That EM HEAT or EMER HEAT label on your thermostat isn’t a glitch — but activating it at the wrong time is one of the most expensive thermostat mistakes we see homeowners make.
At FilterClarity.com, we’ve tracked how emergency heat affects both energy bills and system wear across real households. What we’ve found consistently surprises people: most homeowners who trigger EM heat don’t actually need it, and those who do often leave it on far too long.
This page gives you the straight answer — what EM heat is, exactly when it’s appropriate, and what it’s likely adding to your monthly bill if it’s running right now.
TL;DR Quick Answers
EM Heat Meaning
EM heat means emergency heat. It is a manual backup heating mode found only on heat pump thermostats.
What it does:
- Shuts your heat pump off completely.
- Runs your backup heat source alone — electric resistance coils, gas, or oil.
- Keeps your home warm at significantly higher energy cost.
When to use it:
- Only when your heat pump has failed or been physically damaged.
- Never for cold weather alone.
What it costs:
- A functioning heat pump delivers approximately 10,300 Btu per kilowatt-hour.
- EM heat delivers approximately 3,400 Btu for the same electricity.
- That’s nearly 3x less efficient than normal heat pump operation.
At FilterClarity.com, the most common EM heat mistake we see is homeowners leaving it on after a cold snap without realizing it. The home feels normal. The bill does not.
Top Takeaways
- EM heat is for emergencies only. Use it when your heat pump has failed — not because it’s cold outside.
- EM heat is up to three times less efficient than normal heat pump operation. That gap shows up directly on your monthly bill.
- Space heating is already 42% of your home’s total energy use. Running EM heat unnecessarily compounds your single largest household expense.
- AUX heat and EM heat are not the same thing. AUX assists your heat pump automatically. EM shuts it off entirely. Knowing the difference can save you hundreds.
- Unexpectedly high heating bills are often an installation problem, not a thermostat problem. Improper backup heat strip controls are one of the most commonly violated heat pump installation practices in the U.S. If your system reaches for backup heat more than it should, get a certified technician to check your installation.
Table of Contents
What Is EM Heat or Emer Heat on a Thermostat?
EM heat stands for emergency heat. It’s a backup heating mode found exclusively on heat pump systems—you won’t see it on gas furnaces or standard central air setups.
In normal operation, your heat pump pulls warmth from outdoor air and transfers it inside. It’s efficient, cost-effective, and designed to handle most cold-weather conditions. Emergency heat bypasses that process entirely. It activates a secondary heating element—typically electric resistance coils or, in some systems, a gas or oil backup—and heats your home directly.
Think of it this way: your heat pump is the efficient route. Emergency heat is the detour. It gets you there, but it costs significantly more to travel.
How Does Emergency Heat Actually Work?
Most heat pump systems are installed with two stages of heat:
- Stage 1 is the heat pump itself — the primary, energy-efficient source.
- Stage 2 is the auxiliary or backup heat—electric strips, gas, or oil that kicks in automatically when the heat pump needs support.
When you manually switch to EM heat, you’re cutting Stage 1 off entirely and running Stage 2 on its own, full time. The heat pump compressor shuts down. Your backup system carries the full load.
Your thermostat will typically display an indicator light or alert when EM heat is active. If you see it and didn’t intentionally turn it on, your system may be signaling a heat pump problem that needs professional attention.
When Should You Actually Use Emergency Heat?
This is where most homeowners get it wrong. Emergency heat is not a cold-weather performance boost. It’s a contingency mode for one specific situation: your heat pump has failed or is damaged and cannot operate.
Use EM heat when:
- Your heat pump is visibly damaged — a fallen tree limb, ice accumulation that won’t clear, or a refrigerant leak.
- Your HVAC technician has advised you to disable the heat pump while awaiting repair.
- The outdoor unit has completely stopped functioning and you need heat to protect your household while you arrange service.
