That shocking winter electricity bill often has a simple explanation hiding in plain sight on your thermostat. While your heat pump is a champion of energy efficiency, its backup system is a different story. This backup, known as auxiliary heat, works more like a giant space heater, consuming a massive amount of electricity to generate warmth quickly. It’s a crucial feature for keeping your home comfortable on the coldest North Carolina days, but it’s not meant to run all the time. If you’ve been wondering why your heating costs are so high, we’re here to help. We’ll explain why this system is so expensive and give you actionable ways to manage its use.
Key Takeaways
- Know Its Role as a Backup Heater: Auxiliary heat is a normal, automatic feature that helps your heat pump during extreme cold or defrost cycles. It’s different from the manual “emergency heat” setting, which is only for when your main system has failed.
- Frequent Use Signals a Deeper Issue: If the “AUX” light is on constantly, especially when it’s not freezing outside, your heat pump is struggling. This is a clear warning sign of an underlying problem that leads to high energy bills and potential system damage.
- Take Control with Smart Habits and Maintenance: You can minimize expensive auxiliary heat usage by adjusting your thermostat in small, gradual increments. Sealing air leaks and scheduling regular professional maintenance will also keep your heat pump running efficiently on its own.
What Is Auxiliary Heat?
If you have a heat pump, you’ve probably seen “aux heat” pop up on your thermostat on a chilly day. It might seem alarming, but it’s usually just your system working as designed. Let’s break down what auxiliary heat is and how it keeps your home comfortable.
First, How Do Heat Pumps Work?
Think of a heat pump as a clever two-way air conditioner. In the summer, it moves heat from inside your home to the outdoors. In the winter, it reverses the process, pulling ambient heat from the outside air to warm your home. This process is incredibly efficient because it transfers heat instead of creating it. But it has its limits. When outdoor temperatures drop close to freezing, there isn’t much heat available for the unit to pull inside. Your heat pump starts to work harder for less reward, and that’s when it calls for backup.
What Does Auxiliary Heat Do?
Auxiliary heat is your heat pump’s built-in backup heating source. Your thermostat is smart enough to know when the heat pump is struggling. If the indoor temperature drops about two or three degrees below your set temperature, the thermostat automatically activates the auxiliary heat. This gives your system an extra push to reach and maintain your desired comfort level. Think of it as a helper that steps in to ensure your home stays cozy, even when the weather outside is particularly harsh. It’s a normal and necessary function for all-electric homes in colder climates.
What Are the Different Types of Auxiliary Heat?
The term “auxiliary heat” can refer to a couple of different systems. The most common type is electric resistance heating. This system uses electric coils, much like the ones in a toaster, that heat up to warm the air passing over them. These strips are typically installed within your indoor air handler. In some cases, especially in regions with very cold winters, the auxiliary heat source might be a gas furnace. This is called a dual-fuel system, which pairs the efficiency of a heat pump with the power of a furnace. Knowing which type of residential HVAC system you have can help you understand its performance and energy use.
Why Does My Auxiliary Heat Turn On?
Seeing the “aux heat” light on your thermostat can be a little alarming, especially when you know it costs more to run. But in most cases, it’s just your heat pump’s backup system doing exactly what it’s supposed to do. Your auxiliary heat isn’t meant to run all the time, but it plays a crucial role in keeping your home comfortable when your heat pump needs a hand. Think of it as a helpful teammate rather than a problem.
Several common scenarios will trigger your auxiliary heat to turn on automatically. Understanding these situations can help you know when it’s normal and when it might be a sign that your residential HVAC system needs a check-up. From a sudden cold snap to your system running its own maintenance cycle, here are the main reasons you’ll see that light appear.
When the Temperature Drops
The most common reason for auxiliary heat to kick on is simple: it’s really cold outside. A heat pump works by pulling heat from the outdoor air and moving it inside. When the temperature drops, typically below 35-40°F, there’s much less heat available in the air. Your heat pump has to work harder and may struggle to keep your home at your desired temperature on its own. When your thermostat senses that the heat pump can’t keep up, it automatically activates the auxiliary heat strips to provide that extra warmth and get your space comfortable again.
During the Defrost Cycle
Have you ever noticed ice forming on your outdoor heat pump unit during the winter? This is normal, but too much ice can prevent the system from working correctly. To solve this, your heat pump will periodically enter a “defrost cycle.” During this process, the unit temporarily reverses its function to melt the ice off its coils. While it’s busy defrosting, it can’t send heat into your home. To prevent you from getting a blast of cold air, the auxiliary heat turns on for a few minutes to maintain a comfortable indoor temperature until the defrost cycle is complete.
