Apprentice answer

What do I check when a branch reads zero CFM but dampers are open

3rd YearDampers, Fire/Smoke & Life SafetyCheck first

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.

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Plain-English answer

If the unit is running and dampers are open but a branch reads zero, something is stopping the air. It may be internal packing/shipping material, a closed fire/smoke damper, blocked VAV inlet, crushed flex, disconnected duct, wrong tap, or a damper blade not actually moving.

The field move is to trace the air path from main to outlet and inspect at each choke point. Use existing access, registers, camera/mirror, pressure/noise clues, and photos. Cut access only with approval and patch it correctly.

Field 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?

Verify before acting

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.

What do I check when a branch reads zero CFM but dampers are open

Plain-English answer

Field checklist

Ask Foreman

Verify before acting

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