Emergency Heat on a Heat Pump: What It Is and When to Use It

Heat pumps are a common and efficient way to heat and cool homes, but many homeowners wonder, what is emergency heat on a heat pump and when it should be used. This article explains the function, triggers, costs, and best practices for emergency heat so homeowners can make informed decisions about comfort, safety, and energy use.

Topic	Quick Answer
What Is Emergency Heat	Backup heating mode using electric resistance or auxiliary heat
When To Use	Heat pump failure or extreme cold when heat pump can’t keep up
How To Activate	Thermostat setting labeled “Emergency Heat” or “EM Heat”
Cost Impact	Significantly higher energy use and cost

How A Heat Pump Works And Why Emergency Heat Exists

Heat pumps transfer heat between indoor and outdoor spaces using a refrigerant cycle driven by a compressor and fans, operating similarly to air conditioners but in reverse during heating mode. In moderate temperatures, heat pumps are highly efficient because they move heat rather than generate it.

Emergency heat exists because heat pumps have limitations: in very cold weather efficiency drops, outdoor unit components can fail, or the compressor may stop working. Emergency heat provides a reliable backup by switching to a heating method that does not rely on the outdoor heat-exchange process.

What Is Emergency Heat On A Heat Pump?

Emergency heat is a thermostat setting that forces the heating system to use a secondary source of heat—typically electric resistance heaters, gas furnaces, or oil furnaces—bypassing the heat pump. This backup is sometimes called auxiliary heat, although terminology can vary: auxiliary heat often runs intermittently with the heat pump, while emergency heat is intended for continuous use when the heat pump is inoperable.

Types Of Emergency Heat And Auxiliary Heat

Several backup heating configurations are common in residential systems. The exact setup affects how emergency heat behaves and how costly it is to run.

• Electric Resistance Heat: Electric coils or strips heat air directly and are common in heat pump systems without a gas furnace.
• Gas Or Oil Furnace Backup: A fossil-fuel furnace can be wired to act as auxiliary or emergency heat, often more efficient than electric resistance in some regions.
• Dual-Fuel Systems: These systems use a heat pump until outdoor temperatures make it inefficient, then switch to a gas furnace automatically or via thermostat settings.

Emergency Heat Versus Auxiliary Heat: Key Differences

Users frequently confuse emergency heat and auxiliary heat. Auxiliary heat supplements the heat pump when demand spikes or defrost cycles occur, and it can cycle on and off automatically. Emergency heat is a manual thermostat mode that forces the backup source to be the primary heat, bypassing the heat pump.

When To Use Emergency Heat

Emergency heat should be used sparingly and only in these situations: the heat pump has failed and will not heat the home, the outdoor unit is iced beyond normal defrosting and is not recovering, or the compressor is silent and repair is pending. It also applies when temperatures fall below the operational limits of the heat pump if the system lacks an automatic dual-fuel control.

Using emergency heat because the home feels chilly without checking the heat pump first is not recommended. A qualified HVAC technician should diagnose heat pump issues to avoid unnecessary energy costs.

How To Activate Emergency Heat

Most thermostats have a setting labeled “Emergency Heat,” “EM Heat,” or an “Aux/Emergency” switch. To activate emergency heat, select that mode and set the desired temperature. The thermostat will then call for the backup heat source. Modern thermostats and systems with smart controls or dual-fuel setups may switch automatically if configured.

What Happens After Emergency Heat Is Activated

When emergency heat is engaged, the thermostat stops calling the outdoor heat pump compressor and instead energizes the backup system. In electric-resistance systems, heating elements produce heat directly, causing rapid temperature rise but at a higher electricity draw. In gas or oil backups, combustion furnaces will run to meet the thermostat setpoint.

Costs And Efficiency Considerations

Emergency heat is typically much more expensive to run than the heat pump. Electric resistance heat has a coefficient of performance (COP) near 1, meaning one unit of electricity produces roughly one unit of heat. Heat pumps often have COPs of 2 to 4 in mild conditions, making them two to four times more efficient.

Running emergency heat for extended periods can significantly increase monthly energy bills. Homeowners should estimate costs based on local electricity, natural gas, or oil rates and consider temporary use only until the heat pump is repaired.

