Short Answer
Overview
The term “E M Heat” is a common abbreviation found on thermostats and HVAC control panels, standing for “Emergency Heat.” This setting is specifically relevant to heat pump systems, which move heat from the outside air into the home. Because heat pumps lose efficiency as outdoor temperatures drop significantly, most systems include a secondary, resistive heating elementâsuch as electric heat stripsâto provide warmth when the primary system cannot meet the heating demand.
History / Background
The development of emergency heat modes coincided with the rise of air-source heat pumps in residential heating. Early heat pump technology struggled in extreme cold climates, often failing to maintain indoor temperatures when the outdoor air reached freezing or sub-freezing levels. To make these systems viable in colder regions, engineers integrated auxiliary heat sources. The “Emergency Heat” setting was created as a manual override, allowing users to bypass the compressor and run only the backup heating elements if the outdoor unit became damaged, iced over, or failed entirely.
Importance and Impact
The inclusion of an E M Heat mode ensures residential safety and comfort during extreme weather events. Without this backup, a home relying solely on a heat pump could experience a critical drop in temperature during a deep freeze. By utilizing resistive heating, the system can maintain a habitable environment even when the heat pump’s refrigerant cycle is ineffective. This redundancy is a critical safety feature in northern climates where temperatures frequently fall below the balance point of the heat pump.
Why It Matters
For the modern homeowner, understanding the E M Heat setting is vital for energy management and system maintenance. Activating this mode manually is typically only necessary if the heat pump is malfunctioning. Because resistive heating is significantly more expensive to operate than the heat pump cycle, relying on emergency heat for extended periods can lead to a substantial increase in electricity bills. Recognizing when the system has automatically switched to auxiliary heat versus when it has been manually set to emergency heat helps users diagnose system efficiency issues.
Common Misconceptions
E M Heat is the same as “Auxiliary Heat.”
Auxiliary heat is often automated and works alongside the heat pump; Emergency Heat is typically a manual setting that disables the heat pump entirely.
Using E M Heat is the most efficient way to warm a house quickly.
While it provides heat, it is far less energy-efficient than the standard heat pump operation and should only be used as a last resort.
FAQ
When should I turn on E M Heat?
You should only manually select Emergency Heat if your heat pump's outdoor unit is broken or if the system is not heating the home despite being on the normal setting.
Does E M Heat cost more to run?
Yes, because it uses electric resistance heating instead of the more efficient heat exchange process of the pump.
Is E M Heat the same as a furnace?
No, but it performs a similar function by providing direct heat, whereas the heat pump moves existing heat from outside to inside.
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