It’s a bitterly cold morning, and suddenly, your thermostat flashes a message: Emergency Heat On. Cue the confusion and maybe a slight panic. Is your heat pump broken?
Is this going to cost a fortune? Take a deep breath, we’ve got answers. So, when does a heat pump switch to emergency heat? The answer might surprise you.
Whether it’s due to frigid temps or a system hiccup, your heat pump is simply calling in backup to keep your home warm. In this blog, I’ll explain exactly when and why this happens, what it means for your comfort and wallet, and how to respond like a pro.
What Is Emergency Heat and How Does It Work?
Emergency heat is your system’s backup plan. When your heat pump can’t do its job, this feature steps in. It’s designed to keep your home warm if something goes wrong.
Your regular heat pump pulls heat from outside air, even in winter. But if the temperature drops too low or your outdoor unit stops working, it struggles. That’s where emergency heat takes over.
Unlike your usual system, emergency heat doesn’t pull warmth from the air. Instead, it uses:
- Electric resistance heating (like a big space heater built into your system)
- Or a gas furnace if you have a dual-fuel setup
You have to turn on emergency heat manually using your thermostat. It doesn’t activate on its own. That’s different from auxiliary heat, which kicks in automatically when the system needs help.
When would you use it?
- Your outdoor unit is iced over or not running.
- You’re waiting on a repair.
- It’s dangerously cold, and the heat pump can’t keep up.
Let’s say your outdoor unit is frozen solid and blowing cold air inside. You’d switch the thermostat to “EM Heat” until the unit is fixed.
It’s not meant to be your everyday heat source. But in an emergency, it does its job keeping you and your pipes from freezing.
Emergency Heat vs. Auxiliary Heat
These two sound similar, but they do very different jobs.
- Emergency Heat is manual. You turn it on when your outdoor unit fails. It’s a full backup.
- Auxiliary Heat is automatic. It kicks in when your heat pump needs a little extra help, like during freezing weather or a defrost cycle.
You might see “AUX” or “EM Heat” on your thermostat. They’re not interchangeable.
Why does this matter?
If you confuse them, you might use emergency heat when you don’t need to. That means your system skips the efficient heat pump and runs the energy-hungry backup. The result? Higher bills for no good reason.
Let’s say it’s 30°F outside. Your heat pump can still work, just slowly. It’ll call for auxiliary heat if needed. But if you flip the switch to emergency heat manually, you force the system to use the least efficient method.
Know the difference. It saves you money and avoids unnecessary wear on your system.
When and Why Emergency Heat Gets Activated
Common Triggers
Emergency heat doesn’t turn on for no reason. Your system needs a real problem.
Here’s what usually causes it:
Mechanical Failure
Your outdoor unit stops working. Maybe it’s frozen over. Maybe it’s physically damaged. Either way, the heat pump can’t run.
Extreme Cold
Most heat pumps struggle below 25–30°F. They lose efficiency. If yours can’t keep up and the outdoor unit can’t help, you may need to manually switch to emergency heat.
Defrost Cycle Malfunction
Heat pumps regularly defrost themselves. If that fails, ice builds up and blocks the system. Emergency heat can keep you warm while the issue gets fixed.
Power or Electrical Issues
Sometimes it’s not the weather. If your compressor loses power or there’s a control board failure, emergency heat becomes your only option.
When Emergency Heat Should Be Used?
You should only turn on emergency heat if your outdoor unit is down.
Examples:
The unit is completely iced over
It’s not making any noise or movement.
You’ve called a repair tech, but help won’t arrive for hours.s
In these cases, emergency heat keeps your home livable. You won’t freeze while waiting for a fix.
It’s a temporary backup, not your go-to setting.
When to Avoid Using Emergency Heat?
Just because it’s cold doesn’t mean you need emergency heat.
Avoid switching it on if:
Your heat pump still works, even if it’s slow
Temperatures are cold, but not below freezing.g
You want to keep your energy bill under control. ol
Emergency heat draws way more power. Unless your system is down, it’s not worth the cost.
Ask yourself: Is my system failing, or just working harder than usual?
Knowing the difference can save you money and prevent unnecessary wear.
How to Tell If Emergency Heat Is On?
Signs to Watch For
Wondering if your system is running on emergency heat? It’s usually easy to tell.
Look for these clear signs:
- “EM Heat” or “Emergency” is lit on your thermostat display
- Your blower fan runs nonstop, even when the temperature is stable.
- You notice a spike in your electricity usage or bill.
Another clue? The outdoor unit might be completely silent. That’s because emergency heat bypasses it completely.
If your house suddenly feels warm, but the heat pump isn’t running, check your thermostat.
What to Do If It’s On?
Don’t overthink it. Start with the basics.
- Check the outdoor unit.
Is it frozen over? Not running at all? That could explain the switch. - Look at your thermostat setting.s
Did someone accidentally flip it to EM Heat? Maybe during a cold snap or while troubleshooting - Call a technician if you’re unsure.
If the outdoor unit looks fine but the system still runs emergency heat, something may be wrong internally.
