Cleanroom Air Changes per Hour and Recovery Time Calculator
Air changes per hour, the clean-up time to 100:1 and the references for your grade.
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Enter the room and its supply airflow: the report appears here.
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Results are estimates from the formulas shown, not a professional design or certification. Have a qualified engineer verify anything safety-critical (structures, electrical installations, gas or pressure systems).
About the Cleanroom Air Changes per Hour and Recovery Time Calculator
A cleanroom stays clean by the air it receives. This calculator works out the air changes per hour from the room’s size and either the total supply airflow or the HEPA filters (how many, their face size and the average face velocity), in metric or imperial units, and the clean-up time: how long the room takes to fall 100:1, or by its own grade’s in-operation to at-rest ratio, with well-mixed air or a mixing effectiveness you set.
The report compares the room with the references that apply — the EU GMP Annex 1 clean-up guidance and grade A air speed, FDA’s 20 air changes per hour for ISO 8 supporting rooms and WHO’s 6 to 20 for non-sterile areas — and with your own design target. It gives the airflow needed to meet a clean-up limit, reads a recovery test to show how well the room really mixes, and checks a list of rooms at once.
The free preview runs on your figures and shows the verdict against each reference, the method and the limits; the figures, the PDF, the workbook and the printed airflow record need a Premium pass.
How to use it
- Enter the room’s length, width and height (or its volume) and, if you like, the volume of fixed equipment to take off.
- Enter the total supply airflow, or switch to HEPA filters and enter each filter type: how many, the face width and length, and the average face velocity.
- Choose the area (EU GMP grade, ISO class under the FDA guidance, or a non-sterile area) and, if you have them, your design air changes per hour and clean-up limit.
- Open Recovery and air speed to set the fall (100:1, the grade’s own, or yours), the mixing effectiveness, a recovery test and grade A air speed readings.
- With a Premium pass, download the report as PDF or XLSX or print it with a blank airflow and recovery record; without one, the page shows the free preview with the figures hidden.
Examples
6 × 4 × 3 m, 2 m³ of equipment; four 610 × 610 mm filters at 0.45 m/s and two 610 × 1,220 mm at 0.42 m/s
70 m³ and 4,662 m³/h: 66.6 air changes per hour; 100:1 in 4.1 minutes with well-mixed air, within Annex 1’s guidance of less than 20 minutes
Press Example on the page.
10 × 8 × 3 m with 4,000 m³/h
16.7 air changes per hour: below the 20 per hour the FDA guidance calls typically acceptable; 4,800 m³/h would give 20
20 × 15 × 10 ft with 1,500 CFM
1,500 × 60 ÷ 3,000 ft³ = 30 air changes per hour; 100:1 in 9.2 minutes
Common uses
- HVAC design checks for new or changed cleanrooms and their airlocks.
- Qualification planning: the airflow needed for a clean-up time, before the recovery test.
- Reviewing a recovery test against the room’s supply airflow.
- Checking a building’s list of rooms against their grades.
- Teaching how dilution ventilation cleans a room.
The formulas
- Air changes per hour N = supply airflow (m³/h) ÷ room volume (m³). In imperial units, N = CFM × 60 ÷ room volume (ft³).
- Supply airflow from HEPA filters = Σ number of filters × face area × average face velocity × 3,600 (m³/h).
- Clean-up time with well-mixed air and supply air that brings in no particles: the concentration falls as C(t) = C₀ × e^(−εNt), so the time to fall by a ratio R is t = ln R ÷ (εN). For 100:1, t = 276.3 ÷ (εN) minutes, where ε is the mixing effectiveness (1 for ideal mixing).
- Air changes needed for a clean-up limit of T minutes: N = 60 × ln R ÷ (ε × T).
- Recovery test: from a concentration C₀ falling to C in t minutes, the rate is n = ln(C₀ ÷ C) ÷ t; the effective air changes are 60 n, and 60 n ÷ N shows how close the room comes to ideal mixing.
References for each area
- EU GMP grades B, C and D (Annex 1 §4.29): the at-rest particle limits should be reached after a clean-up period, guidance value less than 20 minutes, determined during qualification. Table 1 sets the limits for particles ≥ 0.5 µm per m³: grade B 3,520 at rest and 352,000 in operation (a 100:1 fall), grade C 352,000 and 3,520,000 (10:1), grade D 3,520,000 at rest.
- EU GMP grade A (§4.30): unidirectional airflow with a homogeneous air speed of 0.36–0.54 m/s (guidance value) at the working position, unless scientifically justified in the contamination control strategy.
- FDA (aseptic processing guidance): for Class 100,000 (ISO 8) supporting rooms, airflow sufficient for at least 20 air changes per hour is typically acceptable; significantly higher rates are normally needed for Class 10,000 (ISO 7) and Class 100 (ISO 5) areas.
- WHO (TRS 1019, Annex 2, non-sterile products): a guidance value of 6 to 20 air changes per hour, and a clean-up or recovery time of about 15–20 minutes.
Why the estimate is only a start
The formula assumes the supply air mixes instantly with the whole room. Real rooms have corners and obstructions where air lingers, people and machines that release particles, and returns placed better or worse, so the measured recovery is usually slower than the estimate. Annex 1 lists the recovery test among the qualification tests (the ISO 14644 series describes them). Enter a recovery test, or a mixing effectiveness below 100 %, to see what the room really achieves.
Limitations
- An estimate for well-mixed air, not a qualification result: classification, airflow visualisation and the recovery test show the grade.
- Filter airflow uses the face size you enter; use the effective face area if the supplier gives it, or a measured airflow.
- Annex 1, FDA and WHO figures are guidance values; your contamination control strategy and design may set others.
- Inputs stay on this page until you reload it; nothing is saved or uploaded.
Privacy
On this device; its files download once
Everything is worked out in your browser: the room sizes, airflows and readings you type are never uploaded or stored.
Frequently asked questions
What do I get without a pass?
Without a pass, Cleanroom Air Changes per Hour and Recovery Time Calculator shows the method, the limits that apply and the verdict for your input; computed figures stay hidden until the pass. Until you unlock it, the result can’t be downloaded or printed. A Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
How do you calculate air changes per hour?
Divide the supply airflow per hour by the room volume: 4,800 m³/h into a 240 m³ room is 20 air changes per hour. In imperial units, multiply the CFM by 60 and divide by the room volume in cubic feet.
How many air changes does a cleanroom need?
There is no single number. The FDA aseptic guidance calls at least 20 per hour typically acceptable for ISO 8 supporting rooms and expects significantly more for ISO 7 and ISO 5; WHO gives 6 to 20 for non-sterile areas; EU GMP Annex 1 sets a clean-up time (less than 20 minutes) instead, and an air speed for grade A.
What is the 100:1 recovery time?
The time for the particle concentration to fall to one hundredth of its starting value, as grade B must fall from its in-operation to its at-rest limit (352,000 to 3,520 particles ≥ 0.5 µm per m³). With well-mixed air it is 276.3 ÷ N minutes: 13.8 minutes at 20 air changes per hour.
What does mixing effectiveness mean?
How well the supply air reaches the whole room: 100 % is ideal mixing. A recovery test that falls more slowly than the formula predicts gives a lower value, which the report works out from your readings.