The Great Heat Debate: Understanding Emergency vs. Auxiliary Heat on Your Heat Pump

Your Thermostat's Mysterious "EM Heat" Setting Explained

Heat pump emergency heat is a manual backup heating mode that bypasses your heat pump's primary system and relies solely on electric resistance coils or a furnace to warm your home. It's designed for true emergencies when your heat pump fails, not for routine cold weather.

Quick Answer: When to Use Emergency Heat

• Use Emergency Heat when: Your heat pump is completely broken, blowing cold air, or frozen solid and won't defrost
• Don't use it when: It's just cold outside—your system has automatic auxiliary heat for that
• Key difference: Emergency heat is manual and bypasses the heat pump; auxiliary heat works with your heat pump automatically

If you've ever glanced at your thermostat on a chilly morning in Tallahassee or Crawfordville and wondered what that "EM Heat" or "Emergency Heat" setting actually does, you're not alone. Many homeowners in Wakulla, Leon, and Franklin Counties see this mysterious switch and assume it's for extra-cold days—but that's not quite right, and flipping it unnecessarily could cause a significant spike in your energy usage.

For reliable HVAC services in Tallahassee and surrounding areas, or to schedule a heat pump inspection before you need that emergency setting, Keith Key Heating & Air is here to help.

The confusion around emergency heat versus auxiliary heat causes homeowners to either panic when they see the "AUX" light on their thermostat or mistakenly switch to emergency mode thinking they're helping their system. The truth is, modern heat pumps are designed to handle most cold weather automatically, and understanding when you actually need to intervene can save you significant energy and prevent unnecessary wear on your system.

The Critical Difference: Auxiliary Heat vs. Emergency Heat

When it comes to keeping your home warm and comfortable, especially during those unexpected cold snaps in Sopchoppy or Woodville, your heat pump is usually the unsung hero. But what happens when temperatures drop lower than usual, or if your system needs a little extra help? That's where auxiliary heat and heat pump emergency heat come into play. Many people use these terms interchangeably, but they are distinctly different functions of your HVAC system. Understanding this difference is key to efficient heating.

A heat pump is an energy-efficient system that moves heat from one place to another. In winter, it extracts heat from the outside air and transfers it inside your home, working like a refrigerator in reverse. You can learn more about how these amazing systems work by visiting What Is a Heat Pump?.

What is Auxiliary (AUX) Heat?

Auxiliary heat is your heat pump's automatic backup. Think of it as a helpful assistant that steps in when your heat pump needs a boost. Unlike heat pump emergency heat, auxiliary heat works with your heat pump to supplement its heating capabilities. It's designed to ensure your home stays warm even when the heat pump alone can't quite keep up.

Most modern thermostats are designed to automatically activate auxiliary heat in a few specific scenarios:

• When the heat pump can’t recover heat quickly enough due to extreme cold: As outside temperatures approach freezing conditions (typically below 35-40°F), heat pumps become less efficient. In colder climates, all heat pumps need a secondary heating source when outside temperatures drop too low. Auxiliary heat kicks in to help reach your desired temperature.
• When the thermostat set point is manually adjusted significantly higher: If you suddenly raise your thermostat by several degrees, your system will call for auxiliary heat to quickly bridge the large temperature gap.
• When the outside compressor detects frost and goes into defrost mode: During the defrost cycle, your heat pump temporarily switches to a cooling mode to melt ice off its outdoor coil. To prevent cold air from blowing into your home during this process, auxiliary heat is activated.

When auxiliary heat is running, you might notice an "AUX" or "SUPP" (supplemental) indicator light on your thermostat. This is a normal function, indicating your system is doing its job to maintain comfort. It's safe and effective, though it uses slightly more energy than your heat pump running solo.

What is Emergency (EM) Heat?

Now, let's talk about heat pump emergency heat. This is a completely different beast. While auxiliary heat works alongside your heat pump, emergency heat completely bypasses it. When you manually switch your thermostat to "EM Heat," you are telling your system to shut down the heat pump entirely and rely solely on its backup heating source.

The backup heating source is typically electric resistance heating coils, similar to those found in a toaster or hair dryer, or it could be a fossil fuel furnace (gas or oil) if you have a dual-fuel system. When emergency heat is on, your outdoor heat pump unit will usually be off, and only the indoor unit and its supplemental heat source will run.

As the name suggests, heat pump emergency heat is meant for true emergencies when your heat pump is malfunctioning. It's not designed to be your primary heating source, nor should it be used simply because it's a cold day.

When to Manually Activate Your Heat Pump Emergency Heat

Understanding the distinction between auxiliary and heat pump emergency heat is crucial for both your comfort and your home's energy efficiency. While your thermostat is smart enough to engage auxiliary heat automatically when needed, manually activating emergency heat is a decision you should make only under very specific circumstances. It's not a button to press just because your feet are a little chilly!