When You Quickly Raise the Thermostat
If you come home to a chilly house and crank the thermostat up by more than a few degrees, you’re likely to trigger the auxiliary heat. Your system sees this large temperature gap as an urgent request for heat. Instead of letting the heat pump slowly raise the temperature on its own, the thermostat calls for backup to get the job done faster. The auxiliary heat strips engage to help your system reach the new setpoint quickly. To avoid this, try adjusting your thermostat gradually, just one or two degrees at a time.
Auxiliary Heat vs. Emergency Heat: What’s the Difference?
It’s easy to mix up auxiliary heat and emergency heat, especially since some thermostats use the terms interchangeably. But they serve very different functions, and knowing which is which can save you from a major headache and a sky-high energy bill. The main thing to remember is that one is an automatic assistant for your heat pump, while the other is a manual override for true emergencies. Understanding how your residential HVAC system operates will help you keep your home comfortable and your costs in check. Let’s break down what each setting does and when you should (or shouldn’t) use it.
Automatic vs. Manual Control
The biggest difference between auxiliary and emergency heat is how they’re activated. Auxiliary heat is your heat pump’s automatic sidekick. When the outdoor temperature drops too low for your heat pump to efficiently pull heat from the air (usually below 40°F), the auxiliary heat kicks in on its own to help reach your set temperature. You might also see it turn on if you raise the thermostat by more than a couple of degrees at once. In contrast, emergency heat is a manual setting. You have to physically switch it on at your thermostat. It’s not designed for daily use; it’s a backup plan you control directly.
When to Use the “Emergency” Setting
Think of the emergency heat setting as your last resort. You should only turn it on if your heat pump completely stops working during a cold snap. For example, if the outdoor unit is iced over and not running its defrost cycle, or if it has malfunctioned entirely, switching to emergency heat will keep your home warm and prevent pipes from freezing. If you find yourself in this situation, your first call should be to a professional. Using the emergency setting is a temporary fix, and running it for an extended period is extremely expensive. It’s a clear signal that your system needs immediate service and repair.
Clearing Up Common Confusion
So, why the confusion? Some thermostats don’t have a separate indicator for auxiliary heat; they just have an “Emergency Heat” or “EM Heat” light that comes on when the electric heat strips are running. This can make you think there’s a problem when your system is just operating normally on a cold day. Remember, if your system is working automatically to maintain the temperature, that’s the auxiliary function doing its job. If you had to manually flip a switch because your heat pump failed, that’s emergency heat. Knowing this difference helps you use your system correctly and avoid unnecessary stress about your heat pump’s performance.
Why Is Auxiliary Heat So Expensive to Run?
If you’ve ever noticed a sudden jump in your electricity bill during a cold snap, your auxiliary heat might be the reason. While it’s a normal feature of your heat pump, it’s designed for short-term use, not as your main source of heat. The primary reason it costs so much is that it uses a completely different, less efficient method to generate warmth compared to your heat pump’s standard operation. Let’s break down why running it can hit your wallet harder.
It Uses More Energy
Your heat pump is incredibly efficient because it doesn’t create heat—it just moves it from one place to another. In the winter, it pulls warmth from the outside air and transfers it into your home. Auxiliary heat, on the other hand, works like a giant toaster or an electric space heater. It uses a method called electric resistance heating, where electricity flows through coils to generate heat directly. This process consumes a massive amount of electricity compared to the heat pump’s transfer method, making it far less energy-efficient.
How It Affects Your Energy Bill
This spike in energy use translates directly to a higher utility bill. Because electric resistance heating requires so much power, running your auxiliary heat frequently can cause a noticeable, and sometimes shocking, increase in your monthly costs. In some cases, relying too heavily on auxiliary heat can raise your heating expenses by as much as 50%. It’s not a sign that your system is broken—it’s just the cost of generating instant, powerful heat when your heat pump needs a helping hand during particularly cold weather.
Why It’s Less Efficient Than Your Heat Pump
So, if it’s so expensive, why have it at all? Think of auxiliary heat as your system’s backup plan. Its job is to kick in and provide a powerful boost to warm your home quickly when the outside temperature is too low for the heat pump to work effectively on its own. It’s a crucial feature that ensures you stay comfortable and prevents issues like frozen pipes on the coldest days. The key is to ensure it only runs when absolutely necessary. The best way to keep your whole system running efficiently is through regular heat pump maintenance, which helps minimize its reliance on this costly backup.
