If “AUX Heat” has appeared on your thermostat, you may be wondering whether something is wrong or whether your next electricity bill is about to jump. It is a reasonable concern, especially when you chose geothermal heating for its energy efficiency.
The good news is that geothermal auxiliary heat is a normal part of many systems. It provides extra warmth when your geothermal equipment needs help. However, it should not be doing most of the work all winter. If it runs too often, your home may feel less comfortable while your electricity costs keep climbing.
What Is Geothermal Auxiliary Heat?
A geothermal system heats your home by collecting heat from the ground and moving it indoors. Since underground temperatures are steadier than outdoor temperatures, geothermal systems can heat homes efficiently, even during an Ontario winter.
Geothermal auxiliary heat is a secondary electric heat source. It turns on when the geothermal system cannot produce enough heat by itself. Your thermostat may call it auxiliary heat, backup heat, supplemental heat, or simply “AUX.”
This backup is meant to support your geothermal equipment for short periods. It is not intended to become your home’s main source of heat.
Why Is My Geothermal System Using Auxiliary Heat?
A sudden cold snap is one of the most common reasons. Geothermal systems provide steady, consistent heat, but your home may begin losing warmth faster than the system can replace it when temperatures drop sharply.
In this situation, geothermal auxiliary heat may run briefly to maintain the thermostat setting. That can be normal during extreme winter weather in Simcoe County. It becomes more concerning when the backup heat stays on, runs during mild weather, or appears more frequently than it did before.
Large Thermostat Changes Can Trigger It
Turning the thermostat up several degrees at once can activate geothermal auxiliary heat. When the controls see a large difference between the current temperature and your new setting, they may call for backup heat to close that gap faster.
Large scheduled setbacks can cause the same problem. Lowering the temperature overnight or while you are away may seem like an easy way to save energy. However, the system could use more expensive auxiliary heat when it is time to warm the house again.
Geothermal systems usually work best when maintaining a steady temperature. Smaller adjustments can reduce unnecessary backup heat use without leaving your family waiting for the house to feel comfortable again.
Restricted Airflow Can Reduce Heating
Your equipment may be producing enough heat, but that warmth still has to reach every room. A dirty filter, closed vent, blocked return, or ductwork problem can restrict airflow. This can leave some rooms chilly while the system runs longer and calls for more backup heat.
Check the filter and make sure supply and return vents are open and unobstructed. If the airflow still feels weak, the problem may be deeper inside the equipment or ductwork.
Ignoring poor airflow can mean longer heating cycles, uneven temperatures, and higher bills. A technician can find the restriction and help the system move heat through the home properly again.
The System May Not Match the Home’s Needs
A geothermal system that is too small may depend on backup heat more than expected. Proper sizing should account for the home’s size, insulation, windows, air leakage, and local climate.
The home may also have changed since the equipment was installed. A finished basement, addition, or major renovation can increase the amount of heat required. The system that once handled the home comfortably may now struggle to keep up.
If frequent geothermal auxiliary heat has become an ongoing problem, a technician can assess the equipment, ground loop, and current heating needs to determine whether system capacity is a factor.
There Could Be a Mechanical Problem
A sudden increase in auxiliary heat use may mean the geothermal system is no longer producing its usual amount of heat. The issue could involve the ground loop, circulation pump, refrigerant system, blower, or another component.
The thermostat or controls can also cause trouble. An incorrect setting, faulty sensor, wiring problem, or incompatible thermostat may activate backup heat unnecessarily. This is worth investigating if the problem began after a thermostat replacement, power outage, or recent service.
These problems are difficult to identify without proper testing. A geothermal technician can check the airflow, temperatures, electrical components, and controls instead of leaving you guessing.
How Much Does Auxiliary Heat Cost?
Geothermal heating is efficient because it moves existing heat rather than creating all its heat directly from electricity. Geothermal auxiliary heat typically uses electric resistance heating, which requires considerably more power.
The cost depends on local electricity rates, the size of the backup heating elements, and how long they operate. A few short cycles during a severe cold snap may not make a major difference. Daily or continuous operation can lead to a frustrating increase in your electricity bill.
If your bill has climbed, compare it with one from a similarly cold period. This provides a more accurate picture than comparing a cold winter month with a milder one.
Auxiliary Heat and Emergency Heat Are Different
Geothermal auxiliary heat normally turns on automatically when the system needs support. Geothermal emergency heat is usually selected manually and may bypass the geothermal heat pump completely. The home then relies mainly or entirely on its electric backup heat.
Emergency heat should not be used simply to warm the house faster. It is intended for situations where the main system cannot operate properly. Because geothermal emergency heat can be expensive, contact a technician if you need it to keep your home warm.
When Should You Call a Technician?
Occasional geothermal auxiliary heat during extreme cold is not usually a concern. It should turn off once the home reaches the selected temperature, allowing the geothermal equipment to return to normal operation.
Schedule an inspection if auxiliary heat runs for long periods, comes on during mild weather, or appears far more often than it used to. Weak airflow, uneven temperatures, unusual noises, warning messages, rising electricity bills, or a system that never reaches the thermostat setting are also good reasons to call.
Before scheduling service, confirm that the thermostat is set to “Heat” rather than “Emergency Heat.” Check the filter, open the vents, and note when the auxiliary heat appears. These details can help your technician find the cause more quickly.
If your geothermal system is using auxiliary heat more than expected, Dave Brown Heating & Air Conditioning can inspect it and explain the problem in plain language. Contact us to schedule geothermal service in Simcoe County and the surrounding area.