Emergency heat, often labeled EM Heat, is a thermostat setting used with heat pump systems. It engages auxiliary or backup heating to maintain comfort when the primary heat pump operation isn’t sufficient. This guide explains how EM Heat works, when to use it, potential energy impacts, and practical tips for efficient use. Understanding EM Heat helps homeowners balance comfort, energy costs, and system longevity, especially during cold snaps or system malfunctions.

What Is Emergency Heat Setting

Emergency heat is a dedicated mode on many heat pump thermostats that switches from the heat pump’s usual operation to a supplemental heating source, typically electric resistance heaters. This setting bypasses the heat pump’s compressor and relying on the backup heater to deliver steady warmth. EM Heat is designed as a temporary safeguard during extreme cold, equipment issues, or when outdoor temperatures exceed the heat pump’s efficient range. In some systems, EM Heat is identical to Auxiliary Heat (AUX) or Back-Up Heat; terminology varies by manufacturer.

How It Works In Practice

When the thermostat is set to Emergency Heat, the thermostat signals the system to engage the auxiliary heat source. The heat pump may still operate in reduced capacity, but the backup heaters provide the majority of heat. The result is rapid warming, but with higher energy consumption. Some systems will display EM Heat as a separate mode, while others show AUX or BACKUP. The exact behavior depends on the brand, system configuration, and whether a forced-auxiliary mode is triggered by very low outdoor temperatures.

When To Use Emergency Heat

Use EM Heat in the following scenarios to maintain comfort and protect the home during extreme conditions or equipment issues:

Outdoor temperatures are well below the heat pump’s efficient range, making the heat pump struggle to meet the setpoint.
There is a refrigerant or compressor fault that prevents normal heat pump operation.
There is a temporary failure of the outdoor unit due to snow, ice, or debris.
During a power outage recovery period when the heat pump cannot start quickly.
When the home needs rapid warming after extended absence, and the thermostat calls for heat.

Important: EM Heat should be used sparingly. Prolonged use increases electricity costs and may reduce the equipment’s lifecycle if used as a default. If EM Heat is needed frequently, it’s wise to schedule a professional inspection to diagnose potential heat pump performance or refrigerant issues.

Energy Implications And Costs

Electric resistance heating, common in EM Heat, is significantly less energy-efficient than a properly functioning heat pump. The U.S. Department of Energy notes that heat pumps are generally more efficient than electric resistance heat at moderate outdoor temperatures, but they lose efficiency as temperatures drop. When EM Heat runs, the system may consume substantially more kilowatt-hours to maintain the same indoor temperature. Homeowners can mitigate cost impact by:

Using EM Heat only during extreme cold spells and switching back to the heat pump when possible.
Ensuring the home is well insulated, with sealed ductwork and proper thermostat placement.
Trailing maintenance on the heat pump, ensuring refrigerant levels and airflow are optimal.
Utilizing a programmable thermostat to reduce heat during unoccupied periods even when EM Heat is active for brief intervals.

Signs You Might Need Emergency Heat

Indicators that EM Heat may be appropriate or that a repair is needed include:

Persistent, unusually high electricity bills during cold months.
Heat pump running continuously without achieving comfort setpoints.
Odd noises or ice buildup on outdoor components indicating mechanical issues.
Cold air coming from vents despite a warm outdoor temperature reading.
Thermostat display showing AUX or EM Heat indicators for extended periods.

In such cases, a professional HVAC technician can confirm whether EM Heat is used correctly or if there is a malfunction that needs repair, such as refrigerant leaks, a faulty reversing valve, or a clogged outdoor coil.

Common Myths About Emergency Heat

Debunking myths helps homeowners use EM Heat wisely:

Myth: EM Heat always means the system is broken. Fact: EM Heat can be a normal fallback mode during very cold weather or high demand; it isn’t inherently a sign of failure.
Myth: EM Heat will damage the heat pump. Fact: Short-term EM Heat use typically does not harm the unit, but prolonged reliance can stress electrical components and reduce efficiency.
Myth: EM Heat costs the same as regular heating. Fact: EM Heat generally costs more per hour due to electric resistance heating, though total cost depends on duration and energy rates.

Maintenance And Best Practices

Regular maintenance keeps heat pumps performing well and reduces unnecessary EM Heat use. Recommended practices include:

Annual professional inspection of the heat pump, refrigerant levels, and electrical connections.
Cleaning or replacing air filters every 1–3 months during heating season to maintain airflow.
Ensuring outdoor unit clearance, removing snow buildup, and keeping coils clean.
Checking ductwork for leaks and sealing gaps to improve overall system efficiency.
Using the thermostat’s energy-saving features, such as setback temperatures, to minimize reliance on EM Heat.

How To Optimize Thermostat Settings For Comfort And Efficiency

The thermostat controls how and when EM Heat engages. Practical optimization tips include:

Set an appropriate recovery ramp so the home reaches the desired temperature before occupants return.
Leverage humidity management; drier air can feel warmer, potentially reducing heating demand.
Pair EM Heat with zoning if available, heating only occupied areas to save energy.
Use a smart thermostat with adaptive recovery and weather-based optimization to reduce unnecessary EM Heat activations.

Frequently Asked Questions

Q: Can EM Heat be turned off completely? A: Yes, most systems can operate normally using the heat pump without EM Heat, provided outdoor conditions and system health allow it.

Q: Is EM Heat dangerous to use in winter? A: Not inherently dangerous, but it is less efficient and more costly. Use it only as needed for comfort and safety.

Q: Will EM Heat help with rapid defrost cycles? A: EM Heat does not directly affect defrost cycles; those are managed by the heat pump’s defrost controls, which operate independently of EM Heat.