Fruiting chamber calculator

Enter the number and size of your fruit blocks (bags, buckets, or monotubs) and the species. The calculator returns the minimum chamber volume, the required fresh-air-exchange (FAE) rate, and a recommended fan size.

How the numbers are derived

• Chamber volume: total container volume × headroom multiplier (3–4× depending on species — higher for oysters that pin sideways and need cap clearance).
• Fresh-air-exchange (FAE): chamber air changes per hour (ACH) needed to keep CO₂ below the species' fruiting threshold. Oysters tolerate ~800 ppm, lion's mane needs <500 ppm, shiitake tolerates up to 1500 ppm.
• Fan CFM: chamber volume (in cubic feet) × ACH ÷ 60.

Practical chamber shapes

• Shotgun fruiting chamber (SGFC): Rubbermaid tote with 1/4" holes every 2", filled with damp perlite. Passive FAE from opening the lid twice daily. Good for ≤30 L total fruit block.
• Martha tent: Wire greenhouse rack wrapped in clear plastic, with an ultrasonic humidifier on a humidistat and an inline duct fan on a timer for active FAE. Good for 30–500 L of fruit block.
• Walk-in / dedicated room: Bathroom or small closet with HEPA filtered intake, exhaust fan, and humidifier. Required at the high end of hobby scale.

Spore safety

Run your FAE fan exhausting outside or through a HEPA filter — not back into living space. Spore concentrations inside a fruiting chamber are orders of magnitude higher than ambient, and chronic exposure can cause hypersensitivity pneumonitis ("mushroom worker's lung"). Wear an N95 when opening the chamber to harvest or mist.