what does auxiliary heat mean on a Honeywell thermostat? – Everything You Need to Know

A Honeywell thermostat is a powerful and intelligent device designed to keep your home at a comfortable temperature year-round. Among its various features, “Auxiliary Heat” plays a crucial role in maintaining warmth during extreme weather conditions.

If you own a Honeywell thermostat, you might have come across the term “Auxiliary Heat” in its settings. Wondering what it means and how it affects your home’s heating system? Look no further! 

In this comprehensive guide, we’ll walk you through everything you need to know what does auxiliary heat mean on a Honeywell thermostat and make sure you understand its purpose and functionality.

What is Auxiliary Heat?

Auxiliary Heat, also known as “Emergency Heat” or “Second Stage Heat,” is an essential functionality integrated into Honeywell Thermostats. It serves as a backup heating system, kicking in when the primary heating source struggles to meet the indoor temperature demands.

The primary heating system in many homes is often a heat pump, which efficiently extracts heat from the outdoor air to warm the indoors. 

However, during extremely cold weather or when the temperature difference between indoors and outdoors is significant, the heat pump may struggle to provide enough warmth. That’s when the Auxiliary Heat comes to the rescue.

Auxiliary Heat typically comes from electric resistance coils or a gas furnace, which can generate heat more rapidly than the heat pump. When activated, the Auxiliary Heat supplements the primary heating system, bridging the gap and ensuring a comfortable environment indoors.

Understand the Mechanism of Auxiliary Heat

Honeywell Thermostats are equipped with sophisticated sensors that constantly monitor the indoor temperature and compare it to the desired set temperature. 

If the difference between the two exceeds a specific threshold, and the primary heating system (usually the heat pump) cannot keep up, the thermostat triggers the Auxiliary Heat.

During normal operations, the thermostat will use the primary heat pump to maintain the desired temperature, as it is more energy-efficient. 

However, when the demand for warmth is high or the outdoor temperatures are freezing, the Auxiliary Heat activates to provide the necessary extra heat quickly.

It’s important to note that the Auxiliary Heat will only be engaged when required. The thermostat’s intelligent algorithm ensures that it optimizes energy consumption and prioritizes the primary heat pump whenever possible.

Determine the Activation Triggers of Auxiliary Heat

1. Extreme Weather Conditions

During severely cold weather, the heat pump’s efficiency decreases, and it may struggle to maintain the desired indoor temperature. As a result, the thermostat may engage the Auxiliary Heat to supplement the heat pump’s efforts.

2. Quick Temperature Adjustments

If you manually adjust the thermostat to a significantly higher temperature than the current indoor temperature, the system may activate the Auxiliary Heat to reach the new setting quickly.

3. Emergency Heat Mode

Some Honeywell Thermostats have an “Emergency Heat” mode that allows you to bypass the primary heat pump and use the Auxiliary Heat exclusively. This mode is typically used in rare situations when the heat pump malfunctions or requires maintenance.

4. Defrost Cycles

Heat pumps occasionally enter defrost cycles to remove frost buildup on their outdoor coils. During this process, the heat pump temporarily switches to cooling mode, and if the indoor temperature drops, the thermostat may activate the Auxiliary Heat to prevent discomfort.

Comfort and Energy Usage Balancing

While Auxiliary Heat is a valuable feature for maintaining warmth during harsh weather, it’s essential to use it wisely to optimize energy efficiency. 

Electric resistance coils, commonly used in Auxiliary Heat, are less energy-efficient than heat pumps, which draw heat from the outdoor air. Therefore, excessive reliance on Auxiliary Heat can lead to higher energy bills.

To maximize efficiency:

1. Automatic Mode

Let your Honeywell Thermostat manage the heating system automatically. Avoid manually switching to “Emergency Heat” mode unless there is a genuine need.

2. Programmable Schedules

Utilize the thermostat’s programmable features to set temperature schedules that align with your daily routine. Lower the temperature when you’re away or asleep to reduce the need for Auxiliary Heat.

3. Insulation and Weatherproofing

Properly insulate your home and seal any air leaks to minimize heat loss, reducing the workload on both the primary heating system and Auxiliary Heat.

4. Regular Maintenance

Schedule regular maintenance for your heating system, including the heat pump and Auxiliary Heat components. Clean or replace air filters, check the ductwork, and have professional inspections to ensure optimal performance.

Maximize the Performance and Efficiency of Auxiliary Heat

1. Learn Your Thermostat

Familiarize yourself with the specific settings and features of your Honeywell Thermostat, as different models may have variations in how Auxiliary Heat is controlled.

2. Monitor Outdoor Temperature

Pay attention to outdoor temperatures. When the weather is mild, rely on the primary heat pump alone to save energy.

3. Check the Thermostat Placement

Ensure your thermostat is installed in a location that accurately represents the overall indoor temperature. Avoid placing it near drafts or heat sources.

4. Zoning Systems

Consider using zoning systems if you have a larger home. This allows you to control heating in different areas independently, optimizing energy usage.

5. Professional Installation

Have your Honeywell Thermostat and heating system installed by a qualified professional to ensure proper configuration and optimal performance.

Frequently Asked Questions (FAQ’s)

Is Auxiliary Heat Energy-Efficient?

A5: Auxiliary Heat can be less energy-efficient than the primary heat pump, especially when generated by electric resistance coils. As such, it’s important to use it judiciously and rely on the heat pump whenever possible. Regular maintenance, proper insulation, and programmable thermostat settings can help improve overall energy efficiency.

Can I Use Auxiliary Heat For Extended Periods?

While Auxiliary Heat is a reliable backup, it’s not meant for extended use. Rely on it only when necessary, such as during extreme weather conditions or heat pump malfunctions. Using it excessively can lead to higher energy consumption and increased utility bills.

Why Is My Honeywell Thermostat Stuck On Auxiliary Heat?

If your Honeywell Thermostat is continuously running on Auxiliary Heat and not reverting to the primary heat pump, there might be an issue with the heat pump itself or the thermostat’s settings. Check for any error messages on the thermostat’s display and consider contacting a qualified HVAC technician for assistance.

Can I Install A Honeywell Thermostat And Auxiliary Heat System Myself?

While some thermostat installations are relatively straightforward, it’s always best to have a qualified professional install a Honeywell Thermostat and set up the heating system correctly. A professional installation ensures proper configuration, reduces the risk of errors, and ensures optimal performance.

Which Honeywell Thermostat Models Have Auxiliary Heat Features?

Many modern Honeywell Thermostat models come equipped with Auxiliary Heat features. Check the specifications and user manual of your specific model to determine if it has this functionality. Most programmable and smart thermostats from Honeywell include this feature for enhanced comfort and efficiency.


Auxiliary Heat is a valuable feature on Honeywell Thermostats, providing extra warmth when needed and ensuring your comfort during chilly conditions. 

By understanding its mechanism, activation triggers, and efficiency considerations, you can use it wisely to strike a balance between comfort and energy usage. 

Remember to follow the tips and guidelines provided in this guide to optimize the performance of your heating system and enjoy a cozy home throughout the year.

Scott Maupin