When you glance at your thermostat and notice “Em Heat” or “Emergency Heat” displayed on the screen, you might wonder whether something has gone wrong with your heating system. This setting plays a specific role in heat pump systems and understanding it can help you avoid expensive utility bills and potential equipment damage.
This guide explains what emergency heat means, when your system uses it, how it differs from auxiliary heat, and what you should do if the setting activates unexpectedly.
What Does Em Heat Mean on a Thermostat?
Emergency heat is a backup heating mode on heat pump thermostats that bypasses the outdoor heat pump unit and relies entirely on secondary heating elements, typically electric resistance coils or a gas furnace. When activated, your system stops attempting to pull heat from the outdoor air and instead generates heat directly inside your home using this less efficient backup method, which costs significantly more to operate.
How Heat Pumps Work in Normal Operation
Heat pumps move heat rather than create it, pulling warmth from outdoor air even when temperatures drop into the 30s or 20s Fahrenheit. This process uses refrigerant to extract heat energy from outside and transfer it indoors, operating efficiently in most moderate winter conditions.
The system runs on electricity but uses far less energy than electric resistance heating because it moves existing heat rather than generating new heat. Most heat pumps can handle the majority of your heating needs down to around 25-40°F, depending on the model and outdoor conditions.
The Difference Between Auxiliary Heat and Emergency Heat
Many homeowners confuse auxiliary heat with emergency heat, but these two modes function differently and serve distinct purposes. Understanding the distinction helps you recognize whether your system is operating normally or needs attention.
Auxiliary Heat Activates Automatically
Auxiliary heat turns on automatically when your heat pump cannot keep up with heating demand. This happens during very cold weather, when you’ve raised the thermostat setting by several degrees, or when the outdoor temperature drops below the heat pump’s efficient operating range.
The system runs both the heat pump and the backup heating elements together temporarily to reach your desired temperature faster. Once the indoor temperature matches the thermostat setting, auxiliary heat shuts off and the heat pump resumes normal operation.
Emergency Heat Requires Manual Activation
Emergency heat completely shuts down the outdoor heat pump unit and relies solely on backup heating. You typically activate this mode manually by switching your thermostat to the “Em Heat” or “Emergency Heat” setting.
The system will not attempt to use the more efficient heat pump at all, resulting in significantly higher energy costs. This mode exists for situations when your heat pump has failed or malfunctioned but you still need heat in your home.
When You Should Use Emergency Heat
Emergency heat serves as a temporary solution during specific equipment problems. Knowing the appropriate situations helps you avoid using this expensive mode unnecessarily.
Heat Pump System Failures
Switch to emergency heat if your outdoor heat pump unit has stopped working completely due to mechanical failure, refrigerant leaks, or compressor problems. This keeps your home warm while you arrange for professional repairs.
You might also use this setting if ice has completely encased your outdoor unit and the defrost cycle is not functioning. Never attempt to chip ice off the unit manually, as this can damage delicate fins and coils.
Temporary Cold Weather Issues
Some homeowners switch to emergency heat during extreme cold snaps when their heat pump struggles to maintain temperature, though this significantly increases operating costs. A better solution involves scheduling a service call to determine why the heat pump cannot handle the load, as properly sized and maintained units should manage most winter conditions in their intended climate zones.
If your area regularly experiences temperatures well below your heat pump’s efficient range, your system may be undersized or you may benefit from a dual-fuel setup with a gas furnace backup.
Why Emergency Heat Costs More to Operate
Electric resistance heating used in emergency heat mode converts electricity directly into heat at a 1:1 ratio. Heat pumps, by comparison, can move 2-3 times more heat energy than the electrical energy they consume, making them far more efficient.
Running emergency heat can double or triple your heating costs compared to normal heat pump operation. A home that typically costs $150 per month to heat with a heat pump might see bills of $300-$450 if emergency heat runs continuously.
What to Do If Emergency Heat Turns On Unexpectedly
If you notice the emergency heat indicator on your thermostat but did not manually activate it, you should investigate promptly. Unexpected activation usually signals a problem that needs attention.
Check Your Thermostat Setting First
Confirm that someone has not accidentally switched the thermostat to emergency heat mode. Many thermostats place this setting near the normal heat/cool selector, making accidental activation possible.
Switch the setting back to normal heat and monitor whether the system operates correctly. If the emergency heat indicator reappears on its own, you likely have a thermostat malfunction or wiring issue.
Examine the Outdoor Unit
Look at your outdoor heat pump to see whether it is running. You should hear the fan and compressor operating, and you should feel air moving from the unit.
Check for obvious problems like tripped breakers, ice buildup beyond normal frost, debris blocking airflow, or visible damage. Do not perform repairs on electrical or refrigerant components yourself—these require licensed HVAC technicians.
