What Is Heat Pump Auxiliary Heat?
Auxiliary heat is a backup heating system that works with your heat pump when it needs extra help. It turns on automatically when your heat pump can’t make enough heat by itself. This usually happens when it’s very cold outside (below 35°F), when you raise your thermostat more than 2-3 degrees at once, or during defrost cycles. Auxiliary heat uses electric resistance heating elements that work like a giant toaster inside your air handler. While this backup system keeps you warm when you need it most, it uses much more electricity than your regular heat pump operation.
Table of Contents
| Heat Pump Mode | Energy Usage | When It Activates |
|---|---|---|
| Normal Operation | Efficient (1 unit of electricity = 3 units of heat) | Above 35-40°F outdoor temperature |
| Auxiliary Heat | Less Efficient (1 unit of electricity = 1 unit of heat) | Below 35°F, quick temperature increases, defrost cycles |
| Emergency Heat | Least Efficient (relies solely on backup heating) | Manual activation when heat pump fails |
How Auxiliary Heat Works With Your Heat Pump
To understand auxiliary heat, you first need to know how heat pumps work. Heat pumps don’t create heat like furnaces do. Instead, they move heat from one place to another.
In winter, your heat pump pulls heat from the outside air and brings it into your home. This works well when temperatures are mild. But when it gets very cold outside, there’s less heat for your heat pump to capture.
That’s when auxiliary heat kicks in. It’s like having a backup plan when your main heating system needs help.
The Two-Stage Heating Process
Your heat pump system has two heating stages:
1. First stage: The heat pump works alone, moving heat from outside to inside.
2. Second stage: Auxiliary heat turns on to help when needed.
This two-stage approach ensures you stay comfortable even in very cold weather. Your thermostat controls this process automatically.
What Makes Auxiliary Heat Different
Auxiliary heat is different from your main heat pump in a few important ways:
– It uses electric resistance heating (like a toaster or space heater)
– It costs more to run than normal heat pump operation
– It produces heat directly instead of moving heat from outside
When you see “AUX” or “auxiliary heat” on your thermostat display, it means this backup system is working.
When Does Auxiliary Heat Activate?
Your heat pump’s auxiliary heat doesn’t run all the time. It only turns on in specific situations when extra heating power is needed.
Cold Outdoor Temperatures
The most common reason auxiliary heat activates is when outdoor temperatures drop below 35-40°F (1.6-4.4°C). At these temperatures, your heat pump struggles to pull enough heat from the outside air.
Your thermostat monitors the outdoor temperature through a sensor. When it detects temperatures falling below the threshold, it automatically activates the auxiliary heating elements.
In very cold climates, auxiliary heat might run more often during winter months. This is normal and exactly what the system was designed to do.
Quick Temperature Increases
Another time auxiliary heat activates is when you raise your thermostat setting by more than 2-3 degrees at once.
For example, if you set your thermostat from 68°F to 72°F, your system sees this as a request for quick heating. Heat pumps work best with gradual temperature changes. For fast warming, your system turns on auxiliary heat to help reach the new temperature quickly.
This is why energy experts recommend small, gradual temperature adjustments with heat pumps rather than big changes.
During Defrost Cycles
Heat pumps need to defrost occasionally in winter. When outdoor temperatures are cold and humidity is present, ice can form on the outdoor unit’s coil.
During defrost mode, your heat pump temporarily reverses operation to melt this ice. While defrosting, it can’t heat your home. The auxiliary heat turns on during these cycles to keep your home warm.
Defrost cycles typically last 5-15 minutes and happen automatically when needed.
Emergency Heating Situations
If your heat pump stops working properly, auxiliary heat can serve as emergency heat. Most thermostats have an “Emergency Heat” setting that forces the system to use only auxiliary heat.
This setting bypasses the heat pump completely and relies solely on the backup heating elements. It should only be used in true emergencies when your heat pump isn’t working and you’re waiting for repairs.
Signs Your Auxiliary Heat Is Running
How do you know when your heat pump is using auxiliary heat? There are several clear indicators to watch for.
Thermostat Indicators
The most obvious sign is your thermostat display. Most modern thermostats will show:
– “AUX” or “Auxiliary Heat” on the display
– A light or indicator that turns on (often red or amber)
– The words “Stage 2” or “Second Stage” heating
These indicators tell you that your backup heating system is currently running.
Changes in System Sound
You might also notice changes in how your system sounds:
– A clicking sound when auxiliary heat activates
– The sound of electric heating elements turning on
– Louder fan operation to distribute the extra heat
These sounds are normal when auxiliary heat is running.
Higher Electricity Bills
If auxiliary heat runs frequently, you’ll likely notice an increase in your electricity bills. Since auxiliary heat uses more electricity than normal heat pump operation, extended use will impact your energy costs.
Comparing your winter bills to previous months or years can help you spot unusual increases that might indicate excessive auxiliary heat use.
Is It Normal for Auxiliary Heat to Run Often?
Many homeowners worry when they see their auxiliary heat running. But is it really a problem?
Normal Operation Patterns
In most climates, it’s normal for auxiliary heat to run:
– During very cold weather (below 35°F)
– For short periods after raising the temperature setting
– Briefly during defrost cycles
– When outdoor temperatures drop suddenly
These are all part of normal heat pump operation and shouldn’t cause concern.
When Auxiliary Heat Use Might Indicate Problems
However, excessive auxiliary heat use might signal issues with your system:
– Running constantly even in mild temperatures
– Activating when outdoor temperatures are above 40°F
– Turning on and off rapidly (short cycling)
– Running for hours without reaching the set temperature
If you notice these patterns, your heat pump might need maintenance or repair.