Troubleshooting Before Using Emergency Heat

Before switching to emergency heat, check common heat pump issues: ensure the thermostat is set to heat and the fan is on auto, verify the outdoor unit has power and is free of snow or debris, inspect air filters for restriction, and look for obvious error codes on heat pump or thermostat displays.

If the outdoor unit is iced, allow it time to complete a defrost cycle; repeat defrosting could indicate a refrigerant leak or malfunction. If the compressor is running but the home remains cold, a technician should inspect refrigerant levels and airflow before relying on emergency heat.

Safety And Maintenance When Using Emergency Heat

When emergency heat is engaged, ensure safety checks are performed. For electric resistance systems, confirm no tripped breakers or overheating signs. For combustion furnaces, check for proper venting, pilot light or ignition function, and carbon monoxide detector operation.

Once normal heat pump operation resumes, switch the thermostat back from emergency heat to avoid prolonged high costs. Schedule a professional inspection to address underlying issues and restore the heat pump to efficient operation.

Smart Thermostats And Dual-Fuel Controls

Smart thermostats can improve management of auxiliary and emergency heat by automatically controlling dual-fuel systems based on outdoor temperature, utility rates, or performance algorithms. This automation helps optimize efficiency and reduce unnecessary reliance on expensive backup heat.

Dual-fuel controls automatically switch between heat pump and fossil-fuel furnace based on thresholds set by the installer or manufacturer. This feature prevents manual mistakes such as leaving the home on emergency heat when it is not required.

Common Myths And Misconceptions

One common myth is that emergency heat warms a home faster. Because emergency heat often uses electric resistance, it can feel quicker for small rooms, but it is far less efficient and more expensive overall.

Another misconception is that using emergency heat can damage a heat pump. Emergency heat itself does not harm the heat pump if used correctly, but leaving it on for extended periods may lead to higher utility bills and unnecessary wear on backup equipment.

Cost-Saving Tips When Emergency Heat Is Necessary

• Use emergency heat only until repairs are completed and avoid long-term use.
• Lower the thermostat setting by a few degrees to reduce run time and energy draw.
• Improve home insulation and seal air leaks to reduce heat loss during backup heating.
• Consider a dual-fuel upgrade or smart thermostat to automate efficient switching.

When To Call A Professional

If the heat pump is unresponsive, making unusual noises, running continuously without producing heat, or if the outdoor unit is frozen and doesn’t defrost, a licensed HVAC technician should be contacted. Professionals can diagnose refrigerant leaks, compressor faults, control board errors, and other failures that justify emergency heat use.

Frequently Asked Questions

Does Emergency Heat Turn On Automatically?

Typically, emergency heat does not activate automatically unless the system includes a dual-fuel control that is configured to switch based on outdoor temperature or other criteria. Manual activation is common with basic thermostats.

How Much More Expensive Is Emergency Heat?

Cost depends on fuel type and local rates, but electric emergency heat can be two to four times more expensive per unit of heat compared with an efficient heat pump in moderate conditions. Gas furnace backups may be cheaper than electric resistance but still costlier than heat pump operation in many scenarios.

Can Emergency Heat Damage The System?

Using emergency heat temporarily does not usually damage the heat pump. However, it bypasses the pump, so unresolved faults can worsen over time if not repaired. Backup heating elements or the furnace may experience normal wear from extended use.

Is Emergency Heat The Same As Backup Heat?

In many contexts, yes. Emergency heat is a form of backup heat, but the term “auxiliary heat” can refer to supplemental heat that operates alongside the heat pump rather than fully replacing it.

Practical Checklist For Homeowners

1. Confirm thermostat settings and try basic troubleshooting before switching to emergency heat.
2. Check outdoor unit for ice, debris, or power issues and allow for defrost cycles.
3. Use emergency heat only when necessary and monitor energy use and safety equipment.
4. Schedule a professional repair promptly and switch back to heat pump mode once fixed.

Key Takeaways

Emergency heat is a manual or backup heating mode that bypasses the heat pump and uses an alternative heat source. It is intended for short-term use during heat pump failure or extreme conditions and is usually less efficient and more costly. Proper troubleshooting, smart controls, and timely professional repairs can minimize reliance on emergency heat and maintain efficient home heating.