Emergency heat, often labeled as EM Heat on many thermostats, is a setting used with heat pump systems. It activates a backup heating source when the heat pump struggles to meet the indoor temperature, such as during very cold weather or when the outdoor unit is malfunctioning. Understanding EM Heat helps homeowners maintain comfort, protect the heat pump, and manage energy costs. This article explains what emergency heat does, when to use it, potential costs, and best practices for efficient home heating.

What Emergency Heat Is

Emergency heat is a separate operating mode for heat pumps that switches the system from the heat pump’s outdoor unit to a supplemental heat source, typically electric resistance coils inside the air handler. In this mode, the heat pump’s efficiency is bypassed, and the system relies on the backup heat to raise indoor temperatures quickly. EM Heat is designed as a temporary measure, not a normal operating mode, and it is useful when outdoor temperatures drop below the heat pump’s efficient range or when a system fault prevents the heat pump from working correctly.

How It Works With A Heat Pump

A heat pump transfers heat from outside to inside using refrigerant and a compressor. When the outdoor temperature is moderate, the heat pump provides efficient heating. If it cannot meet the set temperature, EM Heat activates the auxiliary electric heat strips to deliver immediate warmth. While this delivers rapid comfort, it uses significantly more electricity per BTU than the heat pump alone and can raise energy bills if used for extended periods.

When To Use Emergency Heat

Use EM Heat in these scenarios: outdoor temperatures are extremely cold and the heat pump relies heavily on auxiliary heat to maintain comfort; the heat pump is undergoing a malfunction or is in defrost mode and cannot maintain warmth; or there is a temporary power interruption that limits heat pump operation. It is generally best to run in EM Heat only until the issue is resolved or temperatures moderate, after which you should allow the system to return to standard heat pump operation to maximize efficiency.

Choosing Between EM Heat And Normal Heating

In normal operation, the heat pump extracts heat from outside and transfers it indoors with high efficiency. When EM Heat is engaged, electric coils add warmth, but at a higher cost. To optimize energy use:

Prefer the heat pump mode whenever outdoor temperatures are within its efficient range.
Switch to EM Heat only when the heat pump cannot meet the set point within a reasonable time.
Consider a programmable thermostat schedule that uses EM Heat briefly during extreme lows and reverts to heat pump operation as conditions improve.

Impact On Energy Bills

Electric resistance heating used in EM Heat consumes more electricity per hour than the heat pump’s heating mode. If EM Heat runs for long periods, monthly energy usage can rise quickly. The exact impact depends on the home’s insulation, thermostat settings, and outdoor temperatures. For many homes, EM Heat should be a short-term solution, not a daily setting.

Tips For Efficient Use

Keep doors and windows sealed; improve insulation to reduce reliance on EM Heat.
Set a realistic indoor temperature that avoids excessive heating demand.
Regularly service the heat pump and check for refrigerant issues or coil cleanliness that might reduce performance.
Use a programmable or smart thermostat to optimize when EM Heat is needed and to preheat spaces before occupants arrive.
Monitor outdoor temperatures and switch back to heat pump operation as soon as feasible.

Common Questions About EM Heat

Q: How can I tell if EM Heat is on? Most thermostats display EM Heat or EMHT when the backup heating source is active. The screen may indicate “Emergency Heat” or show a different icon depending on the brand.

Q: Will EM Heat damage my heat pump? EM Heat itself does not damage the heat pump, but extended use can raise energy costs and may indicate the heat pump is undersized, poorly insulated, or experiencing a malfunction. A professional diagnosis is recommended if EM Heat is frequently needed.

Q: Should I switch to EM Heat during cold snaps? Consider EM Heat only if the heat pump cannot maintain comfort efficiently or if the system is in a temporary fault. If the home warms adequately with the heat pump alone, stay in standard mode to maximize efficiency.

Q: Can I program EM Heat with my thermostat? Yes. Many thermostats allow you to schedule daily usage, set back temperatures, or enable smart features that automatically switch between heat pump and emergency heat based on temperature and occupancy.

Maintenance And Professional Help

Regular maintenance helps minimize the need for EM Heat. Schedule annual inspections of the outdoor unit and indoor air handler, check refrigerant levels, inspect electrical connections, and replace filters regularly. If EM Heat is engaged frequently or the system struggles to reach the desired temperature, contact a qualified HVAC technician to inspect for refrigerant leaks, faulty compressors, or thermostat misconfigurations.

Key Takeaways

Emergency heat is a backup heating mode for heat pumps that uses electric resistance coils when the outdoor unit cannot meet demand.
Use EM Heat briefly and only when necessary to maintain comfort or during system faults to prevent prolonged high energy costs.
Optimizing insulation, thermostat scheduling, and regular maintenance helps reduce reliance on EM Heat and improves overall efficiency.