Air changes per hour (ACH) & scrubber CFM

Negative-air machines and air scrubbers are sized by air changes per hour (ACH). The identity is ACH = CFM × 60 ÷ room volume (cu ft), so the airflow you need is required CFM = ACH × volume ÷ 60. Containment and IAQ work usually targets 4–6 ACH. These are labeled planning conventions. Use them in the air-scrubber CFM tool.

Room volumeCFM for 4 ACHCFM for 6 ACHScrubbers @ 500 CFM (6 ACH)
1,500 cu ft100 CFM150 CFM1 unit
2,700 cu ft180 CFM270 CFM1 unit
4,000 cu ft267 CFM400 CFM1 unit
8,000 cu ft533 CFM800 CFM2 units

Required CFM = ACH × room volume ÷ 60; ACH = CFM × 60 ÷ volume. Containment/IAQ usually targets 4–6 ACH. Labeled planning conventions.

Related calculators

Air Scrubber & Negative-Air CFMSize negative-air scrubbers by required CFM from room volume and your ACH target — the ACH formula, a worked example and an air-quality FAQ, no lead-gen.Structural Drying EquipmentSize structural drying: how many air movers and LGR dehumidifiers to dry a room from the affected square footage, using labeled IICRC/AHAM coverage typicals.