Have you ever noticed the EM heat setting on your thermostat and wondered what it is? It stands for emergency heat, and it can be useful in some situations. Before using your EM heat setting, you should know, “What is Emergency Heat?”
Emergency heat, also called supplemental heat, will continue to provide heat when it is too cold outside for the heat pump to work effectively. It consumes more energy than regular heat but can help you stay comfortable in extreme temperatures. Typically, emergency heat will be triggered when it is at or below 35° F.
In this article, you’ll learn about the pros and cons of emergency heat and definitions for related terms. You will also find information about when you should use emergency heat and how to do so, as well as the differences in cost for supplemental heat, auxiliary heat, and regular heat.
Contents (Jump to Topic)
- What is Emergency Heat?
- How Does Emergency Heat Work?
- When to Use Emergency Heat?
- Do All Heat Pumps Have Emergency Heat?
- What Is EM Heat Setting on a Thermostat?
- EM Heat vs Heat: What’s the Difference?
- How Do You Know If Emergency Heat is On?
- How Much Does Emergency Heat Cost?
- Aux Heat vs Emergency Heat
- Can Emergency Heat Cause a Fire?
- Best Emergency Heat Thermostats
What is Emergency Heat?
Emergency heat is necessary for frigid weather and uses a supplemental heat source. Typically, this setting is needed when the outside temperature drops below 35°F. It should come standard with any home in a region where the climate regularly gets that cold that is heated with a heat pump system.
When it gets cold outside, the heat pump will lose efficiency and the home will lose heat faster than the heat pump can provide it. When the temperature in the house drops, the secondary heat source will turn on to help the heat pump. This is known as auxiliary heat.
However, if it gets below 30 degrees for a sustained period, a running heat pump can become damaged or ineffective. Manually turning on the emergency heat switches on the back-up heat, or second-stage heat, and turns off the heat pump, first-stage heat. This can prevent further damage to the heat pump while keeping your home near room temperature.
While there are some benefits to emergency heat, there are also some downsides to be aware of. Keep the pros and cons in mind when thinking about when or if you want to use the emergency heat setting on the thermostat.
- Comfortable temperatures inside your home are the primary benefit of emergency heat. Even if it is freezing outside and the heat pump cannot work properly, emergency heat can keep you comfortable.
- Protects the heat pump when it is too cold outside for the defrost feature to work. This can save the heat pump from potentially irreparable damage that can take a chunk of cash out of your wallet.
- Works in other situations that do not involve chilly temperatures. If something damages the outdoor heating source, then emergency heat can supply heat until the heat pump is fixed or replaced.
- Uses more energy than regular heat. This means that your energy bill will be higher, especially if you have to resort to emergency heat for an extended period.
- Strains the system and backup element. In addition, if there is no airflow or movement, using the emergency heat can damage the outdoor unit.
How Does Emergency Heat Work?
There are three different types of heat pumps: air-sourced, water-sourced, and geothermal. The most common type is an air-source heat pump, and it is probably the type you have for your central heating and cooling system.
An air-source heat pump will use energy to transfer heat from one location to another. It does not create energy by burning fuel and does not create heat. It moves the heat through the air and puts it where you want it. Because of this, it can bring heat inside during the Winter and move the heat outside during the Summer.
A heat pump cannot move enough heat to adequately warm the interior of the home when the weather drops below 35 to 45 degrees Fahrenheit. When this happens, the secondary heat source must help the heat pump to properly heat your home. The secondary heat source can be auxiliary heat, a heat pump-furnace combo system, or remote heating items like space heaters.
This process works automatically when the temperature drops low enough. However, if something happens to the heat pump, then EM backup heating may be necessary. Emergency heat will bypass the heat pump and directly access the secondary heat source, which will either be an electric heat strip or gas furnace.
With an electric system, this will turn the air handler into an electric furnace by using a set of radiant heat strips. They use electric resistance heating to convert 100% of electrical energy into heat. This requires a substantial amount of energy to keep the interior of the home around room temperature.
