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ISO 14644Air changes/hrFree

Cleanroom HVAC
Sizing

Convert room volume and a separately established project air-change rate into airflow. This worksheet does not select ACH or determine cleanroom performance.

Who it's for: mechanical engineers and cleanroom designers verifying that a proposed HVAC system delivers the air-change rate required by the ISO 14644 cleanliness class — you need the room's floor area, ceiling height, and a target ACH at construction documents.

Airflow = entered ACH × room volume
ISO 14644 classifies particle concentration; it does not provide one universal ACH for each class. Establish the airflow regime and ACH from the project contamination-control strategy and qualified design.
Supply Airflow
CFM · m³/h

How to use this calculator

1
Choose units
Select Metric (m, m³/h) or Imperial (ft, CFM) to match your project drawings and specifications.
2
Enter the floor area
The internal floor area of the cleanroom in the selected unit — do not include wall thickness or adjacent corridors.
3
Enter the ceiling height
The clear height from finished floor to ceiling; multiplied by floor area to give room volume.
4
Identify the project basis
Record the approved contamination-control or mechanical design source for the entered value.
5
Enter air changes per hour
Use the verified value established for the actual process, room, airflow regime and qualification strategy.
6
Read the required supply airflow
The result shows total supply airflow in both m³/h and CFM, with room volume as a reference check.

The formula

Metric: Q (m³/h) = entered ACH × V
Imperial: Q (CFM) = entered ACH × V ÷ 60
V = entered floor area × entered height. The arithmetic does not establish an ACH requirement or prove classification.

Worked example

Example
A pharmaceutical lab designed to ISO 7 has a floor area of 50 m² and a ceiling height of 3 m, giving a room volume of 150 m³. At the mid-range ACH for ISO 7 (45 ACH), the required supply airflow is 45 × 150 = 6,750 m³/h (≈ 3,973 CFM). This is the ventilation demand before adding 10–15% for positive-pressure make-up air.

When this estimate will be off

  • Non-unidirectional rooms only — ISO 5 and cleaner are designed on face velocity (~0.45 m/s), not ACH; this calculator gives an indicative number, not a compliant design for those classes.
  • No ACH range is supplied. The selected rate must be established and validated for the actual contamination-control strategy and qualification requirements.
  • Does not include make-up air for positive-pressure offset or local exhaust compensation — add 10–15% over the ventilation demand for a pressurised cleanroom suite.
  • Assumes a uniform ceiling height. Rooms with raised-floor plenums, equipment coffers, or split levels need the volume calculated by zone.

Frequently asked questions

A common mistake: Non-unidirectional rooms only — ISO 5 and cleaner are designed on face velocity (~0.45 m/s), not ACH; this calculator gives an indicative number, not a compliant design for those classes.

ISO 14644 defines cleanliness by particle count, not a mandatory ACH. Typical design ranges used in practice are ISO 5 ≈ 240–600, ISO 6 ≈ 90–180, ISO 7 ≈ 30–60, and ISO 8 ≈ 10–25 ACH. The calculator pre-fills the midpoint; validate your design ACH against the contamination control strategy and qualification data.

At ISO 5 and cleaner, airflow is unidirectional — a laminar-flow ceiling or wall panel sweeps particles away rather than diluting them. The design parameter is face velocity (~0.45 m/s) over the supply area, not total ACH. ACH-based sizing underestimates supply for these classes. Confirm with ISO 14644-3 performance testing after installation.

Yes. A positive-pressure cleanroom typically needs 10–15% additional supply above the ventilation demand to overcome leakage through doors, pass-throughs, and wall cracks. Add this offset to the calculator result. The HVAC designer must also verify that exhaust, recirculation, and make-up air balance correctly across the whole suite.

Total supply airflow — all conditioned air delivered to the room, most of which is recirculated through HEPA filters. Fresh (outside) air is a small fraction, sized for occupant ventilation and pressure offset. Confirm the fresh-air split with the project mechanical engineer and the room's occupancy load.

Sources

  • ISO 14644-1:2015 — classification of air cleanliness by particle concentration — defines ISO classes 1–9 and the particle-count limits for each
  • ISO 14644-4:2001 — cleanroom design and construction — HVAC sizing guidance and typical air-change rates by ISO class

This free Cleanroom HVAC Sizing Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.