When to Use Auxiliary Heat in Winter: Heat Pump Backup Explained

When to Use Auxiliary Heat in Winter: Heat Pump Backup Explained

​Heat pumps are efficient HVAC systems that heat and cool your home year-round. However, in winter, they sometimes need help to keep your home warm. This is where auxiliary heat, also called backup or emergency heat, comes in.
Understanding when and why to use auxiliary heat is crucial to maintain comfort without wasting energy.

🔎 What is Auxiliary Heat?Auxiliary heat is electric resistance heat built into your heat pump system. It turns on when the heat pump alone cannot meet your home’s heating demand.
Key points:

• Often called emergency heat or electric heat strip
  
• Automatically activates in very cold temperatures
  
• Can be manually enabled on some thermostats
  

7 Situations When Auxiliary Heat Should Be Used1️⃣ When Outdoor Temperature Drops Below the Heat Pump’s Efficiency Range

• Most air-source heat pumps operate efficiently down to 25–40°F
  
• Below this range, the heat pump extracts less heat from the outside air
  
• Auxiliary heat ensures your home stays warm
  

Tip: In Southern California, auxiliary heat is rarely needed except during rare cold snaps.

2️⃣ When the Heat Pump Cannot Maintain Set Temperature

• If your thermostat indicates that the room is not reaching the desired temperature
  
• The system will automatically engage auxiliary heat to supplement the heat pump
  

Example: Thermostat set at 72°F, but the indoor temp is 68°F despite heat pump operation

3️⃣ During Rapid Temperature Recovery

• After a period of setback (e.g., night setback), the auxiliary heat can quickly bring the house back to your set temperature
  
• This is why many thermostats have a “heat pump recovery mode”
  

4️⃣ When Defrost Mode is Active

• Heat pumps occasionally enter defrost mode to remove ice buildup on the outdoor coil
  
• During this period, auxiliary heat is used to maintain indoor warmth
  
• This is normal operation and not an indication of a problem
  

5️⃣ Manual Activation for Comfort

• Some homeowners manually enable emergency heat in exceptionally cold conditions
  
• Use sparingly — electric resistance heat is more expensive to run than the heat pump
  

6️⃣ When the Heat Pump Malfunctions

• If your heat pump stops producing enough heat, auxiliary heat may keep your home warm until repairs
  
• Manual activation can serve as a temporary solution during outages or equipment issues
  

7️⃣ In Very Large Homes or Poorly Insulated Buildings

• Homes with high heat loss may need auxiliary heat even at moderately cold temperatures
  
• Ensures consistent comfort in rooms far from the heat pump unit
  

⚡ How Auxiliary Heat Works

1. The heat pump detects insufficient heating output
   
2. Electric resistance strips or coils turn on
   
3. Thermostat monitors indoor temperature and cycles auxiliary heat on/off as needed
   

Note: Auxiliary heat is more costly to operate than the heat pump, so it should only be used when necessary.

✅ Tips for Efficient Use of Auxiliary Heat

1. Use a programmable thermostat — allows the heat pump to operate efficiently before turning on auxiliary heat
   
2. Seal and insulate your home — reduces heat loss and need for backup
   
3. Check the outdoor unit — ensure it is free of ice and debris
   
4. Schedule professional maintenance — ensures your heat pump operates efficiently and reduces auxiliary heat reliance
   

❓ Frequently Asked QuestionsWhen should I avoid using auxiliary heat?Auxiliary heat should not run constantly — if it does, it may indicate undersized heat pump, poor insulation, or a system malfunction.
How much does it cost to run auxiliary heat?Electric resistance heat costs 2–3 times more per kWh than running a heat pump at full capacity.
Can auxiliary heat damage my heat pump?No — it is designed as part of the system, but overreliance increases energy bills.
How can I tell if auxiliary heat is running?Some thermostats show an “emergency heat” indicator, or you may hear higher fan operation and increased energy use.