Mushroom Fruiting Air Exchange Calculator
Work out the fresh-air airflow a fruiting room or tent needs to turn over its full volume at your chosen interval — in both CFM and m³/h.
Learn the method behind this calculatorOne full air exchange means moving a volume of fresh air equal to the whole room, once. Divide the room volume by the interval you want between exchanges and you get the airflow rate.
CFM = room ft³ ÷ interval (minutes) · m³/h = room m³ × 60 ÷ interval (minutes) · Nominal fan target = required ÷ (1 − derating)
Cornell Small Farms gives a general commercial rule of thumb of exchanging the whole room volume roughly every 5–10 minutes. Accepts 1–60 minutes.
A simple allowance for filters, duct bends and everyday flow loss — not an engineering static-pressure calculation. Accepts 0–60%.
Enter room dimensions, an exchange interval and a derating allowance to see the airflow needed.
Worked example
A 2 m × 2 m × 2 m room is 8 m³, or about 282.5 ft³. At one full exchange every 7.5 minutes that is 282.5 ÷ 7.5 ≈ 37.7 CFM (8 × 60 ÷ 7.5 = 64 m³/h). Allowing 20% for ducting and filters, look for a fan rated around 47.1 CFM / 80 m³/h.
How to read this
- This is fan-sizing arithmetic, not a universal biological prescription for your species.
- Actual exchange needs depend on mushroom load, species and strain, chamber leakage, duct and filter resistance, and the CO2 the room is actually holding.
- Measured CO2 is the best feedback loop. Cornell Small Farms suggests keeping CO2 below roughly 1000 ppm for most specialty species, with oysters more demanding at below about 800 ppm — adjust ventilation from your own readings and from fruit body morphology.
- More airflow strips humidity and shifts temperature, so ventilation and humidification have to be balanced against each other.
- A fan's rated airflow is not its installed airflow once ducting, bends and filters are in the way.
- A single block on a kitchen counter is a completely different problem from a sealed tent packed with blocks — the small open setup may need no powered ventilation at all.
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