Air Changes per Hour (ACH)
ACH = CFM × 60 / volume, net delivered ACH and pressurization airflow from unequal supply/return, and a comparison against ASHRAE 62.1 / 170 occupancy targets (residential to operating room).
Formula and source
ACH = supply CFM × 60 / room volume (ft³). Net delivered ACH = min(supply, return) × 60 / volume. Pressurization airflow = supply − return (positive = pressurized).
ASHRAE 62.1-2022 (ventilation for acceptable indoor air quality) by name; ASHRAE 170-2021 (ventilation of health care facilities) by name.
Audience
This tile is built for hvac and the adjacent professions in the HVAC group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.