Scenarios for Using the Emergency Heat Setting

So, when should you actually flip that "EM Heat" switch? We recommend reserving heat pump emergency heat for situations where your primary heat pump system has genuinely failed or is unable to provide any heat at all.

Here are the critical scenarios where manual activation of heat pump emergency heat is appropriate:

• Heat pump malfunction or breakdown: This is the primary reason. If your heat pump is blowing cold air, making strange loud grinding noises, or simply not turning on, it's time for emergency heat. It acts as a temporary measure to keep your home warm while you wait for one of our technicians to arrive.
• No heat production: If your heat pump isn't producing any heat whatsoever, and you've checked the thermostat and circuit breaker, then emergency heat can provide warmth.
• Outdoor unit completely iced over and not defrosting: While a normal defrost cycle involves some ice, excessive ice accumulation that doesn't melt after a couple of hours, or if the unit is encased in ice, could indicate a problem. In such cases, running emergency heat can prevent further damage to the outdoor unit while providing heat indoors.
• Protecting the compressor during severe ice storms: In very rare instances, particularly during a severe ice storm, you might consider activating emergency heat to prevent the outdoor compressor fan from attempting to spin and potentially being damaged by ice. However, this is a very specific situation, and typically, your system's automatic defrost should handle most ice buildup.
• Waiting for repair: If our team at Keith Key Heating & Air is on the way to diagnose and repair your heat pump, using heat pump emergency heat can keep your family comfortable until we can restore your system to full operation.

This setting is a last resort. It's designed to prevent your home from getting dangerously cold, not as a general cold-weather boost.

When Your System Uses Auxiliary Heat Automatically

In most winter conditions in Wakulla, Leon, and Franklin Counties, your heat pump and its auxiliary heat system work together seamlessly without any manual intervention from you. This automatic process is much more efficient than relying on heat pump emergency heat.

Your system automatically engages auxiliary heat in these common situations:

• Normal operation in colder weather: When the outside temperature drops below the heat pump's efficient operating range (typically around 35-40°F), the heat pump might struggle to extract enough heat from the air. Your thermostat will then automatically activate the auxiliary heat to help maintain your desired indoor temperature.
• The defrost cycle explained: Heat pumps periodically enter a "defrost cycle" to melt any ice or frost that accumulates on the outdoor coil. This is a normal and essential function. During this cycle, the heat pump briefly reverses its operation to act like an air conditioner, warming the outdoor coil. To prevent cold air from blowing into your home during this time, the auxiliary heat strips are automatically turned on. This ensures continuous warm air delivery and prevents discomfort.
• Significant thermostat adjustment: If you come home to a chilly house and bump your thermostat up several degrees (e.g., from 68°F to 74°F), your system will call upon auxiliary heat to quickly bring the temperature up to the new set point. Once the temperature is closer to your setting, the auxiliary heat will typically disengage, allowing the heat pump to take over.

Understanding these automatic functions allows you to trust your system and avoid unnecessary manual intervention. As the U.S. Department of Energy explains, adjusting your thermostat settings when you're away can also have a dramatic effect on energy savings. U.S. Department of Energy.

How Backup Heating Works and What to Expect

When your heat pump calls for backup, either automatically (auxiliary heat) or manually (heat pump emergency heat), it relies on dedicated components within your system to generate warmth. These components are different from how your heat pump normally operates, and understanding them can help you know what to expect and why they behave the way they do.

The Components of Your Backup Heating System

The heart of your backup heating system lies within your indoor unit, often called the air handler or furnace.

• Electric Resistance Coils: In most heat pump systems in our area, especially those that are all-electric, the backup heat source consists of electric resistance heating coils, often called "heat strips." These are essentially large heating elements that glow red hot when activated, generating heat directly through electrical resistance. Think of them like giant versions of the coils in a toaster. They are highly effective at producing heat quickly, but they consume a significant amount of electricity.
• Gas or Oil Furnace (Dual-Fuel Systems): Some homes, particularly those that previously had a gas or oil furnace, might have what's called a "dual-fuel" system. This means you have a heat pump for efficient heating in milder weather, and a traditional gas or oil furnace as your backup. In these systems, the furnace acts as the auxiliary or emergency heat. When called upon, the furnace ignites and burns fuel to produce heat. These systems can be very efficient because they switch to the most effective fuel source depending on outdoor temperatures. You can explore different types of heat pumps to understand more about these configurations.
• Indoor Air Handler: Regardless of the specific backup heat source, these components are housed within your indoor air handler. When auxiliary or emergency heat is active, the air handler's fan pushes air over these heated elements or through the furnace, distributing warm air throughout your home's ductwork.

