Should my cleanroom use fan filters or a centralised HVAC system?

When specifying a new Cleanroom, one of the biggest decisions is how to deliver the filtered air: decentralised Fan Filter Units (FFUs) or a traditional centralised HVAC system? Both achieve the required ISO 14644 classification, but they can differ in cost depending on the context, flexibility, maintenance, and performance. Here we break down the pros, cons, and ideal applications for each.

Fan Filter Units (FFUs): The Decentralised Approach

FFUs are self-contained modules with an integrated HEPA/ULPA filter and fan, mounted directly in the Cleanroom ceiling. They draw air from above (often a plenum, interstitial space or they can be directly ducted), filter it, and deliver unidirectional flow downward.

Further to filtration, each element of a HVAC system can be decentralised. Typically smaller, decentralised equipment are utilised to provide temperature control via air conditioning units and relative humidity control by it’s own dedicated plant where these are required environmental parameters. A fresh air make up unit (FAMU) can be used to generate fresh air from outside the building.

Pros

• Modularity and flexibility: Easy to add, remove, or relocate units as processes change. Perfect for phased builds or future expansion without major rework.
• Lower upfront cost for smaller projects: No need for extensive ductwork or a large central plant room – ideal for smaller projects or retrofits into existing buildings.
• Redundancy: If one FFU fails, it can be designed so the others keep running, minimising downtime.
• Energy efficiency in targeted zones: Variable-speed fans allow zoning, so you only run full power where needed.
• Faster installation: Depending on design and application, the installation can be quick.

Cons

• Maintenance intensity: With potentially dozens (or hundreds) of filters to test, certify, and replace during planned maintenance, labour costs add up. Access requires ceiling walkways or scissor lifts.
• Noise and vibration: Fans close to the workspace can create audible hum or minor vibrations, though modern EC motors help.

Best for: small to medium modular setups, R&D labs, or facilities with variable processes like electronics assembly or medical-device prototyping. If your project is budget-constrained or needs quick deployment, FFUs shine.

Centralised HVAC: The Integrated System

A centralised system uses a large Air Handling Unit (AHU) in a dedicated plant room to condition, filter, and distribute air via extensive ductwork to terminal HEPA filters  or diffusers in the Cleanroom ceiling.

Pros

• Superior environmental control: Easier to integrate precise temperature, humidity, and pressure management across the entire facility. Essential for processes sensitive to even minor fluctuations.
• Lower long-term maintenance: Fewer filters to service (all terminals fed from one or two AHUs), and plant-room access simplifies tasks like coil cleaning or belt changes.
• Quieter operation: Fans are remote, so the Cleanroom stays virtually silent – a big plus for operator comfort.
• Scalability for large sites: Handles complex cascades, high air-change rates (>500 ACH), and integration with building-wide systems like chilled water or heat recovery.
• Energy recovery options: Central systems can incorporate economisers or heat wheels for better efficiency in big facilities.

Cons

• Higher capital cost for smaller projects: Ductwork, AHUs, and plant space can increase compared with FFUs on smaller projects.
• Single point of failure: If the AHU goes down, the whole Cleanroom stops – though backups (like a UPS) can mitigate this.
• Less flexible: Changes to layout or classification often require duct modifications, which are disruptive and expensive.
• Longer lead times: Design, fabrication, and commissioning may take longer for smaller projects.

Best for Large-scale Cleanrooms where compliance demands rock-solid control over all parameters. If your process involves sterile filling, high-value batches, or ultra-clean zones, centralised HVAC is usually the safer bet.

Hybrid Systems

A growing third option combines centralised conditioning with decentralised delivery: A smaller AHU pre-conditions air (temperature, humidity, initial filtration, and pressure) and pushes it into a pressurised plenum above the Cleanroom. Fan Filter Units (FFUs) then draw from this plenum and provide the final HEPA/ULPA filtration plus the high velocity needed for demanding air-change rates.

Why choose hybrid?

• Can achieve very high air change rates and excellent airflow uniformity in tall or large-volume Cleanrooms (seen in aerospace, satellite integration, or rocket fairing assembly)
• Delivers precise temperature/humidity control from the central AHU while keeping redundancy and flexibility from FFUs
• Reduces required plant-room size because the AHU only handles part of the total airflow
• Solves headroom or structural restrictions where full ducted terminals are impossible

This approach is increasingly specified for modern high-bay Cleanrooms, complex microelectronics, semiconductor or pharmaceutical suites where neither pure FFUs nor traditional central systems quite meet the brief.

Comparison at a Glance