How to Choose HEPA/ULPA Grade by Cleanroom Class (Class 1 → 100,000)

One of the most common questions in cleanroom projects is: "For this room class, should we use HEPA H13, H14, or jump to ULPA?" Getting it wrong by one grade can double or triple capex — or, worse, fail a GMP audit. This article maps every cleanroom class against the relevant GMP/ISO standard and the matching HEPA/ULPA grade.

1. Understanding the current cleanroom standards

Before talking about filters, the underlying standards need to be aligned. Three systems currently coexist in Vietnamese factories:

a. ISO 14644-1 (the current international standard)

Classifies by number of particles ≥ 0.5 µm per m³ of air. Runs from ISO 1 (cleanest) to ISO 9 (least clean).

b. Federal Standard 209E (US — old, withdrawn in 2001 but still used as a reference)

Classifies by Class 1, 10, 100, 1,000, 10,000, 100,000 (number of ≥ 0.5 µm particles per ft³).

c. GMP-WHO / EU GMP Annex 1

Classifies by letter grade: A, B, C, D, measured both at rest and in operation.

Three-standard mapping table

ISO 14644-1	FS 209E	GMP (at rest)	Short description
ISO 3	Class 1	–	Extremely tight cleanroom (advanced semiconductor)
ISO 4	Class 10	–	Semiconductor fab, hard drive
ISO 5	Class 100	A & B	Sterile pharmaceutical compounding, LAF
ISO 6	Class 1,000	–	Supporting Grade B area
ISO 7	Class 10,000	C	Standard pharmaceutical compounding
ISO 8	Class 100,000	D	Secondary packaging, pharma warehouse
ISO 9	–	–	Ordinary air

2. Rules for choosing HEPA / ULPA by cleanroom class

a. Class 100,000 cleanroom (GMP Grade D, ISO 8)

Choose HEPA H13.

This is the most basic cleanroom grade. Suitable for:

• Pharma warehouses and raw-material stores.
• Preparation and secondary-packaging areas.
• Pre-processing areas for functional foods.
• Gowning transition rooms.

Layout: HEPA H13 at ceiling terminal boxes or integrated into FFUs, downstream of Pre + Medium F8 in the AHU.

b. Class 10,000 cleanroom (GMP Grade C, ISO 7)

Choose HEPA H14.

The most common cleanroom grade in pharma and cosmetics plants. Suitable for:

• Non-sterile compounding (tablets, capsules, syrups).
• Electronics assembly with moderate requirements.
• Premium cosmetics filling.
• Supporting rooms for sterile zones (Grade B background).

Layout: HEPA H14 in terminal boxes or FFUs; upstream chain of Pre G4 + Medium F8/F9 in the AHU.

c. Class 1,000 to Class 100 cleanroom (GMP A & B, ISO 5-6)

Choose ULPA U15.

Sterile-grade cleanrooms — the most demanding in pharma. Suitable for:

• Sterile compounding (Background of Grade A).
• Vial and ampoule filling for vaccines and biologics.
• Cell-culture handling and culture-medium operations.
• Implantable-medical-device cleanrooms.

Layout: ULPA U15 in FFUs or LAF (Laminar Air Flow) boxes, with HEPA H14 at the AHU/MAU stage. Laminar velocity must reach 0.36-0.54 m/s at the working plane for GMP Grade A.

d. Class 1 to Class 10 cleanroom (ISO 3-4)

Choose ULPA U17.

Extremely demanding cleanrooms — mainly in high-tech industry:

• Semiconductor fabs (especially 14nm and below).
• HDD manufacturing.
• EUV photolithography, laser-pickup production.
• Optical and aerospace labs.

Layout: dense ULPA U17 coverage across the entire ceiling, combined with return walls and raised floors to create vertical laminar flow. This is the most expensive configuration but mandatory for nano-tolerance products.

3. Master decision table

Cleanroom class	GMP grade	ISO 14644	HEPA/ULPA grade	Representative application
Class 100,000	D	ISO 8	HEPA H13	Secondary packaging, pharma warehouse
Class 10,000	C	ISO 7	HEPA H14	Standard pharma compounding, electronics assembly
Class 1,000	B (background)	ISO 6	HEPA H14 + ULPA U15	Sterile support area
Class 100	A & B	ISO 5	HEPA H14 + ULPA U15	Sterile compounding, LAF
Class 10	–	ISO 4	ULPA U16/U17	Electronics fab
Class 1	–	ISO 3	ULPA U17	Advanced semiconductor, hard drive

4. Other factors that influence the choice

Cleanroom class is the primary driver, but four further factors deserve consideration:

a. Product type and pharmacological properties

Some biologics and vaccines require sterile air filtration plus endotoxin control — call for ULPA even at Class 10,000. Refer to USP <797>, USP <800>, and EU GMP Annex 1.

b. Operating temperature and humidity

Cleanrooms with very low humidity (<30% RH for effervescent tablets) need HEPAs rated for higher pressure drop and made from anti-moisture-retention materials.

c. Periodic decontamination

Cleanrooms using VHP (Vaporised Hydrogen Peroxide) or H₂O₂ fumigation require HEPAs with 304 stainless-steel frames and chemical-resistant gaskets (chloroprene, not standard PU).

d. Differential pressure between rooms

Multi-grade cleanrooms (Grade D → C → B → A) need at least 15 Pa differential between each grade, which means FFUs must deliver airflow even when the filter is loaded.

5. Common mistakes when selecting HEPA/ULPA

• Using the same filter grade in every room — wasteful for lower-grade rooms or under-spec for higher-grade rooms.
• Ignoring differential pressure when sizing FFUs — the FFU count cannot maintain pressure when HEPAs are 50% loaded.
• Buying cheap, uncertified "multi-standard" HEPAs — they will not pass FAT/SAT/PQ.
• Forgetting replacement cycles in the budget — Grade A HEPAs may need integrity testing every 6 months, and ULPA U17 can cost three times as much as HEPA H14.
• Overlooking exhaust HEPAs — cytotoxic-handling areas need HEPA H14 on the exhaust as well as the supply.

6. A quick design path

For a new cleanroom project, follow 5 steps:

1. Define the class from product requirements (refer to Pharmacopoeia or industry standards).
2. Map class → HEPA/ULPA grade (using the table above).
3. Calculate ACH and required airflow → determine the FFU count.
4. Lay out the 3-stage filter chain in the AHU/MAU plus the final-stage filter at the FFU/terminal.
5. Plan validation — DOP test, scan test, particle count.

Conclusion

Choosing between HEPA H13/H14 and ULPA U15/U17 is not about "wanting things cleaner" — it depends on the cleanroom class required by industry standards. A well-designed filter chain both passes GMP-WHO/EU audits and optimises capex and opex.

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About Green Filter

Green Filter supplies HEPA H13, H14 and ULPA U15, U16, U17 certified to EN 1822-1:2009, with PAO/PSL scan testing, in standard ceiling-module sizes 575×575, 575×1175, 1175×1175 and custom dimensions on request. Green Filter's technical team is ready to advise on filter selection and validation for GMP-WHO/EU projects.

📞 Contact Green Filter to find the right HEPA/ULPA grade for your cleanroom: [insert hotline / email / website]

See also: What is a HEPA Filter? · ULPA Filters U15/U16/U17 · GMP cleanrooms for pharma plants.