What Is Emergency Heat on a Heat Pump and When Should You Use It? A Tupelo HVAC Tech Explains
HVAC, Heat Pumps, Emergency Heat
What Is Emergency Heat on a Heat Pump and When Should You Use It? A Tupelo HVAC Tech Explains
I’m Dan, owner and lead technician at S.I. Service Group here in Tupelo, and every first cold snap in North Mississippi my phone blows up with the same question: “Do I need to turn on that EM HEAT setting on my thermostat?” Let’s talk about what that button really does, when you actually need it, and how to keep your power bill from going through the roof.
First Cold Snap Story: Why That EM HEAT Light Freaks Folks Out
A couple of Octobers ago, we got that first real cold morning—about 34 degrees—up in Saltillo. I pulled up to a house where the homeowner met me in a jacket and flip-flops, pointing at his thermostat like it was about to explode. The EM HEAT light was on, the outdoor unit was steaming, and he was sure the thing was on fire or frozen solid. He’d flipped the switch to emergency heat because “it felt cold” and then watched his power meter spin like a slot machine.
Nothing was actually broken. The heat pump was doing its job. The problem was the thermostat setting and a little misunderstanding about what heat pump emergency heat really is. That’s what I want to clear up for you today—so when it hits the 20s in Tupelo, Verona, or Mantachie, you know exactly what to do and what not to touch.
What Does the EM HEAT Setting Actually Do?
Heat Pump vs. Electric Heat Strips in Plain English
Your heat pump really has two different ways it can heat your house:
- The heat pump itself – that outdoor unit with the fan and compressor. It works kind of like an air conditioner in reverse, pulling heat from the outside air and moving it inside. Even when it’s cold, there’s still some heat out there to grab. This is the efficient part of your system.
- The electric resistance heat strips – these live inside your indoor air handler. Think of them like giant toaster coils. Electricity runs through them, they glow hot, and your blower pushes air across them into your ductwork.
When you flip the thermostat to EM HEAT, you’re telling the system: “Turn the outdoor unit OFF and heat my house with the electric strips only.” No compressor, no outdoor fan—just those power-hungry strips doing all the work. That’s why the EM HEAT light comes on: it’s a warning that you’re in backup mode, not normal operation.
Why Emergency Heat Costs So Much More to Run
The U.S. Department of Energy will tell you heat pumps are very efficient because they move heat instead of making it. A heat pump can often give you two to three units of heat for every one unit of electricity it uses. Those electric strips? They give you about one-for-one—no multiplier effect like with the compressor (DOE: Heat Pump Systems) .
Emergency Heat vs. Auxiliary Heat: Not the Same Thing
- Auxiliary heat (AUX HEAT) – This kicks on automatically when the thermostat senses the heat pump can’t keep up by itself. Maybe it’s 20 degrees in Amory and the house is struggling to reach 70. The thermostat adds in the electric strips along with the heat pump to help it out. You don’t have to touch anything; it’s built into the control logic.
- Emergency heat (EM HEAT) – This is a manual override. You flip the switch, and the thermostat turns the outdoor unit off and runs on strips only, like we talked about above. It’s meant for when something is wrong with the outdoor unit, or conditions are extreme enough that you don’t want that unit running.
When You SHOULD Use Emergency Heat in North Mississippi
1. Outdoor Unit Frozen Solid and Not Defrosting
I’m not talking about a light layer of frost. I’m talking block of ice—fan blades encased, coil buried, top covered. I saw this in Mooreville last January after a wet, windy night. The unit had a defrost control issue and never switched into defrost mode, so it just kept building ice until it choked itself out.
In that situation, yes—flip to EM HEAT. That lets the outdoor unit rest and prevents more damage while we come out to fix the defrost board or sensor. Then call a pro for heat pump repair before you burn through a week of high-dollar strip heat.
