Why Your Heat Pump’s Auxiliary Heat Is Running Too Much
The auxiliary heat of your heat pump turns on too much when outdoor temperatures drop below 35°F, your thermostat is set too high, your heat pump is dirty or broken, or your home has air leaks. This backup heating system uses electric resistance coils that cost 3-5 times more to run than your regular heat pump. When working correctly, auxiliary heat should only activate during defrost cycles or when temperatures are extremely cold. If it’s running constantly, you’re wasting energy and money while putting extra strain on your system.
Table of Contents
| Auxiliary Heat Issue | Possible Cause | Solution |
|---|---|---|
| Running too frequently | Thermostat set too high | Adjust in smaller increments (1-2°F) |
| Stays on constantly | Dirty filters/coils | Clean or replace filters monthly |
| Activates above 35°F | Thermostat settings incorrect | Check emergency heat settings |
| Runs during mild weather | System malfunction | Professional inspection needed |
What Is Auxiliary Heat and How Does It Work?
Auxiliary heat (sometimes called “aux heat”) is your heat pump’s backup heating system. It works like the heating coils in a toaster. When your regular heat pump can’t keep up, these electric resistance coils turn on to help warm your home.
Think of your heat pump like a car, and the auxiliary heat as a backup engine. Your car normally runs on its main engine, but if that engine struggles on a steep hill, a second engine kicks in to help. That’s what auxiliary heat does when your heat pump struggles to warm your home.
When Should Auxiliary Heat Normally Turn On?
Your heat pump’s auxiliary heat should only turn on in three main situations:
1. When outdoor temperatures fall below 35°F (because heat pumps become less efficient in very cold weather)
2. During defrost cycles (when your outdoor unit needs to melt ice buildup)
3. When you raise your thermostat more than 2-3 degrees at once
In normal operation, you might see the “AUX” light on your thermostat flash briefly during these times. This is completely normal and nothing to worry about.
The Difference Between Auxiliary Heat and Emergency Heat
Many people confuse auxiliary heat with emergency heat, but they’re not the same thing:
Auxiliary heat turns on automatically when needed to help your heat pump. It works alongside your heat pump.
Emergency heat is a setting you manually switch on when your heat pump completely fails. It bypasses your heat pump and relies only on the backup heating system.
You should never need to switch to emergency heat unless your heat pump stops working entirely. Using emergency heat unnecessarily will cause your energy bills to skyrocket.
7 Reasons Why Your Auxiliary Heat Runs Too Much
If the auxiliary heat of your heat pump is running more than it should, here are the most common causes:
1. Extremely Cold Weather
The most obvious reason is simply that it’s very cold outside. Heat pumps naturally lose efficiency when temperatures drop below 35°F. When this happens, your auxiliary heat is designed to help.
However, if your auxiliary heat runs constantly during cold weather, your heat pump might be undersized for your home. A properly sized system should still handle most of the heating load, with auxiliary heat only providing occasional support.
2. Thermostat Set Too High
If you raise your thermostat temperature by more than 2-3 degrees at once, your system activates auxiliary heat to reach that temperature faster. This is called “recovery mode.”
For example, if you keep your home at 68°F while you’re away and then set it to 72°F when you return, your auxiliary heat will kick on to help reach that temperature quickly.
To avoid this, make smaller adjustments to your thermostat (1-2 degrees at a time) or use a programmable thermostat that can make gradual changes automatically.
3. Dirty Air Filters
Clogged air filters restrict airflow through your system. When air can’t flow properly, your heat pump can’t distribute heat effectively. This makes your system work harder and often triggers the auxiliary heat to compensate.
You should check and replace your air filters every 1-3 months, depending on your home conditions. If you have pets or allergies, you might need to change them even more frequently.
4. Refrigerant Issues
Your heat pump uses refrigerant to transfer heat. If refrigerant levels are low due to a leak, your system can’t move enough heat into your home. This makes your auxiliary heat work overtime to make up the difference.
Signs of refrigerant problems include:
– Ice buildup on the outdoor unit
– Hissing sounds near the refrigerant lines
– Longer heating cycles
– Higher energy bills
Refrigerant issues require professional repair, as handling refrigerant requires special certification.
5. Outdoor Unit Problems
Your heat pump’s outdoor unit needs proper airflow to function correctly. Several issues can interfere with this:
– Dirt, leaves, or debris around the unit
– Snow or ice buildup
– Plants growing too close to the unit
– Damaged fan or components
Make sure to keep the area around your outdoor unit clear (at least 2 feet on all sides) and remove any snow or ice buildup during winter.
6. Improper Thermostat Settings
Sometimes the problem is as simple as incorrect thermostat settings. Your thermostat might be programmed to use auxiliary heat more often than necessary.
Check your thermostat settings to make sure:
– The heat pump mode is selected (not emergency heat)
– Temperature differential settings aren’t too narrow
– The thermostat is properly calibrated
Some smart thermostats have special heat pump settings that minimize auxiliary heat usage. These can save you significant money over time.
7. Home Insulation and Air Leaks
Poor insulation and air leaks force your heating system to work harder. When heat escapes too quickly from your home, your heat pump struggles to keep up, and auxiliary heat activates more frequently.
Common areas for air leaks include:
– Windows and doors
– Attic hatches
– Electrical outlets on exterior walls
– Plumbing penetrations
– Recessed lighting
Improving your home’s insulation and sealing air leaks can dramatically reduce how often your auxiliary heat runs.
