What Is Auxiliary Heat on a Thermostat? Explained Simply

When the temperature drops, your thermostat might switch to something called auxiliary heat. But what exactly is auxiliary heat and why does it kick in? Understanding this feature can help you manage your heating system more efficiently and avoid unexpected energy costs.

Auxiliary heat acts as a backup heating source that works alongside your primary system. It’s designed to keep your home warm when the main heat pump can’t keep up during extreme cold. Knowing when and why auxiliary heat activates can give you better control over your comfort and energy use throughout the winter months.

Understanding Auxiliary Heat on a Thermostat

Auxiliary heat supports your primary heating system when extra warmth is necessary. Knowing how it functions helps you monitor your energy use and maintain comfort during cold periods.

Definition and Purpose of Auxiliary Heat

Auxiliary heat acts as a secondary heat source in heating systems like heat pumps. It provides additional warmth when the primary system cannot meet the set temperature efficiently. Auxiliary heat commonly uses electric resistance heaters or gas furnaces to deliver fast, supplemental heat. Its role prevents indoor temperatures from dropping too low, ensuring your home stays comfortable even during the coldest weather. Using auxiliary heat increases energy consumption, so understanding its operation benefits energy management.

When Does Auxiliary Heat Activate?

Auxiliary heat activates when outdoor temperatures fall below the heat pump’s efficient operating range, typically below 35°F (1.7°C). It also engages if the heat pump struggles to keep up with the thermostat setting during sudden temperature drops or when defrost cycles temporarily disable the primary heating. Your thermostat senses the temperature difference between the indoor setting and the heat pump output, triggering auxiliary heat if the gap widens beyond a threshold. Some systems also activate auxiliary heat manually through thermostat controls during extreme cold to reduce strain on the primary system.

Types of Auxiliary Heat Systems

Auxiliary heat systems provide backup warmth when your primary heat pump can’t meet your home’s heating demands. These systems fall into two main categories: electric resistance heat and fuel-based auxiliary heat.

Electric Resistance Heat

Electric resistance heat uses electric coils to generate warmth through electrical resistance. Your thermostat activates these coils when outdoor temperatures drop significantly or the heat pump struggles to maintain the set temperature. Electric resistance heaters respond quickly, delivering immediate heat to your living space. Though effective, they consume more electricity, leading to higher energy costs compared to your primary heat pump.

Fuel-Based Auxiliary Heat

Fuel-based auxiliary heat relies on gas, oil, or propane furnaces to provide backup warmth. This system ignites fuel to generate heat, making it a less expensive option in regions with lower electricity rates or abundant fossil fuels. Your auxiliary heat kicks in when the heat pump’s output isn’t sufficient during extreme cold. Fuel-based systems offer consistent heat but require regular maintenance, including fuel supply monitoring and combustion inspections to ensure safety and efficiency.

How Auxiliary Heat Works with Heat Pumps

Auxiliary heat supports your heat pump by stepping in when the primary system can’t maintain your desired indoor temperature. Its activation ensures consistent warmth during colder conditions.

Primary vs. Auxiliary Heat Functions

Primary heat pumps transfer heat from outside air into your home using refrigerant cycles, working efficiently above 35°F (1.7°C). Auxiliary heat uses electric resistance coils or fuel-based systems to generate direct heat when outdoor temperatures fall below this threshold or when the heat pump’s output declines. Primary heat functions as the main heat source, while auxiliary heat operates as a backup, activating only when necessary to prevent temperature drops and maintain comfort.

Benefits of Auxiliary Heat in Cold Weather

Auxiliary heat provides reliable temperature control when your heat pump’s efficiency decreases in cold weather. It prevents prolonged indoor temperature drops and reduces strain on the primary system. By activating only during extreme cold or high heating demand, it ensures your home stays warm without constant use, letting your heat pump focus on efficiency while auxiliary heat manages peak conditions.

Pros and Cons of Using Auxiliary Heat

Auxiliary heat supports your home’s heating system during cold weather but comes with both benefits and drawbacks. Understanding these factors helps optimize comfort and energy use.

Advantages for Home Comfort and Efficiency

• Ensures consistent indoor temperature when primary heat pump output declines.
• Activates automatically at outdoor temperatures below 35°F (1.7°C), preventing cold drafts.
• Reduces wear on the primary heating system by sharing the load during extreme cold.
• Provides quick supplemental heat through electric resistance coils or fuel-based sources.
• Enhances overall system reliability, especially during sudden temperature drops.

Potential Drawbacks and Energy Considerations

• Increases energy consumption as electric resistance heaters use 2-3 times more electricity than heat pumps.
• Raises heating costs significantly if auxiliary heat runs for extended periods.
• May cause uneven heating if thermostat settings or balance points are improperly adjusted.
• Requires regular maintenance if using fuel-based auxiliary heat to ensure safety and efficiency.
• Can activate unnecessarily if thermostat sensitivity or calibration is off, leading to higher bills.

How to Manage and Optimize Auxiliary Heat Use

Controlling auxiliary heat effectively reduces energy consumption and heating expenses. Adjust your thermostat settings and apply energy-saving tips to maximize efficiency.

Thermostat Settings and Controls

Set your thermostat to heat mode with a moderate temperature, typically between 68°F and 72°F. Avoid setting it too high, as this triggers auxiliary heat frequently. Use programmable thermostats to lower temperatures when you’re away or asleep, minimizing unnecessary auxiliary heat activation. Choose the “auto” fan mode to run only when heating is on, preventing constant energy use. If your thermostat offers an auxiliary heat lockout feature, enable it to delay auxiliary heat activation until the heat pump can’t meet the demand. Regularly calibrate your thermostat to maintain accurate temperature readings and prevent false activations of auxiliary heat.

Tips for Reducing Energy Costs

Install a smart thermostat to optimize heating schedules based on your daily routine and local weather. Seal air leaks and improve insulation to reduce heat loss and ease the burden on your heating system. Schedule annual maintenance for your heat pump and auxiliary heat system to maintain peak efficiency. If electric resistance auxiliary heat causes high bills, consider upgrading to a fuel-based auxiliary heat system, where available and cost-effective. Use ceiling fans on low speed to distribute warm air evenly and avoid localized overheating that activates auxiliary heat unnecessarily.

Conclusion

Knowing how auxiliary heat works gives you better control over your home’s heating system. By managing its use wisely, you can keep your space comfortable without facing unexpected energy bills.

Taking simple steps like adjusting your thermostat settings and scheduling regular maintenance helps ensure your heating system runs efficiently. This way, auxiliary heat only kicks in when absolutely necessary, supporting your primary heat source without driving up costs.

With a clear understanding and smart management, you’ll enjoy consistent warmth and improved energy savings all winter long.