Heat pumps are highly efficient systems for both heating and cooling, but their performance can be affected during colder winter months. Many heat pumps come equipped with an auxiliary heat mode to ensure comfort when outdoor temperatures drop. Many homeowners wonder, how do I know if my heat pump has auxiliary heat? This guide will help you determine whether your system is equipped with auxiliary (aux) heating, how it works, and when it should operate. You’ll find tips for identifying aux heat, troubleshooting, and maintenance recommendations to optimize your home’s comfort and energy efficiency.
What Is Auxiliary Heat In Heat Pumps?
Auxiliary heat, often labeled as “AUX HEAT” or “EMERGENCY HEAT” on thermostats, is a supplemental heating feature included in most air-source heat pump systems. It’s designed to provide additional warmth when outdoor temperatures are too low for the heat pump to efficiently extract heat from the outside air.
Auxiliary heat typically relies on electric resistance coils or, occasionally, a gas furnace (in “dual-fuel” systems) to rapidly increase interior temperatures when needed.
When Does Auxiliary Heat Activate?
- During Very Cold Weather: When the temperature outside falls below the efficient range of the heat pump (usually in the 35°F to 40°F range), the system triggers auxiliary heat.
- When There’s A Large Temperature Gap: If the thermostat is set much higher than the room’s current temperature, the heat pump may call for extra help to quickly reach the desired setting.
- During Defrost Cycles: Auxiliary heat may operate during heat pump defrost cycles to maintain indoor comfort while the exterior unit defrosts.
Key Signs Your Heat Pump Has Auxiliary Heat
Identifying whether your system includes auxiliary heat requires checking several features. Use the steps and indicators below to confirm:
Check Your Thermostat Display
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Look for “AUX HEAT” or “EM HEAT” Indicators: When your system runs and it’s especially cold, check your thermostat:
- If “AUX”, “AUX HEAT”, “EM HEAT”, or similar text appears, your system has this feature enabled.
- Some digital thermostats only display this when auxiliary heat is active.
Thermostat Settings Or Switches
- Manual “Emergency Heat” Setting: Many thermostats offer a manual “EM HEAT” mode that, when switched on, activates auxiliary resistance heat exclusively. This indicates your system is set up for auxiliary heating.
Review System Documentation
- Owner’s Manual: The user or installation manual for your heat pump will list auxiliary heat capabilities and provide wiring diagrams.
- Model Lookup: Search your system model number on the manufacturer’s website for specifications. Model numbers are usually on the interior air handler or outdoor unit.
Physical Inspection Of The Air Handler
- Look For Electric Heating Strips: Most auxiliary heat in all-electric systems comes from electric resistance coils, which are usually housed inside the air handler. An HVAC technician can safely open the unit to confirm this component.
Ask Your HVAC Installer Or Service Provider
- Professionals Can Verify: If you are unsure, your HVAC contractor can check the installation history, perform an inspection, or view wiring connections for auxiliary heating components.
How Does Auxiliary Heat Work?
Auxiliary heat acts as a backup or supplement for your heat pump. Normally, heat pumps draw warmth from the outside air right down to near-freezing conditions. When the temperature drops too low – a point called the “balance point” – the heat pump alone can’t keep up with the heating demand. At that point, a signal from the thermostat triggers the auxiliary heating element(s) inside the air handler.
With auxiliary heat on, both the heat pump and the electric (or gas) backup operate together to maintain the desired indoor temperature. If the outdoor unit enters defrost mode, auxiliary heat may briefly operate on its own to keep the house from cooling down.
Electric Vs. Gas (Dual-Fuel) Auxiliary Heat Explained
The type of auxiliary heat varies by heat pump design. Here’s how they differ:
| Auxiliary Heat Type | Description | Common In |
|---|---|---|
| Electric Resistance | Heats air by running current through metal coils | Most standard air-source heat pumps |
| Gas Furnace (Dual Fuel) | A gas furnace takes over heating when needed | Colder climates or systems with natural gas hookup |
Electric auxiliary heat is less efficient but easy to add. Gas auxiliary heat is more energy efficient in colder climates when outdoor temperatures make traditional heat pump operation impractical.
How To Tell When Auxiliary Heat Is Running
Recognizing when your heat pump’s auxiliary heat is on can help you monitor energy use and system health.
- Thermostat Notification: Many thermostats label the status with “AUX HEAT” or “EM HEAT” during operation.
- Sudden Increase In Electric Bill: Auxiliary heat uses more power than the heat pump alone. Spikes in your winter electricity bill may indicate frequent use.
- Warmer-Than-Usual Air Temperature: The air from your vents may feel hotter when auxiliary heat is running.
- Sound Or Smell: Some systems emit a faint click or a slight burnt-dust odor when resistance coils activate (especially if dormant for a while).
Understanding The Difference: Auxiliary Heat vs. Emergency Heat
Auxiliary heat and emergency heat are related but distinct settings:
| Feature | Auxiliary Heat (AUX) | Emergency Heat (EM HEAT) |
|---|---|---|
| Activation | Automatic, controlled by system/thermostat based on conditions | Manual, user selects at thermostat |
| Pump Operation | Heat pump and back-up heater work together as needed | Heat pump is disabled; only backup heater operates |
| Purpose | Helps the heat pump when it can’t keep up with demand | Used if heat pump malfunctions or during extreme cold |
It’s generally not recommended to run emergency heat unless the main heat pump is broken or off due to repairs or defrosting issues.
