Heat Pump Emergency Heat Mode: What It Is & When to Use It

Many people see “Emergency Heat” on their thermostat and think, Oh no, something’s wrong! But it’s not always bad. In fact, in some cases (like emergencies, of course), it’s exactly what you need.

Let’s break it down: What is emergency heat, when should you turn it on, and when should you just let your heat pump run on its own?

What Is Heat Pump Emergency Heat Mode?

Emergency Heat Mode (EM Mode) is a thermostat setting that controls your home’s backup heating system. It’s there for when your heat pump can’t pull enough warmth from the outside air—usually in extreme cold or if the system has a problem.

In colder regions of Canada, older models of heat pumps struggle to keep up (depending on their rated efficiencies). That’s when your backup heating source kicks in. Depending on your setup, emergency heat can come from:

• Electric resistance heating (most common): Giant space heaters built into your system.
• Gas or propane furnace: A traditional furnace that takes over when needed.
• Oil furnace: Less common, but still used in some older homes.

Difference Between Emergency Mode and AUX Mode

Aux or auxiliary heat works with your heat pump, turning on automatically to help when outdoor temperatures are too low. Emergency heat completely bypasses the heat pump and only uses the backup heat source, which is meant for when the heat pump is broken or inoperable.

How Heat Pump Emergency Heat Mode Works

Your heat pump needs backup when it can’t keep up in extremely cold temperatures. Emergency heat mode bypasses the heat pump and switches to a secondary heating system, such as electric coils, a gas furnace, or another backup source. 

This backup system creates heat rather than just moving it, which uses more energy and costs more than heat pumps to run.

Emergency Heat can be turned on in two ways:

• Automatically: If your heat pump can’t maintain the set temperature, the system will trigger the backup heat on its own.
• Manually: If your heat pump stops working due to a malfunction, you can switch emergency heat on yourself using the thermostat.

When emergency heat turns on, your heat pump stops running—either because it’s malfunctioning or can’t pull enough heat from the outside air. Instead, your backup heat source completely keeps your home warm.

If your system uses electric resistance heating, you’ll likely see a noticeable spike in your energy use since this type of heat is expensive to run. Gas or oil furnaces are usually more efficient, but they still cost more than a properly functioning heat pump.

When to Use Heat Pump Emergency Heat Mode

Emergency heat is usually automatic. But you can also turn it on manually if your heat pump isn’t working properly. 

The key thing to remember is that emergency heat is meant for exactly that—emergencies. It’s not a shortcut to faster heating and shouldn’t be used just because it’s a little colder outside.

Here are some situations where you should use emergency heat:

• Your heat pump isn’t working: If the outdoor unit is broken or not running at all, emergency heat keeps your home warm until it’s fixed.
• Your heat pump is short-cycling or blowing cold air: If your system is turning on and off rapidly or only pushing out cool air, something’s wrong. Emergency heat can be a temporary solution until you get it checked out.
• Your heat pump is frozen over: A little frost is normal, but emergency heat may be needed if the entire outdoor unit is covered in thick ice and not defrosting properly.

Pros and Cons of Heat Pump Emergency Heat Mode

While emergency heat mode can keep your home warm in tough situations, it also comes with some drawbacks. Here’s a closer look at the pros and cons:

Pros of Emergency Heat Mode

• Provides instant heat in emergencies.
• Works in extreme cold (lower than 30 degrees Fahrenheit).
• Prevents further damage to the heat pump

Cons of Emergency Heat Mode

• Typically much higher energy costs.
• Puts strain on backup heating if it runs too long.
• Doesn’t fix underlying heat pump problems

How to Activate Heat Pump Emergency Heat Mode

Turning on emergency heat depends on the type of thermostat you have. Here’s how to do it:

Thermostats with an “Emergency Heat” Switch or Button

If your thermostat has a clearly labeled “Emergency Heat” switch or button, simply turn it to “ON” or select “Emergency Heat” mode. Sometimes, you may need to switch your system to “Heat” mode before activating emergency heat.

Nest Thermostats

For Nest Thermostat and Nest Learning Thermostat (4th Gen):

• Using the Google Home App: Open the app, tap and hold your thermostat’s tile, go to “Settings” > “Thermostat,” select “Emergency Heat,” and toggle it on.
• On the Thermostat: Navigate to “Settings,” select “Emergency Heat,” and confirm by choosing “Yes” or “Turn on.”

For Nest Learning Thermostat (older models) and Thermostat E:

• Press the thermostat ring to open the Quick View menu.
• Go to “Settings” > “Equipment” and continue through the wiring diagram and system summary screens.
• Select “Emer. Heat” and confirm by selecting “Turn On.”
• To turn it off, follow the same steps and select “Turn off” when prompted.

