What Is Auxiliary Heat? Your Complete Guide
By Travis Baugh
Auxiliary heat is a supplemental heating source built into heat pump systems that automatically activates when the outdoor temperature drops too low for the heat pump to efficiently maintain your thermostat setting. It bridges the gap between the heat pump’s capacity and the heat loss of your home during freezing weather.
How Does Auxiliary Heat Work?
Your heat pump is designed to extract heat from the outside air and transfer it indoors. However, when temperatures plummet—typically between 30°F and 35°F—there is less ambient heat available to harvest. This is when your system’s "brain" recognizes a need for help and engages the auxiliary heat.
Think of it as a relay race: your heat pump runs the marathon, but the auxiliary heat sprints the final leg when the conditions get tough. This ensures your home stays comfortable without manual intervention.
What Triggers Auxiliary Heat to Turn On?
Aside from freezing outdoor temperatures, your system might trigger auxiliary heat in these scenarios:
- Rapid Temperature Changes: If you increase the thermostat setting by several degrees at once, the system may use auxiliary heat to reach the new temperature faster.
- Defrost Cycle: When frost builds up on the outdoor unit, the heat pump will enter a defrost cycle. During this time, it temporarily reverses operation, and auxiliary heat may turn on to prevent cold air from blowing inside your home.
- High Humidity: In some conditions, a heat pump may struggle to both dehumidify and heat the air effectively, requiring backup heating to manage indoor comfort.
“Auxiliary heat adds an extra layer of protection to a home’s heating system, particularly for homeowners in extremely cold climates where a standalone heat pump may need some added power during a cold spell, “ Melissa Frause, owner of Bob’s Heating and Air Conditioning in Woodinville, WA, said.
How is Auxiliary Heat Different from Emergency Heat?
While they may sound similar, confusing these two settings can lead to significantly higher energy bills.
- Auxiliary Heat: This is an automated function. It runs simultaneously with your heat pump to provide a temporary boost. It is a normal part of efficient operation in cold weather.
- Emergency Heat: This is a manual setting. When you switch to emergency heat, you are telling the system to completely bypass the heat pump and rely 100% on the backup heating source (usually electric resistance strips).
Pro Tip: Only use Emergency Heat if your primary heat pump has physically failed or is covered in deep snow/ice. Relying on it for daily heating is much less efficient and will drive up costs.
Do I Need an Auxiliary Heat System?
Geography plays a major role in this answer. If you live in a mild climate where winter rarely dips below freezing, a high-efficiency heat pump alone may suffice. However, for most regions with distinct winters, auxiliary heat is essential for consistent comfort.
The Dual-Fuel Advantage
For homeowners seeking maximum efficiency, a dual-fuel heat system is a game-changer. This setup pairs a heat pump with a gas furnace. In this scenario, the gas furnace acts as the auxiliary heat source. Gas is often more cost-effective than electric resistance heating, offering a powerful and efficient backup during the coldest days of the year.
“Families with young kids or elderly residents may find that having auxiliary heat provides peace of mind during unpredictable weather conditions,” Frause said.
It’s worth considering your local climate and consulting your local Bryant dealer to determine whether additional auxiliary heat is necessary for your home.
Troubleshooting Your Auxiliary Heat
If your thermostat’s "AUX" light stays on when it’s 45°F outside, something might be wrong. Frequent cycling of auxiliary heat in mild weather can signal inefficiency.
Watch for these signs:
- Skyrocketing Bills: A sudden spike in energy costs often indicates the system is relying too heavily on the backup strip heat.
- Constant Running: The system runs non-stop but the house doesn't feel warm.
- Strange Noises: Grinding or banging sounds could indicate mechanical distress in the outdoor unit.
If you spot these issues, schedule HVAC maintenance immediately. A qualified professional, such as your local Bryant dealer, can optimize your balance point settings to ensure auxiliary heat only runs when absolutely necessary.
Bryant Solutions for Efficient Heating
Bryant delivers innovative solutions designed for exceptional performance, even in the coldest conditions. Our lineup includes advanced cold climate heat pumps that optimize heating efficiency, keeping your home warm and your energy bills low.
Pair your system with a smart thermostats to unlock even greater control. These thermostats allow you to program schedules, adjust settings remotely, and monitor energy use, helping you manage your auxiliary heat effectively and maximize comfort.
Connect With A Bryant Dealer on Auxiliary Heating
A Bryant expert can help you understand the benefits of adding a gas furnace or other auxiliary heating sources to your system, ensuring you stay comfortable no matter how cold it gets outside. They will guide you in selecting the right equipment based on your home's heating needs and provide professional installation and service. Schedule an appointment with your local Bryant dealer today to discuss how auxiliary heating can improve your home's comfort and efficiency.
FAQs On Auxiliary Heat
Auxiliary heat activates when your heat pump can’t keep up with the heating demand, usually in very cold weather or during a defrost cycle.
Yes, auxiliary heat is typically more expensive to run because it relies on electric resistance heating, which uses more energy than the heat pump.
Auxiliary heat should come on only occasionally, such as during extremely cold temperatures or when the system is trying to raise the temperature quickly.
Yes, it’s okay to run auxiliary heat when needed, but it should be temporary—if it runs frequently, it could indicate a problem with your heat pump.
If auxiliary heat runs too long, it can lead to high energy bills, system wear, and may signal that your heat pump is undersized or malfunctioning.
Auxiliary heat is a backup heating feature in heat pump systems that uses electric resistance or a furnace when outdoor temperatures drop too low for efficient heat pump operation.
No, it’s normal during very cold weather or rapid temperature recovery. Frequent use in mild weather, however, may indicate a system issue.
Typically, auxiliary heat activates when outdoor temperatures fall near or below freezing, or when the system can’t maintain the set temperature efficiently.
It turns on automatically when the heat pump can’t meet the thermostat’s demand, such as during extreme cold or defrost cycles.
It’s not recommended—aux heat is meant for temporary use and is less efficient than standard heat pump operation.
It should only run as needed during temperature drops or system defrosts, not continuously.
Yes. The system activates it automatically based on outdoor temperature and thermostat demand.
