What Is Auxiliary Heat? A Simple Guide You Need to Know

What Is Auxiliary Heat?

Auxiliary heat, often called “aux heat” or “emergency heat,” is an additional heat source integrated with your heat pump system. It is designed to provide supplementary warmth when the heat pump alone cannot maintain the thermostat’s set temperature.

Unlike the heat pump, which transfers heat from outside air to inside your home, auxiliary heat generates heat through electrical resistance or fossil fuels, depending on the system. This makes it a more energy-intensive but necessary backup option.

For example, on extremely cold days when outdoor temperatures drop below the heat pump’s effective range, auxiliary heat kicks in to ensure your home stays warm.

How Does Auxiliary Heat Work?

Auxiliary heat activates automatically when your heat pump struggles to maintain the desired indoor temperature. This usually happens during cold weather when the heat pump’s efficiency decreases.

In a typical setup, when the thermostat senses the indoor temperature is falling below the set point, it first relies on the heat pump. If the heat pump can’t produce enough heat, the thermostat signals the auxiliary heat to turn on.

This backup heat source then generates heat through electric resistance coils or a gas furnace, providing the extra warmth needed to keep your home comfortable.

Importantly, auxiliary heat is not meant for continuous use. It serves as a temporary supplement during peak cold periods or when the heat pump is defrosting.

Types of Auxiliary Heat

There are several types of auxiliary heat systems, each with its own benefits and applications. The most common include electric resistance heaters, gas furnaces, and oil furnaces.

Electric Resistance Heaters

Electric resistance heaters use coils that heat up when electricity passes through them, similar to a toaster. They are often built into heat pump systems as the default auxiliary heat source.

While effective and easy to control, electric resistance heaters tend to be more expensive to operate due to high electricity usage. However, they provide reliable backup heat when necessary.

Gas Furnaces

Some heat pump systems use a gas furnace as auxiliary heat. This option can be more cost-effective in areas where natural gas prices are lower than electricity rates.

Gas furnaces also heat up quickly, making them an efficient backup during very cold spells. However, installation and maintenance costs may be higher compared to electric heaters.

Oil Furnaces

In less common scenarios, oil furnaces serve as auxiliary heat. They are mainly used in regions where oil is a preferred heating fuel.

While oil furnaces can provide robust heating, they require regular maintenance and fuel delivery, which can add to overall costs and inconvenience.

When Does Auxiliary Heat Turn On?

Auxiliary heat typically engages under two main conditions: during very cold outdoor temperatures and when the heat pump is defrosting.

Heat pumps extract heat from outside air, but their efficiency drops as temperatures fall below freezing. When this happens, the heat pump alone may not be able to meet the heating demand.

Additionally, heat pumps periodically switch to defrost mode to remove ice buildup from outdoor coils. During defrosting, the system temporarily reverses to cooling mode, which can lower indoor temperatures.

To prevent your home from getting cold during defrost cycles, auxiliary heat activates to maintain warmth. This ensures continuous comfort without noticeable temperature drops.

Signs Your Auxiliary Heat Is Running

It’s important to know when your auxiliary heat is active, as it can impact your energy bills. One common sign is a sudden increase in electricity usage during cold weather.

You may also notice warmer air blowing from your vents, but the fan may sound louder due to the auxiliary heat’s electric coils running. Your thermostat might display an “emergency heat” or “aux heat” indicator, depending on the model.

If you see a spike in energy bills without a corresponding rise in outdoor temperature, this could signal excessive auxiliary heat use. Identifying this early can help you troubleshoot potential issues.

Practical Examples of Auxiliary Heat Usage

Imagine a cold winter night where temperatures plunge below 20°F (-6°C). Your heat pump struggles to extract enough heat from the frigid air. As a result, the auxiliary heat activates to maintain a cozy indoor temperature.

Another example is when your heat pump enters defrost mode. During this time, you might feel a brief blast of warmer air from the auxiliary heater. This prevents the indoor environment from cooling down while the outdoor coil is being thawed.

In homes equipped with a dual-fuel system, the auxiliary gas furnace might kick in on particularly cold days, reducing the reliance on high-cost electric resistance heat. This combination can save money and increase comfort.

Benefits of Auxiliary Heat

Auxiliary heat ensures that your home remains warm even during the harshest weather conditions. It acts as a safety net, preventing uncomfortable cold snaps inside your living space.

Moreover, auxiliary heat protects your heat pump system by reducing strain during extreme cold. This can extend the lifespan of your primary heating equipment.

Additionally, having a reliable backup heating source increases peace of mind, especially in areas prone to sudden temperature drops.

Drawbacks and Considerations

Despite its benefits, auxiliary heat can be costly to operate, especially electric resistance types. These systems consume more electricity compared to heat pumps, leading to higher energy bills.

Another downside is that auxiliary heat may activate more frequently than necessary if the thermostat is set too high or if the heat pump is not functioning optimally. This can result in inefficient heating and increased costs.

Therefore, it’s crucial to monitor your system and maintain it properly to ensure auxiliary heat only runs when absolutely needed.

Optimizing Auxiliary Heat Usage

To reduce auxiliary heat activation, keep your thermostat settings moderate. Avoid setting excessively high temperatures during cold weather, as this forces the system to work harder.

Regular maintenance of your heat pump can also improve its efficiency and reduce reliance on auxiliary heat. Clean filters, inspect coils, and schedule professional check-ups annually.

Consider upgrading to a smart thermostat that can better manage heating cycles and reduce unnecessary auxiliary heat use. These devices learn your schedule and adapt heating accordingly for improved efficiency.

When to Call a Professional

If auxiliary heat seems to be running too often or if your energy bills spike unexpectedly, it may indicate a problem with your heating system. Issues could include a malfunctioning heat pump, thermostat problems, or insulation deficiencies.

Consulting a professional HVAC technician can help diagnose and resolve these issues. They can inspect your system, recommend repairs, or suggest upgrades to optimize performance.

Remember, proper system tuning not only saves money but also enhances comfort and prolongs equipment life.

Conclusion

Auxiliary heat is an essential component of many heating systems, providing critical backup during cold weather and heat pump defrost cycles. Understanding its function helps homeowners manage their heating more effectively and avoid unexpected energy costs.

By maintaining your system, moderating thermostat settings, and recognizing when auxiliary heat is active, you can maximize comfort and efficiency. Always seek professional advice if you suspect your auxiliary heat is overusing or causing issues.

With this knowledge, you are better equipped to keep your home warm and cozy, no matter how low the temperature drops outside.