Heat pump systems are a popular choice for energy-efficient home heating across the United States, but understanding the role and function of emergency heat is essential for optimal comfort and safety in cold weather. This guide explores what emergency heat means, when and how it should be used, the impact on energy bills, troubleshooting tips, and best practices for American homeowners.
| Key Aspect | Quick Summary |
|---|---|
| What Is Emergency Heat? | Auxiliary heating mode activated when the primary heat pump cannot operate effectively. |
| When To Use? | Manual or automatic activation during extreme cold or heat pump malfunction. |
| Energy Impact | Significantly higher energy consumption compared to standard heat pump operation. |
| Troubleshooting | Identify if the system is stuck in emergency mode, and steps to resolve common issues. |
| Best Practices | Proper thermostat settings, regular maintenance, and knowing when to call a professional. |
What Is Heat Pump Emergency Heat?
The emergency heat function on a heat pump system is a secondary heating mode that activates when the primary outdoor heat pump can no longer adequately extract heat from outside air. This typically occurs when outdoor temperatures drop below a certain threshold—often around 30°F or lower.
Emergency heat utilizes a supplemental heat source, most commonly electric resistance heaters, gas furnaces, or oil furnaces, to provide continued warmth. This mode bypasses the heat pump’s compressor, relying entirely on this backup system for heating the home.
Major US brands, such as Trane, Carrier, and Lennox, integrate emergency heat as a crucial safety net in their heat pump systems, ensuring occupant comfort during harsh winters or mechanical failures.
How Does Emergency Heat Differ From Auxiliary Heat?
Although “auxiliary heat” and “emergency heat” are sometimes used interchangeably, there are critical differences. Auxiliary heat kicks in automatically when the heat pump alone can’t keep up, such as during very cold weather or when the thermostat is turned up rapidly.
Emergency heat, on the other hand, is a manual setting triggered by the user when there is an issue with the outdoor unit—such as a malfunction or system icing—requiring immediate backup.
The table below clarifies the key distinctions:
| Feature | Auxiliary Heat | Emergency Heat |
|---|---|---|
| Activation | Automatic | Manual |
| Purpose | Assist Heat Pump | Replace Heat Pump |
| Use Case | Extreme Cold/Shock Loads | Heat Pump Failure/Icing |
| Thermostat Label | Aux Heat (AUX) | Emergency Heat (EM Heat) |
When Should Emergency Heat Be Used?
Emergency heat should only be engaged under certain circumstances. The most common triggers include:
- Outdoor Unit Malfunction: A mechanical failure or component breakdown prevents the primary heat pump from operating.
- Ice Buildup: Excessive frost or ice accumulation on the outdoor unit that cannot be remedied by normal defrost cycles.
- Extreme Cold: Prolonged outdoor temperatures below the heat pump’s minimum efficiency limit (often below 25-30°F).
Manually switching to emergency heat provides an uninterrupted heating source, but it is not intended for continuous use due to efficiency and cost concerns. The homeowner should activate emergency heat only after confirming the outdoor heat pump cannot operate or is at risk of damage.
How Does Emergency Heat Work In Different Heat Pump Systems?
Air-Source Heat Pumps
In air-source heat pump systems, emergency heat usually means electric resistance coils inside the air handler take over. When engaged, the heat pump’s compressor is shut down and only the backup electric heater warms the air circulating through your home.
Dual Fuel Heat Pumps
With dual fuel systems—where a gas or oil furnace is paired with a heat pump—emergency mode switches all heating duties to the fossil fuel furnace. This setup is common in regions with extreme winter lows where electric resistance heat would be impractical.
Geothermal Heat Pumps
For geothermal or ground-source heat pumps, emergency heat may also use electric resistance heaters, though these systems are less likely to require backup due to the more constant ground temperatures.
How To Use Emergency Heat: Steps For Homeowners
If it becomes necessary to use emergency heat, follow these guidelines:
- Identify The Problem: Make sure the outdoor unit isn’t functioning, or ice buildup is severe.
- Check Thermostat: Modern programmable thermostats or smart thermostats will have a clear “EM Heat” setting. Move the mode selector to “Emergency Heat.”
- Monitor System: Once engaged, only the backup heat source will operate. The outdoor unit will shut down to prevent further damage.
- Contact A Professional: Emergency heat is designed only for short-term use. Arrange for immediate professional repair to restore normal heat pump function.
Never use emergency heat as a substitute for regular maintenance or repairs. Prolonged operation will increase your heating costs dramatically.
Energy Consumption: How Much Does Emergency Heat Cost?
Operating in emergency mode is significantly more energy intensive. Electric resistance heat can be up to three times more expensive to run than standard heat pump operation. For example, while a standard heat pump might provide 3 units of heat for every unit of electricity, electric resistance heat offers a 1:1 ratio—much less efficiency.
Dual fuel systems using natural gas or oil as backup heat may see costs increase compared to heat pump mode, but generally not as steeply as electric resistance heating. Homeowners should always return to primary heat pump operation as soon as possible to minimize utility bills.
| System Type | Normal Heat Pump (COP*) | Emergency Heat (COP*) | Estimated Monthly Cost (1000 sq ft, avg) |
|---|---|---|---|
| Electric Backup | 3.0 | 1.0 | $350-$500 |
| Gas/Oil Furnace | 3.0 | 0.7 – 0.9 | $250-$400 |
*COP = Coefficient of Performance
Signs Your Heat Pump Is In Emergency Heat Mode
- Thermostat Display: Many thermostats will indicate “EM Heat” or flash a warning when in emergency mode.