What if Your Auxiliary Heat Runs All the Time?
Seeing the “aux heat” light on your thermostat from time to time is normal, especially on the coldest days of the year. But if that light seems to be on more than it’s off, it’s a sign that something isn’t right. Your heat pump is designed to be the primary source of heat for your home, with the auxiliary heat acting as a backup. When the backup system is running constantly, it’s not just a minor issue—it’s a major drain on your energy bill and a clear signal that your main system is struggling to keep up. Think of it like trying to drive your car everywhere in first gear—it’ll get you there, but it’s going to use a lot more fuel and cause unnecessary wear and tear on the engine. In the same way, over-relying on auxiliary heat puts a strain on your entire HVAC system and your wallet. This is because auxiliary heat is typically a form of electric resistance heating, which consumes significantly more energy than your heat pump. Ignoring the problem won’t make it go away; it will only lead to higher bills and potentially a complete system failure when you need it most. Let’s walk through how to figure out if there’s a real problem and what you can do about it.
How Much Is Too Much?
If your thermostat constantly shows that the auxiliary heat is running, you should pay attention. It means your heat pump can’t warm your home on its own, forcing the less efficient backup system to do all the work. A good rule of thumb is to watch the clock and the thermometer. If your auxiliary heat stays on for more than an hour or two, especially when the outdoor temperature is above 40°F, it’s definitely running too much. This continuous use will cause a noticeable spike in your electricity bill and is a clear indicator of a potential issue with your heat pump that needs to be addressed.
Simple Checks You Can Do Yourself
Before you pick up the phone, there are a couple of quick things you can check yourself. First, look at your thermostat settings. Make sure it hasn’t been accidentally switched to the “Emergency Heat” mode. This setting manually forces the auxiliary heat to run, bypassing the heat pump entirely. If it is, simply switch it back to “Heat.” You can also try turning the thermostat off and then back on to reset it. Next, take note of the outdoor temperature. If it’s relatively mild (above 35-40°F) and your aux heat is still kicking on frequently, it’s a strong sign that your system needs a closer look.
When to Call a Professional
If you’ve done the simple checks and the auxiliary heat is still overactive, it’s time to call for help. Constant auxiliary heat use when it’s not freezing outside often points to a problem with the heat pump itself, such as low refrigerant, a failing compressor, or an issue with the outdoor fan motor. Don’t wait for the system to break down completely. Getting professional residential HVAC service can catch the problem early, saving you from a much larger repair bill and a cold house. A technician can diagnose the exact cause and get your heat pump back to being the efficient workhorse it was designed to be.
How to Use Less Auxiliary Heat and Save Money
Auxiliary heat is a great backup for those extra-cold North Carolina days, but seeing that “AUX” light on your thermostat too often can be a shock to your monthly budget. The good news is you have more control over it than you might think. While you can’t change the weather, you can change how your home responds to it. By making a few smart adjustments to your home and habits, you can keep your heat pump doing the heavy lifting and rely less on that energy-hungry backup. These simple strategies will help you stay comfortable without sending your utility bills through the roof. It’s all about helping your heat pump work smarter, not harder.
Set Your Thermostat for Success
When you get home and feel a chill, it’s tempting to crank the thermostat up by five or ten degrees. But that sudden demand for heat is a direct signal to your system to call in the reserves—your auxiliary heat. A better approach is to only increase the temperature by one or two degrees at a time. This gentle adjustment gives your heat pump a chance to catch up on its own, without triggering the less efficient electric resistance coils. It’s a small habit change that can make a big difference. If you have a programmable or smart thermostat, you can set it to warm the house gradually before you wake up or get home, avoiding those sudden temperature spikes altogether.
Improve Your Home’s Insulation
Think of your home as a thermos. Good insulation keeps the warm air in and the cold air out. When you have drafts from leaky windows, poorly sealed doors, or an under-insulated attic, the heat your system produces escapes quickly. This forces your heat pump to work overtime just to maintain the temperature you’ve set. On cold days, that extra strain is often enough to make it call for auxiliary heat. You can do a quick check yourself by feeling for drafts around window frames and exterior doors. Sealing these air leaks with caulk or weatherstripping is a simple, effective way to weatherize your home and reduce your heating system’s workload.
