CLEANROOM AIR FILTRATION
Filtration is the foundation of every cleanroom. No matter the industry, application, or ISO classification, the ability to remove airborne particles from the environment is what makes a cleanroom a cleanroom. Every other design element — airflow pattern, pressurization, HVAC — exists in support of one core goal: delivering clean, particle-controlled air to the spaces and processes that depend on it.
Filtration doesn’t work in isolation. Filters perform best when paired with a well-designed airflow strategy that moves air efficiently through the space and delivers it consistently to every filtration point.
What Types of Filters Are Used in Cleanrooms?
Cleanroom filtration is typically a multi-stage process, with different filter types targeting different particle sizes at different points in the air handling system. Angstrom Technology offers motorized fan filter units, HEPA filters, ULPA filters, and pre-filters — all configurable to fit your cleanroom layout and classification requirements.
The three core filter types used in cleanroom environments are:
PRE-FILTERS
The first step in filtering/removing large particles.
HEPA FILTERS
Can remove 99.99% of particles 0.3µm or larger.
ULPA FILTERS
9Can remove 99.99% of particles 0.12µm or larger.
| Pre-Filter | HEPA Filter | ULPA Filter | |
|---|---|---|---|
| Minimum Particle Size Captured | Large particles (varies by media) | 0.3µm | 0.12µm |
| Efficiency Rating | Varies by MERV rating | 99.99% | 99.999% |
| Typical Replacement Interval | Every 2 months | Up to 7 years (with leak testing) | Up to 7 years (with leak testing) |
| Recommended ISO Classes | All classes (used in combination) | ISO Class 5–8 | ISO Class 1-4 |
| Relative Cost | Low | Moderate | High |
PRE-FILTERS
As their name suggests, pre-filters serve as the first stage of filtration, intercepting larger airborne particles before they ever reach your HEPA or ULPA filters. By capturing the bulk of heavier particulate upstream, pre-filters reduce the load on downstream filters — extending their service life and helping your entire filtration system operate more efficiently.
Pre-filters require more frequent replacement than primary filters. As a general rule, changing pre-filters approximately every other month — six times per year — keeps your system running cleanly and prevents contamination buildup from working its way further into the air handling train.
HEPA FILTERS
HEPA (High-Efficiency Particulate Air) filters are the most widely used primary filter in cleanroom applications. Rated to remove 99.99% of airborne particles 0.3µm or larger in diameter, HEPA filters meet the filtration requirements for the majority of ISO-classified cleanroom environments, from ISO Class 8 through ISO Class 5.
When properly maintained and operating within appropriate environmental conditions, HEPA filters can last up to seven years. However, there is no universal replacement schedule. Temperature, humidity, air pressure, and the particle load your system handles all influence how a filter ages. Rather than replacing on a fixed calendar, we recommend regular inspection and leak testing — at minimum, every two years. If a leak is identified, it may be repairable; in other cases, replacement is the appropriate response. The goal is to stay ahead of filter degradation before it affects cleanroom performance or classification compliance.
ULPA FILTERS
ULPA (Ultra Low Particulate Air) filters extend filtration performance beyond the HEPA standard, capturing 99.999% of particles 0.12µm or larger. That combination of finer particle capture and higher efficiency makes ULPA filters the right choice for the most demanding cleanroom classifications — ISO Class 4 and stricter — where even submicron particles pose a contamination risk to sensitive processes or products.
The maintenance approach for ULPA filters mirrors that of HEPA filters: regular inspection, routine leak testing, and prompt attention to any identified leaks or performance degradation. Because ULPA filters carry a significantly higher price point than HEPA filters, a proactive maintenance program isn’t just good practice — it’s an important part of protecting your investment.
Fan Filter Units: Delivering Filtration Where It’s Needed
Filters don’t operate independently — they’re housed and powered within fan filter units, or FFUs. An FFU is a self-contained module that combines a motor, a fan, and a HEPA or ULPA filter in a single ceiling-mounted unit. The fan draws air through the filter and delivers clean, filtered air downward into the cleanroom environment in a controlled, consistent flow.
FFUs are the primary delivery mechanism for filtration in modular cleanroom systems. Their modular nature means they can be arranged across the ceiling in configurations that match your cleanroom’s classification requirements and layout. The percentage of ceiling covered by FFUs — referred to as ceiling coverage — directly determines how much filtered air is introduced into the space per unit of time, which in turn drives air change rates.
As ISO classification requirements become more stringent, ceiling coverage requirements increase accordingly. ISO Class 8 cleanrooms may require as little as 5–15% ceiling coverage, while ISO Class 5 environments typically require 35–70%, and the strictest classifications — ISO Class 1 through 3 — approach full ceiling coverage to achieve the continuous, high-velocity filtered airflow those environments demand. See how ceiling coverage and air change rates work together on our cleanroom airflow and air circulation strategies page.
Filter Leak Testing and Maintenance
Installing the right filter is only part of the equation. Maintaining filter integrity over time is equally critical to keeping your cleanroom in classification compliance — and leak testing is the primary tool for doing so.
Leak testing, governed by ISO 14644-3, verifies that filters are seated correctly, that no bypass pathways exist around the filter media, and that the filter itself has not developed any breaches that would allow unfiltered air into the cleanroom. A filter that appears intact can still fail to perform if it’s improperly seated or if the housing or gasket has degraded.
Recommended testing intervals:
-
- ISO Class 5 and lower: particle count testing every 6 months per ISO 14644-2; filter leak testing at minimum every 2 years
- ISO Class 6 through 9: particle count testing annually; filter leak testing at minimum every 2 years
When a leak is found, the appropriate response depends on its size and location. Small leaks in the filter media can sometimes be patched using approved sealants. Larger breaches, failed gaskets, or improperly seated filters typically require repositioning or full filter replacement. In either case, the cleanroom should be re-tested following any corrective action to confirm it has returned to classification.
Consistent maintenance — including pre-filter changes, HEPA and ULPA inspections, and scheduled leak testing — is the most reliable way to extend filter life, protect your classification, and avoid unplanned downtime. Learn more about Angstrom Technology’s cleanroom maintenance services.
Choosing the Right Filter for Your Cleanroom
Filter selection is determined by your ISO cleanroom classification, and the specific contamination risks your application presents. As a general guide:
Pre-filters are used in virtually all cleanroom filtration systems regardless of classification, always in combination with a primary HEPA or ULPA filter.
HEPA filters are the standard choice for ISO Class 5 through 8 environments and cover the majority of cleanroom applications across industries including medical device manufacturing, life sciences, aerospace, automotive, and plastics.
ULPA filters are typically reserved for ISO Class 4 and stricter environments, or for applications where submicron particle control is critical regardless of classification — such as semiconductor fabrication, nanotechnology, or certain advanced aerospace applications.
In all cases, multi-stage filtration combining pre-filters with primary HEPA or ULPA units is strongly recommended. The efficiency gains and extended filter life that come from proper staging more than offset the added system complexity, and they help ensure your cleanroom maintains classification compliance over the long term.
Angstrom Technology’s cleanroom experts can help you evaluate your classification requirements, application demands, and operational goals to design a filtration system that performs reliably from day one. Contact our team to discuss your cleanroom filtration needs or to request a free quote.
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