Containment Air Balance

Required net negative CFM via Q = 2610 * A * sqrt(delta_P) and recommended NAM count.

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Example

You enter

Target pressure differential (in wc) 0.02
Estimated leakage area (in^2) 8

You get

Required net negative CFM 21

Checked against published worked examples from: IICRC S520 negative-pressure-containment air-balance practice.

Details, formula, and sources

Formula or tableOrifice flow Q = 2610 × A × sqrt(ΔP) (cfm; A in ft², ΔP in inches WC). Leakage area is entered in in² and converted to ft² (/144). Recommended NAM count = required_negative_flow / per-NAM rated CFM.

Source and editionClassical orifice-flow theory; constant 2610 from ASHRAE Fundamentals derivation. IICRC S520-2024 §12 for containment guidance.

Free accessOrifice-flow derivations free in published engineering texts.

What governsEstimate. AHJ and licensed professional govern.

API field namestarget_dp_in_wc, leakage_area_in2, required_cfm

Orifice constant 2610 from ASHRAE Fundamentals (sharp-edge orifice, dry air, sea level)ASHRAE Fundamentals
Default ΔP target 0.02 in WC (negative pressure inside containment)IICRC S520-2024 §12