What should I check when flex duct is sagging and starving a room?
Sagging flex can choke the liner before the air ever reaches the diffuser. Re-support the run so the duct is smooth, not crushed, not kinked, and not stretched into a bad bend.
['Flex duct is forgiving, but it is easy to install ugly. Severe sag, sharp bends, crushed straps, or extra-long runs can collapse the inner liner and starve the room even when the diffuser looks connected.', 'The normal correction is to re-hang and clean up the route: support it per the project/manufacturer direction, pull out unnecessary slack, keep bends wide, and make sure straps support without crushing the duct.']
Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.
Check
The outside jacket can look fine while the inner liner is kinked or sagging. That steals airflow and creates comfort/TAB complaints later.
Steps
Look for sags, kinks, crushed straps, torn jacket, or inner liner pulled loose at either end.
Check that the flex is not longer than needed and is not snaked around obstacles for no reason.
Make sure bends are wide and smooth instead of hard folded.
Verify the inner liner is attached and sealed at the collar, not just the outer jacket.
Check project/manufacturer support and bend requirements before calling it corrected.
Say this to your foreman
what should i check when flex duct is sagging and starving a room?