If you have a heat pump and you’ve ever noticed a setting on your thermostat labeled EM Heat or Emergency Heat, you may have wondered what it does and whether you should ever turn it on. It’s one of the more misunderstood settings in home HVAC, and using it incorrectly can lead to unnecessarily high energy bills. Our heat pump team at Southern Air gets this question often. Here’s a clear explanation.
What Is EM Heat?
EM Heat stands for Emergency Heat. It’s a backup heating mode that exists on heat pump systems.
Heat pumps work by extracting heat from the outdoor air and transferring it inside. This is highly efficient under normal conditions. However, when outdoor temperatures drop very low, or when the heat pump itself is not functioning, a secondary heating source is needed.
That secondary source, called auxiliary or emergency heat, is typically an electric resistance heating element built into the air handler. In some systems it may be a gas furnace. When you switch on EM Heat mode, you’re bypassing the heat pump entirely and running on that backup source alone.
What Is the Difference Between Auxiliary Heat and Emergency Heat?
This is where a lot of confusion comes in, and it’s worth understanding clearly.
Auxiliary heat kicks in automatically. When outdoor temperatures drop to a point where the heat pump can’t keep up on its own, the system quietly brings in the auxiliary elements to help out. You don’t have to do anything. This is normal and expected operation.
Emergency heat is manual. When you flip the thermostat to EM Heat, you’re actively telling the system to shut off the heat pump and run entirely on the backup source. The heat pump compressor stops. Only the backup heating elements are running.
Auxiliary heat works alongside the heat pump. Emergency heat replaces it.
When Should You Actually Use EM Heat?
Emergency heat is meant for genuine emergencies only. Specifically, it’s appropriate when your heat pump is damaged or malfunctioning and cannot operate.
If you hear a loud noise from the outdoor unit, see visible damage, notice ice buildup that isn’t clearing on its own, or find that the heat pump simply isn’t producing warmth, switching to EM Heat lets you maintain some level of heating in your home while you wait for a repair.
Think of it as a bridge, not a solution. If you’re in that situation, call our heating repair team as soon as possible. EM Heat is designed to be a short-term measure.
Why You Should Not Leave It On Unnecessarily
Electric resistance heating is far less efficient than a heat pump. A heat pump can deliver two to three units of heat for every unit of electricity it consumes, because it’s moving heat rather than generating it.
Electric resistance elements convert electricity to heat at a 1:1 ratio. Leaving EM Heat on when your heat pump is working fine can dramatically increase your energy bills, sometimes doubling or tripling your heating cost for the month.
If you’ve turned it on and forgotten about it, check your thermostat now. Many thermostats display a light or indicator when EM Heat is active.
Does a Normal Louisiana Winter Require EM Heat?
In the Ruston area, the answer is almost never. Modern heat pumps are designed to operate efficiently well below freezing, and central Louisiana winters rarely push temperatures to levels that challenge them.
Auxiliary heat may come on automatically during the occasional cold snap, which is completely normal. But manually switching to EM Heat during a typical winter day is unnecessary and expensive.
What If the EM Heat Light Is On But You Didn’t Turn It On?
If your thermostat is displaying an EM Heat or AUX indicator without you activating it manually, it likely means your heat pump is running in auxiliary mode automatically due to cold temperatures or a system issue. If temperatures outside are mild and the indicator is still on, that could point to a problem worth having a technician look at. Our heating repair team can diagnose what’s happening and get your system back to normal operation.
Schedule a Visit
Whether you have questions about your heat pump, noticed something unusual with your heating, or want a tune-up heading into cooler weather, Southern Air is ready to help.
