During winter’s harshest days, homeowners may wonder when to switch to emergency heat on a heat pump. Understanding the circumstances—and risks—of activating this setting is crucial for efficiency and comfort. This article provides expert guidance, covering the function of emergency heat, identifying the right situations for its use, and debunks misconceptions to help American homeowners confidently operate their systems.
| Key Question | Quick Answer |
|---|---|
| What Is Emergency Heat? | Backup heating using electric resistance or furnace, not the heat pump. |
| When Should It Be Used? | Only if the outside unit malfunctions or is inoperable due to extreme conditions. |
| What Are The Risks? | Significantly higher energy costs and potential system wear. |
| How To Operate Safely? | Switch manually on thermostat only during heat pump failure and call a technician. |
How Heat Pumps Work In Cold Weather
Heat pumps extract heat from outside air, even in freezing temperatures. They use refrigerant cycles to absorb and transfer heat indoors. While efficient in moderate cold, their performance diminishes as temperatures plunge below 30°F, challenging their ability to maintain comfort.
Modern heat pumps are designed with improved cold-weather capabilities, but every model has its critical temperature threshold. When outdoor air is extremely cold or icy, supplemental heat or backup systems become important to maintain indoor warmth.
What Is Emergency Heat?
Emergency heat, or ‘Em Heat’, is a manual thermostat setting that bypasses the outdoor heat pump unit
This setting activates a secondary heat source—usually electric resistance coils or a gas/oil furnace—to directly heat your home, regardless of outdoor conditions. Emergency heat should not be confused with ‘auxiliary heat’ (or ‘aux heat’), which automatically activates to help the heat pump during regular cold-weather operation.
Key Differences: Auxiliary vs. Emergency Heat
| Feature | Auxiliary Heat | Emergency Heat |
|---|---|---|
| Activation | Automatic | Manual |
| Function | Helps heat pump in extreme cold | Used only when heat pump fails |
| Energy Use | Moderate | Very high |
| Control | Thermostat auto-switching | User sets on thermostat |
When Should You Switch To Emergency Heat?
Emergency heat should only be used if your heat pump’s outdoor unit is inoperable due to malfunction, heavy ice build-up, or physical damage, and you need to maintain a safe indoor temperature until repairs can be made.
Common scenarios include:
- The pump will not turn on or produces no heat after basic troubleshooting (checking breakers, thermostat batteries, etc.).
- Noticeable physical damage or severe ice accumulation on the outdoor unit prevents normal operation.
- Waiting for repairs by a qualified HVAC technician when low temperatures pose a risk to your home’s occupants or your plumbing.
Signs Your Heat Pump Needs Emergency Heat
- Outdoor unit is silent, not running at all
- Home remains cold even after extended runtimes
- No visible heat from vents or very weak airflow
- Outdoor unit emits loud, unusual noises, sparks, or smoke
If none of these signs are present, do not turn on emergency heat—it will substantially increase utility bills and lead to unnecessary operating costs.
Myths And Misconceptions About Emergency Heat
Many homeowners mistakenly believe they should use the emergency heat setting during very cold weather for extra warmth. This is inaccurate—emergency heat is meant solely for heat pump failures, not regular support during cold spells.
- Myth: “Turning on emergency heat helps the heat pump in extra cold weather”
- Myth: “It will boost family comfort and efficiency”
The reality: Emergency heat costs two to three times more than normal heat pump operation. It should not serve as a routine backup during winter, but only as a last resort during a system failure.
How To Activate Emergency Heat On The Thermostat
If you must use emergency heat, follow these steps:
- Locate your programmable or smart thermostat. Look for a button labeled “EM Heat” or “Emergency Heat.”
- Slide or tap the control to enable “Em Heat.” The heat pump will not operate; only the secondary heater will run.
- Contact a licensed HVAC technician immediately to diagnose and fix your outdoor unit.
- Keep the setting in emergency mode only as long as necessary, to minimize energy bills.
Some older thermostats require a combination of buttons or a switch. Consult your user manual for system-specific instructions.
Why Emergency Heat Is So Expensive
Emergency (resistance) heat uses electricity to generate heat, similar to running a giant toaster coil. In contrast, heat pumps transfer existing heat with far less energy input. Gas or oil furnace backups are costlier than heat pump operation but may be less expensive than electric resistance heat, depending on current fuel prices.
As a result, energy use can soar rapidly. For example, running emergency heat in a typical 2,000-square-foot home can triple daily heating costs versus efficient heat pump usage.
| Heating Method | Estimated Energy Efficiency (COP*) | Relative Cost |
|---|---|---|
| Standard Heat Pump | 2.5–4.0 | Low |
| Auxiliary Electric Heat | 1.0 | High |
| Emergency Electric Heat | 1.0 | Very High |
*COP = Coefficient of Performance (higher = better efficiency)
Alternatives To Emergency Heat
If you’re tempted to switch to emergency heat during a cold snap and your system is still running, consider these alternatives first:
- Lower the thermostat by a few degrees to ease the burden on your system while maintaining comfort.
