Seeing “EM Heat” on a thermostat can suggest that the heat pump has failed or a higher power bill is imminent. In reality, emergency heat mode is a backup setting, not a diagnosis.
The important distinction is that auxiliary heat and emergency heat aren’t the same. Since 1984, we have helped homeowners across Upstate South Carolina and parts of Western North Carolina understand and repair their heating systems, and this thermostat setting causes understandable confusion during cold weather.
Emergency Heat & Auxiliary Heat Serve Different Purposes
Auxiliary heat supports the heat pump automatically, while emergency heat takes the heat pump out of operation. Knowing which one is running helps you determine whether the system is responding normally or needs attention.
Auxiliary Heat
Auxiliary heat is backup heat that the system activates automatically when the heat pump needs assistance meeting the thermostat setting. It often comes on during a large temperature increase, a cold snap, or recovery from a defrost cycle. The compressor continues running while supplemental heat adds capacity.
Emergency Heat
Emergency Heat, often labeled “EM Heat,” is typically selected manually at the thermostat. It shuts off the heat pump compressor and uses only a secondary heat source. In many systems, that source is electric resistance heat strips, which create heat as electricity passes through them. A dual-fuel heat pump uses a gas or oil furnace as its secondary source instead.
Emergency heat isn’t simply a stronger version of standard heating. It is a temporary bypass for situations in which the heat pump shouldn’t run. If the thermostat briefly displays Aux Heat without your selecting the emergency setting, leave the system in its regular mode and let it manage the demand.
What Emergency Heat Doesn’t Do
Emergency heat doesn’t defrost the equipment, melt a frozen coil, or repair the reason the heat pump is struggling. It bypasses the compressor, keeping indoor spaces warm while the underlying issue still needs diagnosis.
A heat pump’s defrost cycle is a separate automatic process. When frost forms on the outdoor coil, the system uses defrost controls and coil-temperature sensing to remove it. Light frost in cold, damp weather can be normal. Equipment covered in heavy ice, or still iced over after a defrost cycle, won’t be fixed by leaving emergency heat on.
Common reasons a system may need emergency operation include:
- Extended ice or snow buildup that restricts airflow across the coil.
- A refrigerant problem that reduces the system’s ability to move heat indoors.
- A compressor or other heat-pump component failure.
Don’t chip ice from the coil, pour hot water on the equipment, or repeatedly change thermostat modes. If the equipment is heavily iced or making unusual noises, use emergency heat only when you need temporary indoor warmth, then arrange for the system to be checked.
When Emergency Heat Signals a Repair Need
Frequent reliance on emergency heat is a reason to schedule a diagnosis, particularly when the weather isn’t severely cold. There is no universal safe runtime because secondary heat sources and equipment problems differ, but emergency operation shouldn’t become your routine.
Watch for these signs that point beyond ordinary auxiliary heating:
- The thermostat remains on the emergency setting for more than a short period.
- The heat pump doesn’t run in its standard mode, even though it has power and the thermostat is calling for heat.
- The system blows cool air, runs for long periods without warming the home, or cycles abnormally.
- The coil repeatedly develops thick ice.
- Heating performance drops suddenly or the system makes new grinding, buzzing, or rattling sounds.
Low refrigerant, airflow restrictions, electrical faults, and compressor problems can prevent a heat pump from operating as intended. A technician must identify the cause before restoring standard operation. Emergency heat provides a short-term bridge, but it doesn’t reveal whether the problem is a refrigerant leak, failed component, or defrost-control issue.
Why Emergency Heat Can Raise Electricity Use
A heat pump moves existing heat from outdoors to indoors. Electric resistance heat strips create heat directly with electricity, requiring substantially more energy for the same heating task. The U.S. Department of Energy states that modern heat pumps can reduce electricity use for heating by about 65% compared with electric resistance heating.
That difference is why emergency heat is intended for temporary use, not as a way to warm the house faster. Raising the thermostat several degrees can also trigger auxiliary heat, depending on the system and thermostat programming. Heat-pump thermostat controls raise the indoor temperature gradually to limit unnecessary resistance-heat operation.
Make one reasonable thermostat adjustment and give the system time to respond. If the home still can’t maintain the setting, identify why the heat pump is underperforming rather than relying on emergency heat for days.
How We Diagnose Emergency Heat Problems
A proper service visit begins by finding out why the heat pump isn’t carrying the heating load. We test system operation and inspect airflow, electrical components, and the refrigerant circuit, with additional testing guided by the symptoms.
Our heating and cooling services include heat pump repair, refrigerant leak repair and recharging, and compressor repair. Before repairs begin, we provide transparent upfront Peace of Mind Pricing so you know the recommended work and cost. Our trained, carefully screened technicians arrive with a wide inventory of essential replacement parts to reduce unnecessary delays.
Annual inspections can identify developing concerns before a cold-weather breakdown leaves a household dependent on secondary heat. Home Comfort Club members receive annual inspections, priority scheduling, and discounts.
Emergency heat can keep a home warm temporarily, but it shouldn’t become the standard setting for a working heat pump. If your system repeatedly switches to secondary heat, has a frozen outdoor coil, or won’t warm the home, Five Star Plumbing Heating Cooling and Electrical provides heat pump repair and 24/7 emergency HVAC service without extra charges for evenings or weekends. Speak with a real team member at (864) 306-4898 to discuss what your system is doing.