How this calculator works
Air changes per hour relates volumetric airflow to room volume. It is a nominal mixing measure; an air change does not mean all contaminants have left the room. Fan selection also depends on duct pressure loss, outdoor-air requirements and the process being ventilated. Volume mode solves a compatible room volume regardless of the geometry fields.
Formula
Q_m3/h = room volume x ACH; Q_m3/s = volume x ACH / 3600; CFM = Q_m3/s x 60 / 0.028316846592; ACH = 3600Q_m3/s / volume.
Worked example
A 5 x 4 x 2.5 m room has 50 m^3 volume. At 6 ACH the nominal flow is 300 m^3/h, 83.3333 L/s or 176.5733 CFM.
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Frequently asked questions
Is this a heating or cooling load calculation?
No. It calculates a volume exchange rate, without heat gains, humidity or temperature differences.
Can I use measured airflow?
Yes. ACH mode divides the supplied flow by the room volume.
Does CFM mean imperial gallons?
No. CFM means cubic feet per minute, using the international foot.