Auxiliary heat on a heat pump is a critical backup system that ensures homes remain comfortable during extremely cold weather. Many American homeowners are unaware of how this function works or why it’s essential for efficient heating. This article explores auxiliary heat, how it operates with heat pumps, its benefits, and practical considerations for homeowners seeking better comfort and energy savings.
Heat Pumps: Basics And Operation
A heat pump is an energy-efficient HVAC device that provides both heating and cooling by transferring heat between the outdoors and indoors. It works by extracting heat from the air, ground, or water and moving it into or out of your home. This system is effective in mild to moderate climates but faces efficiency drops as outdoor temperatures plunge.
How Heat Pumps Work
- Heating Mode: The system reverses the refrigeration cycle, drawing heat from outside—even in cold temperatures—and moving it indoors.
- Cooling Mode: The process reverses, pulling heat from indoors and expelling it outside.
- Efficiency: Heat pumps can be three to four times more energy-efficient than conventional electric heating systems under mild conditions.
This efficiency, however, can rapidly decline during extreme cold spells. That’s where auxiliary heat enters the picture.
Auxiliary Heat: Definition And Purpose
Auxiliary heat, often called “aux heat” on thermostats, is a secondary heating element designed to supplement the main heat pump during freezing weather. It ensures warmth when the heat pump’s primary functionality weakens due to low outdoor temperatures.
- Primary Role: To provide additional heating power when the heat pump can’t reach the set temperature fast enough.
- Activation: Automatically engages based on thermostat logic or extreme temperature drops.
- Components: Most often consists of electric resistance coils, but can include fossil fuel burners (dual-fuel systems).
Types Of Auxiliary Heat
There are several types of auxiliary heat that can operate in conjunction with heat pumps.
- Electric Resistance Heat: The most common form, which uses electric coils similar to those in space heaters.
- Duel Fuel Auxiliary Heat: Pairs the heat pump with a gas furnace, switching to gas as auxiliary in very cold weather.
- Hot Water Auxiliary: Less common, uses hydronic heating systems to back up the heat pump.
When Does Auxiliary Heat Activate?
Auxiliary heat turns on automatically based on several conditions:
- Temperature Threshold: When outdoor temperatures drop below 35–40°F, heat pumps lose efficiency and auxiliary heat is typically triggered.
- Setpoint Recovery: If the system struggles to reach or maintain the desired thermostat temperature, aux heat engages to help catch up.
- Defrost Cycle: During defrost, aux heat may power on to maintain indoor comfort while the exterior coil is being thawed.
Auxiliary Heat Vs. Emergency Heat
These two terms are often confused, but their roles are distinct.
| Auxiliary Heat | Emergency Heat |
|---|---|
| Automatically activated by thermostat logic when supplemental heat is needed | Manually activated by the user in case the heat pump fails or requires service |
| Works alongside the heat pump | Runs independently, using only the secondary heat source |
| Short-term, efficiency-focused use | For emergencies; less efficient and costly to run |
Auxiliary heat supports the heat pump before it’s overwhelmed; emergency heat is a full backup mode reserved for equipment failures.
Efficiency And Energy Usage Of Auxiliary Heat
Auxiliary heat relies mostly on electric resistance heating, which is far less efficient than the heat pump’s normal operation. While a heat pump can deliver up to 300-400% efficiency, electric aux heat is around 100% efficient—meaning every unit of electricity produces an equal unit of heat.
- Cost Impact: Expect higher utility bills when aux heat operates for long periods.
- Energy Drains: Frequent or prolonged use signals heat pump inefficiency or extreme cold.
- Smart Use: Modern thermostats limit aux heat usage to brief, necessary intervals.
It’s crucial to minimize aux heat reliance for both energy savings and environmental benefits.
Thermostat Indicators: What Does “Aux Heat” Mean?
Many smart or programmable thermostats display “Aux Heat” when the secondary heating is active. This indicator alerts the homeowner that the backup system supplements the standard heat pump operation.
- Common Thermostats: Honeywell, Ecobee, and Nest all show auxiliary heat status.
- Advice: If “Aux Heat” stays on for long, it may indicate an issue with the primary heating system or extreme cold outside.
Regular display of this icon is normal during very cold spells but should disappear when outdoor temperatures moderate.
Benefits Of Auxiliary Heat In Heat Pumps
Auxiliary heat ensures continuous home comfort even during freezing weather. It bridges the gap when the heat pump alone can’t keep up. Key benefits include:
- Reliable Comfort: Indoor temperatures are maintained even during the coldest days.
- Automatic Function: Homeowners don’t have to intervene—the system handles needs seamlessly.
- Safety: Prevents freezing of pipes or structural damage during severe cold snaps.
- Integration: Works with modern smart thermostats for optimized usage and notification.
Potential Downsides And Cost Considerations
While auxiliary heat is vital for cold climates, it does have drawbacks:
- Higher Energy Bills: Electric resistance heating is expensive compared to heat pump operation.
