type of person who likes to drop the temperature to 60°F at night and back to 70°F at 7:00 AM, a heat pump without auxiliary help will take hours to make that jump in cold weather. My advice? Stop doing deep setbacks. Heat pumps are “set it and forget it” machines. They are designed to maintain a steady state. If you insist on setbacks, you must accept that you either need the expensive auxiliary heat to recover quickly, or you need to start the recovery process two hours earlier than you think. Personally, I keep my home at a steady 69°F all winter. The compressor hums along at a low, efficient stage, and my auxiliary strips never see the light of day.

Frequently Asked Questions

Will locking out my auxiliary heat cause my pipes to freeze? No, provided your Compressor Minimum Outdoor Temperature is set within the actual operating range of your unit. If the outdoor temperature drops below the compressor’s ability to function, the thermostat will automatically bypass the lockout and engage the auxiliary heat to protect the home. Why does my auxiliary heat still turn on for 10 minutes even when it’s 40°F outside? This is likely a “Defrost Cycle.” When it’s cold and humid, ice forms on the outdoor coils. The heat pump temporarily reverses itself to melt that ice. To prevent blowing cold air into your home during this 5-10 minute cycle, the system turns on the auxiliary heat strips. This is normal and cannot (and should not) be locked out. Is it better to use “Comfort” or “Savings” settings on my thermostat? On a heat pump, “Comfort” almost always means “Use the electric strips sooner.” If you want to save money, always choose “Savings” or, better yet, use the manual settings outlined in this guide.