Why is a 45-degree entry bad right at a VAV inlet?
3rd YearYELLOW · Check FirstVAV Inlet 45° Turbulence
Short answer
A VAV inlet needs stable air entering the sensor area. An angled short entry can spin the air and make the box read wrong.
Field answer
A VAV box reads airflow through an internal sensor array. If the air enters at a hard angle or immediately after a short offset, the sensor can see swirl instead of a stable velocity profile.
Check the inlet connection, straight run, flex/round transition, and obstructions. The recovery is usually a straighter rigid inlet spool, revised offset before the straight section, or detailer/TAB-approved connection.
What to check first
- Check if an elbow or 45 enters directly at the VAV collar.
- Look for short flex or offset right at the inlet.
- Confirm airflow arrow and sensor tubing are correct.
- Ask TAB/foreman if readings are unstable.
- Provide straight rigid inlet run where the project/detail requires it.
Do not do this
Do not slam an angled fitting directly onto a VAV inlet and expect stable CFM readings.
Why it matters
Bad inlet geometry can make the VAV hunt, read wrong, or fail air balance.
Ask foreman
VAV [number] has a 45-degree entry right at the inlet and TAB readings may be unstable. I checked the inlet path. Do you want a straight rigid spool added before the box?
Related Field Rescue route
Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.