If a large return duct pulls inward, the duct is not stiff enough for the negative pressure or operating condition. Stop, document, and add approved reinforcement or replace the section.
Do not beat the panels back flat and restart without finding why the duct collapsed.
Check
Stop or reduce system operation if the duct is actively deforming.
Check fan operation, dampers, filters, return path, and whether any intake/opening is blocked.
Photo the panels, seams, reinforcement, and exact system condition when it happened.
Verify pressure class and duct reinforcement requirements from approved drawings/specs.
Get direction before adding stiffeners or tie rods.
Steps
Stop or reduce system operation if the duct is actively deforming.
Check fan operation, dampers, filters, return path, and whether any intake/opening is blocked.
Photo the panels, seams, reinforcement, and exact system condition when it happened.
Verify pressure class and duct reinforcement requirements from approved drawings/specs.
Get direction before adding stiffeners or tie rods.
Say this to your foreman
The return main at [location] pulled inward during startup. I checked fan status, dampers, filters, and blocked openings. Do you want reinforcement added per detail, or should we hold for TAB/engineer review?