Construction
Air Changes Calculator
Work out air changes per hour from room volume and ventilation airflow.
The result shows how many times the air in the room is fully replaced in one hour, so a higher number means fresher air but more energy used for heating or cooling.
Formula
Air changes per hour = airflow in cubic metres per hour divided by room volume in cubic metres.
How it works
Divide the ventilation system's hourly airflow by the room's volume. The result says how many times the room's air is replaced each hour. Kitchens and bathrooms usually need more changes than bedrooms or living rooms.
Worked example
For example, a room of 60 cubic metres with an airflow of 120 cubic metres per hour gives 120 divided by 60, which is 2.00 air changes per hour.
FAQs
What is a typical ACH?
Living spaces often sit around 0.5 to 1, while kitchens and bathrooms need several changes per hour.
Is higher always better?
More fresh air helps air quality but costs more to heat or cool, so balance comfort, health and energy.
Does opening a window count?
Natural ventilation varies with wind and temperature, so this calculation suits mechanical airflow figures best.
Rough estimate only — consult a licensed professional for structural work before building.
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