HVAC Testing, Adjusting & Balancing (TAB)
CSI Division 23, HVAC
The process of measuring a completed HVAC system's actual airflow and water flow at every outlet and adjusting dampers and valves until it matches the values the mechanical design called for, performed by an independent balancing contractor after installation but before the system is considered complete.
Why it matters
An HVAC system that's fully installed and running isn't necessarily delivering the airflow the design actually calls for at every outlet, TAB is what verifies and corrects that, and skipping it means occupants can end up with rooms that are too hot, too cold, or under-ventilated despite the system apparently working.
On a real project
An independent balancing contractor measures airflow at every supply and return diffuser throughout a building, adjusting dampers until each one matches the specific value shown on the mechanical design's airflow schedule.
Who this matters most to
An independent TAB technician performs the balancing, working separately from the HVAC installer specifically to provide an unbiased verification. A Commissioning Agent reviews the balancing report as part of overall building commissioning.
Where this goes wrong
A project skips independent TAB on the chilled water side to save schedule, relying on the installer's own valve settings. Zones at the far end of the hydronic loop never actually get the design flow through their coils, and persistent comfort complaints on the building's top floor trace back months later to balancing valves that were never actually set to the design report's values.