Air changes per hour is hourly airflow divided by room volume.

Why derate rated CFM?

Filters, ducting, bends, and loading reduce delivered airflow.

Does more ACH guarantee contaminant removal?

No. Filtration, source control, leakage, placement, and mixing also matter.

Can this verify negative pressure?

No. Pressure differential must be measured.

Air Scrubber Calculation

Calculate air-scrubber CFM, air changes per hour, unit count, delivered airflow, and treatment cycles. Review assumptions, limitations and current source information before using the result.

Room Length

Room Width

Room Height

Target Air Changes per Hour

Rated Airflow per Unit

Delivered Flow vs Rating

Operating Time

Whole Units Required

Room Volume: 6,000
Required Delivered Airflow: 600
Delivered Airflow per Unit: 400
Calculated Units Required: 1.5
Estimated ACH with Whole Units: 8
Theoretical Air Changes: 192

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ACH is a circulation metric. Effective control also depends on source control, filter efficiency, placement, containment, and mixing.

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How to Use This Calculator

Enter room dimensions, the required ACH from the work plan, rated airflow, expected derating, and runtime.

Formula & Methodology

Required CFM equals room volume multiplied by target ACH and divided by 60. Unit count divides required flow by delivered flow per unit.

Worked example

A 6,000 ft³ room at 6 ACH needs 600 CFM delivered. A 500 CFM unit derated to 80% delivers 400 CFM, so two units are required.

It does not establish hazardous-material procedures, select filters, certify negative pressure, or prove exposure compliance.

Planning estimate only. Hazardous dust, mold, asbestos, lead, silica, smoke, and infectious aerosols require qualified procedures and applicable regulations.

Related Guides

How to Calculate Air Scrubber CFM and Unit Count
Calculate the required CFM and number of HEPA air scrubber units for any room based on volume and target air changes per hour. Size air scrubbers for mold remediation, construction dust control, and indoor air quality projects.

Frequently Asked Questions

What does ACH mean?: Air changes per hour is hourly airflow divided by room volume.
Why derate rated CFM?: Filters, ducting, bends, and loading reduce delivered airflow.
Does more ACH guarantee contaminant removal?: No. Filtration, source control, leakage, placement, and mixing also matter.
Can this verify negative pressure?: No. Pressure differential must be measured.

Published 8/19/2026