The first large branch tap is robbing air from the rest of the trunk
A large first tap can rob the trunk if the branch is uncontrolled or the system was not balanced. Verify the print, branch damper/access, downstream starvation, and TAB direction before cutting in changes.
Do not install or crank down a damper blindly without checking the approved layout and TAB direction.
Check
Verify the branch size and location against the latest drawing.
Check whether the branch has an accessible volume damper, VAV damper, or other balancing device.
Confirm which downstream boxes or rooms are starving and whether dampers are fully open/closed.
Check for an accidental blockage, reversed damper, or wrong tap before blaming design.
Coordinate with TAB/foreman before adding, moving, or throttling dampers.
Steps
Verify the branch size and location against the latest drawing.
Check whether the branch has an accessible volume damper, VAV damper, or other balancing device.
Confirm which downstream boxes or rooms are starving and whether dampers are fully open/closed.
Check for an accidental blockage, reversed damper, or wrong tap before blaming design.
Coordinate with TAB/foreman before adding, moving, or throttling dampers.
Say this to your foreman
The first large branch at [location] seems to be robbing the trunk. I checked the print, damper/access, and downstream boxes. Do you want a balancing damper added/corrected here, or should we hold for TAB/detailer direction?