Negative Air Machine Sizing

Required CFM and unit count from room volume and target ACH.

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Formula and source

Required Negative Air Machine CFM = chamber_volume_ft³ × target_ACH / 60. 4-6 ACH for general containment; 12+ ACH for active mold remediation per IICRC S520-2024 §12.

IICRC S520-2024 §12 (Engineering Controls) by name; ASHRAE 170 (Ventilation of Health Care Facilities) by name for hospital-equivalent ACH.

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Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.