What Is Aux Heat on Thermostat? Simple Guide to Aux Heat Use

When the temperature drops and your home’s heating system kicks in, you might notice a setting called “aux heat” on your thermostat. But what exactly does aux heat mean and when does it come into play? Understanding this feature can help you keep your home comfortable without wasting energy or money.

Auxiliary heat is a backup heating source that works alongside your primary heat pump. It’s designed to provide extra warmth when the main system can’t keep up, especially during very cold weather. Knowing how and when aux heat activates can save you from unexpected spikes in your energy bill and ensure your home stays cozy all winter long.

What Is Aux Heat on Thermostat?

Aux heat, short for auxiliary heat, provides additional warmth when your primary heating system cannot maintain the desired temperature. It ensures your home stays comfortable during extreme cold or when your heat pump struggles.

Definition and Purpose of Auxiliary Heat

Auxiliary heat acts as a backup heating source in heat pump systems. It activates to supplement or replace the heat pump when outdoor temperatures drop below the heat pump’s efficient operating range. Its main purpose prevents your home from becoming too cold and keeps indoor temperatures steady despite severe weather challenges.

How Aux Heat Works in HVAC Systems

Aux heat typically uses electric resistance heating elements or a separate gas furnace to generate warmth. Your thermostat triggers aux heat when it detects the heat pump’s output is insufficient or when defrost cycles temporarily disable the heat pump’s heating. This process increases energy use but ensures consistent indoor heat, avoiding temperature drops that could affect comfort and safety.

When Does Aux Heat Activate?

Aux heat activates to support your home’s heating when the primary heat pump can’t maintain the set temperature. Understanding these triggers helps you manage comfort and energy use effectively.

Conditions Triggering Aux Heat

Aux heat kicks in mainly when outdoor temperatures drop below the heat pump’s efficient range, typically around 35°F (1.7°C). It also activates during a defrost cycle to prevent cold air from circulating inside your home. If your thermostat senses the indoor temperature falling behind the set point despite the heat pump running, it signals aux heat to engage. Additionally, aux heat operates if your heat pump experiences a malfunction or cannot keep up with sudden temperature drops.

Differences Between Aux Heat and Emergency Heat

Aux heat supplements the heat pump during normal cold weather conditions. It runs automatically to maintain comfort when the heat pump struggles. Emergency heat, however, serves as a backup when the heat pump fails completely. You manually switch to emergency heat on your thermostat only if the primary system is broken or under repair. Emergency heat consumes more energy since it relies solely on electric resistance or another heating source without the efficiency benefits of the heat pump.

Benefits of Using Aux Heat

Aux heat improves your home’s heating system by providing reliable warmth when your heat pump faces limitations. It offers key advantages that ensure comfort and system protection.

Enhancing Heating Efficiency

Aux heat activates automatically to support your heat pump during very low outdoor temperatures, typically below 35°F (1.7°C). It provides extra warmth faster, reducing the strain on your primary heat pump. By supplementing your system, aux heat maintains a stable indoor temperature without forcing the heat pump to work beyond its efficient range. This balanced operation prevents energy waste and maintains heating performance during cold spells.

Preventing Heat Pump Freeze-Up

Your heat pump undergoes defrost cycles to avoid ice buildup on the outdoor unit, which can lower efficiency. Aux heat engages during these cycles to replace the reduced heat output temporarily. This prevents cold air from entering your home and protects the heat pump from damage caused by ice accumulation. Using aux heat this way extends the lifespan of your system while keeping your indoor environment consistently warm.

How to Use Aux Heat Properly

You control aux heat through your thermostat, helping it work efficiently without overspending energy. Proper use ensures comfort during cold snaps while limiting unnecessary power consumption.

Tips for Thermostat Settings

Set your thermostat to maintain a steady indoor temperature, avoiding frequent large adjustments that cause aux heat to engage often. Raise the temperature gradually in increments of 1–2 degrees, allowing the heat pump to keep up before aux heat activates. Use programmable thermostats to schedule temperature changes during off-peak hours, reducing aux heat use when you’re away or asleep. Check your thermostat’s manual for specific aux heat settings and avoid manual activation unless you understand your system’s operation.

When to Avoid Using Aux Heat

Avoid turning aux heat on manually during mild weather, since the main heat pump can handle heating efficiently without backup support. Refrain from setting overly high temperatures quickly, because this triggers aux heat unnecessarily and increases energy bills. Skip using aux heat if there’s no significant temperature drop below 35°F (1.7°C), as the system relies mainly on the primary heat pump then. Prevent constant aux heat use by maintaining your heat pump properly, scheduling regular maintenance to keep it running efficiently and reduce backup heating reliance.

Conclusion

Knowing how aux heat works helps you keep your home warm without wasting energy. It kicks in automatically when your heat pump needs extra support, so you don’t have to worry about sudden cold spells.

By managing your thermostat settings wisely and keeping your system well-maintained, you can ensure aux heat runs only when necessary. This balance keeps your heating efficient and your energy bills in check throughout the winter months.