Ask yourself: Was this a manual switch, or did something force your hand?
Knowing how to check and respond helps you avoid wasting energy and gives you control over your comfort.
Common Myths and Misconceptions
Myth: Emergency Heat Works Better in Cold Weather
Truth: It’s less efficient to use only when necessary
This one catches a lot of people off guard.
You might think emergency heat is designed for freezing days. But that’s not the case. It doesn’t work better in cold weather, it just works differently.
Your heat pump can still run in the cold, especially down to 25°F. It might be slower, but it’s efficient. Emergency heat skips the heat pump entirely and uses electric coils or gas heat instead. That uses much more energy.
So, unless your outdoor unit has stopped working, there’s no benefit to using emergency heat. You’ll stay warm, but your utility bill will climb fast.
Ask yourself: Is the unit broken, or just cold? If it’s not broken, let the system handle it.
Myth: Auxiliary and Emergency Heat Are the Same
Reality: One is automatic, the other manual, and meant for emergencies only
It’s easy to confuse these two, especially when your thermostat flashes unfamiliar terms.
But they’re not the same:
- Auxiliary heat turns on automatically. It helps your heat pump during freezing temperatures or defrost cycles.
- Emergency heat is a manual setting. You use it only when your outdoor unit fails.
Accidentally switching to emergency heat when you just need a boost can lead to higher energy bills.
Know what each setting means. That small difference can save you money and help your system last longer.
How to Prevent Emergency Heat Activation?
Seasonal Maintenance Tips
Routine maintenance keeps your system running efficiently. It also reduces the chance your heat pump will switch to emergency heat.
Start with simple steps:
- Clean or replace filters monthly
A clogged filter restricts airflow and makes your system work harder than it should. - Clear debris around the outdoor unit
Leaves, snow, or ice buildup can trigger shutdowns or defrost issues. - Schedule professional HVAC inspections twice a year.
A trained technician can catch minor problems before they become major breakdowns.
These actions help your heat pump handle colder days without switching to high-cost emergency heat.
Use a Smart Thermostat
A smart thermostat does more than just adjust the temperature.
- It can detect outdoor temperatures and switch between heat sources automatically.
- It prevents you from accidentally activating emergency heat when it’s not needed.
Some models even send alerts when something seems off, like a system running constantly.
Ever bumped the settings and wondered why your bill skyrocketed? A smart thermostat helps avoid that mistake.
Upgrade to a Cold Climate Heat Pump
If you live where winters are brutal, it may be time for a system upgrade.
Cold climate heat pumps are built to operate efficiently even below 0°F. They:
- Works better in freezing weather without needing backup heat
- Minimize reliance on electric resistance heating, saving you money
Older heat pumps often struggle once temps drop below 30°F. If your system constantly flips to emergency mode, ask yourself how old is it?
An upgrade can improve comfort and efficiency all winter long.
Conclusion
Those flashing “Emergency Heat” lights don’t have to spark panic. You’re now equipped to make smart decisions when temperatures plummet. Remember, this feature exists as your safety net, not your daily driver. Trust your heat pump to handle most winter days. Save emergency mode for true system failures.
Schedule those maintenance checks. Clear debris regularly. Consider upgrades if you battle extreme cold often. Your wallet will thank you, and your home will stay perfectly cozy through even the harshest winter days. Next time that thermostat flashes, you’ll respond with confidence, not confusion.
FAQs
When does a heat pump switch to emergency heat?
A heat pump only switches to emergency heat when you manually select it on the thermostat. This setting is designed specifically for situations when your outdoor unit has failed or is completely frozen, telling your system to bypass the heat pump entirely and rely solely on your backup heating system.
How does emergency heat differ from auxiliary heat?
Auxiliary heat activates automatically when your heat pump needs temporary assistance during very cold weather or defrost cycles, working alongside your heat pump. Emergency heat is a manual override that completely bypasses your heat pump when it can’t function at all due to mechanical failure or severe weather conditions.
Can using emergency heat damage my system?
Using emergency heat won’t damage your system, but it’s not designed for extended use. Running it for prolonged periods puts unnecessary strain on your backup heating elements and significantly increases your energy costs. Use it only as a temporary measure until repairs can be made.
Should I activate emergency heat whenever temperatures drop below freezing?
No. Modern heat pumps can operate efficiently in temperatures well below freezing. Only activate emergency heat if your outdoor unit has stopped working or if your home cannot maintain comfortable temperatures despite the system running continuously. Otherwise, let your heat pump and automatic auxiliary heat handle cold weather.
What should I do if the emergency heat is running without my having activated it?
If emergency heat has activated without your input, check your thermostat for error codes and inspect your outdoor unit for obvious issues like ice buildup or power loss. This could indicate a thermostat malfunction, a control board issue, or a sensor problem. Contact a professional technician promptly, as this typically signals a system fault requiring immediate attention.
How can I tell if the emergency heat is running?
Your thermostat will typically display “EM Heat” or “Emergency” when this mode is active. You might also notice your outdoor unit isn’t running at all, while your home is still being heated. Another indicator is a sudden, significant increase in your electricity usage.