Schedule Regular Heat Pump Maintenance
Your heat pump is a complex machine, and just like your car, it needs regular tune-ups to run at its best. Over time, parts can get dirty, refrigerant levels can drop, and electrical connections can loosen. These small issues reduce efficiency and can force your system to rely on auxiliary heat more than necessary. Scheduling regular professional maintenance ensures everything is clean, calibrated, and working correctly. A technician can spot and fix minor problems before they lead to a system breakdown or an unexpectedly high energy bill. It’s a proactive step that keeps your entire HVAC system running smoothly and efficiently all winter long.
Is Your Auxiliary Heat a Sign of a Bigger Problem?
While auxiliary heat is a normal feature, it’s designed to be a backup, not the main event. If you notice it running frequently or for long stretches, your heat pump might be trying to tell you something. Think of it as a check engine light for your HVAC system—ignoring it can lead to bigger headaches and higher bills down the road. Understanding the warning signs helps you catch minor issues before they become major, expensive repairs that could have been avoided.
Warning Signs to Watch For
The most obvious red flag is seeing the “AUX” or “AUX HEAT” indicator on your thermostat almost every time you look at it. If your heat pump can’t maintain your home’s temperature without constantly calling for backup, something is wrong. This isn’t just about the outdoor temperature being a little chilly; it points to an underlying issue with your primary system. The problem could be anything from low refrigerant or a failing compressor to a malfunctioning thermostat that’s sending the wrong signals. When your system can’t transfer heat effectively on its own, it relies on the auxiliary strips, which is a clear sign it needs a professional look.
The Risk of Ignoring the Problem
Letting your auxiliary heat run unchecked is a gamble with both your comfort and your wallet. Because it uses so much more energy, you’ll see a significant spike in your utility bills—sometimes by as much as 50%. It’s an incredibly inefficient way to heat your home long-term. More importantly, this constant operation is often masking a problem that could cause further damage to your heat pump. Continuing to run the system this way puts extra strain on its components, potentially leading to a complete breakdown that could have been prevented with a simple repair.
Protect Your HVAC System with Proactive Care
The best way to prevent your auxiliary heat from becoming a problem is through proactive care. Just like your car, your HVAC system needs regular check-ups to perform at its best. Scheduling routine professional maintenance helps a technician spot and fix small issues, like low refrigerant or a dirty filter, before they compromise your heat pump’s performance. QRC’s Service Maintenance Programs are designed to keep your system running efficiently all year long. A tune-up ensures everything is in working order, so your heat pump can handle the cold without constantly leaning on its expensive backup.
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Frequently Asked Questions
Is it normal for my auxiliary heat to turn on? Yes, it’s completely normal and part of your heat pump’s design. Think of it as a built-in helper that automatically steps in on very cold days when your heat pump struggles to pull enough warmth from the outside air. Seeing it turn on periodically during a cold snap means your system is working correctly to keep your home comfortable.
Why is my electric bill so high in the winter with a heat pump? If you’re noticing a significant jump in your bill, frequent auxiliary heat use is the most likely reason. Your heat pump is efficient because it moves existing heat, but auxiliary heat creates new heat using electric resistance coils. This process consumes a great deal more electricity, so if it’s running often, you’ll see the impact on your energy statement.
Can I prevent my auxiliary heat from turning on? While you can’t stop it from activating when it’s truly needed, you can certainly reduce how often it runs. The best way is to avoid making large, sudden adjustments to your thermostat. Instead of cranking it up by five degrees, raise the temperature by only a degree or two at a time. This gives your heat pump a chance to catch up on its own without calling for that expensive backup.
My thermostat says ‘Emergency Heat’ is on, not ‘Auxiliary Heat.’ Is that a problem? Not necessarily. Some thermostats don’t have a separate light for auxiliary heat and use the “Emergency Heat” indicator instead. The key difference is how it was activated. If the light comes on automatically to help maintain your set temperature, that’s the auxiliary function. If you had to manually flip a switch to “Emergency Heat” because your heat pump stopped working, that’s a true emergency and a clear sign you need to call for service.
How do I know if my auxiliary heat is running too much? Pay attention to the outdoor temperature. It’s normal for auxiliary heat to run when it’s below 35-40°F. However, if you notice it’s on for very long periods, or if it’s running when the weather is relatively mild, that’s a red flag. It indicates your heat pump may be struggling to do its job and needs a professional inspection.