What Is Emergency Heat? Is It A Good Idea To Turn On EM Heat When It’s Freezing Outside?

The Emergency Heat setting on your thermostat can be a lifesaver in frigid climates.

The emergency heat, or EM Heat setting, is an important part of your home heating arsenal. As temperatures start to plummet, you want to make sure there’s no threat to your home comfort. You need a backup plan when your heat pump can’t handle the extreme chill or decides to act up. Instead of shivering in the cold while waiting for repairs, you can lean on the EM heat setting to keep your home toasty and comfortable! 

Emergency heat is often used interchangeably with Aux or Auxiliary heat – but more on that later. If you have the EM Heat and/or Aux Heat setting on your thermostat, you have second-stage heating or a backup heating source! While the heat pump is your main source of heating, you have another system ready to step in when the heat pump can’t keep up. 

This secondary system could be electric heat strips, a gas furnace, an oil furnace, or hydronic. When you switch to EM Heat, you bypass the heat pump and use this backup system instead. 

What is emergency heat? How can it be switched on? Is emergency heat expensive to run? How does emergency heat differ from auxiliary heat? Read on to learn everything there is to know about EM Heat.

What Is Emergency Heat?

The Emergency Heat setting is for precisely as its name implies – emergencies. While heat pumps are, without a doubt, very energy efficient and reliable, they can only warm your home when outside temperatures are above freezing.

Other heating sources can heat your home in extreme weather conditions. The downside? They’re not exactly energy efficient. 

Let’s look over how heat pumps work. Heat pumps don’t create hot or cold air. Instead, they work by extracting heat from the outdoors and using it to warm your home. As long as the temperature is above 40F, this process works seamlessly. However, below this temperature, the heat pump can’t find enough heat to transfer and fails to keep your home warm.

Modern HVAC systems pair the two heating sources together to provide utmost energy efficiency, and comfort. When the temperature is mild, your heat pump operates to provide the necessary heat. As soon as the mercury plummets, the secondary heating source kicks into gear with the Aux or EM Heat setting. This helps ensure comfort and efficiency. 

Moreover, any system can malfunction from time to time. With emergency heat, you have the peace of mind of knowing that if your main heat pump suddenly malfunctions in the bone-chilling grip of winter, you can switch on the EM Heat setting and stay warm. 

How Expensive Is Emergency Heat?

Being highly efficient, heat pumps are the ideal choice for all your heating needs. Emergency heat on the other hand will definitely cost more to run. The type of secondary heating system you have and how long you use the emergency heat setting for will play a significant role in determining the cost. 

Electric heat strips, although more expensive, are a highly effective option for secondary heat systems. On the other hand, hydronic or oil and gas furnaces offer lower costs, but their efficiency and fuel prices play a role in determining the overall expenses.

It’s essential to remember that emergency heat should only be used as a last resort when facing heating challenges. Don’t switch to emergency heat mode unless absolutely necessary, and be sure to turn it off as soon as your heat pump is up and running smoothly.

According to Jones-Onslow Electric Corporation if it costs around 30 cents per hour to run your heat pump, it can cost as much as $1.30 per hour to run the Aux or EM Heat setting. 

Why does emergency heat cost more? A heat pump works by extracting the heat from the outside air and moving it indoors while electric coils heat the air to create heat and this process can cost around 3 times more! Energy.gov states that modern air-source heat pumps can reduce electricity by 50% in comparison to furnaces or baseboard heaters. This shows how much more efficient it is to trust your heat pump rather than switch to your secondary electric or furnace heating system with emergency heat setting. 

It’s best to invest in the effective and most cost-efficient heating option with heat pumps, and use emergency heat sparingly for maximum savings and home comfort.

When to Use Emergency Heat?

You should use your emergency heat settings, auxiliary heat, or backup heating – all similar things, in specific situations when your heat pump is unable to maintain the desired home temperature effectively. Once your desired temperature is reached, you should promptly switch off emergency heat. 

Unnecessary usage of emergency heat can significantly spike your energy bills and contribute towards a larger carbon footprint. The setting can also be taxing on your backup heat system which was designed to be used for short periods in extreme circumstances.

Here are some scenarios where it’s appropriate to use emergency heat:

• Your Heat Pump Is Not Working

Imagine it’s bitter cold, you’re cozily nestled in the comfort of your warm home, but suddenly the HVAC system stops working. Technicians can take hours or days to come for a visit. To ensure you stay warm, switch to emergency heat while you wait for repairs. 

• Heat Pump Is in Defrost Mode

Ice or frost commonly develops on the coils of your outdoor HVAC system. Most heat pumps run an automatic defrost cycle to melt this away and switch to your backup heat source for warmth. 

• Heat Pump Is Going Through Maintenance

Your HVAC technician will need to switch off the heat pump during repairs and maintenance. To heat your home during this downtime, you can switch on EM Heat to provide the necessary heating. 

• Weather Is Below Freezing

Heat pumps are designed for milder weather. Thus when it gets extremely cold and your heat pump struggles to extract heat from the outside air, it won’t be able to heat your home as desired. This is when either based on your thermostat settings, it will automatically switch to AUX, or you will need to manually enable EM Heat – especially if your thermostat can’t detect outdoor temperature. 

