Reference table
Recommended air changes per hour by room type
Typical air change targets, and where each number comes from. Use them as a starting point in the ACH calculator or the air scrubber calculator.
Targets by space
| Space | ACH | Source / basis |
|---|---|---|
| Homes — whole-house ventilation | 0.35 or more (outdoor air) | Older ASHRAE 62 baseline; ASHRAE 62.2 now sets ventilation in CFM by floor area and bedrooms |
| Homes and offices — clean air incl. filtration | 5 or more | CDC, Ventilation in Buildings (2023) |
| Classrooms — clean air incl. filtration | 5 or more | CDC guidance; widely used in school IAQ programs |
| Bedroom with an air purifier (allergies) | 4–6 | AHAM two-thirds sizing rule ≈ 5 ACH |
| Mold / water damage containment | 4 minimum, 6+ common | Industry practice; 4 ACH originates in asbestos abatement enclosures |
| Fire and smoke odor removal | 6–10+ | Restoration practice; varies with soot load |
| Construction dust control (occupied building) | 4–6+ with negative pressure | Common ICRA / project specifications |
| Airborne infection isolation room | 12 or more | CDC 2003 guidelines; ASHRAE 170 |
| Operating room | 20 total (4 outdoor) | ASHRAE 170; CDC 2003 cites 15 or more |
| Commercial kitchen | 15–60 | Typical design range; hood exhaust usually governs |
Outdoor air vs clean air
Building codes count outdoor air supplied by ventilation. Health guidance such as the CDC's 5 ACH countsequivalent clean air — ventilation plus anything that removes particles, like HVAC filters and portable HEPA purifiers. A room with 1 ACH of outdoor air and a purifier adding 4 ACH meets a 5 ACH clean-air target.
clean-air ACH = outdoor-air ACH + filtration ACHCleanrooms
ISO 14644-1 classifies cleanrooms by particle count, not by airflow, so there is no required ACH. These are typical design ranges used to reach each class:
| Class | Typical ACH |
|---|---|
| ISO 8 (Class 100,000) | 5–48 |
| ISO 7 (Class 10,000) | 60–90 |
| ISO 6 (Class 1,000) | 90–180 |
| ISO 5 (Class 100) | 240–480 (unidirectional flow) |
Actual requirements depend on process, occupancy and certification testing.
Containments and restoration work
No restoration standard prescribes one ACH number for every job. The 4 ACH floor is a long-standing convention from asbestos abatement enclosures, and most remediation contractors run higher — 6 or more — when the space is heavily contaminated or demolition is under way. What is checked in the field is pressure: a negative differential of about −0.02 in. w.c. (−5 Pa) across the containment barrier.
More calculators
Every result shows the formula behind it.