When customers ask “what is EM heat?” they’re usually standing in front of their thermostat, unsure what to do next. I’ve had this conversation countless times during service calls. Although the label looks simple, the function behind it isn’t always obvious. Still, once you understand what emergency heat is and how it works, using it correctly becomes much easier.
At Whale Worth It! Plumbing, Heating & Air, we believe homeowners deserve clear explanations. So, instead of overloading you with technical jargon, let’s walk through this step by step.
EM Heat Explained: Why Thermostats Have This Setting
At its core, EM heat refers to emergency heat mode on a heat pump system. This setting tells your system to stop relying on the outdoor unit and switch to a backup heat source instead.
In most homes, that backup is electric resistance heat. Some systems use gas or oil instead. Either way, the goal stays the same: maintain indoor comfort when the primary heating system can’t keep up.
Emergency heat exists for one reason. It keeps your home warm when the heat pump can’t operate effectively on its own.
Because heat pumps pull warmth from outdoor air, their performance can be affected during extreme conditions. When outdoor temperatures drop too low, emergency heat provides a direct and reliable heat source inside the system.
According to the U.S. Department of Energy, extreme cold conditions can reduce heat pump performance, which is why backup heating is sometimes necessary.
EM Heat vs Auxiliary Heat: What’s the Difference
This is where confusion often starts. Although both settings provide backup heat, EM heat differs from auxiliary heat in an important way.
Aux heat turns on automatically when the system detects it needs extra help. Emergency heat, however, is manually activated by the homeowner. That manual switch changes how the system operates.
When you select emergency heat, the heat pump shuts off completely. Only the backup heat runs. Because of that, emergency heat uses more energy, but it can also help avoid stressing damaged equipment.
When EM Heat Should Be Used
Emergency heat isn’t meant for everyday comfort. It’s intended for specific situations when the heat pump can’t operate properly.
You may need to use EM heat when:
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the outdoor heat pump unit is frozen or damaged
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the heat pump stops running entirely
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outdoor temperatures are extremely low for extended periods
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a technician advises you to switch it on
In these situations, switching to emergency heat can help prevent further damage by taking the heat pump out of operation. While it costs more to run, it protects the system.
That trade-off is important for homeowners to understand.
How Emergency Heat Works Inside the System
When emergency heat is activated, airflow stays the same, but the heat source changes completely. The system bypasses the outdoor coil and heats air using internal resistance elements or a secondary furnace instead.
Because resistance heat generates warmth directly, it doesn’t depend on outdoor conditions. That’s why emergency heat works reliably during extreme weather or system issues.
However, that reliability comes at a cost. Efficiency drops sharply, which is why EM heat is meant to be temporary rather than a long-term heating solution.
Why EM Heat Increases Energy Costs
Many homeowners ask why their energy bills increase so quickly.
Because emergency heat relies on resistance heating, it uses significantly more electricity than a heat pump. Instead of transferring heat from outside, resistance heat generates warmth directly inside the system.
That difference matters. So while EM heat keeps your home warm, it can raise utility costs quickly.
That’s normal. It doesn’t mean the system is failing.
What EM Heat Is Not Designed For
It’s important to say this clearly. Emergency heat is a backup setting, not a replacement for normal system operation.
Emergency heat is not meant to:
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replace your heat pump long term
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run all winter
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improve comfort efficiency
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lower heating bills
Instead, it’s a safety net. It’s there when something isn’t right and temporary protection matters more than efficiency.
When Emergency Heat Should Be Turned Off
Once outdoor conditions improve or repairs are complete, emergency heat should be turned off. At that point, the heat pump can safely resume normal operation.
Leaving emergency heat on longer than necessary wastes energy and can mask underlying system problems. At Whale Worth It! Plumbing, Heating & Air, we often find systems stuck in EM heat without homeowners realizing it. That’s usually when utility bills spike unexpectedly.
If you’re unsure, it’s always better to ask.
How We Help Homeowners Use EM Heat Correctly
We don’t believe in one-size-fits-all advice. Every heat pump system behaves differently, and factors like climate, insulation, and equipment age all play a role.
That’s why we take the time to explain how EM heat works during service visits, not just online. If something feels off, it usually is, and early questions often prevent bigger problems later.
Understanding how weather impacts your system helps homeowners make smarter heating decisions and avoid unnecessary costs.
Emergency Heat and Why Professional Guidance Matters
Emergency heat can solve short-term comfort problems, but it doesn’t fix the underlying issue.
If your system frequently relies on EM heat, something else may be wrong. Common causes include airflow issues, refrigerant problems, sensor failures, or system installation issues. That’s where professional diagnostics make a real difference.
At Whale Worth It! Plumbing, Heating & Air, we serve customers throughout the North Shore with expert heating support for both residential and commercial systems. If you’re ever unsure about when or how to use emergency heat, contact us. We’re always happy to help you protect both your comfort and your system.
Frequently Asked Questions About EM Heat
Before we wrap up, here are a few common questions we hear from homeowners.
It’s a manual setting that turns off the heat pump and uses backup heat only.
Yes. It increases energy costs and hides system problems.
It provides reliable heat when the outdoor unit can’t operate normally due to severe conditions.
Harsh winter conditions may trigger backup heating. However, repeated use outside extreme weather suggests a system issue. What is EM heat on a thermostat?
Is it bad to leave emergency heat on?
What is emergency heat used for during winter storms?
Should homeowners in North Shore, MA use EM heat often?
If you’re dealing with emergency heat questions or system concerns, contact Whale Worth It! Plumbing, Heating & Air today. We’ll help you stay warm without guessing.
