Measurement method · measured in h⁻¹ (air changes per hour) or L/s per person
Air exchange rate (air changes per hour)
Also: ACH, air change rate, ventilation rate
How many times per hour the air in a room is replaced by outdoor air. It is the physical quantity behind ventilation: concentrations of indoor-generated pollutants fall in inverse proportion to it.
Why it matters indoors
An air change rate of 0.5 per hour — a common minimum for dwellings — means half the room’s air volume is replaced each hour. Typical values range from 0.1 in tight, closed modern flats to several per hour with windows open. It is measured by tracer-gas decay (releasing a gas such as CO₂ or SF₆ and timing its fall) or estimated from the decay of occupant-generated CO₂ after a room empties. Standards express the requirement either as air changes per hour or as litres per second per person.
What the studies report
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| — | other 0.61 | office workers (3-5 regular occupants) · office | measurement study in one office test room in Seoul with 145 mm circular window openings: every-minute indoor and outdoor CO2, temperature, humidity and PM2.5 from August to December, infiltration and ventilation rates estimated from occupant-generated CO2 decay during unoccupied periods | F-0460 Estimation of infiltration and ventilation rates in an offic… (2023) | machine |
| — | other 0.22 | office workers (3-5 regular occupants) · office | measurement study in one office test room in Seoul with 145 mm circular window openings: every-minute indoor and outdoor CO2, temperature, humidity and PM2.5 from August to December, infiltration and ventilation rates estimated from occupant-generated CO2 decay during unoccupied periods | F-0461 Estimation of infiltration and ventilation rates in an offic… (2023) | machine |
| — | other 51 | surgical staff and patients · operating room | measurement of particle number concentration (0.3-10 μm) and CO2 in one surgical room with a window/wall air-conditioning system and the adjacent corridor in Brazil during a single surgery and two subsequent surgeries, with outdoor air ventilation calculated from CO2 and compared with the requirement | F-0485 Particle and Carbon Dioxide Concentration Levels in a Surgic… (2020) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
In the literature
- Omori et al. Impact of wind speed on response of diffusion-type radon-thoron detectors to thoron… (2020). International journal of environmental research and public health. doi:10.3390/ijerph17093178 CKB 0415
- Guehot Evaluation of air exchange rate and particulate matter deposition rate in a classroom… (2024). E3S Web of Conferences. doi:10.17605/osf.io/9h5br CKB 0313
- Ge et al. Effects of Air Exchange Rate on VOCs and Odor Emission from PVC Veneered Plywood Used in Indoor Built Environment (2023). Coatings. doi:10.3390/coatings13091608 CKB 0212
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. Air exchange rate (air changes per hour). Coridum Knowledge G-0073, 16 September 2026. https://coridum.com/k/G-0073/