Auxiliary Heat vs Emergency Heat: What Is the Difference?

If your heat pump thermostat displays AUX HEAT or EM HEAT, the two settings may sound similar, but they usually serve different purposes. Auxiliary heat is backup heating that the HVAC system can activate automatically when the heat pump alone cannot satisfy the home's heating demand. Emergency heat is typically a manually selected backup mode used when the heat pump itself should not operate, such as after a heat pump failure. The exact terminology and control sequence vary by thermostat and HVAC system, so homeowners should always follow the equipment manufacturer's instructions. However, understanding the basic difference can help Richmond Hill homeowners avoid unnecessary energy use and know when a heat pump may actually require service. What Is Auxiliary Heat on a Heat Pump? Auxiliary heat is supplemental heating that supports the heat pump. In an all electric system, auxiliary heat is commonly provided by electric resistance heating elements installed in the air handler. The system may automatically activate auxiliary heating when: Outdoor temperatures become very low. The heat pump cannot maintain the thermostat setting. The thermostat temperature is raised significantly. Additional heat is required during certain defrost cycles. Natural Resources Canada describes auxiliary backup heating as a secondary system used when the heat pump cannot provide enough heat for the building. Seeing AUX HEAT occasionally during an Ontario winter therefore does not automatically indicate a malfunction. What Is Emergency Heat? Emergency heat generally means the backup heating source is being used instead of the heat pump compressor. In systems with electric resistance backup heat, activating emergency heat typically prevents normal compressor heating and relies on the secondary heat source. U.S. Department of Energy heat pump training materials distinguish auxiliary heating from emergency heating by whether the compressor remains part of the heating operation. Emergency heat should therefore not normally be used simply because the weather feels unusually cold. It is intended for situations where the primary heat pump cannot or should not operate. What Is the Main Difference Between AUX and EM Heat? The simplest explanation is: AUX HEAT The system decides additional heating is required. EM HEAT The homeowner or control system intentionally relies on backup heat because the heat pump is unavailable or should not operate. Think of auxiliary heat as support and emergency heat as replacement heating. The exact behaviour varies between equipment configurations, especially in hybrid systems, so your thermostat manual and HVAC contractor should confirm how your specific installation works. Is Auxiliary Heat Normal During a Richmond Hill Winter? Yes. Temporary auxiliary heating can be completely normal. Heat pump heating capacity and household heating demand change as outdoor temperatures fall. Cold climate heat pumps are designed to continue operating at low temperatures, but backup heat can still be incorporated into the system design for the coldest conditions. Natural Resources Canada notes that cold climate heat pumps can operate in temperatures as low as approximately minus 30°C, while backup heating remains useful for the coldest periods. ENERGY STAR also recommends considering how a cold climate heat pump integrates with a backup heating system when selecting equipment for colder climates. A professional HVAC Toronto assessment should consider both the heat pump's low temperature capacity and the home's actual heating requirement. When Does AUX Heat Usually Turn On? The exact activation strategy depends on the thermostat, controls, outdoor temperature, and equipment. Common situations include: Extremely cold weather As outdoor temperatures fall, the home's heating load increases. If the heat pump alone cannot provide enough heating capacity, auxiliary heat may activate. Large thermostat adjustments Suppose the home is 18°C and you suddenly raise the thermostat to 22°C. Some systems may activate auxiliary heat to reach the new setting faster. Defrost cycles During cold weather, frost may form on the outdoor heat pump coil. The system periodically enters defrost mode to remove it. Depending on system design, supplemental heat may operate temporarily to maintain indoor comfort. Heat pump performance problems If the heat pump is malfunctioning and cannot produce sufficient heat, the thermostat may repeatedly request backup heat. This is why frequent AUX operation during mild weather deserves attention. Does AUX Heat Mean My Heat Pump Is Broken? No. Occasional AUX heat is not necessarily a warning sign. It may simply mean the system needs temporary additional heating. However, AUX heat deserves investigation when: It operates almost continuously. It appears during relatively mild weather. Electricity consumption rises sharply. Indoor temperatures still remain low. The heat pump appears not to be operating properly. In these situations, possible causes include: Dirty air filter Incorrect thermostat settings Heat pump sizing problems Refrigerant issues Outdoor unit icing Equipment malfunction Why Can Auxiliary Heat Increase Electricity Use? Electric resistance backup heating operates differently from a heat pump. A heat pump transfers heat rather than creating all its heat directly from electrical resistance. ENERGY STAR notes that air source heat pumps can deliver considerably more heat energy than the electrical energy they consume because they move heat rather than generating it through combustion or resistance alone. Electric resistance backup heating does not receive