Air Exchange & Fan Calculator

Calculate the extraction fan size needed for your grow room

Room dimensions

Length

Width

Height

Metres Feet

Target air changes per hour (ACH): 60

15 ACH (CO₂ enriched) 60 ACH (standard) 120 ACH (hot/humid)

Room volume

m³

Extraction fan

m³/h

- CFM

Intake fan (negative pressure)

m³/h

- CFM

Recommended ACH by Setup

Scenario	Suggested ACH	Air change interval
CO₂-enriched room (sealed)	15 - 30	2 - 4 min
Standard grow room (temperate)	40 - 60	1 - 1.5 min
High-intensity / high-wattage lighting	60 - 90	40 - 60 sec
Hot climate or poor insulation	90 - 120	30 - 40 sec

Formulas: Volume (m³) = L × W × H | Extraction (m³/h) = Volume × ACH | CFM = m³/h × 0.5886

Tip: Size the intake fan 15 - 20% smaller than the extraction fan to maintain slight negative pressure, which prevents odour escaping and improves air distribution. Add 20 - 25% to fan ratings to account for duct resistance, bends, and carbon filters.

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