Understanding Emergency Heat Operation
The “EM Heat” setting activates a secondary, manually controlled heating source for the home. This setting is distinct from the regular “Heat” mode, which relies on the heat pump’s primary function of transferring heat energy from the outdoor air using refrigerant and a compressor. Standard operation is highly efficient because it moves existing heat rather than generating it.
When Emergency Heat is activated, the system completely bypasses and deactivates the outdoor compressor unit. It relies solely on the backup heat source, typically electric resistance coils located inside the indoor air handler. This resistance heating method converts electricity directly into thermal energy, similar to a large electric toaster.
This direct conversion process is significantly less efficient than heat transfer. Operating EM Heat can be three to four times more expensive than running the heat pump in its normal mode. Therefore, this supplemental heat source is intended for temporary use only, serving as an emergency measure when the primary system is compromised.
It is important to distinguish EM Heat from automatic auxiliary heat. Auxiliary heat automatically engages the secondary heat alongside the compressor to supplement warmth during cold weather or defrost cycles. EM Heat must be manually selected and deactivates the compressor entirely.
Specific Situations for Activating EM Heat
The Emergency Heat setting should only be engaged when a homeowner confirms a failure in the main heat pump system. The primary indicator is a complete lack of heat delivery when the thermostat is set to the normal “Heat” mode. This action provides temporary warmth until a professional technician can arrive to perform repairs.
A clear sign of a system failure is when the outdoor compressor unit is not running at all, or if it is running but only blowing cold air into the home. Another situation requiring manual activation is when the outdoor unit is encased in a thick layer of ice that the system’s automatic defrost cycle is unable to clear. This heavy ice accumulation can prevent the transfer of heat and potentially damage the internal components of the unit.
If the heat pump has sustained visible physical damage, such as a component being struck or broken by debris, the EM Heat setting should be turned on immediately. Before activating, the homeowner must confirm that the lack of heat is due to a system malfunction, not just the heat pump running an automatic defrost cycle or struggling during a brief period of very low outdoor temperature. Manually switching to EM Heat ensures the home is heated while protecting the main unit from operating under a compromised condition.
Deactivating Emergency Heat and Next Steps
Once the immediate heating emergency has passed or the repair has been completed, Emergency Heat mode must be manually deactivated. This involves switching the thermostat’s system mode back to “Heat” or “Auto.” The “EM Heat” indicator light should disappear, confirming the system has returned to its standard, more efficient operation.
The need to use EM Heat confirms a serious underlying problem with the main heat pump system. Therefore, the most important next step after activation is to contact a qualified HVAC professional to diagnose and repair the issue. Leaving the system in Emergency Heat for an extended period should be avoided, as the high cost of resistance heating leads to significantly increased utility bills.