If you're staring at your thermostat during a cold snap and wondering what's the difference between heat and emergency heat, you aren't alone. Most of us don't even think about that "Em Heat" setting until the temperature outside drops below freezing and the house starts feeling a bit chilly. It looks like a tempting button to press when you want to get warm fast, but flipping that switch without knowing how it works can lead to a pretty nasty surprise when your electric bill arrives.
To really understand the difference, you first have to understand how a heat pump works compared to a traditional furnace. Most people with an "Emergency Heat" setting have a heat pump system. Unlike a gas furnace that creates heat by burning fuel, a heat pump is more like an air conditioner working in reverse. It pulls heat from the outside air and moves it into your home. Even when it's 40 degrees outside, there's actually still heat in the air that the system can grab and use.
How the "Heat" setting works
When your thermostat is set to "Heat," your heat pump is the star of the show. It's incredibly efficient because it's moving heat rather than generating it from scratch. It uses a compressor and refrigerant to do the heavy lifting. This is your primary source of warmth, and under normal conditions—say, anything above 35 or 40 degrees Fahrenheit—it does a great job of keeping things cozy without using a ton of electricity.
However, heat pumps have a bit of a weakness: they struggle when it gets really cold. Once the temperature outside drops toward the freezing mark, there isn't as much ambient heat for the pump to pull indoors. The system has to work harder and longer to maintain your desired temperature. This is where the backup system usually kicks in automatically, but that's still different from the manual "Emergency Heat" mode.
What exactly is emergency heat?
Think of emergency heat as your "Plan B." Inside your indoor air handler, there are usually electric resistance heating strips. If you've ever looked inside a toaster and seen those orange glowing wires, that's essentially what's sitting in your ductwork, just on a much larger scale.
When you manually switch your thermostat to Emergency Heat, you are telling the outdoor heat pump to shut down entirely. You're effectively saying, "Stop trying to pull heat from the outside; it's too cold or the unit is broken. Just use the electric strips."
In this mode, the heat pump stays off, and those electric coils do 100% of the work. They get hot fast, and the air coming out of your vents will likely feel much warmer than it does in the regular "Heat" mode. But there's a catch—and it's a big one.
The massive cost difference
The biggest thing to keep in mind when comparing these two settings is the cost. Because the regular heat pump cycle is just moving heat, it's remarkably cheap to run. Electric resistance heat (Emergency Heat), on the other hand, is one of the most expensive ways to heat a home.
It's roughly three to four times more expensive to run your emergency heat than it is to run your standard heat pump. If you leave your system on "Em Heat" for a whole month just because you like the feel of the warmer air, don't be shocked if your utility bill jumps from $150 to $500. It's literally like running several giant toasters 24/7.
"Aux Heat" vs. "Emergency Heat"
This is where a lot of people get confused. You might see "Aux Heat" pop up on your thermostat screen while the system is still set to "Heat." This is normal. Auxiliary heat is the system's way of saying, "I'm trying to use the heat pump, but it's too cold outside to keep up, so I'm going to use the electric strips to help out a little."
The system manages this on its own. It uses the heat pump and the strips together to reach your target temperature. Once the house is warm, it turns the strips off.
Emergency Heat, however, is a manual override. It doesn't turn off once the house gets warm; it stays as the sole heat source until you manually switch the thermostat back to "Heat." You should only be doing this if something is actually wrong.
When should you actually flip that switch?
As the name suggests, you should only use emergency heat in an actual emergency. Here are a few scenarios where it makes sense:
- The outdoor unit is encased in ice: If a winter storm hits and your outdoor heat pump is literally a block of ice, it can't breathe or move air. While the unit has a "defrost mode" to handle light frosting, it can't handle being buried in a snowbank or thick ice. In this case, switch to Em Heat until you can safely clear the ice.
- The outdoor unit is making scary noises: If you hear grinding, loud banging, or the fan won't spin, something is wrong with the compressor or the motor. Turn the system to Em Heat to stay warm while you wait for a technician to show up.
- The heat pump has failed completely: If the outdoor unit isn't running at all and your house is getting colder, Em Heat is your literal lifesaver. It'll keep your pipes from freezing and your family comfortable until repairs are made.
Does it heat your house faster?
A common myth is that if you come home to a cold house, switching to emergency heat will warm it up faster. While the air coming out of the vents feels hotter to the touch (usually around 120 degrees compared to the 90-100 degrees of a heat pump), it isn't necessarily a "turbo" button for your HVAC.
Most thermostats are smart enough to kick on the auxiliary heat anyway if they notice a big gap (usually more than 2 degrees) between the current temperature and the set temperature. So, manually switching to emergency heat doesn't really save you time; it just ensures you're paying the maximum possible price for that warmth by disabling the efficient half of your system.
Keeping your system healthy
To avoid needing that emergency switch, it helps to do a little bit of maintenance. Make sure your outdoor unit isn't blocked by leaves, tall grass, or snow. Check your air filters regularly—a clogged filter makes the heat pump work way harder than it needs to, which might trigger the aux heat more often than necessary.
If you notice your system staying in "Aux Heat" mode even when it's 50 degrees outside, that's a sign that your heat pump might be low on refrigerant or having a mechanical issue. In that case, you're basically paying for emergency heat prices without even realizing it.
The bottom line
In short, the difference between heat and emergency heat is all about efficiency versus reliability. The "Heat" setting is your everyday, budget-friendly friend that works slowly but steadily by moving heat from the outside. "Emergency Heat" is your expensive, power-hungry backup that you only call when the primary system can't do its job.
Unless your outdoor unit is broken or completely frozen over, keep it on the regular "Heat" setting. Your wallet will definitely thank you when the winter ends!