Does Emergency Heat Come On Automatically?

When your heat pump can’t keep up in freezing temperatures, the Aux setting automatically switches on. However, emergency heat does not come on automatically (considering you have separate wiring for both features). 

To activate emergency heat, you need to manually switch your thermostat to the settings labeled “Emergency Heat” or “EM Heat”. Some thermostat manufacturers may refer to it as “Aux Heat” only. Simply tap the setting to activate emergency heat. 

Auxiliary Heat vs. Emergency Heat

While aux and emergency heat are interchangeably used, they have different operating mechanisms. Aux heat is a term used when the thermostat automatically turns on the supplement heat source in cold temperatures.  EM heat, on the other hand, is used when you have to force your house heating system to bypass the first stage heating and use the secondary heat only in case of emergency. This is also useful if your thermostat can’t detect the outdoor weather. During freezing conditions, you will need to manually switch to your secondary heating. 

The backup heating system in both modes, however, remains the same. 

Aux Heat	Emergency Heat
Your thermostat automatically switches on the aux heat.	You have to turn on the emergency heat manually.
It usually turns on when the outside temperature drops and the heat pump alone is insufficient.	It is mostly used when your primary heat system or first-stage heating has stopped working.
Mostly both the heat pump and aux heat work together to maintain your set home temperature.	In emergency mode, your second-stage heating works independently without using the primary heat unit.

It’s important to note that they both operate the same backup heating source. In some home auxiliary and emergency heat may have the same thermostat wiring and thus will be used similarly. The differences only apply when you have separate settings for each. 

5 Things You Need to Know About the Emergency Setting on Your HVAC System

Before you click that button for EM heat on your thermostat, you should know a few basics.

1. Emergency Heat is Not a Replacement for Your Primary Heating System

Your primary heating system, the heat pump, should be enough to keep your house warm and cozy in even the coldest weather. It’s only in periods of extreme cold that you might need a backup system to keep up with your heating needs. However, if you find yourself often having to run the EM heat, your HVAC system might not be sufficient for your home, or it might need maintenance. Check in with an expert to fix the issue.

2. Your HVAC System May Not Have an Emergency Heat Setting

If you live in an area with a warmer climate where the cold is always moderate, and temperatures stay above 40 degrees, your HVAC system might not have an Emergency Heat setting at all. However, you don’t need to worry about this since the EM heat option is designed chiefly for temperatures consistently close to or below freezing.

3. Check Your HVAC System for Damage Before Running the Emergency Setting

If your HVAC system is not keeping up, you should check for damaged components before switching the Emergency Heat on. While it is true that this setting is for emergencies, it’s still better to know what sort of damage your system has. Not only will this make your service call easier, but it will also prevent any further damage to your system if you address the issue quickly.

4. Emergency Heat Light Staying on Could Signal a Problem with Your Heat Pump

If your system is running in Emergency Heat, it’s normal for the EM heat indicator light to stay on until you turn it off. However, if you’re not using the Emergency Heat mode and the indicator is still on, there could be a problem with your heat pump.

In this case, you can try and troubleshoot the issue yourself or call an expert for help.

To do the process yourself, you first need to count the number of flashes since certain units flash a code that you can then check in the manual to determine the problem. These flashes can range from two to nine. Next, you should turn your thermostat off and wait 30 seconds before powering it back on to restart your system.

Once you’ve done that, shut down the indoor unit and turn it on after five minutes if the light continues to blink. If your system has shut down during inclement weather, this will fix that. Lastly, wait ten minutes and inspect the outdoor unit to see if it is running. If the light on the thermostat is still on, turn off all the circuit breakers located in an electrical panel next to the outdoor unit. You can also check the user manual to find the circuit breakers. Then, turn the circuit breakers on again after a few minutes.

If the icon for EM heat on the thermostat still doesn’t go away, schedule an appointment with a professional.

5. Emergency Heat Could Be a Lifesaver

Your heat pump’s emergency heat mode can be a lifesaver at times. For example, imagine your primary heating system goes out in the dead of winter. This issue can be potentially life-threatening. In times like these, the Emergency Heat setting can be your only line of defense, so you should make sure that the backup system stays in usable condition.

Thermostat Wiring for Emergency Heat

For a two-stage heating system the W terminal on the thermostat controls your heating system however this varies greatly depending on your thermostat and HVAC system manufacturer. 

If you have Aux and E wiring and the same terminals on your thermostat, it’s simple. Insert them at the correct places and you’re set up. If your thermostat doesn’t have the E terminal, Aux will be inserted in W1 and E can go in W2. 

To summarize the AUX/AUX1 wire will be inserted into the W1 or AUX terminal on your thermostat. If you’ve got wires labeled AUX/AUX1/W2 and AUX2, be sure to put the first one in your W1 terminal and the AUX2 in your W2 terminal on your thermostat.

You can read more on thermostat wiring here. 

Final Thoughts

Emergency Heat is a backup heating source that your heat pump uses when it cannot keep up with your heating needs or breaks down. While many people switch this system on whenever they feel that the temperatures outside are too low, this is not wise since the EM Heat system is more expensive than a traditional heat pump. Therefore, to keep using your system efficiently, only use this system when your primary heat source is non-functional.