- System Wear: Prolonged reliance may increase maintenance requirements over time.
- Carbon Footprint: More electricity use increases environmental impacts unless powered by renewables.
Strategic home insulation and system maintenance can limit unnecessary aux heat usage for cost control.
Optimizing Auxiliary Heat Performance
There are practical ways to ensure auxiliary heat is used only when truly needed, keeping costs down and comfort up:
- Insulation Upgrades: Improve walls, attics, and windows to minimize heat loss.
- Programmable Thermostats: Set back temperatures during overnight hours to reduce aux activation.
- Routine Maintenance: Schedule heat pump service annually to ensure peak efficiency.
- Weatherization: Seal leaks around doors and windows to maintain indoor temperature.
Signs Of Problems With Auxiliary Or Heat Pump Systems
Monitoring for signs of trouble helps prevent energy waste and keeps the system running smoothly. Watch for:
- Constant “Aux Heat” Indicator: May suggest an underperforming heat pump or very poor insulation.
- Uneven Heating: Indicates airflow or mechanical issues requiring professional service.
- High Power Bills: Could mean aux heat is active too often.
- Noisy Operation: Suggests system strain or frozen components.
Address these symptoms early to avoid higher repair or energy costs.
Should You Manually Enable Emergency Heat?
Emergency heat is designed for true equipment failures, not routine use. Do not switch to emergency heat unless:
- The heat pump is not operational.
- There’s a mechanical fault registered by the system.
- A technician advises it during service or repairs.
Relying on emergency heat unnecessarily can double or triple energy usage and utility bills.
Auxiliary Heat In Modern Smart Homes
Smart thermostats and connected home systems now manage auxiliary heat more efficiently. Features include:
- Learning Algorithms: Adjusts aux heat activation based on outdoor temperature trends and occupancy.
- Notifications: Alerts users if aux heat runs excessively or if energy usage spikes.
- Remote Control: Lets homeowners monitor and adjust heat remotely to balance comfort and savings.
Embracing these technologies improves efficiency, cuts costs, and ensures reliable warmth.
Geographic Considerations For Auxiliary Heat Usage
Auxiliary heat is most relevant in climates where winter temperatures routinely fall near or below freezing.
- Southern U.S.: Often require aux heat for brief cold snaps; main heat pump serves well otherwise.
- Northern U.S.: Frequent aux heat activation; may warrant a dual-fuel system with gas backup.
- Pacific and Milder Areas: Rarely trigger auxiliary heat, leading to lower overall energy costs.
Maintenance Tips For Reliable Auxiliary Heating
Annual inspections of your heat pump and auxiliary systems are essential. Key tips include:
- Check Air Filters: Dirty filters limit air flow and can trigger unnecessary aux heat usage.
- Inspect Coils: Clean indoor and outdoor coils for peak efficiency.
- Test Backup Elements: Ensure electric strips or gas backups engage and disengage appropriately.
Expert service helps maximize both comfort and equipment lifespan.
Comparing Auxiliary Heat With Other Backup Methods
| Backup System | Advantages | Drawbacks |
|---|---|---|
| Electric Resistance | Widely available, integrates easily | High cost, energy-intensive |
| Gas Furnace (Dual Fuel) | More efficient and less costly in cold climates | Requires separate fuel source and more complex installation |
| Wood/Pellet Stove | Supplementary, emergency use | Manual operation, emissions |
Frequently Asked Questions About Auxiliary Heat
- Is auxiliary heat bad if it runs all the time? If it runs constantly, there’s likely an issue with the main heat pump or your home’s insulation.
- How long should aux heat run? Auxiliary heat should run only long enough to support the heat pump during temperature dips or rapid recovery.
- Can I disable auxiliary heat? Disabling is not recommended; it’s essential for comfort and safety during very cold spells.
Best Practices For Homeowners
To get the most from your heat pump and auxiliary heat:
- Set Realistic Thermostat Goals: Avoid drastic temperature spikes which increase aux heat use.
- Invest In Insulation: Good thermal barriers minimize energy loss and assist both systems.
- Consult With HVAC Professionals: Regular system health checks prevent surprises in the dead of winter.
- Monitor Utility Bills: Sharp increases signal aux or overall system issues.
Summary Table: Auxiliary Heat At A Glance
| Aspect | Details |
|---|---|
| Purpose | Backs up heat pump in extreme cold |
| Types | Electric resistance, dual fuel, hydronic |
| Energy Efficiency | Lower than main heat pump (100% vs. 300-400%) |
| Activation | Automatic via thermostat, temperature-driven |
| Concerns | High costs, frequent usage means potential system or insulation problems |
| Solutions | Maintenance, insulation upgrades, smart thermostats |
Auxiliary heat is a valuable safety net for American homes relying on heat pumps, providing comfort and peace of mind during winter’s worst. Understanding how, when, and why it works empowers homeowners to manage energy costs and HVAC longevity.