Understanding the Heat Pump Defrost Cycle

The defrost cycle is a normal, vital function of your heat pump that often leads to confusion and sometimes even panic among homeowners. We've heard stories of people thinking their unit is on fire because of the "smoke" coming from it! Rest assured, it's usually just your heat pump doing its job.

Here's how it works:

• Reversing Valve Function: When your heat pump is operating in heating mode in cold weather, the outdoor coil gets very cold as it extracts heat from the air. This can cause moisture in the air to freeze and accumulate as frost or ice on the coil. To melt this ice, your heat pump temporarily reverses the flow of refrigerant using a component called the "reversing valve."
• Temporary Cooling Mode: When the reversing valve shifts, your outdoor unit briefly operates like an air conditioner. It pulls warm refrigerant from the indoor coil to the outdoor coil, heating it up to melt the ice.
• Steam or Vapor: As the ice melts and hits the warm outdoor coil, it can create a cloud of steam or vapor. This is perfectly normal and is often mistaken for smoke. It's just water vapor, like steam from a hot shower.
• Loud Noises: You might also hear a whooshing sound, sometimes compared to air brakes, as the reversing valve shifts. This is also a normal part of the process.
• Auxiliary Heat Engagement: While your outdoor unit is in defrost mode, it's not providing heat to your home. To prevent cold air from blowing through your vents and to maintain your indoor temperature, your auxiliary heat strips are automatically activated during the defrost cycle. This ensures your comfort is not interrupted.

A normal defrost cycle usually lasts for about 10-15 minutes, and your system will then return to normal heating operation. If you notice excessive ice buildup that doesn't melt after a couple of hours, or if your outdoor fan motor doesn't restart after a defrost cycle, then it might be a sign of a problem that requires professional attention.

Efficiency, Risks, and the Importance of Maintenance

While auxiliary and heat pump emergency heat are invaluable for keeping your home warm when needed, it's important to understand their efficiency and the potential risks of relying on them too heavily. Our goal at Keith Key Heating & Air is to help you keep your heat pump running as efficiently as possible, saving you energy and extending the life of your system.

Why Emergency Heat Uses More Energy

Homeowners are often surprised by the spike in energy usage when heat pump emergency heat is used for extended periods. The difference in energy consumption between a heat pump and its backup electric resistance heating is substantial.

To understand the difference, consider how each system works. An electric heating element (like those in emergency heat strips) generates heat directly by resisting an electrical current. This process consumes one unit of electrical energy to produce one unit of heat. A heat pump, however, works by moving existing heat from the outside air into your home. This transfer process is far more efficient, often allowing it to produce several units of heat for every one unit of electricity it consumes. This is why a heat pump is a much more energy-efficient way to warm your home.

Because heat pump emergency heat relies on direct electric resistance, it consumes significantly more electricity to produce the same amount of heat compared to your heat pump. This higher energy consumption will be reflected in your utility bills. So, while emergency heat provides warmth, it does so with much higher energy use.

Risks of Long-Term Use and How Maintenance Helps

Beyond the impact on your energy consumption, prolonged or unnecessary use of heat pump emergency heat can lead to other issues:

• System Strain: Constantly running the electric heat strips or furnace can put more wear and tear on these components, potentially shortening their lifespan.
• Masking Underlying Problems: If you're relying on emergency heat because your heat pump isn't working correctly, you might be delaying necessary repairs. This can lead to more severe damage to the heat pump itself, turning a minor issue into a major, extensive repair.
• Wear and Tear: Any mechanical system benefits from operating within its designed parameters. Over-reliance on backup systems can lead to accelerated wear on the backup components.

The best way to prevent the need for heat pump emergency heat is through regular, professional maintenance. Our family-owned and operated business has been dedicated to delivering honest, reliable, and compassionate HVAC service in Wakulla, Leon, and Franklin Counties since 1991.

Here’s how regular maintenance helps:

• Preventing Malfunctions: During a routine tune-up, our technicians can identify and address minor issues before they escalate into major breakdowns that would necessitate emergency heat. This includes checking refrigerant levels, electrical connections, and all system components.
• Filter Changes: A clogged air filter restricts airflow, making your heat pump work harder and less efficiently. This can cause it to struggle in cold weather, potentially calling for auxiliary heat more often or even leading to a breakdown that requires emergency heat. We recommend replacing your air filter every 1-3 months, depending on your filter type and home environment.
• Optimizing Efficiency: Regular maintenance ensures your heat pump is operating at its peak efficiency, reducing the likelihood of it needing auxiliary heat, and certainly minimizing any chance of needing heat pump emergency heat.
• Humidity Control: A properly functioning and maintained HVAC system also plays a crucial role in controlling indoor humidity. According to the Environmental Protection Agency, indoor relative humidity should be kept below 60 percent, with the ideal range between 30 and 50 percent. A struggling system or one constantly in emergency mode might not effectively manage humidity, potentially leading to issues like mold growth.