Why Is Auxiliary Heat Needed?
Auxiliary heat ensures comfort and protection of your home in several scenarios:
- Extreme Cold Weather: Heat pumps become less efficient as temperatures drop below freezing. Auxiliary heat maintains indoor warmth and prevents pipes from freezing in very low temperatures.
- Fast Recovery: If you want to raise the temperature several degrees quickly, the system may use auxiliary heat for brief periods.
- During Defrost Cycles: Auxiliary heat engages while the outdoor unit thaws frost to prevent cold air from circulating indoors.
How To Optimize Auxiliary Heat Use
Reducing reliance on auxiliary heat saves energy and limits unnecessary wear. Consider these strategies:
- Maintain Your System: Schedule annual professional tune-ups and replace filters regularly to ensure peak heat pump performance.
- Avoid Large Thermostat Changes: Increase the temperature gradually to prevent the thermostat from kicking in auxiliary heat unnecessarily.
- Seal Air Leaks: Improve your home’s insulation and seal drafts to keep heated air inside.
- Upgrade Thermostats: Use programmable or smart thermostats with adaptive recovery to minimize auxiliary heat use.
- Consider Dual-Fuel Systems: In colder regions, dual-fuel heat pumps switch to gas or oil backup heat for improved efficiency and lower heating costs.
Should Auxiliary Heat Run Constantly?
Auxiliary heat is meant for temporary support, not constant operation. If your system frequently depends on auxiliary heat, you may have issues such as:
- Undersized Heat Pump: The system may not be powerful enough for your space.
- Poor Maintenance: Clogged air filters, dirty coils, or failing components reduce efficiency.
- Thermostat Problems: Incorrect programming or malfunctioning sensors may trigger auxiliary heat inappropriately.
- Home Insulation Problems: Insufficient insulation leads to rapid heat loss and increased aux heat use.
How To Troubleshoot Auxiliary Heat Problems
If you notice auxiliary heat is running too often, or not coming on when needed, consider these troubleshooting steps:
- Check Thermostat Mode: Confirm it’s set to “Heat” rather than “Emergency Heat”.
- Monitor Outdoor Temperature: Review the weather. During deep cold snaps, auxiliary use is normal. If moderate temperatures persist and auxiliary heat runs often, service may be needed.
- Inspect Air Filters: Dirty filters restrict airflow and reduce system efficiency. Replace them regularly.
- Schedule Professional Service: Technicians can check if components – including sensors and backup heat strips – are functioning properly.
Upgrading Or Replacing Heat Pumps With Auxiliary Heat
If your current heat pump struggles in winter and auxiliary heat runs too frequently, it may be time for an upgrade. Consider:
- Cold-Climate Heat Pumps: New models are optimized for sub-zero operation, reducing auxiliary heat reliance.
- Larger Capacity Units: Properly sizing your system helps meet your home’s demands without frequent backup use.
- Dual-Fuel Systems: Combining a heat pump with a high-efficiency gas furnace provides both comfort and savings in cold areas.
Tips For Homeowners With Auxiliary Heat
- Regular Maintenance: Schedule both spring and fall HVAC checkups for longevity and top performance.
- Educate Your Household: Make sure everyone knows not to use the “Emergency Heat” setting unless advised by a technician.
- Keep Vents Clear: Blocked vents strain the system and reduce heating efficiency.
- Monitor Energy Bills: Sudden increases may signal overuse of auxiliary heat or a system issue.
Frequently Asked Questions
Is It Bad If Auxiliary Heat Comes On?
Auxiliary heat is normal during temperature extremes or rapid thermostat increases. Excessive use may indicate efficiency or sizing problems.
Can I Disable Auxiliary Heat?
Most systems automatically manage auxiliary heat. Disabling it is not recommended as it can leave your home without adequate heating during cold snaps. Consult an HVAC professional before making changes.
Does Every Heat Pump Have Auxiliary Heat?
Not all, but the vast majority of air-source residential heat pumps in climates with freezing temperatures include auxiliary heat strips or a dual-fuel backup.
Where Is The Auxiliary Heat Located?
The heating elements or gas backup are typically housed inside the air handler (indoor unit), sometimes adjacent to the blower or coil assembly.
Summary Table: How To Know If Your Heat Pump Has Auxiliary Heat
| Check Method | What To Look For | Action Needed |
|---|---|---|
| Thermostat Display | AUX HEAT / EM HEAT indicator | Review display when heat is running |
| Thermostat Settings | Emergency Heat mode available | Switch to “EM HEAT” to test backup heat |
| System Documentation | Manual mentions auxiliary/back-up heat | Locate or download relevant manuals |
| Physical Inspection | Presence of heat strips or gas furnace in air handler | Have a technician confirm if unsure |
| Manufacturer’s Website | Specifications list auxiliary heat | Search for your model number |
| Installer/Technician | Professional verification | Request inspection or service report |
Final Thoughts
Knowing if your heat pump has auxiliary heat helps homeowners manage comfort, efficiency, and maintenance. Reviewing your thermostat, system documentation, or consulting with an HVAC professional will give you a clear answer. Keep an eye on your system’s operation—especially during winter—to ensure reliable, cost-effective heating all season long.