A duct system delivers the design only after someone measures it. Balancing is where drawings meet rooms — and where quiet, comfortable buildings are made.
Start at the fan, not at the diffuser
Prove total airflow at the air handler first. If the fan delivers ninety percent of design, no amount of damper work downstream will invent the missing ten — find the duct leak or the wrong pulley before touching a branch.
Balance proportionally, not sequentially
Set branch dampers so every outlet misses its target by the same proportion, then trim the fan to bring the whole system up together. Sequential balancing chases its own tail; proportional balancing converges in one pass.
Respect the terminal’s minimums
VAV boxes have a floor below which their flow sensors read noise. Verify minimum airflow settings against the sensor’s stated range — a box commanded below it hunts forever and takes the zone temperature along.
Leave numbers, not impressions
The balancing report should let a stranger reproduce the system state: measured flow per outlet, damper positions, fan speed and the instruments used. That document is the baseline every future complaint gets measured against.
