Auxillary Heat

If you’ve ever noticed the words “AUX Heat” or “Auxiliary Heat” appear on your thermostat during the winter, you might wonder — what does that mean, and should I be worried?
The short answer: Auxiliary heat is a backup heating feature in your heat pump system that helps your home stay warm when temperatures drop. It’s normal for it to come on occasionally, but if you see it too often, it could signal a problem.
At HVAC Tempe Pros, we help homeowners across Tempe, AZ understand their HVAC systems so they can keep their homes comfortable and energy-efficient. Here’s everything you need to know about auxiliary heat, when it should turn on, and what to do if it stays on longer than it should.

🔍 What Is Auxiliary Heat?Auxiliary heat (often shown as AUX on your thermostat) is a secondary heating source that works alongside your heat pump.
When outdoor temperatures drop too low for your heat pump to extract enough warmth from the outside air, the system automatically turns on electric resistance heating coils — or sometimes a gas furnace in dual-fuel systems — to help out.
This backup heat ensures your home stays warm even during unusually cold weather.
In Arizona, where winters are mild, your auxiliary heat shouldn’t come on very often. If it does, it may be a sign your heat pump needs maintenance or repair.

🧠 How Auxiliary Heat WorksHere’s a simple breakdown of what happens inside your HVAC system:

1. Your thermostat detects the temperature drop
   When your indoor temperature falls a few degrees below the set point, your heat pump kicks on to warm things up.
   
2. Heat pump struggles in colder air
   As outdoor temperatures drop (typically below 40°F), the heat pump becomes less efficient at transferring heat from the outside air.
   
3. Auxiliary heat activates
   Your thermostat signals the backup heating elements — usually electric coils — to turn on and provide extra warmth.
   
4. System returns to normal mode
   Once indoor temperatures reach the thermostat setting, the auxiliary heat turns off, and your heat pump resumes normal operation.
   

Essentially, auxiliary heat bridges the gap between what your heat pump can produce and what your home needs for comfort.

🌡️ When Should Auxiliary Heat Come On?In Tempe, Arizona, auxiliary heat typically activates under these conditions:

• Outdoor temperatures fall below 40°F (rare, but possible on cold winter nights).
  
• Your thermostat is turned up several degrees at once, creating a large demand for heat.
  
• The heat pump is defrosting — AUX heat may turn on temporarily to maintain comfort while the outdoor unit clears ice.
  

In short, occasional AUX Heat is normal. But if it stays on constantly or comes on when it’s mild outside, that’s worth investigating.

⚠️ When Auxiliary Heat Becomes a ProblemIf you see “AUX Heat” on your thermostat frequently, even when it’s not particularly cold, your system could be running inefficiently — which means higher energy bills and unnecessary wear and tear.
Here are the most common causes:
1. Malfunctioning Heat PumpIf your heat pump can’t extract enough heat due to a mechanical issue or refrigerant problem, your system may rely on AUX heat too often.
2. Dirty Air Filter or CoilsRestricted airflow forces your system to work harder, leading to more frequent backup heat use.
3. Thermostat MiscalibrationA faulty thermostat may incorrectly signal the system to turn on AUX heat even when it’s not needed.
4. Defrost Cycle Running Too LongDuring defrost mode, auxiliary heat activates to keep the home warm. If this cycle runs excessively, something may be wrong with the outdoor sensor.
5. Undersized or Aging Heat PumpIf your system isn’t powerful enough for your home or is losing efficiency with age, it will struggle to maintain set temperatures.

💡 How to Tell If Your Auxiliary Heat Is On Too OftenHere’s how you can check:

• Look for “AUX” or “AUX HEAT” displayed on your thermostat.
  
• Watch your energy bills — a sudden spike can indicate excessive AUX use.
  
• Feel the air from your vents — auxiliary heat air is warmer (and sometimes drier) than normal heat pump air.
  

If AUX heat runs constantly or for hours at a time, call HVAC Tempe Pros to inspect your system. Our certified technicians can determine whether it’s operating normally or wasting energy.

🛠️ How HVAC Tempe Pros Can HelpAt HVAC Tempe Pros, we provide full-service heat pump repair and maintenance to keep your system running efficiently year-round.
Our services include:

• Comprehensive system diagnostics
  
• Heat pump efficiency testing
  
• Thermostat calibration and programming
  
• Electrical and coil inspections
  
• Preventative maintenance and tune-ups
  

We’ll ensure your system only uses auxiliary heat when absolutely necessary — saving you money and preventing premature wear on your equipment.

💰 How Much Does Auxiliary Heat Cost to Run?Electric auxiliary heat uses resistance coils, which consume a large amount of electricity.
On average, running AUX heat can cost two to three times more per hour than your heat pump alone.
That’s why keeping your system properly maintained — and ensuring it doesn’t rely on backup heat too often — can make a significant difference in your monthly energy bills.

🧊 Auxiliary Heat vs Emergency Heat: What’s the Difference?Many homeowners confuse auxiliary heat with emergency heat, but they’re not the same:

• Auxiliary Heat:
  
  • Automatically activates when your heat pump needs help.
    
  • Works with your heat pump.
    
• Emergency Heat:
  
  • Must be manually switched on at the thermostat.
    
  • Runs without the heat pump (used only when the outdoor unit fails).
    

If your thermostat says “Emergency Heat”, contact HVAC Tempe Pros immediately — your heat pump may need repair.

🏠 Why Tempe Homeowners Trust HVAC Tempe ProsWhen it comes to heating and cooling in Tempe, homeowners choose HVAC Tempe Pros for quality service, honest pricing, and lasting results.
✅ Licensed & Certified HVAC Technicians
✅ Same-Day Service Available
✅ Transparent, Upfront Pricing
✅ Smart Thermostat Installation & Setup
✅ 100% Satisfaction Guarantee
We’re locally owned, deeply experienced, and always ready to help keep your home comfortable — no matter the season.

📞 Call HVAC Tempe Pros Today!If your thermostat shows “Aux Heat” more often than it should, or you’re worried your system isn’t running efficiently, call HVAC Tempe Pros today.
Our expert technicians will inspect your heat pump, thermostat, and backup heating system to ensure everything’s working perfectly.
📞 Call now: 602-566-9684
🌐 Visit: www.hvactempepros.com
Serving Tempe, Chandler, Mesa, Gilbert, and surrounding East Valley areas.
Don’t waste money on excessive auxiliary heat — schedule your heat pump service with HVAC Tempe Pros today!

❓ Frequently asked questions on Auxiliary Heat on ThermostatQ1: Is it normal for auxiliary heat to come on in Arizona?
Yes — it’s normal during rare cold mornings, but it shouldn’t stay on for long.
Q2: Does auxiliary heat mean my heat pump is broken?
Not necessarily. AUX heat is a normal backup function, but if it runs too often, your heat pump may need maintenance.
Q3: How can I stop my AUX heat from turning on?
Set smaller temperature adjustments (1–2°F at a time) and keep your system maintained for better efficiency.
Q4: What temperature does AUX heat turn on?
Usually around 35–40°F, depending on your system settings and thermostat programming.
Q5: Should I turn off auxiliary heat manually?
No — your system automatically controls it. If AUX heat is running continuously, call a professional to inspect your system.