How many duct diameters of straight pipe do I need before the inlet of a VAV box?

You need a minimum of 3 to 5 straight, uninterrupted duct diameters of straight round pipe before entering the VAV box inlet. If you place an elbow or a sharp transition directly on the inlet collar, the air will spin turbulently, causing the flow sensor tubes inside the VAV inlet to read incorrectly, ruining the system balance.

['You need a minimum of 3 to 5 straight, uninterrupted duct diameters of straight round pipe before entering the VAV box inlet. If you place an elbow or a sharp transition directly on the inlet collar, the air will spin turbulently, causing the flow sensor tubes inside the VAV inlet to read incorrectly, ruining the system balance.']

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.

Steps

• You need a minimum of 3 to 5 straight, uninterrupted duct diameters of straight round pipe before entering the VAV box inlet. If you place an elbow or a sharp transition directly on...

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