What Is Emergency Heat on a Thermostat?
Emergency heat is a thermostat setting that uses your heat pump’s backup heat instead of relying on the outdoor heat pump to warm your home. Call Dallas 24 Hour HVAC at (469) 369-0748 if your system will not heat or the setting stays on.
Need help now? (469) 369-0748
What Is Emergency Heat on a Heat Pump Thermostat?
Emergency heat is a backup mode for a heat pump. When you select it, the system relies on its secondary heat source rather than using the outdoor heat pump to pull warmth from outside air. The exact backup equipment depends on the system, so check your thermostat or equipment manual if you are unsure what your home has.
The setting is different from normal heat. In normal heat mode, the heat pump runs and backup heat may assist when the system needs extra warmth. In emergency heat mode, the thermostat tells the system to use backup heat instead. That distinction matters: emergency heat is a temporary alternative when the heat pump cannot operate properly, not a routine winter setting.
If the thermostat displays “AUX” rather than “EM HEAT,” that usually signals backup heat is assisting while the heat pump is still being used. See what aux heat means for the difference between that display and manually selecting emergency heat.
How Emergency Heat, Auxiliary Heat, and Normal Heat Differ
Use the mode that matches what the system is doing, not just how cold the day feels. These thermostat settings serve different purposes.
Normal heat
The heat pump runs to warm your home. Leave the thermostat on this mode during ordinary heating; check that it is set to HEAT, not COOL or OFF.
Auxiliary heat
Backup heat may turn on automatically to help the heat pump maintain the requested temperature. A brief AUX display during a cold spell or recovery from a thermostat setback can be normal; check whether the home is still warming.
Emergency heat
You select this setting when the heat pump is not operating properly or a technician directs you to use backup heat. Check whether the thermostat shows EM HEAT and whether the indoor temperature begins to rise.
When Emergency Heat Makes Sense—and When It Does Not
Emergency heat can keep a heat-pump home warm when the outdoor unit is disabled, damaged, or unable to run. It is not automatically the better choice just because the weather is cold: a working heat pump is designed to provide heat in cold conditions, with backup heat available when needed.
- Consider emergency heat if the outdoor unit is visibly damaged or not running — Look from a safe distance for obvious damage or a unit that has stopped operating while the thermostat calls for heat. Do not open the outdoor unit or touch wiring; call for heat pump service to diagnose the cause.
- Use it as a temporary measure if a technician advises it — Follow the technician’s direction and watch whether the indoor temperature holds or rises. If the backup setting does not produce heat, switch off the experiment and arrange service rather than repeatedly changing modes.
- Do not select it just because AUX appears briefly — Auxiliary heat can assist automatically without meaning the heat pump has failed. Keep the thermostat in normal HEAT mode if the system is warming the home and there are no signs of a fault.
- Do not rely on it as a repair — Emergency heat cannot correct a failed component, blocked airflow, or an electrical issue. If the system still cannot maintain warmth, leave the thermostat setting stable and request a diagnosis.
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Seven Safe Checks Before You Select Emergency Heat
Start with the thermostat and simple visual checks. Do not remove equipment panels, handle wiring, or try to thaw the outdoor unit with tools or hot water.
- Read the thermostat display — Note whether it says HEAT, AUX, or EM HEAT, and check the temperature setting. Confirm HEAT is selected if you want the heat pump to run normally.
- Compare the set temperature with the room temperature — Check whether the room reading is below the setting and whether the system has had time to respond. A large gap after lowering the thermostat can bring on backup heat while the system catches up.
- Check the thermostat schedule — Look for a programmed setback or schedule that may have changed the target temperature. Restore the setting you intend and see whether the thermostat continues to call for heat.
- Look at the air filter — Check the filter at its normal access point. If it is visibly clogged, replace it with the correct size and airflow direction shown on the filter or holder; then check whether air moves more freely at the vents.
- Check supply vents and returns — Make sure supply vents are open and not covered by furniture, and keep return grilles clear. After clearing an obstruction, check whether airflow improves in the affected room.
- Observe the outdoor unit from a distance — Look for obvious damage, heavy ice, or a unit that is not running while the thermostat calls for heat. Do not chip ice, reach inside, or pour water on the equipment; note what you see for the service technician.
- Choose the mode and monitor the result — If the heat pump appears unable to operate and you need temporary backup heat, select EM HEAT and check whether the indoor temperature rises. If it does not, or the setting remains necessary, call for a system diagnosis.
What Can Go Wrong When Emergency Heat Stays On?
Emergency heat can cost more to run than normal heat because many systems use electric resistance backup heat, which uses substantial electricity. A short period may be useful when the heat pump cannot run, but leaving the system in that mode can raise energy use without fixing the reason the outdoor unit stopped.
The thermostat setting may also fail to warm the home if the backup heat has a fault, airflow is restricted, or another system problem is present. Check the filter and clear vents first; if those simple checks do not help, avoid repeated switching between modes. A technician can test the thermostat, backup heat, and heat-pump operation.
A little frost on an outdoor heat-pump coil can occur in cold weather, but heavy ice that remains or prevents operation needs attention. Do not scrape the coil or try to force a defrost cycle; take a photo from a safe distance and share what you observed when arranging service.
Why North Texas Cold Snaps Can Bring on Backup Heat
Heat pumps draw warmth from outdoor air, so a sharp cold snap can increase the need for backup heat. During the February 2021 winter storm, DFW Airport recorded a low of -2°F on February 16, according to the National Weather Service Fort Worth. That exceptional event shows why backup heat can matter in North Texas; it does not mean you should switch to emergency heat for every cold day.
For cold-weather precautions specific to an ice event, read our guide to using emergency heat during a Texas ice storm. If your thermostat is showing AUX while the indoor temperature is recovering, keep the system in normal HEAT mode unless you have a reason to believe the heat pump has failed.
Need help now? (469) 369-0748
When to Request Heat Pump Service for Emergency Heat
Request service if the outdoor unit will not run, the system blows cool air while calling for heat, heavy ice persists, or the indoor temperature keeps falling. Also call if emergency heat does not warm the home or the thermostat repeatedly returns to that mode. Share the thermostat display, filter condition, and anything you observed at the outdoor unit; those details help focus the inspection.
Dallas 24 Hour HVAC serves Dallas and towns within 40 miles. Our heat pump service starts with a $29 inspection for a heating or cooling problem, so the system can be checked before deciding what repair it needs.
Frequently asked questions
Can I leave my heat pump on emergency heat overnight?
You can use emergency heat temporarily if the heat pump cannot operate and the backup system is working, but it may use more electricity than normal heat. If you need it through the night because the outdoor unit has stopped or the home is still getting colder, arrange service rather than treating the setting as a repair.
Why does emergency heat stay on even after the house warms up?
The thermostat may still be set to EM HEAT, which keeps the system in backup mode until you change it. If you return to normal HEAT and the outdoor unit still does not run or the thermostat switches modes repeatedly, have the heat pump checked.
Should I use emergency heat if the outdoor unit has ice on it?
A light frost can be part of normal operation, but heavy ice that remains or interferes with the unit is a reason to seek service. Do not chip at the coil or pour water on it; use emergency heat only as a temporary measure if the heat pump cannot provide heat.
Do all heat pumps have emergency heat?
Not every system uses the same thermostat labels or backup equipment. Check the thermostat and equipment manual for the settings your system supports, or ask a technician to identify the backup heat before relying on the emergency setting.
Need Your Heat Pump Checked?
Call Dallas 24 Hour HVAC at (469) 369-0748 to request heat pump service.