What does auxiliary heat mean on my thermostat?
If you’ve ever noticed “Auxiliary Heat” displayed on your thermostat, you may be wondering what it means and whether it’s a cause for concern. Auxiliary heat (or aux heat) is a backup heating system that turns on when your heat pump needs extra help warming your home usually in extremely cold weather or during a defrost cycle. While aux heat is a normal function, if it runs too often, it can lead to higher energy bills and signal potential issues with your HVAC system. In this guide, we’ll explain what auxiliary heat means, why it turns on, and how to prevent it from running unnecessarily.
How Does Auxiliary Heat Work?
Your heat pump is designed to pull warmth from the outside air to heat your home. But when temperatures drop too low (typically below 35–40°F), your heat pump may need extra help.
That’s when auxiliary heat turns on—activating electric resistance heating (or another backup heat source) to warm your home faster.
When Does Auxiliary Heat Turn On?
Your thermostat will automatically activate aux heat if:
✅ The indoor temperature drops 2–3°F below your thermostat setting
✅ Your heat pump is in “defrost mode”
✅ The outdoor temperature is too cold for your heat pump to work efficiently
Auxiliary heat turns off once your home reaches the set temperature.
📌 Important: If your thermostat is stuck on aux heat for long periods, it could signal a problem with your heat pump or thermostat settings.
Why Is My Heat Pump Using Auxiliary Heat?
There are two common reasons why auxiliary heat turns on:
1. Your Heat Pump Needs Extra Help Heating Your Home
When the temperature outside is too cold, your heat pump may struggle to maintain the desired indoor temperature. Instead of running inefficiently, the system activates auxiliary heat strips to warm your home faster.
2. Your Heat Pump is in Defrost Mode
If you see steam or water around your outdoor unit, your heat pump might be in defrost mode. This happens when ice forms on the coils, and the system temporarily reverses operation to melt the ice.
📌 How to Tell If Your Heat Pump Is in Defrost Mode:
- The outdoor unit stops running or the fan turns off
- Steam or water is coming from the unit
- Your system automatically switches to auxiliary heat
💡 Tip: Once the defrost cycle is complete, your heat pump will resume normal operation, and aux heat should turn off.
Auxiliary Heat vs. Emergency Heat: What’s the Difference?
While both auxiliary heat and emergency heat provide backup heating, they work very differently:
| Feature | Auxiliary Heat | Emergency Heat |
|---|---|---|
| Turns on automatically? | ✅ Yes | ❌ No (manual) |
| Used in normal operation? | ✅ Yes | ❌ Only when heat pump fails |
| Expensive to run? | ⚠️ Somewhat | 🔥 Yes, very expensive |
| Should I use it? | ✅ When needed | ❌ Only in emergencies |
When Should You Use Emergency Heat?
🚨 Only use emergency heat when your heat pump stops working. It runs solely on electric, gas, or oil heating, which is much more expensive.
📌 How to Tell If You Need Emergency Heat:
- Your heat pump isn’t working at all
- The outdoor unit is completely frozen or broken
- Your home isn’t heating even with aux heat running
If you need to turn on emergency heat, call an HVAC professional immediately to diagnose and fix your heat pump.
How to Stop Auxiliary Heat From Turning On
If your thermostat keeps switching to aux heat, you may be able to reduce its usage and save on energy bills.
1. Lower Your Thermostat Setting
📌 If your thermostat is set too high, your heat pump will struggle to keep up. Try setting it between 62–68°F to prevent unnecessary aux heat use.
2. Improve Your Home’s Insulation
- Close curtains and blinds at night to keep warmth inside
- Seal drafty windows and doors
- Use area rugs on cold floors
3. Close Unused Rooms
If you have extra rooms that don’t need to be heated, close the vents and doors to redirect warm air where it’s needed most.
4. Schedule a Seasonal Heating Tune-Up
If your system is constantly using aux heat, it may need a maintenance check. Dirty filters, low refrigerant levels, or failing heat strips can all cause aux heat to run longer than necessary.
✅ When to Call a Professional:
- Your aux heat stays on constantly
- Your home isn’t heating properly
- Your energy bills are unusually high
An HVAC technician can inspect your system and ensure everything is working efficiently.
FAQ: People Also Ask
Is It Bad for My System to Use Auxiliary Heat?
No, auxiliary heat is a normal part of a heat pump system. However, if it runs constantly, it may indicate an issue.
Why Does My Thermostat Keep Switching to Aux Heat?
Your heat pump may not be able to keep up with demand. Try lowering your thermostat setting and improving insulation.
Should I Turn Off Auxiliary Heat?
No, your system automatically uses aux heat when needed. But if it runs too often, consider scheduling an HVAC checkup.
How Can I Tell If My Heat Pump is in Defrost Mode?
Look for steam coming from the outdoor unit and listen for the fan turning off temporarily.
Need Help With Your Heat Pump? Call Us Today!
If your auxiliary heat stays on constantly, your energy bills are rising, or your home isn’t heating properly, you may need a professional HVAC checkup.
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📞 Call Now: 623-584-4706