2. Compressor or Outdoor Fan Is Down
If you walk outside in Plantersville and the house is cold, and you notice the indoor fan is running but the outdoor unit is dead silent—no fan, no compressor, maybe even a buzzing or humming—go ahead and switch to EM HEAT. That tells the system to stop trying to run a sick compressor and just use the backup strips until we can get there for HVAC repair .
3. Ice Storm or Dangerous Conditions Around the Outdoor Unit
During that bad ice event we had a few winters back, I was out near Fulton and Mantachie seeing branches snap and power lines sag. If your outdoor unit is buried in ice, or there’s falling limbs and you’re worried about physical damage, you can shut off power to the outdoor unit at the disconnect and run EM HEAT inside until things thaw out or we can safely get to you. It’ll keep pipes from freezing and your family from shivering.
When You Should NOT Use Emergency Heat (The 40-Degree Mistake)
Here’s the most common mistake I see around Tupelo and New Albany: It’s 40–45 degrees, a little damp, and the house feels chilly. Somebody thinks, “It’s cold outside, this heat pump can’t handle it,” and they flip the stat to EM HEAT “to help it out.”
That’s backwards. At 40 degrees, your heat pump is in its sweet spot. It might need a little auxiliary help now and then, but it’s absolutely capable of heating your home efficiently. When you choose EM HEAT, you’re actually shutting off the efficient part and going straight to the expensive backup. You’ll feel warm, sure—but you’ll pay for it next month when the bill shows up.
So in normal North Mississippi fall and winter weather—30s and 40s, maybe dipping into the 20s at night—leave that thermostat on regular HEAT. Let the system decide when to bring on AUX. Save EM HEAT for when something is wrong or conditions are extreme.
What a Normal Defrost Cycle Looks Like (Don’t Panic at the Steam)
- When it’s cold and damp, frost builds up on the outdoor coil as the heat pump runs.
- Every so often, the unit switches into defrost mode. It briefly runs like an air conditioner to warm the outdoor coil and melt the ice.
- You’ll see steam rising off the unit, and sometimes the outdoor fan will stop for a few minutes. Inside, the strips may kick on as AUX heat so you don’t feel cold air.
That steam is just water vapor—frost melting off. As long as it cycles back to normal after a few minutes and the whole unit isn’t encased in ice, that’s just your system taking care of itself. No need to flip to EM HEAT or kill the power. If you’re seeing constant ice buildup that never clears, that’s when it’s time to call for heat pump repair .
Thermostat Setting Tips for North Mississippi Fall and Winter
Set It, Program It, and Let the Heat Pump Work
Around Tupelo, Saltillo, and Verona, our winters are more “up and down” than “brutal.” That actually works great for a heat pump. Here’s how I tell most homeowners to run theirs:
- Pick a comfortable temp—usually 68–70°F during the day for most families.
- If you like it cooler at night, drop it 2–3 degrees, not 10–15. Big swings can make AUX heat kick on more than needed.
- Don’t keep bumping the stat up and down all day. That constant chasing makes the system run longer and can trigger AUX more often.
Signs Your Heat Pump Needs Repair (Before You Rely on EM HEAT)
Emergency heat is a backup, not a band-aid. If you’re seeing these signs in Tupelo, Plantersville, or Mooreville, it’s time to call for heat pump repair instead of just flipping that EM HEAT switch and forgetting about it:
- House never reaches set temperature – It runs and runs, but you’re always 2–4 degrees shy of the thermostat setting, even on mild days.
- Unusual noises – Grinding, squealing, or loud rattling from the outdoor unit or air handler. A little hum is normal; banging is not.
- Power bill suddenly jumps – If your usage pattern hasn’t changed but the bill shoots up, your strips may be running too often or the heat pump may not be carrying its share.
What to Check Before You Call the HVAC Guy
I’m in business to fix systems, but I’m also not out here trying to charge you for a flipped switch. Before you call S.I. Service Group out to your place in Tupelo, Amory, or Fulton, here are a few simple checks you can safely do yourself:
- Check the filter. If it’s caked with dust, your system can’t move air. Change it and give the system an hour to catch up.
