That mysterious “EM” on your thermostat stands for emergency heat—a backup setting designed for heat pump systems. At Filterbuy, we’ve seen firsthand how a misunderstood thermostat setting leads to sky-high energy bills and unnecessary service calls. Our experience working with thousands of homeowners across the country has taught us one thing: most people activate EM heat when they don’t need to, and skip it when they actually do. This guide gives you the straight answer on what EM heat means, when to use it, and how to avoid the mistakes that cost real money—backed by what we’ve learned from helping families keep their HVAC systems running efficiently every season.
TL;DR Quick Answers
EM heat stands for emergency heat. It’s a manual thermostat setting on heat pump systems that bypasses the outdoor unit and activates backup heating—typically electric resistance coils. Use EM heat only when your heat pump has failed or is frozen and won’t defrost. It is not designed for daily use. Running EM heat when your system is functioning normally wastes energy and can cost 3–4 times more per hour than standard heat pump operation. If you see EM heat on your thermostat, switch it on only temporarily and call a professional for service. While you wait, check that your HVAC air filter is clean—a clogged filter restricts airflow and can make heating problems worse.
Top Takeaways
EM heat stands for emergency heat. It’s a manual thermostat setting that shuts down your heat pump and runs only on backup heating.
Only use it in a real emergency. Activate EM heat when your heat pump stops working, the outdoor unit is frozen and won’t defrost, or you need temporary warmth while waiting for repair.
EM heat is not aux heat. Aux heat works automatically alongside your heat pump. EM heat bypasses the heat pump entirely and costs significantly more to run.
Running EM heat unnecessarily can cost 3–4x more per hour. Electric resistance backup is far less efficient than your heat pump’s normal operation.
Regular HVAC maintenance prevents emergencies. Replace your air filter on schedule, keep up with annual service, and clear your outdoor unit to reduce the risk of heat pump failures that require EM heat.
How Your Heat Pump Normally Works
A heat pump heats your home by pulling warmth from outdoor air and transferring it inside. Even in cool weather, there’s enough thermal energy in the air for your heat pump to do its job efficiently. When temperatures drop very low, your system automatically activates auxiliary (aux) heat—a secondary boost that assists the heat pump without shutting it down. This process happens on its own and requires no action from you. However, proper air filtration plays a supporting role—when your filter is clean, air flows freely through the system, allowing your heat pump to operate at peak efficiency.
What EM Heat Actually Does
EM heat—short for emergency heat—is a manual thermostat setting that bypasses your heat pump entirely. When you switch to EM heat, you’re telling your system to stop using the outdoor unit and rely solely on the backup heat source. That backup is typically electric resistance coils, though some systems use a gas or oil furnace. The key difference from aux heat is control: aux heat activates automatically alongside your heat pump, while EM heat shuts the heat pump down completely and runs only on the backup.
When to Use Emergency Heat
Activate EM heat only in genuine emergency scenarios:
Your heat pump has stopped producing heat entirely.
The outdoor unit is frozen solid and will not defrost.
You need temporary warmth while waiting for a professional repair.
Do not switch to EM heat simply because it’s cold outside. Your heat pump and its automatic aux heat setting are designed to handle cold weather on their own. Running EM heat when it’s not needed wastes significant energy and drives up your utility costs.
EM Heat vs. Aux Heat: Know the Difference
Understanding the distinction prevents costly errors:
Aux Heat: Automatic. Works alongside your heat pump to supplement warmth during cold spells. No action required from you.
EM Heat: Manual. Shuts down the heat pump and relies entirely on the backup source. Uses significantly more energy. Activate only when the heat pump fails.
The Cost of Getting It Wrong
Emergency heat uses electric resistance coils in most setups, which consume far more electricity than a heat pump. Running EM heat can cost three to four times more per hour than standard heat pump operation. What might normally cost around $0.50 per hour could jump to $2.00 or more. Over days or weeks, those costs add up fast. That’s why EM heat should be a temporary solution—not a daily heating strategy.
“In our experience helping homeowners maintain their HVAC systems, we’ve found that most EM heat problems aren’t equipment failures—they’re knowledge gaps. Something as simple as replacing a dirty HVAC filter or choosing the right MERV rating can keep a system from overworking and needing emergency heat. A homeowner who understands their thermostat settings and their filtration needs can save hundreds of dollars a season and avoid unnecessary emergency service calls altogether.”
— Filterbuy HVAC Solutions Team
Essential Resources on Em Heat Meaning
At Filterbuy, we believe informed homeowners make the best decisions for their families and their systems. We’ve hand-selected these resources from trusted government, educational, and nonprofit sources to give you the most reliable information on heat pump systems and emergency heat.
1. Understand How Your Heat Pump System Works
The U.S. Department of Energy’s heat pump guide explains how air-source and geothermal systems transfer heat, helping you see exactly why EM heat should be a last resort—not a first response.
Source: https://www.energy.gov/energysaver/heat-pump-systems
2. Learn What Drives Your Home’s Energy Costs
The EIA’s residential energy use breakdown shows that heating and cooling account for over half of household energy consumption. Understanding this helps you see the real cost impact of running EM heat unnecessarily.