When to Use Emergency Heat?
While the secondary heat source will help the heat pump during cold weather, the emergency heat setting should only be used in, you guessed it, emergencies. It should not be used unless there is something wrong with the first-stage heating.
Just because it is cold inside does not mean you should immediately switch on the emergency heat. If there is damage to the exterior heat pump, like a tree falling onto it or freezing due to malfunction, then the emergency heat can be used. Since it is significantly more expensive, you will also want to call for service as soon as possible.
Do All Heat Pumps Have Emergency Heat?
Not every heat pump comes equipped with a backup heat source, but most do have emergency heat. If you live in a northern climate that regularly sees temperatures below 35 to 40 degrees Fahrenheit, then you should have a heat pump with a secondary heat source.
Even in warmer climates, many heat pumps will still have emergency heat. However, some heat pumps in the South will not have emergency heat, and, depending on where the home is located, it may be very unlikely that you would need it, anyway.
What Is EM Heat Setting on a Thermostat?
The emergency heat setting on the thermostat will switch off the heat pump and switch on the supplemental heat. Sometimes this setting is a manual switch on the panel or, on older thermostats, on the bottom or side of the thermostat box.
For newer thermostats, this control will probably be digital. If you have trouble finding where the emergency setting is, then you should refer to the user’s manual or call the thermostat manufacturer. It’s good to know how to turn the EM heat setting on with your thermostat just in case of an emergency or damage to the heat pump that requires backup heating.
EM Heat vs Heat: What’s the Difference?
Regular heat uses only the first-stage heat, which is the exterior heat pump. This is usually sufficient for any temperatures above 40°F and may work until 35°F or lower. You do not have to turn on the emergency heat when it gets colder than this because the second-stage heat will automatically kick on to help the heat pump.
The difference between EM Heat is that it completely turns off the heat pump. This means that the heat will be supplied solely from the secondary heat source. This should keep the interior temperature as comfortable as regular heat but is much less energy-efficient.
How Do You Know If Emergency Heat is On?
When the EM heat setting is on, there will be a red indicator light and may also have a symbol on the thermostat display. If you see the emergency heat indicator on when you did not trigger the EM heat setting, then you could use extra energy for no benefit. If this is the case, then you should call for HVAC service as soon as possible.
How Much Does Emergency Heat Cost?
Emergency heat uses a lot more energy than regular heat, which will increase your electricity bill. The cost and amount of energy will depend on the size of the home, the outside temperature, and many other factors. Generally, you can expect the emergency heat to consume 2 to 3 times more energy than an efficient heat pump. If the temperature is low enough, this could skyrocket your energy bill to 3 times or more than the normal for the time that you have the emergency heat on.
Aux Heat vs Emergency Heat
Aux heat, or auxiliary heat, is a component of emergency heat, but they are not the same thing. Auxiliary heat will kick on automatically to work with the heat pump. This happens when the outside temperature is too low for the heat pump to effectively heat the interior of the home. Auxiliary heat, therefore, uses both first-stage and second-stage heat. Emergency heat, on the other hand, will shut off the first-stage heat and only use second-stage heat.
Can Emergency Heat Cause a Fire?
Emergency heat that is functioning properly should not cause a fire. It is a useful setting for emergencies that impacts the production of the heat pump. If you are afraid that there may be some reason the emergency heat would cause a fire, then call an HVAC technician to check out your system.
Best Emergency Heat Thermostats
Your heat will only work properly if you have an easy-to-use and accurate thermostat to adjust the temperature or, when needed, to switch on emergency heat. Here are a couple of the best thermostats on the market.
Knowing when to use emergency heat and what it does can help you prepare for those times when it is needed (And know to expect a higher bill!). It is an important feature of heat pump systems in colder climates and may even be useful for those rare cold fronts in warmer regions. Just make sure you do not use it too long, and remember to get the heat pump serviced or fixed as soon as you can.