This article was originally published on April 25, 2022, and updated on October 1, 2025.
Heating, ventilation and air conditioning (HVAC) systems are the backbone of building comfort and safety. Because these systems operate continuously and consume significant energy, even small inefficiencies can drive up operating costs.
At Ashcroft, a leading producer of pressure instruments for multiple industries, including HVAC, we provide insights and recommendations to engineers and facility managers like you to help improve system performance and reliability.
For instance, we know that instrument accuracy is one of the most important factors in maintaining HVAC efficiency. Pressure sensing instruments, like transducers, monitor the system’s conditions and help automation controls that adjust fan speeds, pump flows and valve positions. Inaccurate sensor measurements can cause systems to overwork, leading to wasted energy and unnecessary expense.
Read this article to:
- Examine how HVAC systems function and the factors that can influence measurement reliability.
- Learn how pressure sensors optimize HVAC system performance
- Understand why accuracy is so important
- Compare the different methods used to determine accuracy
By understanding these elements, you’ll be better equipped to evaluate pressure sensors that support both building performance and cost savings.
What is the role of a pressure sensor in your HVAC system?
An HVAC system balances multiple processes to maintain indoor comfort and efficiency. Key functions include:
- Air distribution. Fans and ductwork move conditioned air throughout the building.
- Heating and cooling. Hot water circulates through coils for heating, while chilled water runs through coils for cooling and dehumidification.
- Air quality control. Filtration and ventilation ensure proper oxygen levels, remove particulates and maintain humidity within safe limits.
All of these processes use energy and cost money, so it stands to reason that the more efficiently they run, the less the system costs to operate. To ensure high efficiency, you must verify that the pressure sensors you use to monitor and control the flow of air through ducts, hot water through heating coils, and cold water through chillers and dehumidification coils are highly accurate.
One way to ensure an efficient HVAC system is to verify the accuracy of the pressure instruments used in the system.
What can affect pressure sensor accuracy in HVAC applications?
Even though pressure instruments are designed for reliable measurement, five conditions in HVAC systems can affect their accuracy:
- Temperature changes. Shifts in ambient or process temperature may cause zero or span drift.
- Mechanical stress. Vibration from fans, pumps or compressors can introduce error or reduce service life.
- Installation factors. Improper mounting or orientation may require recalibration.
- System dynamics. Rapid load changes can cause hysteresis or repeatability issues.
- Environmental influences. Dust, moisture or corrosive air streams can degrade performance over time.
Understanding these influences is essential when selecting and maintaining pressure instruments for HVAC service
Why does pressure sensor accuracy matter in HVAC systems?
Accuracy refers to how far the measured value of a specific pressure is from the accepted allowable error of that measurement. The accuracy of a pressure instrument is determined by the maximum positive and negative difference between the measured value and its ideal value. This allowable error is calculated as a percentage of the measured output of the sensor versus the ideal output, and it is expressed as a percentage of the full span of the sensor.
Pressure instruments with greater accuracy provide a more accurate indication of the actual pressure conditions, which allows HVAC controllers to better manage the heating and cooling needs of the building. However, the accuracy alone does not fully define an instrument’s ability to measure pressure, which is why pressure instrument manufacturers incorporate accuracy as part of a larger accuracy statement. 
Are all accuracy statements the same?
No. Because the HVAC industry lacks a universal standard, accuracy statements can differ widely. Some use root sum squared (RSS) or best fit straight line (BFSL) methods, which may exclude important errors such as zero offsets, span shifts or temperature effects. The result: additional on-site calibration, higher installation costs and reduced out-of-the-box equivalency.
RSS and BFSL accuracy statements often overlook important factors, resulting in reported accuracy that may not reflect actual instrument performance. These methods typically exclude zero and span offsets, meaning additional installation errors may occur at both the low and high ends of the measurement range. As a result, installers may need to calibrate instruments on-site using a secondary standard, increasing startup costs, eliminating out-of-box interchangeability, and impacting overall system performance. Ultimately, these required adjustments add expenses for building owners who expect pre-calibrated sensors.
What are common sources of accuracy error?
In determining the accuracy of pressure instruments, consider all factors relevant to the specific application that could lead to measurement errors. Some of the most common sources of error include:
- Nonlinearity error – deviation from a straight output line
- Hysteresis error – output differences in response to increasing versus decreasing pressure
- Non-repeatability error – inconsistent readings under identical conditions
- Zero and span errors – offsets at both ends of the measurement range
- Temperature coefficient errors – zero and span shift caused by ambient temperature changes
What is the best method to determine accuracy?
While not all methods consider each of these errors, the terminal point method, which includes zero and span offsets in its error determination, is the most reliable calculation for HVAC applications. This method determines the actual error for a pressure instrument, allowing manufacturers to better indicate the accuracy of their products and contractors to better manage the heating, cooling and subsequent low airflow in their HVAC systems.
At Ashcroft, many of our pressure instruments are manufactured to our TruAccuracy™ standard, which is based on the terminal point method. Some of the products with this specification include our CXLdp differential pressure transducer, DXLdp differential pressure transducer, and GXLdp differential indicating pressure transducer. These products meet their rated accuracies out of the box without the need for field calibration adjustments.
Ready to learn more?
After reading this article, your key takeaway is: When selecting HVAC pressure instruments, you want to evaluate the stated accuracy percentage as well as the calculation method, potential error sources and environmental conditions that may affect measurement reliability. By understanding how accuracy is defined—and what truly affects it—building owners and engineers can make better-informed decisions when specifying instruments.
Here are a few more articles that you may find interesting:
- Choosing a Pressure Transducer for Critical Environments
- 4 Factors When Choosing a Pressure Transducer for Ammonia Applications
- Differential Pressure Sensors for Data Center Applications
If you need more help with your HVAC system needs, contact us to ask our experts a question. They’ll help you ensure your pressure instruments are running smoothly and efficiently to keep your HVAC system at peak performance.
In the meantime, download our guide, "How Accurate is your Accuracy Statement for Pressure Instruments?" to learn more.