Static field route #19075

What do I do when a VAV discharge is necked down right after the box?

Equipment Connections: RTU, AHU, VAV, Fans & Louvers🟨 CHECK FIRSTV190 answer-gap expansion

📖 Verified core answer

An immediate neck-down after a VAV can choke airflow, raise static, and cause heat/reheat or noise problems. Keep discharge transitions approved and preserve airflow area where possible.

Open in Field Rescue Open category

Field verification checklist

Confirm VAV tag, discharge size, downstream duct size, and obstacle causing the neck-down.
Check VAV manufacturer/submittal and project detail for discharge requirements.
Look for reheat coil, noise, high static, or TAB concerns downstream.
Measure space for a longer transition or wide/flat duct shape.
Ask before changing size/shape at equipment discharge.

Ask foreman

VAV [tag] is necked down immediately after discharge to clear [obstacle]. I checked available space and downstream run. Do you want a longer transition, flatter equivalent-area duct, box shift, or detailer direction?

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 slam a small neck-down directly onto a VAV discharge just to clear another trade.

Why this matters

A bad discharge connection can choke airflow, increase noise/static, affect heat performance, and create TAB/startup problems.

Verification basis

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