Emergency heat, often labeled EMH on many thermostats, is a dedicated mode for heat pump systems that activates when the primary heating source isn’t able to provide adequate warmth. This mode is designed to ensure reliable indoor comfort during extreme cold, equipment issues, or when the heat pump is unavailable. Understanding how EMH works helps homeowners manage energy use and system performance more effectively, especially in regions with harsh winters.
What EMH Is
Emergency heat is abackup heating method for heat pump systems. In normal operation, a heat pump transfers heat from outside to indoors using refrigerant cycles. When outdoor temperatures drop or the heat pump struggles, EMH switches the system to a supplemental heat source—typically electric resistance heat or a backup furnace—brying in warmth without relying on the outdoor unit. In this mode, the thermostat bypasses the heat pump and powers the auxiliary heating elements directly to meet the thermostat’s set point.
How Emergency Heat Works
When EMH is activated, the thermostat commands the auxiliary heat source to engage, delivering faster warming to offset the reduced efficiency of the heat pump in extreme conditions. This mode generally results in higher energy consumption because electric resistance heat is less efficient than a well-functioning heat pump. Some systems automatically enter EMH if the heat pump detects a malfunction or if there is a significant temperature differential between indoor and outdoor environments. The transition is designed to be seamless, preserving comfort while protecting the home from cold snaps.
When To Use EMH
EMH should be used primarily during extremely cold weather or when the heat pump cannot meet the heating demand. Typical scenarios include prolonged subfreezing temperatures, a refrigerant issue, a malfunctioning outdoor unit, or a thermostat misconfiguration. It is also common to see EMH engage during temporary outages or while awaiting service. For day-to-day comfort, homeowners should rely on the heat pump’s normal operation and only switch to EMH when necessary or as advised by a servicing professional.
Pros And Cons Of Emergency Heat
- Pros: Ensures reliable warmth during severe cold or system faults; prevents rapid temperature drops; offers a straightforward way to maintain comfort when the primary system is compromised.
- Cons: Higher energy consumption and operating costs; reduced overall system efficiency; longer-term overuse can lead to faster wear on auxiliary heating elements; potential for higher electricity bills in cold months.
Operational Tips For EMH
- Energy Monitoring: Be mindful of energy use when EMH is active. If the mode remains engaged for extended periods, schedule a diagnostic with a HVAC professional.
- Thermostat Settings: Keep the Thermostat at a reasonable temperature to minimize reliance on EMH, and use programmable setbacks to avoid unnecessary operation.
- Preventive Maintenance: Annual or biannual system checks help ensure the heat pump and auxiliary components function correctly, reducing the likelihood of unnecessary EMH activation.
How To Enable Or Disable EMH On Common Systems
Most modern thermostats provide a clear EMH or Emergency Heat option, often accessed by switching the mode from HEAT PUMP to EMERGENCY HEAT or AUX. The exact steps vary by brand, but the general process is as follows:
- Access the thermostat menu and locate the heating mode options.
- Choose EMERGENCY HEAT or AUX, depending on the model.
- Confirm the selection and allow the thermostat to engage the auxiliary heat source.
Households should refer to the user manual for brand-specific instructions and safety notes. If there is any uncertainty about the system’s configuration, contacting a licensed technician is recommended.
Common Misconceptions
- EMH is always a bad thing: Not true. EMH ensures warmth when the heat pump is unable to meet demand, preventing frozen pipes and discomfort.
- EMH automatically damages equipment: When used correctly and intermittently, EMH does not damage the system, but prolonged use of electric resistance heat can increase wear and energy costs.
- EMH means the heat pump is broken: EMH often indicates a fault or an imminent issue with the outdoor unit or refrigerant system. A professional assessment is advised.
Energy Considerations And Efficiency
EMH typically uses electric resistance heat, which has a higher operating cost per BTU than a functioning heat pump. Homeowners can mitigate costs by maintaining a well-insulated home, ensuring ductwork is sealed, and scheduling regular heat pump maintenance. In milder climates, EMH usage is infrequent, but in regions with severe winters, energy planning becomes essential. Some systems offer a hybrid approach, where the thermostat optimizes the balance between heat pump and auxiliary heat based on outdoor temperatures and energy prices.