Negative Air Machine Sizing

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

Run the calculator

Example

You enter

Room volume (ft³) 8000
Target air changes per hour 6

You get

Required CFM 800

Checked against published worked examples from: IICRC.

Details, formula, and sources

Formula or tableRequired 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.

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

Free accessIICRC / ASHRAE standards licensed; ACH principles free in published engineering texts.

What governsEstimate. AHJ and licensed professional govern.

API field namesroom_volume_ft3, target_ach, required_cfm

Default target ACH 6 ACH (prefilled; 12+ for active mold remediation per IICRC S520-2024 §12)IICRC S520-2024 §12