Welcome to Miller's Heating & Air, your trusted partner for heating and cooling in Vancouver, WA. In this article, we're going to clear up some common confusion about auxiliary heat and emergency heat in heat pump systems.
If you've ever noticed “AUX Heat” or “EM Heat” on your thermostat, you might wonder what the difference is and whether something is wrong with your system.
Both involve backup heating, but they don't work exactly the same way. Understanding when each is used can help you manage heating costs and recognize when your heat pump may need service.
How a Heat Pump Works
Before we dive into auxiliary and emergency heat, let's get a solid understanding of how a heat pump operates. A heat pump is a versatile HVAC system that both heats and cools your home. It achieves this by moving heat rather than generating it through combustion.
In heating mode:
The heat pump extracts heat from the outdoor air, even in chilly weather.
It then moves this heat into your home, warming your indoor space.
This process can be highly energy-efficient, although operating costs depend on outdoor temperatures, equipment efficiency, and local energy prices.
Want to know more about how this works during colder weather? Read our guide to How Does a Heat Pump Work in Winter?
What's the Difference Between Auxiliary Heat and Emergency Heat?
Auxiliary heat and emergency heat both involve a backup heating source, but there's an important difference in how they're used.
Auxiliary heat (AUX) typically turns on automatically when your heat pump needs additional help warming your home. In a standard system with electric backup heating, the heat strips normally run alongside the outdoor unit, adding warmth rather than replacing its heating. This can happen during very cold weather, a defrost cycle, or when you've raised the thermostat several degrees.
There's one important exception to normal AUX operation. Some thermostats are programmed with a compressor lockout temperature.
When the outdoor temperature drops below that setting, the thermostat can automatically shut off the heat pump's compressor and use only the electric heat strips. This is still considered auxiliary heat operation, not emergency heat, because the homeowner hasn't manually selected EM Heat.
Emergency heat (EM Heat) is usually a setting you select manually on your thermostat. It tells the system to rely on its backup heating source instead of normal heat-pump heating. It's generally intended for situations when the heat pump cannot operate properly.
Many heat pumps use electric resistance heat strips for backup heating. Dual-fuel systems work differently.
They combine a heat pump with a gas furnace, and the system can switch from the heat pump to the furnace when outdoor temperatures reach a programmed changeover point. In this setup, the furnace takes over heating rather than running at the same time as the heat pump.
Auxiliary Heat vs Emergency Heat
Dual-fuel systems operate differently: the gas furnace takes over from the heat pump at the programmed changeover temperature.
When Should You Use Emergency Heat?
Emergency heat is generally intended for situations when your heat pump isn't working properly and you need to rely on the backup heating system.
For example, if the outdoor heat pump has stopped working and your home isn't staying warm, emergency heat may provide temporary heating while you arrange for repairs.
A few things to remember:
Cold weather alone doesn't mean you should turn on emergency heat. Many heat pumps continue operating effectively below freezing.
Emergency heat isn't meant to be your everyday heating setting. In many systems, selecting it bypasses the heat pump and relies entirely on backup heating.
Not every heat pump has the same backup system. Some use electric heat strips, while others have a furnace or another heating source.
If you're unsure whether to use emergency heat, contact Miller's Heating & Air before changing your thermostat settings.
Why Is My Thermostat Showing AUX Heat?
If you've noticed AUX Heat on your thermostat, don't assume something is wrong.
Auxiliary heat is designed to provide additional heating when your heat pump needs help. Depending on your equipment, it may activate when:
Outdoor temperatures drop and the heat pump needs additional heating capacity.
You raise the thermostat several degrees and the system needs to warm the house quickly.
Your heat pump enters a defrost cycle: During cold weather, the outdoor unit may need to melt frost from its coil. Electric auxiliary heat may turn on briefly to help maintain indoor comfort. This typically lasts only a few minutes.
The thermostat or system controls call for backup heating based on their settings.
Keep in mind that AUX heat doesn't always mean something is wrong or that your heat pump has stopped working. It can be a normal part of heating your home, especially during colder weather or short defrost cycles.
Occasional AUX heat use can be normal. However, if it's running for long periods during relatively mild weather, or your home isn't reaching the temperature you've set, it may be time to have your heat pump checked.
Maximizing Heat Pump Efficiency
To minimize the need for emergency heat and keep your energy bills in check, consider implementing the following strategies to maximize your heat pump's efficiency:
Regular Maintenance
Schedule regular maintenance for your heat pump to ensure it operates optimally. Professional technicians can inspect and clean components, check system operation, evaluate refrigerant performance when appropriate, and identify problems that may affect heating efficiency.
Insulation and Sealing
Proper insulation and sealing gaps in your home's envelope are essential for retaining heat. A well-insulated and sealed home requires less heating, reducing the reliance on emergency heat.
Programmable Thermostats
Invest in a programmable thermostat to maintain consistent indoor temperatures. Avoid making drastic adjustments, as this can cause the system to work harder and increase energy consumption.
A properly configured thermostat can help your heat pump maintain a comfortable temperature without unnecessary changes. Large temperature adjustments may cause some systems to use auxiliary heat more often, so it's worth asking your technician about the best thermostat settings for your equipment.
Air Filter Maintenance
Regularly check and replace your air filters according to your equipment's recommendations. A clogged filter can hinder the heat pump's efficiency, leading to higher energy bills.
Does Emergency Heat Cost More to Run?
In many homes, emergency heat uses electric resistance heating, which generally requires more electricity to provide the same amount of heat as a properly operating heat pump.
That's why leaving your thermostat on emergency heat unnecessarily can increase your winter energy bills.
However, operating costs depend on your equipment and backup heating source. Homes with dual-fuel systems, for example, may use a gas furnace rather than electric heat strips.
The important thing is to understand how your particular system works and use emergency heat only when appropriate.
When to Call Miller's for Heat Pump Service
Seeing AUX Heat on your thermostat doesn't automatically mean something is wrong. But if your heat pump isn't keeping the house comfortable, the outdoor unit isn't operating normally, or your system is relying on backup heat more often than usual, it's worth having it checked.
Miller's Heating & Air provides heat pump service and repair in Vancouver, WA. Our technicians can inspect your equipment, check thermostat operation, and help determine whether your system is working the way it should.
Learn the difference between AUX heat and emergency heat, when each is used, how they affect heating costs, and when your heat pump may need service.
