If hanger spacing is beyond the approved detail for that duct size and system, add support before loading, insulating, or covering the run. First map exactly where the long spans are.
Ask before moving anchors, changing spacing, deleting supports, drilling structure, or altering trapeze/seismic layout.
Watch out
Do not guess that a long span is close enough. Hanger spacing affects duct sag, joint stress, and inspection/QA compliance.
Check
Walk the run and mark each hanger location.
Measure the actual span between hangers and compare it to the approved detail, project spec, SMACNA table, or company standard for that duct.
Mark every span that appears over the allowed limit.
Check whether the structure allows a new hanger at the needed location without hitting conflicts.
Do not insulate, close, or keep loading a run that is sagging or obviously over-spanned.
Steps
Walk the run and mark each hanger location.
Measure the actual span between hangers and compare it to the approved detail, project spec, SMACNA table, or company standard for that duct.
Mark every span that appears over the allowed limit.
Check whether the structure allows a new hanger at the needed location without hitting conflicts.
Do not insulate, close, or keep loading a run that is sagging or obviously over-spanned.
Say this to your foreman
I have a long span between hangers on this [size/system] duct run at [location]. I think it needs another hanger here. Is there a specific anchor or support detail you want me to use?