By investing in regular maintenance, you're not just preventing emergencies; you're also ensuring a healthier, more comfortable, and more energy-efficient home.

Frequently Asked Questions About Heat Pump Emergency Heat

We know that understanding your home's heating system can sometimes feel like trying to solve a puzzle. Here are some of the most common questions we hear about heat pump emergency heat.

Do newer heat pumps need emergency heat as often?

The short answer is no, newer heat pumps generally need heat pump emergency heat much less often than older models. Heat pump technology has advanced significantly. Modern heat pumps, especially variable-speed and cold-climate models, are engineered to operate efficiently and effectively in much lower temperatures.

While older heat pumps might have struggled when temperatures dipped below 35-40°F, requiring their auxiliary heat (or even emergency heat) to kick in frequently, many modern heat pumps can maintain excellent efficiency (a COP well above 1) even down to 0°F or lower. This means they can extract enough heat from the outdoor air to warm your home without constantly relying on supplemental heat, let alone the less efficient heat pump emergency heat setting. So, if you have a newer system, you should expect to see the "AUX" light less often, and hopefully never need to manually switch to "EM Heat."

What are the signs my heat pump is failing and needs the heat pump emergency heat setting?

Knowing the signs of a malfunctioning heat pump can help you react quickly and potentially prevent further damage. If you notice any of these issues, it's time to call our team at Keith Key Heating & Air and consider activating your heat pump emergency heat temporarily:

• Blowing cold air: If your heat pump is running but the air coming from your vents is cold, it's a clear sign of a problem. This could be due to low refrigerant, a faulty reversing valve, or a compressor issue.
• Loud grinding or banging noises: While some noises are normal (like during a defrost cycle), persistent loud grinding, banging, or screeching sounds indicate a serious mechanical problem that needs immediate attention.
• Frequent cycling: If your heat pump is turning on and off much more frequently than usual, it's "short-cycling." This can be a symptom of various issues, from refrigerant leaks to electrical problems, and it's inefficient.
• Ice buildup that won't melt: While some ice during a defrost cycle is normal, if your outdoor unit is completely encased in ice, or if ice persists for more than two hours after a defrost cycle should have completed, your system has a problem.
• Inability to reach set temperature: If your heat pump runs continuously but simply cannot bring your home up to the temperature set on your thermostat, it's struggling to keep up, indicating a potential malfunction.

If you observe any of these signs, switch to heat pump emergency heat for temporary warmth and contact us right away for a professional diagnosis and repair.

Can I just leave my thermostat on the emergency heat setting all winter?

We strongly advise against leaving your thermostat on the heat pump emergency heat setting all winter. While it will keep your home warm, it comes with significant downsides:

• Significantly higher energy use: As we discussed, emergency heat is far less efficient than your heat pump. Running it continuously will lead to a drastic increase in your home's energy consumption.
• Bypasses efficient primary system: By using emergency heat, you're essentially bypassing the most energy-efficient part of your heating system—the heat pump itself. This defeats the purpose of having a heat pump in the first place.
• Potential for system damage: While the emergency heat components are designed to work, they are not meant for continuous, long-term operation as a primary heat source. Overuse can lead to premature wear and tear on these components.
• Masks underlying problems: If you leave it on emergency heat because your heat pump isn't working, you're ignoring the underlying issue, which could worsen over time and lead to a more extensive repair down the road.

Heat pump emergency heat is for temporary, emergency use only. It's a stop-gap measure to keep your family warm until your heat pump can be repaired or until extreme conditions pass. For efficient, long-term heating, always rely on your heat pump in its normal operating mode, allowing auxiliary heat to kick in automatically when needed.

Keep Your Home Warm and Efficient

Navigating the nuances of your heat pump's heating modes can seem daunting, but understanding the difference between auxiliary heat and heat pump emergency heat is a crucial step toward smarter home comfort. Auxiliary heat is your system's intelligent assistant, automatically stepping in to help your heat pump when temperatures dip low or during defrost cycles. Heat pump emergency heat, on the other hand, is your manual backup, reserved only for true emergencies when your heat pump has failed.

Here at Keith Key Heating & Air, we've been serving our neighbors in Wakulla, Leon, and Franklin Counties since 1991, bringing honest, reliable, and compassionate HVAC service to every home and business. We're dedicated to ensuring your comfort, quality, and trust in every job we do.

The key takeaway is this: trust your thermostat's automatic functions for everyday heating. If you suspect your heat pump is malfunctioning, or if you find yourself needing to manually activate heat pump emergency heat, don't delay. Proactive maintenance and timely repairs are the best way to keep your system running efficiently, avoid major emergency situations, and ensure your home stays warm and cozy all winter long.

For expert heat pump service in Wakulla, Leon, and Franklin Counties, contact us today. We're here to help you understand your system and provide the reliable service you deserve.