Testing, adjusting, balancing. HVAC Testing, Adjusting and Balancing (TAB) are the three major steps used to achieve proper operation of HVAC (heating, ventilation, and air conditioning) 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.