Source: https://www.eia.gov/energyexplained/use-of-energy/homes.php
3. Compare Heat Pump Types for Your Climate
The EPA’s heat pump overview covers air-source, geothermal, and ductless options—plus available federal tax credits that can offset upgrade costs.
Source: https://www.epa.gov/burnwise/heat-pumps
4. Maximize Heat Pump Performance with Proper Maintenance
DOE’s maintenance guide covers thermostat settings, filter changes, and annual service—all of which help prevent the breakdowns that trigger EM heat activation in the first place.
Source: https://www.energy.gov/energysaver/operating-and-maintaining-your-heat-pump
5. See If a Heat Pump Can Lower Your Bills
DOE research shows that for over 90% of assessed U.S. households, the right heat pump replacement can reduce energy bills—making the switch away from EM heat reliance a financially sound move.
Source: https://www.energy.gov/policy/articles/most-americans-heat-pump-can-lower-bills-right-now
6. Explore Air-Source Heat Pump Efficiency Ratings
DOE’s air-source heat pump page explains HSPF and SEER ratings, helping you evaluate whether your current system is efficient enough to handle cold weather without frequent EM heat use.
Source: https://www.energy.gov/energysaver/air-source-heat-pumps
7. Review Winter Heating Cost Forecasts
EIA’s Residential Energy Consumption Survey offers data on household heating expenditures by fuel type and region—giving you a benchmark for what your heating should actually cost.
Source: https://www.eia.gov/consumption/residential/
Supporting Statistics
At Filterbuy, we rely on real data—not guesswork—to help homeowners make informed decisions about their heating systems. These statistics highlight why understanding your EM heat setting matters for your wallet and your home’s efficiency.
Heating and cooling account for 52% of a typical household’s annual energy consumption. Running EM heat unnecessarily adds directly to this cost. In our experience, homeowners who understand when to use EM heat versus aux heat—and who maintain proper HVAC filtration—can cut avoidable heating expenses significantly during peak winter months.
Source: https://www.eia.gov/energyexplained/use-of-energy/homes.php
In 2024, 42% of U.S. households reported electricity as their main space heating fuel. With more homes relying on electric heat pumps, the EM heat setting is relevant to a growing share of American households. We’ve seen this trend firsthand—more customers than ever are asking what that EM setting actually does.
Source: https://www.eia.gov/todayinenergy/detail.php?id=66324
Air-source heat pumps can deliver up to 2–4 times more heat energy than the electricity they consume. That’s why bypassing your heat pump with EM heat is so costly—electric resistance backup can’t match that efficiency. From what we’ve observed working with homeowners, the energy cost difference between running a heat pump versus EM heat can be 3–4x per hour of operation.
Source: https://www.energy.gov/energysaver/air-source-heat-pumps
Final Thoughts & Opinion
Understanding the EM heat setting on your thermostat is one of the simplest ways to protect your wallet and your comfort during winter. The key takeaway is straightforward: EM heat is a backup for genuine emergencies—not a substitute for your heat pump’s normal operation.
Our perspective: At Filterbuy, we’ve worked with thousands of homeowners who activated EM heat simply because it was cold. In nearly every case, their heat pump and aux heat were more than capable of handling the job. The result of switching to EM heat prematurely? Heating bills that doubled or tripled with no improvement in comfort.
Prevention matters more than reaction. Regular maintenance—replacing your air filter with the right MERV rating, scheduling annual professional HVAC service, and clearing debris from your outdoor unit—reduces the likelihood of a heat pump failure that would require EM heat in the first place.
When in doubt, call a professional. If EM heat activates on its own or your system isn’t maintaining temperature, that’s a signal to schedule a service call—not to leave it running indefinitely.
The bottom line: know your system, maintain it properly, and reserve EM heat for what it was designed for—emergencies only.
FAQ on Em Heat Meaning
Q: What does EM heat mean on my thermostat?
A: EM heat stands for emergency heat. It’s a manual setting on heat pump thermostats that bypasses the outdoor heat pump unit and relies entirely on a backup heat source—usually electric resistance coils, gas, or oil. At Filterbuy, we’ve found that most homeowners encounter this setting for the first time during a cold snap and aren’t sure what it does. The short answer: it’s your system’s safety net, not its everyday operating mode.
Q: Should I turn on EM heat when it’s very cold outside?
A: No. Your heat pump is designed to operate in cold weather, and it will automatically activate auxiliary heat when it needs a boost. Switching to EM heat manually shuts down the heat pump and forces your system to run solely on expensive backup heating. In our experience, homeowners who flip to EM heat “just because it’s freezing” see their energy bills spike dramatically with no real comfort improvement.
Q: What is the difference between EM heat and aux heat?
A: Aux heat (auxiliary heat) activates automatically to supplement your heat pump during cold conditions. Both systems work together. EM heat is a manual override that shuts the heat pump down completely, relying 100% on backup heating. From what we’ve seen at Filterbuy, confusing the two is one of the most common and expensive thermostat mistakes homeowners make.
Q: How much more does EM heat cost to run?
A: EM heat can cost three to four times more per hour than standard heat pump operation. While a heat pump might cost roughly $0.50 per hour to run, emergency heat using electric resistance coils could cost $2.00 or more per hour. Over a full day or week, those costs accumulate fast. That’s why we always advise treating EM heat as a temporary measure—not a long-term heating solution.
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