Emergency heat is a critical function found on most modern thermostats, yet it remains one of the least understood features for homeowners. When the temperature plummets and your primary heating system struggles, this setting is designed to keep your home livable, but it comes with significant trade-offs. Understanding what emergency heat does and when to use it can prevent discomfort, high energy bills, and potential system damage.
How Emergency Heat Works
To grasp the purpose of emergency heat, you first need to understand the standard operation of a heat pump system. During normal heating mode, a heat pump extracts warmth from the outdoor air and transfers it indoors. When the temperature drops below a certain threshold, usually around 35-40°F, the system becomes inefficient and may begin to accumulate ice. This is where the auxiliary heat strip kicks in, acting like a giant toaster to provide the extra warmth needed. The emergency heat setting bypasses the heat pump entirely, activating only the electric resistance heating elements.
When to Activate the Setting
You should only use the emergency heat setting under specific circumstances outlined in your thermostat’s manual. The primary scenario is during a complete heat pump failure, such as when the unit is malfunctioning or covered in ice and unable to defrost. If your heat pump is broken and you rely on the "Emergency Heat" mode, you are essentially switching your entire heating strategy to inefficient electric strip heating. It is a backup for the machine, not a replacement for a malfunctioning system.
Severe Weather Conditions
In regions that experience extreme cold snaps, the heat pump may be unable to extract any heat from the frozen air. If your system is overwhelmed and blowing cold air, engaging emergency heat can provide a temporary solution to keep pipes from freezing. However, this is a short-term fix. Running this setting for extended periods during a deep freeze can lead to skyrocketing electricity bills because electric resistance heating consumes significantly more energy than the heat pump's usual operation.
The Energy Efficiency Consequence
One of the most important aspects of understanding what emergency heat does is recognizing its impact on your energy consumption. Heat pumps are highly efficient because they move heat rather than generate it. In contrast, electric resistance heating is one of the least efficient ways to warm a home, often costing three to five times more to operate than the heat pump. Your thermostat will usually display an "EM Heat" indicator when this mode is active, serving as a constant reminder that efficiency is no longer the priority. Operational Differences and Indicators When the emergency heat is engaged, you will notice distinct operational changes in your HVAC system. The outdoor unit will stop running, as the system relies solely on the indoor air handler. The airflow from your vents will likely be hotter than usual because the electric strips run at a very high temperature to generate enough warmth. This is a stark contrast to the milder, distributed warmth produced by a functioning heat pump.
Operational Differences and Indicators
System Safety and Alerts
Modern thermostats are designed to protect the equipment and the occupants. If you leave the emergency heat on for too long, especially in unoccupied spaces, the system may trigger safety shutdowns to prevent overheating or electrical fires. Additionally, many systems are wired to activate the emergency heat automatically during a power loss to the compressor, ensuring that some level of warmth is maintained even if the main unit is down.
Best Practices for Homeowners
To use this feature effectively, treat it as a true emergency setting rather than a daily control. If you turn it on because you are cold, you are likely wasting energy and damaging your wallet. Only activate it if your heat pump is making unusual noises, emitting cold air in freezing weather, or if your energy bill suddenly spikes due to a malfunction. Always consult a professional HVAC technician to diagnose the root cause of the issue rather than relying on the strips to heat your home.