Do not use EM heat because it’s very cold outside. Modern heat pumps are engineered to operate efficiently in temperatures well below freezing. In our experience at FilterClarity.com, this is the most common misunderstanding we see — homeowners switching to EM heat during cold snaps thinking it will perform better, when in fact it just costs more.
Is Emergency Heat Costing You More?
Yes — significantly more, in most cases.
Electric resistance heating, the most common backup source in EM heat systems, converts electricity to heat at roughly a 1:1 ratio. Your heat pump, by contrast, can deliver two to four units of heat for every one unit of electricity consumed, depending on outdoor conditions.
Running emergency heat for an extended period can increase your heating costs by 50% or more compared to normal heat pump operation. For a household spending $150 per month on heating, that could mean an added $75 or higher per billing cycle — every cycle it stays on.
We’ve seen real households at FilterClarity.com report bill increases of $100 or more after leaving EM heat active through a cold stretch without realizing it. The system heats the home effectively, so there’s no obvious symptom to tell you something is wrong. The bill is often the first sign.
Auxiliary Heat vs. Emergency Heat: What’s the Difference?
These two terms get conflated constantly, and the distinction matters.
Auxiliary heat activates automatically. When outdoor temperatures drop low enough that the heat pump alone can’t maintain your set temperature, your system brings in the backup heat source to assist. Both Stage 1 and Stage 2 run together. This is normal, expected behavior.
Emergency heat is manual. You switch it on. It disables the heat pump entirely and runs only the backup system. Nothing about this mode is automatic or self-correcting.
If your thermostat shows “AUX” on a cold day, that’s normal operation. If it shows “EM” or “EMER” and you didn’t activate it, check your heat pump immediately.
What to Do If You’ve Been Running EM Heat by Mistake
First, switch your thermostat back to the standard heat setting. Your system will return to normal heat pump operation.
Next, monitor your heat pump’s outdoor unit for the next full heating cycle. You should hear it running and feel warm air moving through your vents within a few minutes of the thermostat calling for heat. If the outdoor unit stays quiet or the heat pump fails to engage, contact an HVAC technician — your system may have an underlying issue that triggered the confusion in the first place.
Finally, review your last one to two energy bills. If costs spiked unexpectedly during a period you weren’t aware EM heat was active, that’s likely your explanation.
“In our testing and research at FilterClarity.com, the single most costly thermostat habit we’ve documented is homeowners manually switching to emergency heat during cold snaps — believing it performs better when temperatures drop, when in reality they’re simply trading an efficient system for an expensive one.”
The 7 Most Trusted Resources for Understanding EM Heat and Heat Pump Efficiency
Researching emergency heat means sorting through a lot of contractor opinions and manufacturer marketing. We’ve done that work for you at FilterClarity.com. Every source below is government-verified, industry-certified, or utility-backed — chosen because it gives you unbiased, actionable information, not a sales pitch.
1. How Heat Pumps Actually Work — and When Backup Heat Kicks In
Source: U.S. Department of Energy
Best for: Homeowners who want to understand the full picture before touching that EM heat switch.
Your heat pump’s job is to move heat, not make it. The DOE’s core heat pump resource explains that efficiency gap in plain terms — and shows you exactly where backup heating fits into a properly functioning system. If you only read one resource before making any thermostat decision, start here.
2. The Real Reason Your System Might Lean on Backup Heat Too Often
Source: U.S. Department of Energy
Best for: Homeowners whose systems seem to run auxiliary or emergency heat more than they should.
Oversized backup heat use isn’t always a thermostat problem. This DOE resource walks through how air-source heat pump efficiency ratings, auxiliary heat strip wiring, and installation quality all affect how often your system reaches for backup heat. A system that triggers EM heat frequently may have an installation issue, not a temperature problem.
3. What Federal Certification Tells You About Your Heat Pump’s Cold-Weather Limits
Source: U.S. Environmental Protection Agency
Best for: Homeowners wondering whether their heat pump is actually built to handle cold temperatures without defaulting to backup heat.