Contact an HVAC Professional
Schedule service if your heat pump is not running, if emergency heat activates repeatedly, or if you notice unusual noises, odors, or performance issues. Continuing to run on emergency heat while avoiding repairs only delays the inevitable service call while dramatically increasing your utility bills.
Most heat pump problems worsen over time, and components like compressors cost significantly more to replace than repair when caught early.
Common Causes of Heat Pump Problems That Trigger Emergency Heat Use
Several issues can force you to rely on emergency heat while waiting for repairs. Recognizing these problems helps you communicate clearly with service technicians.
Refrigerant Leaks
Low refrigerant prevents your heat pump from transferring heat effectively, causing the system to blow lukewarm or cool air. You might notice ice forming on the outdoor coils even in moderate temperatures, or the system may run continuously without reaching the set temperature.
Refrigerant work requires EPA-certified technicians and cannot be performed as a DIY repair. Simply adding refrigerant without finding and fixing the leak wastes money and harms the environment.
Defrost Cycle Malfunctions
Heat pumps naturally accumulate frost on outdoor coils during cold weather and periodically reverse operation to melt this ice. If the defrost cycle fails, ice builds up excessively and blocks airflow, preventing the unit from heating your home.
This problem often involves a faulty defrost control board, defrost thermostat, or reversing valve. Professional diagnosis determines which component has failed.
Failed Compressor or Fan Motor
The compressor circulates refrigerant through the system, while the outdoor fan disperses heat during cooling mode and draws in heat during heating mode. When either component fails, the outdoor unit cannot function.
Compressor replacement represents one of the most expensive heat pump repairs, sometimes approaching the cost of a new system for older units. A qualified technician can help you weigh repair versus replacement based on the unit’s age, efficiency, and overall condition.
How to Minimize Emergency Heat Usage
Taking care of your heat pump system reduces the likelihood that you will need to rely on emergency heat. Regular maintenance and prompt repairs keep the system running efficiently.
Schedule Annual Professional Maintenance
Have an HVAC technician inspect and service your heat pump before each heating season. This service typically includes checking refrigerant levels, testing the defrost cycle, cleaning coils, lubricating motors, tightening electrical connections, and verifying proper airflow.
Preventive maintenance catches developing problems before they cause complete system failure. The cost of an annual service visit is far less than running emergency heat for days or weeks.
Keep the Outdoor Unit Clear
Maintain at least two feet of clearance around your outdoor unit, removing leaves, grass clippings, snow, and debris regularly. Trim back vegetation that grows too close, and avoid stacking items near the unit.
Clean airflow allows the system to operate efficiently and prevents overheating or icing problems. Never cover your heat pump during winter operation, as this blocks necessary ventilation.
Replace Air Filters Regularly
Change indoor air filters every 1-3 months depending on filter type, household dust levels, and whether you have pets. Clogged filters restrict airflow, forcing your system to work harder and potentially triggering auxiliary or emergency heat more frequently.
Mark filter changes on your calendar or set phone reminders to maintain this simple but important task. Check filters monthly and replace them when they appear gray or clogged, even if it has not been a full three months.
Understanding Your Specific Thermostat Model
Thermostats display emergency heat status differently depending on the manufacturer and model. Familiarize yourself with how your specific unit indicates this mode to avoid confusion.
Some thermostats show “Em Heat” or “Emergency Heat” on the display screen, while others use “E” or a special icon. Smart thermostats may send alerts to your phone if emergency heat activates, helping you catch problems quickly.
Consult your thermostat manual to understand all displayed codes and symbols. Many manufacturers provide PDF manuals on their websites if you have misplaced the original documentation.
Managing Heating Costs When Repairs Take Time
If you must run emergency heat for several days while waiting for parts or scheduled repairs, you can reduce costs through temperature management. Lower your thermostat setting by a few degrees and use space heaters in occupied rooms, supplementing the emergency heat rather than relying on it completely.
Wear warmer clothing indoors, close off unused rooms, and use window treatments to reduce heat loss. These temporary measures make emergency heat operation less expensive without leaving you uncomfortable.
Moving Forward With Your Heating System
Emergency heat serves an important backup function but should only run when absolutely necessary due to heat pump failure. Understanding the difference between auxiliary and emergency heat, recognizing when professional service is needed, and maintaining your system properly all help you avoid expensive surprise heating bills and keep your home comfortable through winter.
If you find yourself using emergency heat, treat it as a temporary measure and schedule professional diagnosis and repair promptly. Your heating system will operate more efficiently, your utility bills will return to normal levels, and you will avoid the stress of wondering whether your heat will continue working during the coldest weather.
We hope this guide has helped clarify what emergency heat means and how to handle it appropriately in your home. Continue exploring more helpful Home and Garden articles to make informed decisions about maintaining and improving your living space.