If your commercial building’s HVAC system seems like it’s working against you, rooms are too cold, energy bills are too high, or complaints from occupants, the problem may not be your equipment. It might be your sensors. These small but essential parts act as the eyes and ears of the system. And when they stop working correctly, the HVAC system can "lie" about what’s going on in your building.
At Harold Brothers Mechanical, we’ve helped many facility managers uncover hidden HVAC problems caused by faulty sensors. Whether you're running an office, school, or healthcare facility, catching these issues early can save thousands in energy and repair costs.
In this article, you’ll learn what causes HVAC sensors to give false readings, how to test them, how to calibrate them, and how this process can help reduce costs and improve comfort across your building.
It’s not that HVAC sensors want to mislead you, it’s that over time, they drift, get dirty, or become poorly placed. When that happens, they send the wrong information to the building’s HVAC controls. The system then makes decisions based on bad data.
For example, if a temperature sensor is placed near a window with direct sunlight, it may read much warmer than the actual room temperature. As a result, the air conditioning runs longer than needed, even though the rest of the space is comfortable. That wastes energy, stresses the system, and can confuse maintenance teams trying to understand what’s wrong.
This kind of false information can happen with all kinds of sensors, not just temperature. Humidity, carbon dioxide (CO2), airflow, pressure, and occupancy sensors all play a role in helping the system operate correctly. When even one is off, the HVAC controls can act in ways that make the building less efficient and less comfortable.
When these readings are wrong, the entire system gets confused. This can lead to rooms being overcooled or overheated, poor air quality, or even safety problems. Over time, this also leads to higher energy bills and more wear on your equipment.
The good news? These problems can often be fixed with regular testing and calibration of your HVAC sensors.
Testing sensors starts with comparing what the sensor says to what’s really happening in the space.
A technician usually begins by using a trusted measurement tool, such as a handheld digital thermometer or air quality meter. They place it near the sensor and check if the readings match. If the sensor says the temperature is 75°F, but the handheld tool says 70°F, that’s a red flag.
Next, the technician looks at where the sensor is located. A sensor stuck behind a filing cabinet or placed near a supply vent might not give an accurate view of the whole space. Proper sensor placement is just as important as the sensor itself. If it’s placed poorly, even a perfectly working sensor will give misleading readings.
The wiring is also checked. If a sensor’s wires are loose, corroded, or damaged, it can cause the sensor to fail or give unreliable data. Some issues can be fixed right away, while others may require replacement.
In commercial buildings with a Building Management System (BMS), technicians can also view sensor trends over time. If a temperature sensor is always showing the same number or if the readings jump around for no reason, that may be a sign of sensor failure or signal interference.
The technician starts by comparing the sensor reading to a certified tool, often one that follows national standards for accuracy. If the sensor is off, it can usually be adjusted through software or manual control. For example, if a sensor reads 3 degrees too high, the technician can program an offset to bring it back into alignment.
Once the sensor is adjusted, the technician records the change. They note the date, the person who performed the calibration, the tool used for reference, and how much the sensor was adjusted. Keeping this history helps with future inspections, audits, and system troubleshooting.
Calibrating sensors doesn’t take long, but skipping it can cause months or years of wasteful HVAC operation.
Most experts recommend that commercial buildings test their HVAC sensors at least once or twice a year. How often depends on the building’s usage and environment.
For example, in high-traffic buildings like hospitals, schools, or office towers, testing every 6 months is a smart idea. These spaces are used daily and often have sensitive air quality needs. In less demanding buildings, annual testing might be enough.
Humidity and CO2 sensors may need to be tested more frequently because they’re more sensitive to environmental changes. Airflow and pressure sensors can usually be checked once a year unless specific issues are noticed.
Over time, sensors that are never tested or calibrated can cause real damage to your HVAC system’s performance. Here’s what can happen:
Your energy bills may rise because the system runs more often than necessary. Spaces may feel too warm or too cold, even if the equipment seems fine. People may complain about indoor air quality, especially in spaces where CO2 or humidity isn’t being controlled properly.
Equipment may also wear out faster, because it’s running harder to meet “needs” that don’t exist, all because the sensors are lying.
In the worst cases, ignoring sensor maintenance can lead to system failures, mold growth due to humidity, or even safety violations if ventilation systems aren’t working properly.
When your HVAC sensors are accurate and placed correctly, everything just works better. The system can respond to real needs in real time, which reduces waste and improves comfort for everyone in the building.
You’ll also see fewer complaints from building occupants and fewer calls for emergency maintenance. Long-term, your system will last longer, and your energy use will drop.
Most importantly, calibration brings trust back into your system. When a sensor says it’s 72°F, you’ll know it really is. And your HVAC system can stop “guessing” and start performing the way it was designed to.
Now that you understand why sensors fail and how to correct them, your next step is to schedule a building-wide sensor check. A trained HVAC technician can guide you through the process, help you correct sensor placement, and calibrate any devices that are drifting out of range.
At Harold Brothers Mechanical, our team specializes in commercial HVAC diagnostics and sensor calibration. We know how to uncover the small issues that lead to big inefficiencies, and we’re here to help you restore accuracy, comfort, and control to your building.
If your sensors seem off, and controls are not acting the way that they should be, check out our article “Harold Brothers BAS/Controls Tune-Up: Trend Logs, Setpoint Resets, and Sequence Fixes”. In it, we explain how Harold Brothers bridges the gap between your HVAC system and your BMS and Controls systems, and how we can help your facility operate at peak efficiency.