If your thermostat shows “EM Heat” or “Emergency Heat,” you are not alone in wondering whether to worry. This is one of the most misunderstood settings on a heat pump system, and using it wrong can cost hundreds of extra dollars in a single billing cycle. So what is emergency heat on a thermostat? It is a backup mode that bypasses your heat pump entirely, pulling warmth from a secondary source, meant to run only when your primary system cannot heat your home alone.
At Hutchinson Heating and Air, we get calls every winter from Temecula and Murrieta homeowners who flip this switch by accident. Here is when to use it, and when to leave it alone.
What Does “EM Heat” Mean on Your Thermostat
EM Heat stands for Emergency Heat. It is a manual override setting found on thermostats connected to heat pump systems, and it tells your unit to stop using the outdoor compressor and rely completely on the backup heat source instead.
Most homeowners never touch this setting because their heat pump handles everything automatically. But if you see the EM Heat light glowing and you did not turn it on yourself, that is usually your first clue that something is wrong with the outdoor unit. Heat pumps are common across Southern California because our winters rarely drop low enough to justify a full gas furnace as the primary system, so understanding this setting matters more here than homeowners might expect.
How Emergency Heat Works With Your Heat Pump
To understand what is emergency heat on a thermostat, it helps to know how a heat pump normally operates in stages.
Stage One: Normal Heat Pump Operation
Under normal conditions, your heat pump pulls warmth from the outside air, even when it feels cold outside, and moves it into your home through the refrigerant cycle. This is the most efficient way to heat a house because the system is transferring heat rather than generating it from scratch.
Stage Two: Auxiliary Heat Activation
When outdoor temperatures drop low enough that the heat pump alone cannot keep up, or during the defrost cycle when the outdoor coil needs to melt off ice, the system automatically brings in auxiliary heat to assist. This happens without you touching the thermostat, and it usually lasts only a few minutes at a time.
Stage Three: Full Emergency Mode
Emergency Heat is different from auxiliary heat because it shuts the heat pump off completely rather than assisting it. This stage only activates manually, and it means one hundred percent of your heating is now coming from the backup source. This is the stage most homeowners confuse with a normal cold weather setting, when it is actually meant for a broken heat pump.
Emergency Heat vs Auxiliary Heat
These two terms get mixed up constantly, so here is a side by side breakdown.
| Feature | Auxiliary Heat | Emergency Heat |
| Activation | Automatic | Manual only |
| Heat pump status | Still running, assisted | Completely shut off |
| Trigger | Cold weather or defrost cycle | Heat pump failure |
| Typical duration | Minutes at a time | Until repair is complete |
| Energy cost | Slightly higher | Significantly higher |
Once you see this side by side, the difference becomes much clearer. Auxiliary heat is your system helping itself. Emergency heat is you telling the system to stop trying.
When It’s Appropriate to Use Emergency Heat
Heat Pump Failure
If your outdoor unit has stopped running entirely, whether from a failed compressor, a tripped breaker that will not reset, or a refrigerant leak, switching to emergency heat keeps your home warm while you sort out repairs.
Waiting for Professional Repairs
This is the most common legitimate reason homeowners use this setting. If a technician has diagnosed a problem and parts need to be ordered, running on emergency heat for a day or two is a reasonable bridge, as long as you understand the cost tradeoff.
Rare Extreme Cold or Ice Buildup
Occasionally, an outdoor unit gets coated in ice from a storm or freezing rain and cannot safely operate. In this narrow situation, switching to emergency heat protects the compressor fan from spinning against ice damage until conditions improve or a technician can inspect it.
When You Should NOT Use Emergency Heat
High Energy Consumption
Electric resistance heat is far less efficient than a heat pump moving warm air from outside. Running your entire home on backup coils for an extended period can double or even triple your heating costs during that stretch, which is a shock many homeowners do not expect until the bill arrives.
Extra Wear on Backup Heating Components
Backup heating elements are designed for short, occasional bursts, not for carrying your whole home’s heating load day after day. Leaving your system on emergency heat for weeks puts stress on components that were never built for that kind of continuous demand, and it can shorten their lifespan.