Other Smart Thermostats (Example: 824, 850, 1050 Models)

• Press the “System Mode” button.
• Navigate to “System Options” (usually at the bottom left of the display).
• Select “Emergency Heat” and choose “Enable” to activate it.
• Confirm by selecting “Done.”
• To turn it off, repeat the steps and select “Disable” instead.

How Long Should Heat Pump Emergency Heat Mode Be Used?

There’s no set time limit for using emergency heat. It should be on for as long as you need it and as long as your wallet allows. Your system can handle running in emergency heat for a few hours or even a couple of days without issue. 

However, since it’s much more expensive to run than your heat pump, it’s best to switch back to normal heating as soon as possible.

If you frequently need emergency heat, that’s a red flag. If emergency heat is becoming a regular part of your winter routine, it’s worth having a technician check out your system.

Reasons Your Heat Pump Might Go Into Emergency Heat Mode

Here are some common reasons your heat pump switches to emergency heat on its own:

• Extremely cold temperatures: If the outdoor temperature drops below what your heat pump can handle (usually around 35°F or 2°C for standard models), the system may switch to emergency heat to maintain indoor comfort.
• Frozen or iced-over outdoor unit: A heat pump has a defrost cycle, but if the outdoor unit is completely covered in ice and can’t thaw out, the system may trigger emergency heat to prevent damage.
• Malfunctioning heat pump components: If a critical part like the compressor or outdoor fan fails, the system may automatically switch to emergency heat as a backup. Low refrigerant levels make it harder for the heat pump to transfer heat.
• Electrical or control board failure: If there’s an issue with the control board or wiring, the heat pump may stop running, and the system will default to emergency heat to keep the house warm.
• The power goes out: If your home loses power and then comes back on, your heat pump may not restart properly, causing it to default to emergency heat until it stabilizes.
• Your thermostat is set too high: If you set your thermostat to a temperature that’s too high for your heat pump to reach efficiently, the system may engage emergency heat to try and meet the demand. A faulty thermostat or sensor can also misread temperatures.

When Emergency Heat Mode Represents a Problem

Emergency heat mode is meant to be a temporary fix, not a long-term heating solution. If your heat pump switches to emergency heat and stays there for an extended period, it could signal a serious issue.

In most cases, heat pumps shouldn’t need emergency heat unless outdoor temperatures drop below what they’re designed to handle. If your system engages emergency heat when it’s only slightly cold outside, it could indicate a refrigerant issue, a failing compressor, or another mechanical problem.

If you’ve manually turned on emergency heat and forgotten about it, your system won’t switch back to normal heating on its own. Unlike auxiliary heat, which turns on and off as needed, emergency heat stays on until you manually turn it off. 

How Much More Expensive is Emergency Heat?

On average, running emergency heat can add approximately $20 per day to your energy bill compared to regular heat pump operation (especially if your backup heating source is electric resistance heating). Modern heat pumps are about 2–4 times more efficient than electric resistance heating.

For example, if your heat pump normally costs $3–$5 per day to run, switching to emergency heat could push that cost to $25 or more daily. The longer you use it, the bigger the impact on your energy bill.

The cost increase is usually lower if your backup heat is a gas or propane furnace. However, it’s still more expensive than running a properly functioning heat pump.

Maintenance Tips to Avoid Heat Pump Emergency Heat Mode

The best way to avoid relying on emergency heat is to keep your heat pump in top shape. Here are some key maintenance tips:

• Change your air filters regularly: A clogged filter restricts airflow, making your heat pump work harder and less efficiently. Replace it every 1–3 months.
• Keep the outdoor unit clear: Remove leaves, snow, and ice buildup to ensure proper airflow and prevent the system from overworking.
• Schedule professional maintenance: Have an HVAC technician inspect your heat pump at least once a year to catch potential issues before they become big problems.
• Monitor your thermostat settings: Setting the thermostat too high can force your system to rely on auxiliary heat, which may increase wear and tear.
• Check refrigerant levels: Low refrigerant can make it harder for your heat pump to heat efficiently, leading to higher energy use and possible system failure.
• Ensure proper insulation: A well-insulated home helps your heat pump maintain the set temperature without struggling, reducing the need for backup heating.

EM Heat vs Heat: What is the Difference?

In regular heat mode, your heat pump pulls warmth from the outside air and gradually warms your home. The air from your vents might feel mildly warm (not hot), but it keeps your home comfortable without using too much energy.

If you have electric resistance heating, you’ll feel hot air blowing from the vents—similar to a space heater. If your system uses a gas or propane furnace, the heat will feel stronger and more immediate than a heat pump. 

Conclusion

Emergency heat isn’t always bad, but it’s not meant to always be on. If your system constantly switches to emergency heat or is not running as it should, it’s time to get it checked by a professional.

FurnacePrices.ca connects you with certified local HVAC contractors in your area. We only work with the top 1% of vetted HVAC companies in Canada, so you can trust you’re getting quality service.

Keep your home warm the right way. Get your free quotes today!

Frequently Asked Questions About Emergency Heat Mode