Not all heat pumps perform equally in cold weather. The EPA’s ENERGY STAR program tests certified systems down to 5°F, so you can see exactly where your unit’s efficiency holds — and where it starts to struggle. Knowing your system’s certified performance range is the fastest way to judge whether your EM heat use is a real necessity or a habit worth breaking.
4. Why Cold Weather Alone Is Not a Reason to Switch to EM Heat
Source: U.S. Department of Energy
Best for: Homeowners who’ve been told — or assumed — that freezing temperatures require switching to emergency heat mode.
This is the resource we point to most often at FilterClarity.com when homeowners ask us whether cold snaps justify EM heat use. The DOE’s Cold Climate Heat Pump Challenge documents how modern systems deliver reliable, efficient heating well below 32°F. The short answer: your heat pump can almost certainly handle the cold. Emergency heat mode usually can’t.
5. The Industry Standards That Define How Efficiently Your System Heats
Source: Air-Conditioning, Heating and Refrigeration Institute (AHRI)
Best for: DIYers and detail-oriented homeowners who want to understand what HSPF2 efficiency ratings actually mean in practice.
Every heat pump sold in the U.S. is tested against AHRI’s efficiency standards. Understanding the updated 2023 metrics — including HSPF2, which measures heating efficiency across a full season — helps you evaluate whether your system is performing as rated or quietly underperforming in ways that make backup heat use higher than it should be.
6. The Connection Between Your Heating Mode and Your Indoor Air Quality
Source: U.S. Environmental Protection Agency
Best for: Homeowners who care about more than just the energy bill — specifically, how heating system decisions affect the air you’re breathing.
Most homeowners think about EM heat purely as a cost issue. It’s also an air quality issue. The EPA’s indoor air quality guidance explains how heating system operation affects ventilation rates and airborne pollutant levels inside your home. Extended emergency heat use changes how air moves through your system in ways that matter beyond the monthly bill.
7. A Utility’s No-Nonsense Explanation of Why EM Heat Costs More
Source: Craighead Electric Cooperative
Best for: Homeowners who want a straightforward, non-commercial answer to why emergency heat hits the wallet harder than normal heat pump operation.
This one comes from an electric utility cooperative — not an HVAC contractor with equipment to sell. It explains, in plain language, why electric resistance backup heat converts one unit of electricity into one unit of heat, while your heat pump delivers two to four units of heat for the same electricity. That gap is exactly why your bill spikes when EM heat runs longer than it should.
Supporting Statistics
At FilterClarity.com, we pair the data with what we’ve observed firsthand. Here’s what the research tells us about emergency heat and home heating costs.
Stat #1: Space Heating Accounts for 42% of a Home’s Total Energy Consumption
Space heating is the single largest energy-consuming end use in U.S. homes, accounting for 42% of total residential energy consumption, per the EIA’s 2020 Residential Energy Consumption Survey.
- Nearly half your energy budget goes to heating before anything else runs.
- EM heat misuse inflates your single largest household expense — not a minor surcharge.
- Most homeowners we hear from didn’t switch EM heat on deliberately. They forgot to turn it off.
Stat #2: A Heat Pump Delivers Up to Three Times More Heat Per Kilowatt-Hour Than EM Heat
A 10.3 HSPF heat pump provides 10,300 Btu per kilowatt-hour. An electric resistance element — the technology behind most EM heat systems — delivers only approximately 3,400 Btu for the same kilowatt-hour, per the U.S. Department of Energy.
- Your heat pump produces roughly 3x more heat per dollar than EM heat.
- The DOE confirms heat pumps cut electricity use by 50% compared to electric resistance heating in most climates.
- EM heat isn’t slightly more expensive. It’s the least efficient heating mode your system has.
Stat #3: Improper Backup Heat Controls Are Among the Most Common Heat Pump Installation Violations Nationwide
Energy codes require controls to prevent unnecessary heat strip operation in heat pump systems. The DOE identifies improper backup heat strip control as one of the most commonly violated heat pump installation practices in the U.S.
