🔬 HEPA Face Velocity
🏭 Makeup Air for Pressurization
Sizing Breakdown
Full Calculation Table
| Component | Basis | Value | Result |
|---|
How to Use the Cleanroom HVAC Calculator
Choose the ISO 14644-1 classification your room needs to hold, or select Custom ACH if your process specification calls out a specific air change rate.
Enter floor area and ceiling height. The calculator uses room volume together with the ISO air change rate to determine required supply airflow.
Enter the percentage of ceiling covered by HEPA filters and your target face velocity to check whether the layout can deliver the required airflow within a safe velocity range.
Click Calculate Cleanroom Sizing to see supply airflow, HEPA face velocity, makeup air for pressurization, and recirculation airflow.
Understanding Cleanroom HVAC Design
Cleanroom HVAC systems exist to control airborne particle concentration to a specific classification, not just to condition temperature and humidity. That means air change rate, not sensible cooling load, usually drives supply airflow, and the mechanical system has to hold a specific classification continuously while people, equipment, and processes generate particles inside the space.
| ISO Class | Typical ACH Range | Typical Face Velocity | Common Application |
|---|---|---|---|
| ISO 5 | 350–600 | 0.45 m/s | Aseptic fill lines, semiconductor lithography |
| ISO 6 | 150–240 | 0.40–0.45 m/s | Sterile compounding, wafer handling |
| ISO 7 | 60–90 | 0.35–0.45 m/s | Pharmaceutical packaging, gowning areas |
| ISO 8 | 10–40 | 0.30–0.40 m/s | General cleanroom support, warehousing |
Ranges are general engineering guidance, not a specific standard requirement. Confirm exact air change rate against your process specification, since particle generation from equipment and personnel activity level significantly affects the number needed to hold classification under dynamic conditions.
Air Change Rate Sets Supply Airflow
Supply airflow for a cleanroom is calculated by multiplying room volume by the target air changes per hour, then converting to a continuous flow rate. This number is almost always larger than what a sensible cooling load calculation alone would call for, and it follows a similar dilution logic to the dilution air calculator used for contaminant control in less specialized spaces, which is why cleanroom mechanical systems recirculate most of their supply air through HEPA filtration rather than conditioning fresh outdoor air at that volume.
HEPA Face Velocity and Ceiling Coverage
Once you know total supply airflow, the HEPA filter ceiling area needed depends on your target face velocity, a relationship the HEPA filter calculator also uses when sizing filtration for general air quality applications. A room with limited ceiling HEPA coverage will need a higher face velocity to move the same airflow, which increases filter pressure drop and can eventually push velocity outside the filter's rated efficiency range. Increasing ceiling coverage percentage is often more practical than raising face velocity when a room cannot achieve its air change target.
Pressurization Cascade Between Classifications
A pressurization cascade holds each cleaner room at a higher pressure than the adjacent, less clean space, so air always flows from clean to dirty even when a door briefly opens. This calculator estimates makeup air needed to overcome door and penetration leakage at your specified pressure differential, using a simplified orifice flow relationship. Real commissioning will need to verify actual leakage area and confirm every boundary in the cascade holds its designed pressure step, since a single weak link can undermine the whole cascade.
Health Canada Considerations for Pharmaceutical Cleanrooms
Pharmaceutical cleanrooms in Canada operate under Health Canada's Good Manufacturing Practices guide, which references cleanliness classification requirements by dosage form and processing step. This regulatory framework does not replace a project-specific validation and commissioning process, but it expects the mechanical design to demonstrate it can hold its stated classification under both at-rest and operational conditions.
CFIA Considerations for Food-Grade Cleanrooms
Food-grade cleanrooms fall under CFIA Safe Food for Canadians guidance where applicable, which similarly does not replace a project-specific validation and commissioning process but expects the mechanical design to demonstrate it can hold its stated classification under both at-rest and operational conditions.
Frequently Asked Questions
ISO Class 7 cleanrooms typically require 60 to 90 air changes per hour, though the exact number depends on room activity level, particle generation from processes and personnel, and how tightly you need to hold the classification under dynamic operating conditions. Rooms with more people or particle-generating equipment need air changes toward the higher end of that range.
HEPA face velocity equals the total supply airflow divided by the total HEPA filter face area. Most cleanroom HEPA filters are designed for a face velocity between 0.35 and 0.55 metres per second. Higher face velocities can push the filter beyond its rated efficiency and increase pressure drop, while lower velocities waste filter ceiling coverage and increase capital cost.
A common design target is 10 to 15 pascals of positive pressure differential between adjacent cleanroom classifications in a cascade, such as between an ISO 7 room and an ISO 8 anteroom. This differential needs to be maintained even with doors closed and should be verified through commissioning, since a cascade only works if every boundary holds its designed pressure step. See the building pressurization calculator for broader building pressure control beyond the cleanroom cascade itself.
Most cleanrooms recirculate the majority of supply air through HEPA filters rather than using 100 percent outdoor air, since the high air change rates required for particle control would make full outdoor air conditioning cost prohibitive in most Canadian climates. Outdoor air is limited to what is needed for ventilation, process exhaust makeup, and pressurization, with the remainder recirculated through the HEPA filtration system.
Related HVAC Tools
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Air handler for cleanroom supply
High-density adjacent facility type
Outdoor air makeup sizing
Not recommended for cross-contamination risk, see notes
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Broader process facility loads