Air Scrubber (ACH) Calculator
Size HEPA air scrubbers for containment. This air scrubber calculator converts room volume and a target air-changes-per-hour into the CFM and number of scrubbers you need.
Required air scrubber CFM = room volume (ft³) × target air changes per hour ÷ 60. A 30 × 20 × 8 ft room at 6 ACH needs 480 CFM — one 500 CFM HEPA scrubber. Most remediation targets 4–6 ACH. Restoration Equipment Supply’s calculator below does the math.
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About This Calculator
An air scrubber calculator sizes HEPA filtration for mold remediation and demolition containment. Required CFM = room volume × target air changes per hour ÷ 60. Most remediation runs 4–6 air changes per hour; active demolition or occupied work runs higher.
Is this air scrubber calculator accurate?
It gives a solid planning estimate using the standard volume × ACH ÷ 60 airflow formula used in IICRC S520 mold remediation practice. For a job we always confirm the exact equipment with you by phone before delivery.
Can I rent or buy the equipment?
Both. Restoration Equipment Supply rents and sells the full drying and power fleet across NJ, NY, CT, PA, NC, SC and Florida, with same-day delivery for emergencies. Browse the full catalog →
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Use our equipment sizing calculator, generator sizing calculator, and the tools in the Calculators menu to build a complete package.
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How Many Air Scrubbers Do I Need?
Multiply the room’s cubic feet by the air changes per hour you want, divide by 60 to get CFM, then divide by each scrubber’s delivered CFM.
The air scrubber CFM formula
CFM = length × width × height × ACH ÷ 60. Scrubbers = CFM ÷ scrubber CFM, rounded up. Size on the airflow a unit actually delivers with filters and ducting installed — loaded HEPA filters and long lay-flat duct both cut airflow.
| Application | Typical ACH | Notes |
|---|---|---|
| General air cleaning / odor after water damage | 2–4 | Recirculating HEPA scrubbing |
| Mold remediation, negative air containment | 4–6 | 4 ACH is a common minimum; this calculator defaults to 6 |
| Active demolition / heavy contamination | 6–12 | More dust generation needs more air changes |
Mold work follows IICRC S520 and the EPA mold remediation guide. In negative-air setups the scrubber exhausts outside the containment, and crews commonly verify a slight negative pressure (around −0.02 in. w.c.) with a manometer.
| Room | Volume | 4 ACH | 6 ACH | 12 ACH |
|---|---|---|---|---|
| 10 × 10 × 8 ft | 800 ft³ | 53 CFM | 80 CFM | 160 CFM |
| 30 × 20 × 8 ft | 4,800 ft³ | 320 CFM | 480 CFM | 960 CFM |
| 40 × 20 × 8 ft | 6,400 ft³ | 427 CFM | 640 CFM | 1,280 CFM |
| 50 × 40 × 10 ft | 20,000 ft³ | 1,333 CFM | 2,000 CFM | 4,000 CFM |
Example: a 40 × 20 × 8 ft basement at 6 ACH needs 6,400 × 6 ÷ 60 = 640 CFM — two 500 CFM scrubbers. See air scrubber rental and negative air machine rental, or size the whole job in the equipment calculator.
How do I calculate air scrubber CFM?
Multiply room volume in cubic feet by the target air changes per hour, then divide by 60. A 4,800 ft³ room at 6 ACH needs 480 CFM.
How many air changes per hour for mold remediation?
Typically 4–6 ACH for containment, with 4 a common minimum and more during heavy demolition. Follow your project’s remediation protocol and IICRC S520.
How many air scrubbers do I need?
Divide the required CFM by each unit’s delivered CFM and round up. 640 CFM of required airflow with 500 CFM scrubbers = 2 units.
What is the difference between an air scrubber and a negative air machine?
Often the same HEPA unit. Run inside the room it recirculates and scrubs (air scrubber); ducted outside the containment it creates negative pressure (negative air machine).
Updated October 2026 · Reviewed by the Restoration Equipment Supply dispatch team
How Our Air Scrubber Calculator Works
Drying plans and equipment counts follow the IICRC S500 Standard for Professional Water Damage Restoration. Restoration Equipment Supply is an IICRC Certified Firm.
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