ISO 14644Air changes/hrFree

Cleanroom HVAC
Sizing

Required supply airflow for a cleanroom from its volume and the air-change rate for the target ISO cleanliness class. Pick a class for a typical ACH, then refine to your design value.

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.

Airflow = ACH × volume / 60

Typical recommended air-change rates (ISO 14644): ISO 5 ≈ 240–600, ISO 6 ≈ 90–180, ISO 7 ≈ 30–60, ISO 8 ≈ 10–25 ACH. Unidirectional (ISO 5 and cleaner) is usually designed on face velocity (~0.45 m/s), not ACH — treat this as a non-unidirectional estimate.

Supply Airflow

CFM · m³/h

How to use this calculator

Choose units

Select Metric (m, m³/h) or Imperial (ft, CFM) to match your project drawings and specifications.

Enter the floor area

The internal floor area of the cleanroom in the selected unit — do not include wall thickness or adjacent corridors.

Enter the ceiling height

The clear height from finished floor to ceiling; multiplied by floor area to give room volume.

Pick the ISO class

Sets the mid-range ACH for that class as a starting point — ISO 7 pre-fills 45 ACH, reflecting the typical 30–60 ACH design range.

Adjust air changes per hour

Override the class default with your design ACH if your contamination control strategy calls for a value outside the typical range.

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

In plain terms: the supply airflow is the room volume multiplied by how many complete air changes per hour the cleanliness class requires. In metric the result is already in m³/h; in imperial divide by 60 to convert the hourly volume to cubic feet per minute.

Metric: Q (m³/h) = ACH × V
Imperial: Q (CFM) = ACH × V ÷ 60

Q = required supply airflow (m³/h or CFM)
ACH = air changes per hour for the ISO class (ISO 7 typical: 30–60)
V = room volume = floor area × ceiling height (m³ or ft³)

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.
ACH midpoints are typical design ranges from ISO 14644-4 guidance. Your final ACH must be validated against the actual contamination control strategy and qualification (DQ/OQ/PQ) 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

What ACH does each ISO class require?

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.

Why does ISO 5 use face velocity instead of ACH?

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.

Should I add extra air for positive pressure?

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.

Does the result show total supply or fresh air only?

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