Air Changes Per Hour (ACH) Calculator

Cleanroom classification: ISO 14644 cleanroom classes are achieved through specific ACH rates (e.g., ISO Class 7 = 60+ ACH).

Laboratory ventilation: chemical fume hood makeup air and general lab exhaust ensuring safe contaminant dilution.

Infection control: hospital isolation rooms require minimum ACH (typically 12 ACH).

In commercial office building HVAC design per ASHRAE 62.1, the minimum outdoor air ACH is 0.06 ACH for office space (1 CFM/ft² × 8 ft ceiling ÷ 60 min/hr × 60 min/hr = approximately 0.1 ACH), with the actual design typically 0.2–0.5 ACH to maintain good indoor air quality.

A 10,000 ft² office with 10 ft ceilings has a volume of 100,000 ft³, and 0.3 ACH corresponds to 500 CFM of outdoor air.

Cleanroom design for semiconductor fabrication (ISO 3 / Class 1) requires 500–600 ACH to maintain the particle count below 1,000/m³, with the supply air going through ULPA filters (99.999% efficiency at 0.12 μm) and the return air typically through a raised floor plenum.

A 1,000 ft² ISO 3 cleanroom with 10 ft ceiling (10,000 ft³) requires 83,000–100,000 CFM of supply air — requiring 5–10 large air handlers and a 50–100 ton chiller to handle the cooling load.

Hospital infection control per ASHRAE 170 and the CDC HICPAC guidelines requires 12 ACH for airborne infection isolation rooms (AIIR, formerly negative pressure isolation rooms) used for tuberculosis, measles, and COVID-19 patients, with HEPA filtration on the exhaust air to prevent the escape of infectious aerosols.

The 12 ACH is the absolute minimum, with newer guidelines recommending 12–15 ACH for AIIRs and 15–25 ACH for operating rooms.

Pharmaceutical cleanroom design per EU GMP Annex 1 (2022) and FDA Process Validation Guidance specifies 20 ACH for ISO 8 / Class 100,000 background, 30–60 ACH for ISO 7 / Class 10,000, and 100–200 ACH for ISO 5 / Class 100 unidirectional flow cabinets and aseptic processing zones.

Laboratory ventilation design per ANSI/AIHA Z9.5 and ASHRAE 62.1 specifies 6–10 ACH for general chemistry laboratories (with adequate fume hood face velocity and exhaust), and 10–15 ACH for biosafety laboratories (BSL-2 and BSL-3), with the fume hood exhaust requiring once-through outdoor air (no recirculation).

Laboratory animal facility ventilation per the Guide for the Care and Use of Laboratory Animals specifies 10–15 ACH for animal holding rooms, with 15 ACH for rodent rooms, 10 ACH for dog rooms, and 12–15 ACH for non-human primate rooms.

Mine ventilation per MSHA 30 CFR 75 requires a minimum air quantity in each working face of the mine, expressed in CFM per person or CFM per brake horsepower of diesel equipment (typically 100–200 CFM per person and 100–150 CFM per HP for diesel equipment), with the equivalent ACH typically 0.5–1.0 for a working face of a longwall mining section.