How to Reduce Auxiliary Heat Usage
Since auxiliary heat uses more electricity, most homeowners want to minimize its use. Here are effective strategies to reduce how often your backup heating activates.
Proper Thermostat Settings
How you set your thermostat makes a big difference:
– Avoid raising the temperature more than 2 degrees at once
– Use programmable or smart thermostats that make gradual changes
– Consider keeping a consistent temperature instead of big setbacks
– Use the “heat” setting, not “emergency heat” for normal operation
Small adjustments help your heat pump work efficiently without needing backup heat.
Regular Maintenance
Keeping your system in good condition helps reduce auxiliary heat use:
– Change air filters monthly during heating season
– Have professional maintenance done annually
– Keep outdoor units clear of snow, leaves, and debris
– Make sure air vents inside your home aren’t blocked
A well-maintained heat pump works more efficiently in cold weather.
Home Weatherization
Improving your home’s insulation and sealing helps maintain temperature:
– Seal air leaks around windows and doors
– Add insulation to attics and walls if needed
– Use weatherstripping to prevent drafts
– Close fireplace dampers when not in use
Better insulation means less heat loss, which reduces the need for auxiliary heat.
Auxiliary Heat vs. Emergency Heat: Understanding the Difference
People often confuse auxiliary heat and emergency heat, but they’re not the same thing.
What Is Emergency Heat?
Emergency heat is a manual setting on your thermostat that forces your system to use only the backup heating elements. When you switch to emergency heat:
– The heat pump stops running completely
– Only the auxiliary heating elements provide warmth
– Your system uses much more electricity
– The “EM” or “Emergency” indicator shows on your thermostat
This setting is designed for emergencies only, such as when your heat pump fails or needs repair.
When to Use Emergency Heat
You should only use the emergency heat setting when:
– Your heat pump is damaged or not working
– You notice the outdoor unit is covered in ice and not defrosting
– A service technician advises you to use it temporarily
– Outdoor temperatures are extremely cold and your heat pump can’t keep up
Using emergency heat unnecessarily will cause very high electricity bills.
Key Differences
The main differences between auxiliary and emergency heat are:
– Auxiliary heat activates automatically; emergency heat is manually selected
– Auxiliary heat works together with your heat pump; emergency heat works instead of it
– Auxiliary heat is part of normal operation; emergency heat is for unusual situations
Understanding these differences helps you use your system correctly and avoid unnecessary energy costs.
Common Problems with Auxiliary Heat
Like any heating system, auxiliary heat can sometimes have issues. Here are common problems and what to do about them.
Auxiliary Heat Running Too Often
If your auxiliary heat seems to run more than it should:
– Check your thermostat settings and make sure it’s not set to “Emergency Heat”
– Look for drafts or air leaks that might be causing heat loss
– Make sure your outdoor unit isn’t covered or blocked
– Consider having your refrigerant levels checked
A professional can determine if your heat pump is working properly or needs service.
Auxiliary Heat Not Turning On
If your home isn’t getting warm enough in cold weather, your auxiliary heat might not be working:
– Check your circuit breaker to make sure it hasn’t tripped
– Inspect for blown fuses in your air handler
– Test your thermostat to ensure it’s working correctly
– Look for error codes on your thermostat display
This problem usually requires professional diagnosis and repair.
High Energy Bills
If your energy bills seem unusually high during winter:
– Monitor how often auxiliary heat runs
– Check for thermostat setting issues
– Consider a programmable thermostat that minimizes auxiliary heat use
– Have your system inspected for efficiency problems
A well-tuned system uses auxiliary heat only when truly necessary.
Frequently Asked Questions About Auxiliary Heat
Does auxiliary heat use a lot of electricity?
Yes, auxiliary heat uses significantly more electricity than normal heat pump operation. While a heat pump might produce 3 units of heat for every unit of electricity used, auxiliary heat produces only 1 unit of heat per unit of electricity. This makes it about 2-3 times more expensive to run than your heat pump alone.
Should I turn off auxiliary heat to save money?
No, you shouldn’t disable auxiliary heat completely. It’s an essential part of your heating system that ensures comfort in cold weather. Instead, focus on reducing how often it activates by maintaining your system, using appropriate thermostat settings, and improving home insulation.
Why does my auxiliary heat run when it’s not that cold outside?
If auxiliary heat runs when temperatures are above 40°F, possible causes include: thermostat issues, sensor problems, improper settings, or heat pump malfunction. A professional inspection can identify and fix the underlying cause.
How long should auxiliary heat run?
Auxiliary heat typically runs for 15-20 minutes when helping your heat pump reach the desired temperature. During defrost cycles, it might run for 5-15 minutes. If it runs continuously for hours, your system might need service.
Can I run just my auxiliary heat without the heat pump?
Yes, this is what the “Emergency Heat” setting does. However, this should only be used when your heat pump isn’t working properly. Running on auxiliary heat alone is much more expensive than normal operation.
Stay Warm While Keeping Your Energy Bills Under Control
Understanding how auxiliary heat works helps you get the most from your heat pump system. This backup heating source is an important part of keeping your home comfortable during cold weather.
By knowing when auxiliary heat should activate and how to minimize its use, you can stay warm while keeping your energy bills under control. Remember that some auxiliary heat use is normal and necessary, especially during very cold weather.
For the best performance from your heat pump system, regular maintenance is key. Professional inspections can catch small issues before they become big problems and ensure your system runs efficiently all winter long.
If you’re experiencing issues with your heat pump or auxiliary heating system, don’t wait until you’re left in the cold. Contact Shipton’s Heating & Cooling to schedule an appointment with our experienced technicians who can diagnose and solve your heating challenges.