- Seal drafts and insulate your home to prevent heat loss.
- Close unused rooms and doors to concentrate heat where you need it most.
- Let sunlight in during the day to add natural warmth.
- Run ceiling fans in reverse to circulate warm air downward.
These simple strategies can boost comfort without drastically increasing your utility bill.
How To Prepare A Heat Pump For Cold Weather
Prevent the need for emergency heat by maintaining your system and checking its operation before winter weather arrives. Routine care can prevent many common failures that trigger the ‘Em Heat’ switch.
- Schedule regular professional service to inspect coils, wiring, and refrigerant levels.
- Clear debris, leaves, or snow from the outdoor unit weekly.
- Change your air filter every 1-3 months to maximize airflow.
- Check and update your thermostat for proper operation and programmed schedules.
Modern smart thermostats may alert you to system faults, so keep notification settings enabled for early warnings.
How To Troubleshoot A Non-Working Heat Pump
If your home isn’t heating and you suspect a heat pump malfunction, try these steps before enabling emergency heat:
- Check your home’s electrical panel for any tripped breakers and reset if needed.
- Test thermostat batteries—replace weak or dead batteries.
- Check outdoor unit for visible ice, snow, debris, or damaged parts.
- Listen for unusual sounds—grinding, buzzing, or silence may indicate a motor or compressor issue.
- Reset the system by turning the thermostat and breakers off for five minutes, then restore power.
If your system still does not run, set the thermostat to emergency heat temporarily and call a professional for diagnosis.
Emergency Heat And Different Types Of Heat Pump Systems
Various backup heat sources exist, depending on your heating system’s configuration.
| System Type | Backup Heat Source | Common In |
|---|---|---|
| Air-Source Heat Pump | Electric resistance strips | Southern and mid-Atlantic U.S. |
| Duel-Fuel Heat Pump | Gas or propane furnace | Colder northern climates |
| Geothermal Heat Pump | Electric backup or hydronic | Variable |
Always know which backup source your system uses, as fuel type affects both efficiency and emergency cost.
Energy Costs: Estimating The Financial Impact
Emergency heat can quickly increase electricity bills, especially when left running for several days. For instance, a typical electric resistance backup can draw 10,000 to 20,000 watts per hour. If electricity costs $0.14 per kWh:
- Running 20,000W for 10 hours costs $28 per day.
- Typical heat pump costs for the same period: $7–$10 per day.
For a week-long emergency heat event, utility costs could rise by $100–$150 more than normal operation.
The Role Of Smart Thermostats And Technology
Modern thermostats can detect heat pump malfunctions and alert homeowners faster than ever. Some smart thermostats even lock out emergency heat unless system faults are registered, helping to prevent wasteful use.
Consider upgrading to a smart thermostat to receive push notifications, remote diagnostics, and energy-use data to further reduce risks and costs associated with improper emergency heat activation.
Professional Recommendations And Safety Considerations
HVAC experts universally urge homeowners to reserve emergency heat for true emergencies only. Overuse stresses electrical wiring, increases fire risk, and raises bills. If you must use it, limit its duration and seek professional repairs immediately.
Never attempt to repair the heat pump outdoor unit yourself—high-voltage components and refrigerant lines pose safety risks and require licensed handling.
Frequently Asked Questions On Emergency Heat For Heat Pumps
Is it bad to run emergency heat for more than a day? Yes, for both cost and equipment-wear reasons. Prolonged emergency heat operation risks excessive utility bills and increased system strain.
Can running emergency heat damage my unit? Using emergency heat alone does not harm the backup system, but it can mask underlying issues if used as a crutch, delaying needed repairs.
Should I try resetting my thermostat before switching to emergency heat? Absolutely—thermostat resets often resolve minor faults. Only move to emergency heat if the outdoor unit still does not operate.
Do all heat pumps have emergency heat? No, but all modern dual-fuel or all-electric heat pump systems in cold U.S. climates will include some form of backup heating labeled as emergency or auxiliary heat.
Summary: The Right Time To Use Emergency Heat On Your Heat Pump
Reserve emergency heat for temporary use only when your outdoor heat pump fails and you must maintain safety. For routine winter heating, let your heat pump and its automated auxiliary functions operate as designed. If in doubt, contact a licensed HVAC professional to assess the situation before switching modes. This approach will help you protect your home, your comfort, and your energy bills during every cold snap.