- Look at the thermostat mode. Make sure it’s on HEAT, not “EM HEAT” or “COOL” or just “OFF.” I see this every year in homes from Verona to New Albany.
- Check the breakers. You’ll usually have one breaker for the air handler and one or two for the outdoor unit/strips. If one is tripped, reset it once. If it trips again, leave it off and call for HVAC repair —something’s wrong down the line.
Why a Fall Tune-Up Matters for Heat Pumps in Tupelo and North Mississippi
When we come out for a fall HVAC maintenance visit on your heat pump in Tupelo, Saltillo, or Mooreville, here’s some of what we do:
- Check refrigerant levels and look for leaks, so the heat pump can actually move enough heat.
- Inspect and clean the outdoor coil and indoor coil for good airflow and heat transfer.
- Test the defrost cycle so you don’t end up with a block of ice when the first freeze hits.
- Verify strip heat operation and make sure the thermostat is calling for AUX and EM correctly—not overusing strips when it doesn’t need to.
Frequently Asked Questions About Heat Pump Emergency Heat
1. Is it bad to run emergency heat all the time?
“Bad” depends on what you mean. Will it heat your house? Yes. Will it run your power bill up in Tupelo or North Mississippi? Absolutely. Those electric strips are meant as backup. If you run EM HEAT all winter, you’re basically heating your house with giant space heaters. You’re not hurting the equipment by itself, but you’re definitely hurting your wallet—and you might be ignoring a real problem with the heat pump that needs attention from an HVAC repair North Mississippi pro.
2. At what temperature should a heat pump switch to emergency heat?
There’s no outdoor temperature where you should switch to EM HEAT just because it’s cold. Modern heat pumps are designed to work in pretty low temperatures (Consumer Reports on cold-weather heat pumps) . In North Mississippi, we rarely get cold enough to truly “need” emergency heat based on temperature alone. EM HEAT is for equipment problems or ice storms, not for 25-degree mornings.
3. Why does my thermostat say AUX HEAT sometimes?
AUX HEAT means the thermostat decided the heat pump needed a little help. Maybe the temperature dropped fast, or you bumped the stat up a couple degrees and it wants to warm you up quicker. The strips come on with the heat pump. That’s normal in cold snaps. If you see AUX HEAT on all the time, even on 40-degree days, that’s worth a call to check the system out.
4. Is a heat pump really a good idea in Tupelo, MS?
Yes. Our climate is actually perfect for heat pumps. We get hot summers and mostly mild winters with a few cold snaps. A properly sized, well-maintained heat pump Tupelo MS setup will usually beat straight electric heat on efficiency and comfort. The key is understanding how emergency and auxiliary heat work so you’re not accidentally burning money every time it dips below 40.
Conclusion: Treat Emergency Heat Like the Backup It Is
Use EM HEAT when the outdoor unit is frozen solid, clearly broken, or in dangerous ice-storm conditions. Trust AUX HEAT to kick in automatically when the system needs a hand. Keep your filters clean, your thermostat set steady, and your system maintained. Do that, and you’ll stay comfortable in Tupelo, Saltillo, Verona, Plantersville, Mooreville, Mantachie, Fulton, Amory, New Albany—without getting a power bill that makes you spit your coffee.
Need Help with Your Heat Pump in North Mississippi? Call S.I. Service Group
If you’re staring at that EM HEAT light, your outdoor unit’s a block of ice, or your house just won’t warm up, don’t guess. My crew and I work on heat pumps all over the Tupelo area every single day. We handle heat pump repair , HVAC repair , furnace repair , and seasonal HVAC maintenance to keep your system running like it should.
Give me, Dan at S.I. Service Group, a call at 662-523-5514 . We’ll get you squared away, explain what’s going on in plain language, and make sure that EM HEAT setting only gets used when you truly need it.
