How the results are calculated

All calculations run locally from the values entered by the user.

CADR / ACH

CADR = room volume × target ACH. ACH = CADR / room volume.

Humidity

We approximate saturation vapour pressure and calculate the absolute-humidity difference in g/m³.

Dilution time

t = −ln(1 − reduction) / ACH.

How home readings are interpreted

The room score is a heuristic that organises the readings entered by the user. It is not a health assessment and does not confirm compliance with a standard. The PM2.5 value of 15 µg/m³ comes from the WHO 24-hour mean guideline and must not be treated as a threshold for one instantaneous sensor reading. CO₂ is used only as a cautious proxy for ventilation performance in an occupied room; interpretation depends on occupancy, time and sensor accuracy.

Sources and review date

• US EPA — Guide to Air Cleaners in the Home: CADR, room sizing and filtration limitations.
• US EPA — What can I do to improve indoor air quality?: source control, ventilation, filtration and humidity.
• US EPA — Use and Care of Home Humidifiers: device hygiene and excess-moisture cautions.
• US EPA — CO₂ and ventilation: limits of interpreting indoor CO₂ measurements.
• WHO — Types of pollutants: the 24-hour PM2.5 guideline.

Sources reviewed on 16 July 2026. External links point to the original material; the service does not reproduce it.