- Outdoor Unit Is Off: The exterior compressor and fan will not operate during emergency heat.
- Higher Electricity Use: Utility bills may spike, or you may feel hotter-than-usual air coming from vents due to the electric coils.
- Blower Runs Continuously: Expect the indoor air handler to operate for longer cycles to compensate for lost heat pump efficiency.
Troubleshooting Common Emergency Heat Issues
Thermostat Problems
Some programmable thermostats may switch to emergency heat inadvertently if settings are not configured properly. Double-check scheduling and mode settings, and refer to the device’s manual for troubleshooting steps.
Outdoor Unit Freezing
Temporary frost on the unit is normal, but excessive ice buildup indicates a problem. Make sure the unit is not blocked by snow or leaves and that downspouts are not flooding the area.
Continuous Emergency Heat Run
If emergency heat runs continuously even after restoring outdoor temperatures, a faulty relay, control board, or sensor might be to blame. Professional diagnosis is recommended.
Mismatched System Types
Ensure your thermostat is compatible with your specific heat pump setup, especially if a system upgrade has occurred. An incorrect thermostat may default to emergency mode unnecessarily.
How To Avoid Unnecessary Emergency Heat Usage
- Schedule Regular Maintenance: Annual checkups by a certified HVAC technician will help avoid breakdowns and ensure defrost systems operate correctly.
- Keep Outdoor Unit Clear: Remove snow, ice, and debris—never cover the heat pump or allow household items to crowd the unit.
- Seal Drafts: Weatherproofing your home reduces heating demand on the system, minimizing auxiliary and emergency heat operation.
- Upgrade Insulation: Enhanced attic and wall insulation allows the heat pump to operate more efficiently during cold spells.
- Monitor Thermostat Settings: Avoid frequent bumping of the thermostat or setting temperatures drastically higher than normal.
Smart Thermostats And Emergency Heat Features
Modern smart thermostats (such as ecobee, Nest, and Honeywell Lyric models) offer advanced emergency heat management. They can alert homeowners via mobile apps when emergency heat is engaged, provide diagnostics, and help schedule repairs.
Integration with smart home systems allows users to monitor energy consumption and avoid accidentally running in emergency mode—a major advantage in managing heating costs and comfort.
Emergency Heat In Different American Climates
Northern States
Homeowners in northern states with harsh winters are more likely to require occasional emergency heat. Investing in dual fuel systems can mitigate high electric costs and provide reliable comfort during cold snaps.
Southern States
In milder southern climates, emergency heat is rarely needed. However, understanding how to activate it and monitor system health remains crucial in rare severe cold events.
Advantages And Disadvantages Of Emergency Heat
| Advantages | Disadvantages |
|---|---|
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Heat Pump Emergency Heat Maintenance Checklist
- Schedule annual service inspections for heat pump and backup heat source
- Clear away debris and check drainage around the outdoor unit
- Test emergency heat mode at the start of the heating season under supervision, to ensure backup elements function correctly
- Replace thermostat batteries regularly and keep firmware updated if using a smart thermostat
Routine preventative maintenance is the best way to avoid having to rely on emergency heat.
Professional Repair Vs. DIY: What Not To Do
While homeowners can check for obstructions and adjust settings, emergency heat issues that persist should always be handled by an HVAC professional. Attempting to repair compressors, electrical elements, or defrost controls without training can pose electrical and fire risks.
If you must use emergency heat, call a licensed technician without delay to restore your primary heat pump function and avoid extended periods of inefficient operation.
Frequently Asked Questions (FAQs) About Heat Pump Emergency Heat
- Can I run emergency heat all winter? – No. Emergency heat is much more expensive and is meant for very short-term use only.
- Will my heat pump automatically switch to emergency heat? – No, emergency heat must be engaged manually by the user. “Aux” heat, however, turns on automatically as needed.
- Why is my emergency heat not working? – Potential reasons include blown fuses, faulty heating coils, wiring issues, or thermostat malfunctions. Professional diagnosis is required.
- What does “EM HEAT” mean on my thermostat? – This indicates that the system is running on the backup heat source after being set to emergency mode.
- Can I test emergency heat myself? – Yes, briefly test at the beginning of the heating season, but do not leave it on for long periods.
Choosing The Right System For Emergency Heat Needs
When installing or upgrading a heat pump, consult with HVAC professionals about your climate and backup needs. Properly sized and equipped systems reduce the frequency and cost of emergency heat use.
Considerations include:
- Local climate averages and record lows
- Home insulation and air sealing levels
- The type and efficiency of available backup heating sources
- Smart thermostat compatibility
Resources For Further Support
For in-depth technical information, review Energy Star’s guides on heat pump efficiency and the US Department of Energy’s heat pump resources for homeowners. Major equipment manufacturers provide detailed system manuals and troubleshooting guides online.
Consult local utility companies for energy rate information and possible incentives to install high-efficiency systems with smarter emergency heat management.