Buyer guide
Fan filter unit selection: fan type, noise, control and sizing
Select a fan filter unit (FFU) by the airflow and uniformity it delivers at your pressure, its power per unit of airflow, its noise and its control range, not by size alone. Laboratory tests found wide differences between commercial units, so ask for measured data.
By ZY Cleanroom · Updated · Sources at the end of the page
What the tests measured
The authors of a Lawrence Berkeley National Laboratory (LBNL) report, LBNL-55039 (2004), tested 20 commercial FFUs: 13 of 4 × 2 ft (1,220 × 610 mm) and 7 of 4 × 4 ft. Energy performance differed considerably between units.
LBNL's 2006 test method measures five things per unit: total electric power, total pressure efficiency, airflow rate, pressure difference and airflow uniformity, under different control schemes. Use the same five as headings in your data sheet.
Fan and motor type
LBNL-49106 measured three FFU-based recirculation systems at 1,276 to 2,374 cfm per kW of total fan power. That is about 2,170 to 4,030 m³/h per kW by our conversion.
The paper says an FFU with an electronically commutated DC motor can run as much as 60% more efficiently than one with a conventional motor. It cites a 2001 trade article, and it notes that no standard comparison data existed then. Ask for the motor type and for measured power at your duty point.
The sources checked compare motor type and control, not blade design. Ask the supplier to state the fan type and the motor type in the data sheet.
Airflow and uniformity
Two texts give air speed for unidirectional flow. The two ranges match: 0.45 m/s with ±20% is 0.36 to 0.54 m/s.
| Source | Value | Where |
|---|---|---|
| FDA aseptic guidance, 2004 | 0.45 m/s (90 ft/min), ±20% | Critical area, generally established |
| EU GMP Annex 1, para 4.30 | 0.36 to 0.54 m/s, guidance value | Working position |
| FDA aseptic guidance, 2004 | Measure 6 in (about 15 cm) from the filter face | HEPA filters in the critical area |
Why uniformity matters
FDA says velocity variation across and between filters can cause turbulence. It asks for filters to be replaced when non-uniform velocity is found.
Noise
None of the GMP texts checked sets an FFU noise limit. Healthcare guidance does for one case: HTM 03-01 para 8.106 caps an operating theatre with an ultra-clean ventilation terminal at 53 dB(A).
GB 50591-2010 lists a sound level test among its cleanroom performance tests (Appendix E.6). Set a room noise target and test it at handover. Ask the supplier for noise at your duty point, with the test distance stated.
Control and sizing
Annex 1 para 4.14 asks cleanrooms to keep pressure and flush the room under all operational conditions. Check that a reduced fan speed still holds your pressure and class. HTM 03-01 links ultra-clean terminal fans to the air-handling set-back mode (para 6.12 note).
Airflow needed is velocity times covered area. Worked example, assumed values: a 10 m² unidirectional zone at 0.45 m/s needs 0.45 × 10 = 4.5 m³/s, which is 16,200 m³/h. If each FFU delivers an assumed 1,160 m³/h, then 16,200 ÷ 1,160 = 13.97, so 14 units. LBNL-49106 lists redundancy as an advantage of FFU systems.
Install and test
GB 50591-2010 lists purification device installation (clause 11.2) and supply air terminal installation (clause 5.6) as separate items. Its Appendix D gives an in-situ leak scan of HEPA filters by photometer or particle counter. Decide who installs the units and who scans the filters.
Put these in the data sheet
State the filter grade, the unit size, the airflow at duty point, the uniformity target and test position, the noise target, the motor type, the control method and range, the power draw and the alarm points.
Who approves the room
Your regulator or customer auditor judges the facility. The contractor builds to your data sheet and supplies test results. The owner keeps the responsibility. 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
What airflow should an FFU deliver?
Enough for your velocity target over the covered area. FDA gives 0.45 m/s ±20%. Annex 1 gives 0.36 to 0.54 m/s at the working position.
Are EC motor FFUs more efficient?
LBNL-49106 reports up to 60% better efficiency than a conventional motor, citing a 2001 trade article. Ask for current measured data.
How noisy should an FFU be?
No GMP text checked sets a limit. UK healthcare guidance caps an operating theatre with an ultra-clean terminal at 53 dB(A). Set a room target and test it.
How do I size FFUs?
Multiply the velocity you need by the covered area. Divide by each unit's airflow at duty point and round up.
How do I calculate FFU coverage?
Multiply the number of units by the face area of one unit, then divide by the ceiling area. With assumed values, 12 units of 1.2 m by 0.6 m in a 40 m² ceiling give 12 × 0.72 = 8.64 m², or about 22% coverage. The standards cited here set no coverage figure for a class, so work from the airflow your room needs.
What is the HS code for a fan filter unit?
US customs ruling H009854 of 2007 placed a pre-wired fan filter unit under subheading 8421.39, filtering or purifying machinery for gases. A unit shipped without its filter may be classified differently. Customs in each country decides, so ask your importer or broker to confirm the code.
Related guides
- Cleanroom cost per m²: published ranges by ISO class
- Building a cleanroom inside an existing building
- How long does it take to build a cleanroom?
- What a cleanroom costs to run: energy, filters and testing
- Turnkey cleanroom contractor
- Room list builder
Sources
- Ming-Shan Jeng, Tengfang Xu and Chao-Ho Lan, Towards Green Systems for Cleanrooms: Energy-Efficient Fan Filter Units, LBNL-55039 (July 2004; abstract page; checked 1 November 2026)
- Tengfang Xu, An Innovative Method for Dynamic Characterization of Fan Filter Unit Operation, Journal of the IEST, volume 50 (2006; abstract page; checked 1 November 2026)
- Tengfang Xu and William Tschudi, Energy Performance of Cleanroom Environmental Systems, LBNL-49106 (November 2001; checked 1 November 2026)
- FDA, Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing Practice (September 2004, nonbinding; checked 1 November 2026)
- EudraLex Volume 4, Annex 1: Manufacture of Sterile Medicinal Products (published 25 August 2022, applied from 25 August 2023; checked 1 November 2026)
- NHS England, Health Technical Memorandum 03-01, Specialised ventilation for healthcare premises, Part A (published 22 June 2021; healthcare guidance; checked 1 November 2026)
- GB 50591-2010, Code for Construction and Acceptance of Cleanroom (issued 15 July 2010, in force 1 February 2011; contents list, chapter 4 and Appendices E and G; checked 1 November 2026)
Project enquiry
Send what you have
A room list, a floor plan or only the floor area is enough to start. After you submit, send drawings by email or WhatsApp.
We reply by email within one working day. We can sign an NDA before you send drawings.
WhatsApp +44 7962 561184 is our UK number for export enquiries. The factory is in Tianjin, China.
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