CO₂ and Fresh Air Control in Mushroom Rooms
CO₂ targets by growth stage, fresh-air damper sizing, duct throw and humidity interaction — the airflow method behind MushroomWale grow rooms.
What CO₂ level should a button mushroom room hold?
During spawn run CO₂ is deliberately held high (5,000–15,000 ppm) to favour mycelial growth. From pinning through cropping it must be brought down to under 1,000 ppm using fresh air. High CO₂ during cropping produces long stalks, small caps and open veils — the most common airflow fault on Indian farms.
Estimate your own numbers
Pick a room size and count — the tool applies the same engineering constants used in MushroomWale BOQs and returns a recommended plan summary.
Total built-up area
~1,440 sq ft
720 sq ft per room
Cooling requirement
~16 TR
8 TR per room
Bag capacity
~3,200 bags
1,600 bags per room
Phase-III compost
~80–96 T
per full filling (25–30 kg/bag)
MS racking material
~4,100 kg angle
+ ~450 kg jali (incl. wastage)
PUF doors
2 nos.
insulated cold-room doors
Yield per cycle
~6,400 kg
~106 kg/day at peak flush
Annual yield @ 5 cycles
~32,000 kg
fresh weight, all flushes
Recommended plan summary
Climate unit per room: Daikin 8 TR (~28 kW Outdoor Unit)
2× Outdoor Unit (4 HP ea., R32 3ph HMT) + 1× Indoor Unit (HMT Dual-Circuit Evap, 550mm fan)
Airflow target: hold CO₂ under 1,000 ppm during cropping (the SOP) across all 2 room(s), with fresh-air dampers and duct throw sized per room volume.
Compost planning: ~80–96 tonnes of Phase-III compost per filling, staggered across rooms so tunnel turns stay continuous.
Indicative engineering estimate only — not a price quotation. Final sizing depends on site conditions, climate zone, ceiling height and grower practice. GST and transportation are extra; any additional client requirement is charged extra.
How MushroomWale calculates it
- 1
Set CO₂ targets per growth stage
Spawn run tolerates and benefits from high CO₂. Pinning requires a decisive drop in CO₂ — it is one of the triggers for pin formation. Cropping holds the low band continuously through each flush.
- 2
Size fresh air against biomass, not room volume alone
CO₂ generation scales with active compost and mushroom biomass in the room, which peaks during flush. Fresh-air capacity must be set for the peak flush, not the room average.
- 3
Control fresh air with dampers, not by opening doors
Aluminium fresh-air and exhaust dampers with filters — manual, gravity or actuated — give repeatable control. Door-opening 'ventilation' dumps unconditioned, unfiltered, dry air on the beds and imports spores.
- 4
Design the duct throw so no bed is dead or blasted
Air cloth/poly ducting distributes air evenly along the room. Direct high-velocity air on beds dries the casing layer and causes scaling; dead corners accumulate CO₂ and grow long-stalked mushrooms. Both faults appear in the same room when the duct is wrong.
- 5
Re-humidify what you exhaust
Every unit of fresh air brought in must be cooled and re-humidified to hold 85–90% RH. Fresh-air capacity, cooling capacity and humidification capacity have to be designed as one system — sizing them separately is why many retrofits never stabilise.
Reference data
Stage-wise climate targets — button mushroom
| Stage | Air temperature | RH | CO₂ |
|---|---|---|---|
| Spawn run | 22–24 °C | 90–95% | 5,000–15,000 ppm |
| Case run | 24–25 °C | 92–95% | 5,000–10,000 ppm |
| Pinning (airing) | 17–18 °C | 88–92% | under 1,000 ppm |
| Cropping / flush | 16–18 °C | 85–90% | under 1,000 ppm |
Spawn run
- Air temperature
- 22–24 °C
- RH
- 90–95%
- CO₂
- 5,000–15,000 ppm
Case run
- Air temperature
- 24–25 °C
- RH
- 92–95%
- CO₂
- 5,000–10,000 ppm
Pinning (airing)
- Air temperature
- 17–18 °C
- RH
- 88–92%
- CO₂
- under 1,000 ppm
Cropping / flush
- Air temperature
- 16–18 °C
- RH
- 85–90%
- CO₂
- under 1,000 ppm
Air-side equipment in a standard room
| Component | Purpose |
|---|---|
| Fresh-air damper with filter | Controlled outside-air intake, filtered |
| Exhaust damper | Removes CO₂-laden air during flush |
| Damper actuator | Automated modulation against the CO₂ sensor |
| Air cloth / poly duct | Even low-velocity distribution over all beds |
| CO₂ meter | Set-point verification and fault diagnosis |
Fresh-air damper with filter
- Purpose
- Controlled outside-air intake, filtered
Exhaust damper
- Purpose
- Removes CO₂-laden air during flush
Damper actuator
- Purpose
- Automated modulation against the CO₂ sensor
Air cloth / poly duct
- Purpose
- Even low-velocity distribution over all beds
CO₂ meter
- Purpose
- Set-point verification and fault diagnosis
- CO₂ and RH set points differ by species; the table above is for Agaricus bisporus (button).
- Automation packages that modulate dampers against a CO₂ sensor are available as a retrofit on existing rooms.
Frequently asked questions
Related engineering pages
Talk to a MushroomWale engineer
Send your question on CO₂ and Fresh Air Control in Mushroom Rooms and our project engineer will verify the sizing for your site — no cost, no obligation.
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Share your plot size and target capacity — our engineers return a sized BOQ with room, machine and compost figures.
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