Buyer guide
Cleanroom air changes per hour: published values and their limits
No general cleanroom standard fixes one air change rate for a class, and ISO 14644-1 sets particle limits only. Published guidance gives starting points, from at least 20 per hour for ISO 8 supporting rooms (FDA) to 240 to 480 per hour for ISO 5 (IEST, as cited by Berkeley Lab), and each must be checked by calculation and test.
By ZY Cleanroom · Updated · Sources at the end of the page
Published values by class and use
Air changes per hour is written ACH below. Many trade charts list ISO 6 to 8 ranges, but none could be traced to a primary standard, so none appear here.
| Class or use | Published value | Source |
|---|---|---|
| ISO 4, unidirectional | 300 to 540 ACH | IEST-RP-CC012.1 (1993), as cited by LBNL |
| ISO 5 | 240 to 480 ACH | IEST-RP-CC012.1, as cited by LBNL |
| ISO 5, eight rooms measured | 98 to 479 ACH; most below 240 | LBNL field data, 2001 |
| ISO 8 supporting room | At least 20 ACH is typically acceptable; much higher for ISO 7 and ISO 5 | FDA, 2004 |
| UK pharmacy aseptic suite | At least 20 ACH | HTM 03-01, Table 6 |
| Pharmacy ISO 7 room | At least 30 total HEPA-filtered ACH, 15 from ceiling HEPA via the HVAC | USP <797> 4.2.4 |
| Pharmacy ISO 8 room | At least 20 total, 15 from ceiling HEPA via the HVAC | USP <797> 4.2.4 |
| Operating room, US | 20 total, 4 outdoor | ASHRAE 170, Table 7-1 |
| Isolation rooms | At least 10 (UK); at least 12 (CDC, new) | HTM 03-01; CDC 2003 |
| EU GMP sterile | No ACH; clean-up guidance under 20 minutes | Annex 1, para 4.29 |
Formula and worked example
ACH equals supply airflow in m³/h divided by room volume in m³. For full ceiling coverage, ACH equals air velocity in m/s times 3,600 divided by ceiling height in m.
Example only, with assumed values. A room 8 m by 5 m and 3 m high holds 120 m³.
| Air changes | Airflow in m³/h | Airflow in m³/s |
|---|---|---|
| 20 ACH | 2,400 m³/h | 0.67 m³/s |
| 30 ACH | 3,600 m³/h | 1.00 m³/s |
| 60 ACH | 7,200 m³/h | 2.00 m³/s |
Same rate, different air
Ceiling height changes the air needed for the same rate. Take 20 ACH over a 40 m² floor. A 2.7 m ceiling gives 108 m³ and 2,160 m³/h. A 3.6 m ceiling gives 144 m³ and 2,880 m³/h. That is 33% more air at the same ACH. All values are calculated.
Why these are only starting points
Berkeley Lab reports a lack of scientific basis for an optimal recirculation rate. It says acceptable contamination levels have been reached at rates well above and below the recommended ranges.
Lenegan and Eaton (Cleanroom Technology, 2024) add that mixing is imperfect, with ventilation effectiveness of 0.7 to 0.9 at some locations and an expected value of about 0.4 for their example room. Particles come from people, equipment and process, and a simple rate ignores them.
Pressure leakage and recovery time also set the airflow. HTM 03-01 Appendix 4 shows door leakage rising with pressure. Annex 1 para 4.25 lists a recovery test in qualification.
Local codes
For projects in China, GB 50073-2013 sets airflow pattern and supply air volume in section 6.3. Read its current text. Other markets follow their own pharmaceutical, hospital or sector rules.
Test the result
ISO 14644-3:2019 covers airflow velocity and uniformity, airflow direction and visualisation, and recovery. Put the target, the measuring position and the room state in the room data sheet.
Who approves the room
Your regulator or customer auditor judges the facility, not the contractor. The contractor builds to your room data sheet and supplies test data. To have a room list reviewed, send it to ZY Cleanroom, a cleanroom design-and-build contractor with its own panel factory in Tianjin, China.
Questions
Common questions
How many air changes does an ISO 7 room need?
No general standard sets one. FDA says ISO 7 areas normally need significantly more than 20. USP <797> asks 30 for pharmacy ISO 7 rooms.
How do I convert velocity to air changes?
ACH equals velocity times 3,600 divided by ceiling height. For example, 0.3 m/s under a 3 m ceiling gives 360.
Does more air always give a cleaner room?
Not necessarily. Berkeley Lab says acceptable contamination levels have been reached at rates both above and below the recommended ranges.
Does Annex 1 give an air change rate?
No. It gives a clean-up guidance of under 20 minutes, a 10 Pa pressure guidance and a unidirectional air speed range.
Related guides
- FFU ceiling layout: coverage, class and grids
- Class 100, 1,000, 10,000 and 100,000 Cleanrooms Explained
- ISO 5 and ISO 6 cleanroom requirements
- Cleanroom failed particle count: causes and fixes
- Turnkey cleanroom contractor
- Room list builder
Sources
- Tengfang Xu and William Tschudi, Energy Performance of Cleanroom Environmental Systems, LBNL-49106 (November 2001; checked 31 October 2026)
- Nigel Lenegan and Tim Eaton, Calculating supply airflow rates using simple air-changes or a scientific approach, Cleanroom Technology (23 September 2024; checked 31 October 2026)
- FDA, Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing Practice (September 2004, nonbinding; checked 31 October 2026)
- NHS England, Health Technical Memorandum 03-01, Specialised ventilation for healthcare premises, Part A (published 22 June 2021; checked 31 October 2026)
- Washington State Department of Health, Pharmacy Self-Inspection Worksheet, 2026 USP 797 Sterile Compounding Addendum, DOH 690-296 (January 2026), which reproduces USP <797> text by section; checked 31 October 2026
- ANSI/ASHRAE/ASHE Addendum y to Standard 170-2025, Ventilation of Health Care Facilities, Table 7-1 (approved 22 September 2026; checked 31 October 2026)
- CDC, Guidelines for Environmental Infection Control in Health-Care Facilities (2003), B. Key Terms Used in this Guideline (checked 31 October 2026)
- EudraLex Volume 4, Annex 1: Manufacture of Sterile Medicinal Products (published 25 August 2022; applied from 25 August 2023, and from 25 August 2024 for point 8.123; checked 31 October 2026)
- ISO 14644-3:2019, Cleanrooms and associated controlled environments, Part 3: Test methods (published August 2019; contents list; checked 31 October 2026)
- GB 50073-2013, Code for design of clean room (issued 28 January 2013, in force 1 September 2013; catalogue page with contents list; checked 31 October 2026)
Project enquiry
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