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Alliance Calibration Blog

The Calibration Bench | Blog

What Air Balancers Need To Know About Accuracy, Tolerance and Resolution.

Posted by Phil Wiseman on Feb 5, 2019 12:05:24 PM



 Air balancing is a crucial step in assuring the efficiency of your heating, ventilation and air conditioning system. Air balancing ensures your HVAC system is operating to its optimal efficiency and distributing air correctly throughout your facility.

Accuracy, tolerance and resolution are three important tools you need to keep in your tool box in order to understand air balancing.

The National Environmental Balancing Bureau defines accuracy as the capability of an instrument to indicate the true value of a measured quantity.

accuracy_alliance calibration

With a less than accurate system, you will run the risk of outputting air differently than your system has been set for, which could result in changes to your environment. Changes to your environment have potential to throw off instrument calibrations or other test results.

According to recent updates by NEBB, accuracy of air pressure must be within 2 percent of the reading, accuracy of temperature must be within .5 percent of the reading and accuracy of humidity must be within 3 percent of the reading. NEBB also recommends that systems be calibrated every 12 months.

 A system must continuously read accurately to maintain a constant and correct space. This will ensure the best results for your system within your environment.

Click here to see a chart with NEBB’s recently revised standards of accuracy.


Tolerance is not defined as an error, but as a limit of permissible deviation of a measurement from the specified value, according to Measuring Technology, a handbook by Siemens.

Tolerances can be absolute values, such as temperature degree, or as relative values, such as percentage of the measuring range. They can be defined asymmetrically as a plus or minus tolerance or symmetrically as a plus-minus tolerance, according to Measuring Technology.

tolerance with caliper_alliance calibration


The smallest change of air pressure, temperature or humidity can unbalance an environment. A low tolerance creates an HVAC system with little room for error, resulting in a more consistent and correct environment.



NEBB defines resolution as the smallest change in a measured variable that an instrument can detect.

instrument resolution_alliance calibration 

The resolution of temperature, set by the NEBB, is 1 degree celsius or one degree fahrenheit, depending on what you use to gauge temperature in your space, resolution of air pressure should be 0.1 inches water gauge and humidity resolution should be one percent. NEBB recommends systems be calibrated every 12 months.

With low tolerance in an HVAC system, your output should not stray far from what it has been set at but if it does, high resolution is a necessity to detect even the slightest change in order to maintain an accurate system and environment.


Click the image below see a chart of all NEBB recent revisions for standards of resolution.

NEBB Instrument Calibration Requirements 2019 

Accuracy, tolerance and resolution are a must when it comes to HVAC systems. Knowing the differences and standards will ensure a consistent and correct environment.

 In conclusion, having an HVAC system with high accuracy, low tolerance and high resolution is key in maintaining a well balanced environment.

Visit our HVAC & Air Balancing page to find out what we calibrate.