the same heat transfer advantage. Therefore, if electric auxiliary heat operates for long periods, total electricity consumption can rise substantially. This does not mean homeowners should prevent AUX heat from operating when it is genuinely needed. Instead, unusually frequent auxiliary heating should prompt an investigation into why it is being requested. Should You Manually Turn On Emergency Heat During Very Cold Weather? Usually not simply because it is cold outside. Modern cold climate heat pumps are designed to continue operating during severe winter conditions. ENERGY STAR states that many cold climate air source heat pumps maintain heating capacity at low temperatures and recommends pairing systems with appropriately designed backup heating where necessary. If the heat pump is functioning normally, manually switching to emergency heat may unnecessarily stop efficient compressor heating. Allow the system's normal controls to manage cold weather operation unless: The heat pump has failed. The outdoor equipment is damaged. A technician advises you to disable the heat pump. The manufacturer instructs you to use emergency heat. When Should Emergency Heat Be Used? Emergency heat may be appropriate when the primary heat pump cannot safely or effectively operate. Examples include: Outdoor unit failure The compressor or outdoor fan has stopped functioning. Serious mechanical problem The heat pump develops a major fault requiring professional repair. Physical outdoor unit damage Equipment damaged by ice, falling objects, severe weather, or another event may need to remain off until inspected. Technician instructions An HVAC professional may advise operating backup heating while waiting for the heat pump to be repaired. Emergency heat is therefore best treated as a temporary backup mode rather than a normal everyday heating setting. What Happens if You Leave Emergency Heat On? If the system uses electric resistance backup heat, leaving emergency heat on for extended periods can significantly increase electricity consumption compared with normal heat pump operation. It can also hide the underlying heat pump problem. For example, your house may remain warm because the backup heaters are functioning, even though the outdoor heat pump has stopped working entirely. Once the immediate heating need is addressed, the primary equipment should still be diagnosed. Is AUX Heat the Same as a Gas Furnace Backup? Not always. Many Richmond Hill homes use hybrid systems combining: Heat pump Gas furnace Instead of electric resistance elements, the gas furnace provides backup heating. ENERGY STAR describes dual fuel systems as installations that allow homeowners to heat with either a heat pump or a conventional furnace depending on operating conditions. In these systems, the thermostat may not display AUX or EM HEAT exactly the same way as an all electric system. The furnace and heat pump controls may automatically determine which heating source operates. When Does a Furnace Take Over From a Heat Pump? In a properly configured hybrid system, the furnace may take over when: Outdoor temperature reaches the programmed changeover point. Heat pump capacity becomes insufficient. Operating the furnace becomes preferable under the configured strategy. The heat pump develops a fault. The changeover temperature should not simply be guessed. It should reflect: Home heating load Heat pump capacity Furnace capacity Equipment specifications Energy costs Control strategy If the backup furnace should activate but does not, professional furnace repair Toronto may be required. What if My Furnace Backup Doesn't Turn On? Suppose your heat pump operates during extreme cold but the indoor temperature continues dropping. Your hybrid controls are supposed to switch to the furnace, but nothing happens. Possible furnace problems include: Ignition failure Thermostat or wiring issue Flame sensor problem Control board problem Blower malfunction Gas supply issue Venting or safety shutdown A homeowner searching for furnace repair near me Toronto should tell the service provider that the home has a hybrid heat pump and furnace system. That detail matters because the problem could involve the furnace itself, the heat pump, the thermostat, or the controls connecting both systems. Why Does AUX Heat Come On After I Raise the Thermostat? Many thermostats consider both: How far the indoor temperature is from the desired setting How quickly the temperature needs to change If you suddenly raise the thermostat several degrees, the system may decide the heat pump alone will not recover quickly enough. Backup heating may then activate. For heat pump homes, keeping a relatively steady temperature can help reduce unnecessary supplemental heating. ENERGY STAR recommends maintaining a comfortable steady temperature when operating a heat pump rather than frequently making large setbacks. Should You Use Large Nighttime Temperature Setbacks? Usually, moderate adjustments are easier for a heat pump to manage. For example: Moderate approach Day: 21°C Night: 19°C or 20°C may create less recovery demand than: Large setback Day: 22°C Night: 16°C When the thermostat must recover six degrees in the morning, backup heating may activate depending on the control strategy. The best settings depend on the specific thermostat and HVAC system. Could a Dirty Filter Trigger More Auxiliary Heat? Potentially. A dirty filter restricts airflow. Reduced airflow can lower the system's ability to distribute heat effectively. The thermostat may continue requesting additional heating because the home is not warming as expected. Before assuming there is a major equipment problem: Check the thermostat. Inspect the