If you live in Bucks County, Philadelphia, or the Delaware Valley and notice “Aux Heat” or “Emergency Heat” on your thermostat during winter, you are not alone. Many homeowners worry that something is wrong with their heating system when they see these settings turn on.
In most cases, this is normal. Understanding what auxiliary heat and emergency heat are, and why your system switches to them, can help you avoid high energy bills and unnecessary strain on your heat pump.
What Is Auxiliary Heat?
Auxiliary heat, often displayed as “Aux Heat” on your thermostat, is backup heat that works together with your heat pump when outdoor temperatures drop too low.
Why heat pumps use auxiliary heat in winter
Heat pumps do not create heat. They move heat from outside air into your home. During winter in southeastern Pennsylvania and the Delaware Valley, there is still heat outdoors, but when temperatures fall into the 30s or lower, there is less heat available to pull inside.
When this happens, auxiliary heat automatically turns on to help keep your home comfortable.
How auxiliary heat works
Auxiliary heat:
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Turns on automatically
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Helps your heat pump maintain the set temperature
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Typically uses electric heat strips or a gas furnace in dual fuel systems
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Commonly runs during:
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Very cold outdoor temperatures
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Large thermostat increases, usually 5 degrees or more
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Auxiliary heat costs more to operate than your heat pump alone, but it is designed to run when needed during cold Pennsylvania winters.
What Is Emergency Heat?
Emergency heat is a manual setting on your thermostat. It should only be used when your heat pump cannot operate at all. Emergency heat relies entirely on the backup heat source and shuts off the outdoor heat pump unit.
When to use emergency heat
Emergency heat should only be turned on if:
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Your heat pump has stopped working
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The outdoor unit is damaged or completely iced over
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An HVAC technician instructs you to use it
When emergency heat is running:
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The heat pump is turned off
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Only the backup heat source operates
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Energy usage is significantly higher
Emergency heat is not meant for everyday winter heating. Leaving it on by mistake can cause very high utility bills.
Why Did My Heater Switch to Auxiliary Heat?
If auxiliary heat turns on by itself, it is usually for one of these reasons:
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Outdoor temperatures are very low
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The thermostat was raised too quickly
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Your home is losing heat faster than normal due to insulation or air leaks
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The system is programmed to use auxiliary heat below a certain outdoor temperature
This is common during cold snaps in Bucks County and the Philadelphia area, especially overnight or during extended periods of freezing weather.
Is It Normal for Auxiliary Heat to Run?
Yes, occasional auxiliary heat use is normal during winter. However, you should contact a local HVAC professional if:
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Auxiliary heat runs constantly, even in mild winter weather
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Your home does not warm up properly
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The system switches to emergency heat without manual input
These issues may point to heat pump problems, refrigerant issues, thermostat malfunctions, or a system that is not properly sized for your home.
How to Reduce Auxiliary Heat Usage
Homeowners in the Delaware Valley can reduce auxiliary heat use by:
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Adjusting the thermostat gradually, 1 to 2 degrees at a time
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Sealing air leaks around doors and windows
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Replacing air filters regularly
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Scheduling professional winter HVAC maintenance
Cold climate and inverter driven heat pumps are designed to rely less on auxiliary heat, even during freezing temperatures common in Pennsylvania winters.
Emergency Heat and Auxiliary Heat Explained Simply
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Auxiliary heat is automatic backup that supports your heat pump
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Emergency heat is a manual setting for heat pump failure
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Seeing auxiliary heat during winter is normal, but constant use is not
If you are unsure whether your heat pump is operating efficiently, or if you are concerned about high winter heating costs in Bucks County or the Philadelphia area, a professional HVAC inspection can help ensure your system is working properly. If you have questions about emergency heat, auxiliary heat, or heat pump performance during winter, a local HVAC expert can help keep your home comfortable and energy efficient.
If you live in the Delaware Valley/Greater Philadelphia area and would like to find comfort within your home, visit our website or give us a call at 215 - 245 - 3200 to learn more.