How to Reduce Auxiliary Heat Usage and Save Money
Since the auxiliary heat of your heat pump uses 3-5 times more electricity than normal operation, reducing its usage can save you a lot of money. Here are practical steps you can take:
Regular Maintenance Is Key
The most important thing you can do is maintain your heat pump properly:
– Change air filters monthly during heating season
– Keep outdoor units clear of debris, snow, and ice
– Schedule professional maintenance once a year before heating season
Professional maintenance typically includes cleaning coils, checking refrigerant levels, inspecting electrical components, and ensuring proper operation. This preventive care helps your system run efficiently and reduces auxiliary heat usage.
Adjust Your Thermostat Habits
Small changes to how you use your thermostat can make a big difference:
– Set your thermostat to a lower temperature (68°F is recommended during winter)
– Make small temperature adjustments (1-2°F at a time)
– Use a programmable or smart thermostat designed for heat pumps
– Never use the emergency heat setting unless your heat pump is completely broken
Some smart thermostats can learn your heat pump’s performance and minimize auxiliary heat usage automatically. These can pay for themselves quickly through energy savings.
Improve Your Home’s Efficiency
Making your home more energy-efficient reduces the load on your heat pump:
– Seal air leaks around windows, doors, and other openings
– Add insulation to your attic, walls, and floors
– Use ceiling fans on low speed to circulate warm air
– Keep curtains open during sunny days to capture solar heat
– Close curtains at night to reduce heat loss
Even simple measures like using door sweeps and caulking around windows can significantly reduce how often your auxiliary heat runs.
When to Call a Professional
While some auxiliary heat issues can be fixed yourself, others require professional help. Call an HVAC technician if:
– Your auxiliary heat runs constantly, even when it’s not extremely cold
– You’ve checked filters and they’re clean, but problems persist
– Your system makes unusual noises
– Your energy bills have increased dramatically
– Your heat pump is more than 10 years old and having frequent problems
A professional can perform diagnostic tests to identify exactly what’s causing your auxiliary heat to run too much. They can also recommend whether repairs or replacement make more sense based on your system’s age and condition.
Understanding the Cost Impact of Excessive Auxiliary Heat
When the auxiliary heat of your heat pump runs too much, it directly impacts your wallet. Let’s look at the numbers:
A typical heat pump might use about 3-5 kilowatts (kW) when running normally. But when auxiliary heat activates, power consumption jumps to 10-15 kW or more.
If electricity costs $0.13 per kilowatt-hour (kWh), here’s what that means:
– Normal heat pump operation: $0.39-$0.65 per hour
– With auxiliary heat: $1.30-$1.95 per hour
If your auxiliary heat runs unnecessarily for just 4 hours a day, that’s an extra $3.64-$5.20 daily, or about $109-$156 monthly in wasted energy.
Beyond money, excessive auxiliary heat usage also:
– Puts more strain on your electrical system
– Increases your carbon footprint
– Shortens the lifespan of your heating equipment
This is why fixing auxiliary heat problems quickly is so important for both your budget and your system.
Frequently Asked Questions About Auxiliary Heat
Is it normal to see the AUX light on my thermostat during cold weather?
Yes, it’s normal for the auxiliary heat of your heat pump to activate briefly when outdoor temperatures fall below 35°F. You might see the AUX light flash occasionally. However, if it stays on continuously during mild weather, that indicates a problem.
How much more does auxiliary heat cost to run compared to normal heat pump operation?
Auxiliary heat typically costs 3-5 times more to operate than your heat pump’s normal heating mode. This is because it uses electric resistance heating rather than the more efficient heat transfer process of your heat pump.
Should I use emergency heat when it’s very cold outside?
No, you should never use the emergency heat setting just because it’s cold. Emergency heat is only for when your heat pump completely fails. Your system will automatically use auxiliary heat as needed during cold weather without switching to emergency mode.
How can I tell if my auxiliary heat is running too much?
Signs include:
– The AUX indicator on your thermostat stays lit for long periods
– Unusually high electric bills during heating season
– Your system runs constantly but struggles to maintain temperature
– You notice a burning dust smell (from electric heating elements that rarely run)
Will a heat pump work without auxiliary heat?
In moderate climates where temperatures rarely drop below freezing, a heat pump can work without auxiliary heat. However, in colder regions, auxiliary heat is essential for comfort during extreme cold snaps and defrost cycles.
Keep Your Heat Pump Running Efficiently
Understanding why the auxiliary heat of your heat pump kicks on too frequently is the first step to solving the problem. In most cases, the solution involves simple maintenance, thermostat adjustments, or improving your home’s efficiency.
Remember that your heat pump is designed to be highly efficient, but it needs proper care to perform at its best. Regular maintenance and prompt attention to problems will help you stay comfortable while keeping your energy bills under control.
If you’ve tried the basic troubleshooting steps and your auxiliary heat still runs excessively, it’s time to call in the experts. A professional HVAC technician can diagnose more complex issues and recommend the most cost-effective solution.
Don’t let auxiliary heat problems drain your wallet this winter. Contact T. Byrd’s Heating and Air today to schedule a professional inspection of your heat pump system. Our experienced technicians can identify and fix the issues causing your auxiliary heat to run too much, helping you stay comfortable and save money all season long.