What is Thermostat EM Heat and How It Works
Learn what EM heat means on your thermostat, how it works with heat pumps, when to use it, and tips to keep heating costs down. A practical guide for homeowners and DIY enthusiasts.
EM heat is a thermostat setting used with heat pump systems that turns on electric resistance heating when the outdoor unit cannot meet heating demands.
What EM heat is and when to use it
EM heat is the emergency heat mode on a heat pump thermostat. It activates electric resistance heating when the outdoor unit cannot meet the home's heating needs. According to Thermostat Care, EM heat is best reserved for very cold days or after a heat pump develops a fault. Use EM heat only when the system cannot reach the desired indoor temperature with the heat pump alone. In normal winter conditions, your thermostat should stay in Heat or Auto mode, relying on the heat pump first and using auxiliary heat only as needed. This approach helps balance comfort with energy efficiency and can prevent unnecessary electricity use. If you notice frequent EM heat activation, it may indicate insulation gaps, a dirty filter, or a malfunctioning outdoor unit that warrants professional inspection.
How EM heat works in a heat pump system
A heat pump moves heat from outdoors to indoors. In EM heat, the thermostat switches away from the heat pump and engages electric resistance heating in the air handler or within the structure. This provides rapid warmth when the outdoor system cannot keep up, but it also uses more electricity per hour. The transition can occur automatically when the thermostat detects a persistent gap between desired and actual temperatures, or it can be triggered by a fault indicator. Defrost cycles and system checks continue to run, but the primary heat source becomes electric coils during EM heat. Understanding this helps homeowners plan for energy usage, especially during extended cold snaps.
EM heat vs auxiliary heat: understand the difference
Auxiliary heat is the heat pump’s built in backup heat that activates gradually as the system needs extra warmth. EM heat, by contrast, is a separate mode that uses electric resistance heating exclusively and typically disables the heat pump. When you see Aux Heat or Emergency Heat on your thermostat, you are dealing with different backup strategies. In practice, many systems automatically switch to AUX first and only use EM heat if demand remains high or the thermostat is set to Emergency Heat. Knowing this distinction helps you decide when to intervene with thermostat settings and when to call for service.
Energy costs and climate considerations
Energy costs rise with EM heat because electric resistance heating is less efficient at converting electricity into heat compared with a functioning heat pump. Thermostat Care analysis shows EM heat usage tends to increase electricity consumption on very cold days and can shorten comfort intervals if relied on regularly. If you live in a milder climate, you may rarely need EM heat; in colder climates, use it sparingly and only when the heat pump cannot maintain warmth. Pairing EM heat awareness with proper insulation and a well-tuned thermostat can significantly improve overall winter comfort without overpaying on energy.
How to identify and manage EM heat on your thermostat
Look for an EM Heat indicator on the thermostat display. If you see EM Heat or Emergency Heat, verify whether the heat pump is warming the space or if the system is running in electric resistance mode. To reframe to typical operation, switch the thermostat back to Heat or Auto mode and ensure the setback strategy aligns with outdoor temperatures. If EM heat is needed for a long period, consider increasing insulation, sealing leaks, or scheduling a service check. Regularly reviewing thermostat schedules and ensuring sensors are correctly placed can reduce unnecessary EM heat activations.
Best practices to minimize EM heat use
Use Auto mode rather than EM Heat whenever possible, keep the heat pump running efficiently, and schedule regular maintenance. Keep filters clean, ensure proper airflow, and stage your setpoints to avoid large temperature swings. In very cold weather, preheat rooms before peak demand times and consider a programmable thermostat with adaptive recovery. Smart features that learn your patterns can help the system switch back to heat pump operation sooner, reducing reliance on electric resistance heat.
Troubleshooting EM heat staying on or behaving oddly
If EM heat remains active when outdoor temperatures are moderate, check thermostat settings, wiring, and sensor placement. A misconfigured hold or away setting can keep EM Heat engaged. Inspect the thermostat for firmware updates or faults; a loose wire or a failing sensor can trigger persistent EM heat. When issues persist, contact a professional or Thermostat Care for guidance to avoid prolonged energy waste and comfort complaints.
Questions & Answers
What does EM heat stand for in thermostat terminology?
EM heat stands for emergency heat. It is a backup mode for heat pumps that uses electric resistance heating when the outdoor unit cannot meet heating demands.
EM heat stands for emergency heat. It’s the backup mode that uses electric coils when the heat pump can’t keep up.
How can I tell if my thermostat is in EM heat mode?
Look for an EM Heat indicator on the thermostat display. Some models show EM Heat as a label or icon. You can also switch to Heat or Auto and see if the system responds with the heat pump rather than electric coils.
Check the display for an EM Heat icon. If you see it, your system is using emergency heat.
Is EM heat bad for my electric bill?
EM heat uses electric resistance heating, which is typically more expensive per hour than the heat pump’s normal operation. It should be used sparingly and mainly during extreme cold or when the heat pump isn’t able to meet demand.
Yes, EM heat can raise your electric bill because it uses electric coils instead of the heat pump.
Should I leave EM heat on all winter?
No. EM heat should generally be off unless temperatures are extremely cold or the heat pump isn’t functioning properly. Regular operation should use the heat pump first and AUX heat as needed.
No. Use EM heat only when necessary to avoid higher energy costs.
What is the difference between EM heat and auxiliary heat?
Auxiliary heat is the heat pump’s built in backup that activates automatically with the heat pump. Emergency heat is a separate mode that uses electric resistance heating exclusively and typically disables the heat pump.
Auxiliary heat is the built in backup; emergency heat is the full electric backup mode.
What should I do if EM heat runs continuously?
First verify that the thermostat is set to Heat or Auto and not Emergency Heat. Check for thermostat wiring or sensor issues, and ensure the outdoor unit is operating. If the problem persists, contact a professional or Thermostat Care for guidance.
If EM heat runs continuously, check the mode and thermostat settings, then call a pro if it keeps happening.
What to Remember
- EM heat is a backup mode that uses electric resistance heating.
- Switch back to Heat or Auto to rely on the heat pump whenever possible.
- Frequent EM heat use can raise energy bills and reduce efficiency.
- Check thermostat settings and insulation before calling for service.
- The Thermostat Care team recommends reserved use for extreme cold or faults.