Static field route #18937

What do I check when a branch line has zero CFM but the dampers are open?

Airflow/TAB Impacts From Installation🟨 CHECK FIRSTV189 answer-gap expansion

📖 Verified core answer

Zero CFM with open dampers usually means a real blockage, closed/tripped device, wrong connection, or disconnected path. Trace the branch before blaming the balancer.

Open in Field Rescue Open category

Field verification checklist

Confirm the balancer reading and which exact branch/zone is zero.
Check that the unit is running and main/zone dampers are actually open, not just handles turned.
Trace from main tap to VAV/damper/flex/diffuser for disconnection, crushed duct, tripped damper, or blockage.
Use camera/mirror/register access before cutting holes.
Document what you found and coordinate correction with TAB/foreman.

Ask foreman

Zone/branch [tag] reads zero CFM even with dampers open. I traced from the main to [point] and checked for crushed duct/tripped damper/blockage. Do you want me to open access at [location] or have TAB/controls verify next?

Text to foreman

Route options

AMake the field correction only if it is within your assignment and the approved method.

BHold and document the condition if the fix affects airflow, access, life safety, pressure class, rated assemblies, equipment, or another trade.

CBring the foreman/detailer the location, what you checked, and what decision you need before cover, startup, or rework.

Do not do this

Do not assume controls or TAB are wrong until the physical air path is checked.

Why this matters

A hidden blockage can leave an entire zone dead and waste hours if everyone argues instead of tracing the duct path.

Verification basis

Approved drawings/specs, project coordination drawings, manufacturer instructions/submittals, shop standards, foreman/detailer direction, employer policy, and AHJ/code requirements.