- High heating bills aren’t always a thermostat problem. Often they’re an installation problem.
- Many homeowners aren’t triggering EM heat themselves — a missing safeguard is doing it for them.
- At FilterClarity.com, misconfigured backup heat controls are one of the most consistent patterns behind unexpectedly high heating bills we see reported.
Watch for these warning signs:
- AUX or EM heat runs frequently in mild weather.
- Your outdoor unit cycles off earlier than expected.
- Your bills run higher than neighbors with similar systems.
If any of these apply, a certified HVAC technician review is the right next step.
FAQ on EM Heat Meaning
Q: What does EM heat mean on a thermostat?
A: EM heat stands for emergency heat. It is a manual backup heating mode found only on heat pump systems.
When activated:
- Your heat pump shuts off completely.
- Your secondary heat source takes over — typically electric resistance coils, gas, or oil.
- Your home stays warm, but at a significantly higher energy cost.
At FilterClarity.com, the question we get most isn’t what EM heat is. It’s why it’s on when the homeowner never turned it on. The label is easy to activate accidentally, and the only warning you get is a higher bill at the end of the month if your filters and system aren’t working together efficiently.
Q: When should I use EM heat?
A: Only when your heat pump has failed or been physically damaged.
Legitimate reasons to activate EM heat:
- A fallen tree limb or debris has damaged your outdoor unit.
- A refrigerant leak has been confirmed.
- Your compressor has completely stopped functioning.
Never use EM heat because it’s cold outside. Modern heat pumps are engineered to handle subfreezing temperatures efficiently. In our experience at FilterClarity.com, cold-weather misuse is the most common and most costly EM heat mistake we document.
Q: Does EM heat cost more to run?
A: Yes — significantly more than most homeowners expect.
The efficiency gap in plain numbers:
- Heat pump: approximately 10,300 Btu per kilowatt-hour.
- EM heat: approximately 3,400 Btu per kilowatt-hour.
- That’s nearly 3x less output for the same electricity cost.
What makes this worse:
- Space heating already accounts for 42% of a home’s total energy use.
- EM heat compounds your single largest household expense.
- A home running EM heat feels identical to a home running normal heat. There’s no comfort signal telling you something is wrong. The bill is the only indicator.
At FilterClarity.com, the efficiency gap itself rarely surprises homeowners. How fast it accumulates does.
Q: What is the difference between EM heat and AUX heat?
A: They are not the same thing. Confusing the two is responsible for more unnecessary EM heat use than almost anything else we see at FilterClarity.com.
AUX heat:
- Activates automatically.
- Runs alongside your heat pump for extra support in cold weather.
- Is normal system behavior.
EM heat:
- Activated manually by you.
- Shuts your heat pump off entirely.
- Runs backup heat alone — at full cost, with no heat pump efficiency.
The practical rule: if your thermostat shows AUX on a cold day, your system is working correctly. If it shows EM and you didn’t activate it, inspect your heat pump immediately.
Q: How do I know if my EM heat is on by mistake?
A: Your thermostat will display an EM, EMER, or emergency heat indicator when the mode is active.
Watch for these signs:
- The EM or EMER indicator is lit on your thermostat display.
- Your energy bill spikes without a clear explanation.
- Your outdoor unit is not running during a heating cycle.
If you find EM heat running unintentionally:
- Switch your thermostat back to standard heat immediately.
- Monitor your outdoor unit through the next full heating cycle.
- If the outdoor unit stays quiet, contact a certified HVAC technician.
At FilterClarity.com, accidental EM heat activation is often the system’s way of flagging an underlying problem. If it switched on without your input, your heat pump may already be trying to tell you something is wrong.
Now That You Know What EM Heat Means, Check Your Thermostat Today
If your thermostat is showing EM or EMER right now — and you didn’t turn it on — your heat pump needs attention before your next energy bill does. Browse our HVAC troubleshooting guides at FilterClarity.com to diagnose the problem, keep your filters changed on schedule, and get your system back to efficient, cost-effective heating.