Cleanroom Air Changes per Hour and Recovery Time Calculator
Air changes per hour is the first number anyone asks for when a pharmaceutical cleanroom is designed or troubleshot. This calculator gives ACH, the supply airflow a target would require, and a quick estimate of how long the room needs to clear particles after an upset.
Your numbers
Sum of HEPA terminal airflows measured at the filters.
Design target from your URS, not a regulatory number.
100:1 is the common recovery test ratio.
Your results
Ideal-mixing model only. Classification, recovery and airflow pattern acceptance are determined by qualification testing per ISO 14644 and your approved protocols.
ACH and recovery minutes vs supply airflow
Sweeps Total HEPA supply airflow from 1000 to 9000, holding your other inputs fixed.
Facility data in one view
Optional expert review of how room, filter and calibration records could be joined to ERP data.
Optional. The tool and every export work without this. No spam.
How to use it
Enter room dimensions and the total measured HEPA supply airflow. Add your design ACH target and the recovery ratio you want to evaluate. The calculator returns volume, actual ACH, the airflow your target would need, and the surplus or shortfall. Measure airflow at the filters, not at the fan, and remember that ceiling height should be the plenum-to-floor height of the occupied space.
Formulas
ACH equals supply airflow in cubic metres per hour divided by room volume. Under ideal mixing, concentration decays exponentially, so the time to drop by a ratio R is ln(R) divided by ACH hours. At 40 ACH a 100:1 reduction takes about 7 minutes in theory. Unidirectional zones and turbulent rooms behave differently, so treat the number as a design estimate.
- Volume = L x W x H
- ACH = Q / V
- Recovery time (h) = ln(R) / ACH
Reading results and common mistakes
A room can meet ACH and still fail recovery because of dead zones, poor return placement or high internal particle generation. Another mistake is counting ACH from fresh air only when HEPA recirculation is what drives particle removal. Always verify with the particle challenge and recovery test during qualification, and re-check after filter changes or airflow rebalancing.
Frequently Asked Questions
What ACH does a Grade B or ISO 7 room need?
There is no single regulatory ACH. Designs often range from tens of air changes per hour upward depending on classification, heat load and process. Your URS and qualification data decide, not a lookup table.
Is ideal mixing realistic?
It is a useful lower bound for planning. Real rooms usually recover slower because of stagnant zones. The recovery test in ISO 14644-3 measures the real behaviour.
Should I use supply or return airflow?
Use total HEPA supply airflow that actually enters the room, measured at the terminals. Return airflow helps with pressure balance but is not the number for ACH.
Why does recovery time matter in GMP?
It shows how fast the room returns to its classified state after an intervention or event, which supports cleaning, personnel flow and shutdown decisions.
If room data, certification dates and filter changes live in your maintenance system, Netray can help surface them alongside ERP records on-prem. Ask for an expert review.
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