What Does Auxiliary Heat Mean on a Thermostat and Heat Pump Systems?
If you’ve ever noticed the words “auxiliary heat” on your thermostat or a red light indicating its activation, you might have wondered what it is and whether it’s a cause for concern. Auxiliary heat, also known as supplemental heat, is an important part of many HVAC systems, particularly those that use heat pumps.
What Is Auxiliary Heat?
Auxiliary heat is used whenever your heat pump cannot keep up with the heating demand of your home on its own. Unlike a standard air conditioner, a heat pump can both cool and heat your home. However, when outside temperatures drop usually below 40°F the heat pump may struggle to maintain comfortable indoor temperatures. At this point, the system activates auxiliary heat to provide supplemental warmth.
This heat is delivered through a secondary source, such as electric resistance coils, and ensures your home stays warm even in colder conditions.
How to Know When Auxiliary Heat Is Running
- Thermostat Display: Many thermostats, including models like the Honeywell Vision Pro IAQ, display “Aux Heat” or “OX Heat” when active.
- Hot Air from Vents: The air coming from your vents will feel noticeably hotter than the regular heat pump output, similar to traditional propane or forced-air systems.
- Red Indicator Light: Some systems use a red light to indicate the auxiliary heat is engaged.
If auxiliary heat is running when it’s not cold or without a recent thermostat change, it could indicate a system issue.
Call a licensed HVAC professional to check your system.
Why Auxiliary Heat Is Important
Auxiliary heat ensures:
- Consistent indoor temperature even during very cold weather
- Backup heating when the heat pump alone cannot provide sufficient heat
- Protection of the HVAC system by preventing overworking the heat pump
It’s normal to see auxiliary heat occasionally in colder months, but unusual activation may signal a system issue.
What to Do If Auxiliary Heat Is On Unusually
- Check Your Thermostat: Ensure it’s set to regular heat and not accidentally left on auxiliary heat.
- Assess Recent Temperature Settings: Make sure you haven’t increased the temperature suddenly by more than 2°F.
- Call a Professional: If everything is set correctly but auxiliary heat is still running unnecessarily, contact an HVAC technician to inspect the system. Persistent or unexpected activation may indicate a malfunction that requires professional attention.
Auxiliary Heat Increases Energy Use
Auxiliary heat relies on electric resistance heating, which uses more electricity than your heat pump running normally. When aux heat is active, energy use can gradually rise, especially during extended cold periods or frequent thermostat adjustments.
Occasional use is normal, but frequent or prolonged activation may indicate inefficiency or system strain.
Noticing frequent auxiliary heat operation or higher-than-expected energy use? Call a licensed HVAC professional now to optimize your system and reduce unnecessary energy consumption.
Frequently Asked Questions
What is auxiliary heat on a thermostat?
It’s a supplemental heat source activated when your heat pump alone cannot maintain indoor temperatures, usually in colder weather.
What is auxiliary heat on a heat pump?
Auxiliary heat provides additional warmth using electric resistance or other secondary heating sources when the heat pump struggles in low temperatures.
What is auxiliary heat on a Honeywell thermostat?
Certain Honeywell models display “Aux Heat” or “OX” when the supplemental heat is active, letting you know the system is providing extra heat.
What is an auxiliary heater?
An auxiliary heater is any secondary heating element that supplements the main heating system to ensure consistent indoor temperatures.
What does auxiliary heat mean?
It means your HVAC system has engaged a backup or supplemental heat source to maintain comfort when your primary system cannot provide sufficient heat on its own.