filter. Make sure supply registers are open. Make sure return vents are unobstructed. Check the outdoor unit for excessive snow or ice. Simple airflow problems can sometimes contribute to unnecessary backup heat operation. Could an Undersized Heat Pump Use AUX Heat Too Often? Yes. Heat pump sizing directly affects how often backup heating is required. A system that is too small for the home's heating load may rely heavily on supplemental heat during winter. ENERGY STAR stresses proper system sizing because equipment that is either too large or too small can struggle to provide optimal comfort and performance. Proper heat pump design should consider: Home size Insulation Windows Air leakage Local design temperatures Ductwork Heat pump capacity at cold temperatures The nominal capacity printed on the equipment is only part of the calculation. Should You Replace an Older Furnace Used as Backup? Not automatically. If an existing furnace is still: Safe Reliable Compatible In reasonable condition it may continue serving as the backup source for a new heat pump. Replacement becomes more reasonable when the furnace has: Repeated breakdowns Major component problems Safety concerns Poor compatibility Significant age related deterioration Before replacing it, compare repair expenses with current furnace prices Toronto so you can evaluate the long term cost of maintaining versus replacing the equipment. Who Should Inspect a Hybrid Heat Pump and Furnace System? A hybrid system combines refrigeration, electrical controls, airflow, gas heating, combustion, and thermostat programming. That means the technician needs to understand how all these components interact. A qualified furnace technician Toronto can evaluate the furnace portion of the system and determine whether it activates correctly when backup heating is required. A complete inspection may include: Heat pump performance Furnace operation Thermostat configuration Outdoor temperature sensors Changeover settings Airflow Defrost controls Safety systems How Can You Tell Whether AUX Heat Is Operating Too Much? Watch for these patterns. AUX only during extreme cold Usually less concerning. AUX after a large thermostat adjustment May simply be the thermostat trying to recover quickly. AUX occasionally during defrost Can be part of normal system operation. AUX almost continuously Needs investigation. AUX during mild weather May indicate incorrect controls or poor heat pump performance. AUX plus falling indoor temperature Professional service is recommended. The goal is not to eliminate auxiliary heat completely. The goal is to make sure it operates only when the system actually requires supplemental heating. What Should You Do When EM HEAT Appears Unexpectedly? If you did not intentionally activate emergency heat: Check the thermostat mode. Look for error messages. Verify whether the outdoor heat pump is operating. Check for excessive ice. Listen for abnormal noises. Avoid repeatedly resetting breakers. If the primary heat pump does not operate, schedule professional diagnosis. Do not simply leave emergency heat running indefinitely without determining why the heat pump stopped. How Can You Remember the Difference? Use the AID rule. Auxiliary means Assistance Backup heat assists the normal heating system when extra capacity is required. Emergency means Isolation The normal heat pump may be taken out of the heating process while the backup source provides heat. Diagnose frequent use Occasional backup heating can be normal. Constant or unexplained backup operation deserves professional evaluation. This simple distinction can help homeowners understand thermostat messages without immediately assuming the equipment has failed. What Is the Bottom Line? Auxiliary heat and emergency heat both involve backup heating, but they are not the same operating mode. Auxiliary heat normally supports the heat pump automatically when additional heating is required. Emergency heat is generally used when the primary heat pump is unavailable or should not operate. For Richmond Hill homeowners, occasional AUX HEAT during extreme winter weather may be completely normal. Constant auxiliary heat during mild weather, unexpectedly activated emergency heat, rising electricity consumption, or failure of the heat pump to operate should be investigated. Cold climate heat pumps are capable of operating effectively at very low outdoor temperatures, and backup heating should be treated as part of a properly designed heating strategy rather than something homeowners manually activate every time the temperature drops. Frequently Asked Questions Is AUX heat bad for my heat pump? No. Auxiliary heat is a normal backup function on many heat pump systems. The concern is when it operates much more frequently than expected. Should I turn on emergency heat when it is extremely cold outside? Usually not simply because the weather is cold. If the heat pump is functioning normally, allow the system controls to manage heating unless the manufacturer or technician instructs you otherwise. Why does AUX heat come on when I raise the thermostat? A large temperature increase may cause the thermostat to request supplemental heating so the home reaches the desired temperature faster. Is emergency heat more expensive? When emergency heat relies entirely on electric resistance heating, operating costs can be significantly higher than normal heat pump operation. When should I call an HVAC technician? Arrange professional service when emergency heat activates unexpectedly, AUX heat operates continuously during mild weather, the outdoor heat pump stops working, indoor temperatures keep falling, or electricity consumption suddenly rises.