Ever noticed “EM Heat” (or EMH) flashing on your thermostat and thought something was broken? Don’t worry—it’s not an error. EMH stands for Emergency Heat, a backup mode that kicks in when your heat pump can’t keep up. In this guide, I’ll explain what EMH really means, when to use it, how it affects your energy bill, and when to call for help.
What Does EMH Stand for on My Thermostat?
Emergency Auxiliary Heat or EMH may be utilized if your primary system, like a heat pump, cannot adequately warm your home. In that case, your system switches over to backup heat, like electric strips or a gas furnace, just to keep the house warm.
Why Does My Thermostat Have EMH?
Emergency Heat exists for two primary purposes:
Heat Pump Inefficiency
Heat pumps rely on outdoor air for warmth in your home; however, once temperatures fall below 30°F or -1°C, they become far less effective at providing comfort to you and may need EMH as backup heating to remain effective in creating warmth for comfort in the house.
Heat Pump Malfunction
Should your heat pump stop working or become inoperative, EMH will act swiftly to safeguard both you and your home against colder climate conditions.
Once EMH has been enabled on a thermostat, its heat pump stops operating automatically in favour of using only its backup heating system in times of extreme cold or other emergencies.
How Does Emergency Heating Work (EMH)?
When Your Thermostat Switches On Emergency Heat:
- The heat pump compressor is powered off.
- Electric resistance heating elements or the secondary furnace ignite.
- Warm air can be produced and distributed throughout your home’s ductwork like traditional heating methods, providing comfortable warmth at a more cost-efficient pace than standard options.
Electric resistance heat requires significant electricity use; thus, making this mode more expensive to run than standard heat pump operation.
When Should EMH Be Used?
Many modern thermostats and heat pump systems automatically activate EMH when necessary:
- Outdoor temperatures often fall too low for heat pump efficiency to remain at its maximum potential.
- Heat pumps typically utilize defrost mode to temporarily dissolve frost build-up on their coils and surfaces, such as coil fins.
- The system detects a heat pump malfunction.
Manual Activation – Only activate EMH manually when necessary:
- Your heat pump has broken down or frozen, and insufficient heating is available.
- Your immediate heating requirements must be addressed immediately.
- You are concerned that your heat pump is underperforming.
Manual EMH usage should only be employed temporarily and as necessary in an emergency.
What Happens If EMH Is Active?
Once EMH is engaged, your thermostat no longer relies on your heat pump for heat delivery.
- Energy costs could skyrocket as electric resistance heat or fuel furnaces become less energy-efficient.
- EMH indicators will appear on your thermostat’s display.
- Heating will continue until you disable EMH or until its normal operations resume.
What Are EMH and Auxiliary Heat Differences?
While both terms can sometimes be used interchangeably:
- On particularly frigid days, auxiliary heating may automatically supplement heat pump heating systems to meet demand.
- Emergency Heat (EMH) typically refers to manual activation of backup heat if your heat pump stops working, providing backup heat when required.
Understanding this distinction helps you use these features efficiently.
Why Not Always Rely on EMH for Heat Generation?
EMH heating solutions tend to be less energy-efficient and more costly than their heat pump counterparts; using EMH regularly could incur high utility bills; therefore, it should only ever serve as backup heat generation in an emergency scenario.
How Can You Determine If Your System Has EMH?
- Check for “EM Heat” or “Emergency Heat” buttons on your thermostat to confirm this is in use.
- Check for an “E” terminal wire on the control panel of your thermostat.
- Read your heat pump manual or consult an HVAC specialist.
Signs You Might Require an Electric Modulated Heater
- Your home lacks sufficient heating during cold weather conditions.
- Your heat pump appears to be cycling quickly, making unusual sounds, or straining to operate effectively.
- The heat pump is frozen or has frozen over.
- Your thermostat displays an EMH icon or error.
Locate and Activate EMH on Your Thermostat [How-To Guide]
- Press and hold for 3–5 seconds until the EMH indicator lights.
- To turn off, press again or switch your thermostat back into heat pump heating mode.
Troubleshooting Tips for EMH
If the EMH becomes stuck or won’t turn on:
- Verify wiring and connections on your thermostat.
- Power cycle your system by switching off the power at its circuit breaker for several minutes and restarting it.
Cost Impact of EMH
EMH systems use considerable electricity or fuel consumption; resistance heaters and secondary furnaces tend to be ineffective heat source alternatives compared to heat pumps, thus adding significantly to monthly heating bills if used regularly. Therefore, use EMH only when necessary, as overusing it will drastically increase monthly heating bills.
Maintenance Tips to Prevent Unnecessary EMH Use
- Be sure to regularly service your heat pump to reduce malfunctions.
- Clear snow and ice off outdoor heat pump units.
- Verify proper settings and wiring of the thermostat.
- Check backup heating components at regular intervals.
- Schedule annual HVAC inspections.
Environmental and Seasonal Considerations
Colder climates present heat pump systems with additional challenges, increasing the use of electricity-based heating methods (EMH). By taking steps such as improving home insulation before winter hits, your heat pump’s effectiveness could decrease, and you could rely less on EMH for heating needs.
Real User Scenarios
- A homeowner detects poor heating during a deep freeze; activating EMH keeps their home warmer temporarily.
- The heat pump freezes up, switching automatically into EMH until the thaw process occurs.
- Manual EMH should be activated before the technician arrives for repairs.
Conclusions and Advice Regarding Emergency Heat (EMH) for Comfort and Savings
Emergency Heating is an indispensable feature of heat pump systems, providing peace of mind if the cold overwhelms or breaks down primary heating sources. While EMH offers reliable warmth at higher costs, use it only when necessary for maximum savings and comfort.
Understanding EMH on your thermostat, its functions, and when and how it should be activated will keep you comfortable without wasting energy or money. I also have problems with your LG washer, so read this.
Q&A About EMH
Can EMH serve as my primary heat source?
Although possible, EMH should only ever be relied upon when there’s an urgent situation or during emergencies due to its increased cost and inefficiency.
Will Emergency Heat damage my system?
EMH was designed as a backup; however, prolonged usage can increase costs.
My EMH light is on, yet the room feels warm – is this normal?
Yes. In specific heat pumps, backup heating may occasionally run alongside them for short durations.
How can I determine whether my electric heat strips are functioning?
A technician should conduct tests; failing strips reduce backup heating reliability.
Could a malfunctioning thermostat cause EMH activation to persist?
Yes, malfunctioning thermostats may result in inappropriate EMH activation.
About the Author:
Alif Littel is a home tech & appliance troubleshooting writer with over 10 years of hands-on experience fixing household gadgets and smart home installs. Read more about me.