Why Emergency Heat Increases Your Energy Bill
Southern California Edison rates are structured with tiered pricing, meaning the more electricity you use, the higher your per kilowatt-hour rate climbs. Emergency heat pulls a lot more current than your heat pump’s normal operation, so not only are you using more energy, you are often paying a higher rate for that extra usage too.
For a typical three bedroom home in Temecula or Murrieta, running emergency heat continuously instead of a properly functioning heat pump can add well over a hundred dollars to a single month’s electric bill, depending on the size of the backup system and how long it runs. This is exactly why our team at Hutchinson Heating and Air encourages customers to treat this setting as a short term bridge, not a long term fix.
Signs Your Thermostat Is Stuck on Emergency Heat by Accident
Sometimes a family member flips the setting without realizing what it does, or a thermostat gets bumped during cleaning. Watch for these signs.
- The EM Heat indicator light stays on continuously, not just for a few minutes
- Your outdoor unit is silent even though the system is calling for heat
- The air coming from your vents feels warm but noticeably less hot than usual heat pump output
- Your electric bill jumps sharply compared to the same month last year
If you notice more than one of these at the same time, check your thermostat mode before assuming something bigger is broken.
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How to Switch Off Emergency Heat Safely
Most thermostats let you switch out of emergency heat by simply selecting “Heat” or “Auto” mode instead. Once you do this, give the system a few minutes to cycle back to normal heat pump operation.
If switching back causes the same symptoms that led to emergency heat in the first place, such as the outdoor unit not running or the home not warming up properly, do not keep cycling the system on and off. Repeated cycling can cause additional strain on the compressor and electrical components, and it rarely resolves the underlying issue on its own.
When to Call a Professional Technician
Warning Signs That Need Attention
If your outdoor unit will not start, makes unusual noises when it does run, or the emergency heat light comes on by itself without you touching the thermostat, these are signs the heat pump needs a professional diagnosis rather than a homeowner fix.
Persistent Ice or Cost Spikes
Ice that keeps returning to the outdoor coil even after a normal defrost cycle, or an electric bill that stays elevated month after month, usually points to a refrigerant issue, a failing defrost control board, or a compressor nearing the end of its life. Our lead technician Hector, who is NATE certified, has walked through this exact troubleshooting process with dozens of local households, and catching these signs early almost always saves money compared to waiting for a full system failure.
If you are dealing with any of these symptoms, our HVAC Services in Murrieta team can inspect your heat pump, diagnose the root cause, and get your system back to normal operation quickly.
Final Thought
Understanding what is emergency heat on a thermostat can save you from an unpleasant electric bill and help you catch a failing heat pump before it turns into a bigger repair. Use it when your system genuinely needs a backup, and switch back to normal heat mode as soon as your heat pump is running properly again.
If your thermostat keeps showing emergency heat, or your heating bill has climbed without explanation, contact us at Hutchinson Heating and Air. With over 21 years serving Temecula and Murrieta and a NATE certified team backed by contractor license #842625, we will get your system diagnosed and running the right way again.
FAQs
Is emergency heat bad for my heat pump?
Using emergency heat occasionally while waiting for a repair is not harmful to your system. The concern is running it for extended periods, which increases wear on backup components and significantly raises your energy costs without addressing the actual problem.
Why did my thermostat switch to emergency heat on its own?
If emergency heat activates without you touching the thermostat, it typically means the system’s control board detected a fault with the heat pump and automatically switched to backup heat. This is different from auxiliary heat and usually indicates a repair is needed soon.
How long can I safely run emergency heat?
There is no strict time limit, but running emergency heat for more than a day or two while waiting on repairs will noticeably increase your electric bill. It is best treated as a temporary bridge rather than a normal heating mode.
Does emergency heat feel different from regular heat pump heat?
Yes, many homeowners notice the air feels warmer at the vents but takes longer to raise the overall home temperature, since backup systems often have a different output pattern than a heat pump running efficiently.
Do all thermostats have an emergency heat setting?
Only thermostats connected to heat pump systems typically include this setting, since it is designed specifically to bypass the heat pump and activate a backup heat source. Straight gas furnace systems generally do not have this option.
