Why is a hard elbow right at a VAV inlet a problem?

A hard elbow at the VAV inlet can make the airflow sensor read dirty, uneven air. Check the VAV manufacturer/install detail and bring options like a straight spool, box shift, or approved inlet fitting before TAB/startup.

['A VAV box needs the airflow sensor to see a usable air profile. If a hard elbow is slammed right onto the inlet, the air can spin or crowd one side of the sensor and give the controls/TAB tech unstable readings.', 'The fix is not to guess a magic distance. Check the VAV submittal/manufacturer requirements and approved shop drawing. Likely options are adding straight duct, rotating or shifting the box, using an approved inlet fitting, or getting detailer direction if the ceiling space is too tight.']

Stop if

• 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

• A bad inlet condition can make balancing difficult, cause hunting controls, and create comfort complaints even when the duct is physically connected.

Steps

• Confirm VAV tag, airflow direction, inlet size, sensor orientation, and manufacturer installation requirements.
• Check how much straight duct is actually available before the inlet.
• Look for an elbow, transition, flex, damper, or offset right at the sensor.
• Check ceiling/access constraints before moving the box.
• Document the condition before TAB/startup so the issue is not blamed on controls only.

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