HEPA vs ULPA vs Medium vs Pre Filter: Picking the Right One for Every Filter Stage

When designing any air-filtration system — for a pharma plant, an operating theatre, or an office AHU — the first question is always: how many stages and what filter at each? This article compares the four most common filter types (Pre, Medium, HEPA, ULPA) head-to-head so you can decide quickly.

1. Four filter types — four different roles

Picture the four filter stages as a strategic defence formation:

• Pre Filter — the outer-perimeter guard, blocking every coarse threat (hair, fur, dust >10 µm).
• Medium Filter — the inner-perimeter guard, handling moderate fine dust (0.5 µm and above).
• HEPA Filter — the special-operations unit, capturing 0.3 µm dust at >99.95% efficiency.
• ULPA Filter — the elite guard, controlling ultrafine 0.12 µm particles at >99.999% efficiency.

Every stage is essential — no grade "replaces" another. Skip a stage (e.g. no Pre Filter) and the next stage clogs fast, multiplying replacement cost.

2. Master comparison table

Criterion	Pre Filter	Medium Filter	HEPA Filter	ULPA Filter
Standard grade	G3 - G4 (EN 779) / Coarse 65-85% (ISO 16890)	F6 - F9 (EN 779) / ePM1 50-90% (ISO 16890)	H10 - H14 (EN 1822)	U15 - U17 (EN 1822)
Target particle size	>10 µm	0.5 - 1 µm	0.3 µm @ MPPS	0.12 µm @ MPPS
Efficiency	65 - 85%	60 - 95%	99.95 - 99.995%	≥ 99.9995%
Initial pressure drop (Pa)	30 - 80	80 - 200	200 - 250	250 - 600
Typical replacement cycle	1 - 3 months	3 - 12 months	1 - 5 years	3 - 10 years
Reference price (VND)	100k - few hundred k	500k - few million	2 - 15 million	8 - 40 million
Position	AHU inlet	Mid-AHU	After Medium, at supply	Final stage (terminal/FFU)
Material	Polyester wool, plastic mesh	Pleated paper, synthetic cloth, bag	Glass fibre mini-pleat	Ultrafine glass fibre
Representative application	All AHUs, home purifiers	Hospital AHU, Grade C/D cleanrooms	Grade C, B cleanrooms, GMP, premium purifiers	Semiconductor, sterile pharma, Class 1 fabs

3. Efficiency comparison @ particle size

For visualisation: at 0.3 µm, the four types' capture efficiencies look like this:

• Pre Filter G4: ~5-15%
• Medium F8: ~70-85%
• HEPA H13: 99.95%
• HEPA H14: 99.995%
• ULPA U17: 99.9999%

At 0.12 µm (very hard to capture):

• Pre Filter / Medium: essentially ineffective.
• HEPA H14: ~99.5-99.9%.
• ULPA U17: 99.9999% or better.

That is why you cannot "replace HEPA with stacked Medium filters" — the physics differs. Only HEPA and ULPA meet ISO 14644 and GMP-WHO standards.

4. The standard 3-stage cleanroom filter chain

Today's standard chains for pharma and electronics cleanrooms:

Configuration A — Grade D cleanroom (Class 100,000)

Pre G4 → Medium F8 → HEPA H13 (at terminal box or FFU)

For secondary-packaging zones, pharma warehouses, standard food processing.

Configuration B — Grade C cleanroom (Class 10,000)

Pre G4 → Medium F8 → HEPA H14 (terminal box or FFU)

For standard pharma compounding, electronics assembly, primary packaging.

Configuration C — Grade B cleanroom (Class 1,000)

Pre G4 → Medium F9 → HEPA H14 (AHU) → ULPA U15 (FFU)

For sterile support zones (background of Grade A), Grade B compounding.

Configuration D — Grade A cleanroom (Class 100, laminar)

Pre G4 → Medium F9 → HEPA H14 (AHU) → ULPA U15/U17 (LAF box / FFU)

For Grade A sterile compounding, vaccine vial filling, biologics production.

Configuration E — Electronics cleanroom Class 10 or higher

Pre G4 → Medium F9 → HEPA H14 (MAU) → ULPA U17 (full-coverage ceiling FFU)

For semiconductor fabs, hard-drive plants, optical-pickup production.

5. Selection for non-cleanroom environments

For other applications:

• Premium offices / hotels / airports: Pre G4 + Medium F7 (sufficient).
• General hospital (outpatient zones): Pre G4 + Medium F8 (recommended).
• Home air purifiers during PM2.5 season: Pre (washable plastic mesh) + HEPA H11/H12 + activated carbon.
• Paint shops, woodworking shops: Pre G4 + Pulse-jet Cartridge (replacing Medium due to heavy dust).

6. Common mistakes to avoid

• ❌ Skipping the Pre Filter to save capex — result: HEPA clogs in 6 months, replacement costs 5-10× the Pre cost.
• ❌ Buying "no-name" HEPAs without EN 1822 certification — no way to know the real efficiency, big risk for GMP audits.
• ❌ Choosing ULPA for secondary packaging — wasteful; ULPA is not needed at Class 100,000.
• ❌ No ΔP gauge — you have no idea when to replace, leading to both waste (early replacement) and risk (late replacement).
• ❌ Installing the filter backwards — 30-50% bypass, efficiency collapses.

7. Quick decision table

When to use which configuration?

Cleanroom requirement	Suggested configuration
Offices, hotels	Pre G4 + F7
General clinic	Pre G4 + F8
Standard OR	Pre G4 + F8 + HEPA H13
Negative-pressure isolation room	Pre G4 + F9 + HEPA H14
Pharma D	Pre G4 + F8 + HEPA H13
Pharma C	Pre G4 + F8 + HEPA H14
Pharma B	Pre G4 + F9 + HEPA H14 + ULPA U15
Pharma A (LAF)	Pre G4 + F9 + HEPA H14 + ULPA U15/U17
Electronics Class 1,000	Pre G4 + F9 + HEPA H14
Semiconductor fab Class 1-10	Pre G4 + F9 + HEPA H14 + ULPA U17

Conclusion

There is no "best filter" — only the right filter chain for the specific requirement. Pre, Medium, HEPA, and ULPA complement each other; each has its own mission. Investing and maintaining them properly is the fastest path to GMP/ISO compliance while optimising 5-10 year operating cost.

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About Green Filter

Green Filter supplies all four filter grades — Pre, Medium, HEPA and ULPA — together with design consulting for the right filter chain per cleanroom and AHU. We guarantee full certification (EN 779 / ISO 16890 / EN 1822) and hold stock in common sizes.

📞 Contact Green Filter for surveying and 3-stage filter chain consulting: [insert hotline / email / website]

See also: What is a HEPA Filter? · ULPA Filters U15/U16/U17 · How to choose HEPA/ULPA by cleanroom class.