Air testing, adjusting and balancing (TAB) are the three major steps used to achieve proper operation of heating, ventilating, and air conditioning (HVAC) systems. TAB usually refers to commercial building construction and the specialized contractors who employ personnel that perform this service. In general, the TAB specialist performs air and hydronic measurements on the HVAC systems and adjusts the flows as required to achieve optimum performance of the building environmental equipment. The air balancing is usually based upon the design flow values required by the Mechanical Engineer for the project, and the TAB contractor submits a written report which summarizes the testing and balancing and notes any deficiencies found during the TAB work.

Testing
Testing is the use of specialized and calibrated instruments to measure temperatures, pressures, rotational speeds, electrical characteristics, velocities and air and water quantities for an evaluation of equipment and system performance.

Adjusting
Adjusting is the final setting of balancing devices such as dampers and valves, adjusting fan speeds and pump impeller sizes, in addition to automatic control devices such as thermostats and pressure controllers to achieve maximum specified system performance and efficiency during normal operation.

Balancing
Balancing is the methodical regulation of system fluid flows (air or water) through the use of acceptable procedures to achieve the desired or specified airflow or water flow.

*FromWikipedia, the free encylclopedia (describing HVAC Testing, Adjusting and Balancing) (as of Feb. 29, 2012, 12:22 GMT).