Free grow tool
Mushroom fresh air and humidity planner
Updated
Enter your chamber size and fan flow, and this planner works out how many times an hour your fan replaces the air in the chamber, next to the humidity and fan cycle your mushroom's profile uses. Oyster growing rooms are commonly run at about 4 to 6 fresh air changes an hour while fruiting, so you get a number to compare against.
- Chamber volume
- 36 L
- Air changes per hour
- 15.7
- Air changes per fan run
- 2.62
- Fan on
- 6.7% of the time
- Humidity target
- 88%
- Profile fan cycle
- 40 s every 10 min
15.7 air changes an hour, above the 4 to 6 air changes an hour that oyster growing rooms are run at. Pearl Oyster fruiting runs at 88% humidity and 16 °C (61 °F) in its profile.
More air than that dries the surface faster. Watch for dry or cracked caps, and raise misting or humidity before cutting the air.
How do you work out air changes per hour?
One air change moves as much air as the chamber holds. Multiply the fan's flow by the share of each hour it runs, then divide by the chamber volume.
Air changes per hour = fan flow per hour × (seconds on ÷ seconds in each cycle) ÷ chamber volume
Worked example: a 40 × 30 × 30 cm chamber holds 36 L. A fan rated at 5 CFM moves 142 L a minute. Running 40 s every 10 min, the Pearl Oyster fruiting cycle, it moves 94 L per run, about 15.7 air changes an hour.
A fan rarely moves its full rated flow once it pushes through a filter or a small vent, and air does not mix perfectly, so treat the result as the most fresh air you could be getting.
How many air changes an hour do mushrooms need?
The University of California grower guide lists 4 fresh air exchanges an hour while oyster pins form and 4 to 6 an hour while they crop, with carbon dioxide under 600 ppm, and none during spawn run (UC ANR). A SARE funded oyster guide says to keep carbon dioxide under 800 ppm and to replace all the air at least every 10 minutes in a fruiting room, and that above about 1,200 ppm oysters may not fruit at all (SARE and FungiAlly).
Those numbers are for rooms full of blocks. A small chamber with one block makes far less carbon dioxide, so it can do well with fewer changes. Use the reference as a starting point and let the mushrooms tell you the rest: long stems and small caps mean more air, dry or cracked caps mean more humidity.
Does more fresh air lower humidity?
Yes. Fresh air from a room is almost always drier than the air in a fruiting chamber, so every air change pulls humidity down for a while. That is why the profiles run the fan in short bursts and give humidity time to recover. If more air leaves caps dry, mist more often or add a humidifier instead of cutting the air. Read how much humidity and fresh air mushrooms need for the signs of each.
What humidity and fan cycle does each mushroom use?
| Mushroom | Fruiting humidity | Fan cycle |
|---|---|---|
| Beech / Buna Shimeji | 90% | 25 s every 18 min |
| Blue Oyster | 87% | 40 s every 10 min |
| Button / Cremini | 88% | 25 s every 20 min |
| Chestnut Mushroom | 92% | 30 s every 15 min |
| Cordyceps militaris | 84% | 20 s every 25 min |
| Elm Oyster | 86% | 30 s every 14 min |
| Enoki | 93% | 15 s every 90 min |
| Golden Oyster | 87% | 40 s every 10 min |
| King Oyster | 82% | 25 s every 25 min |
| Lion's Mane | 90% | 25 s every 18 min |
| Maitake | 88% | 25 s every 20 min |
| Nameko | 93% | 25 s every 18 min |
| Pearl Oyster | 88% | 40 s every 10 min |
| Pink Oyster | 86% | 40 s every 10 min |
| Pioppino | 86% | 30 s every 15 min |
| Reishi | 85% | 30 s every 20 min |
| Shiitake | 85% | 35 s every 12 min |
| Turkey Tail | 86% | 30 s every 12 min |
| Wine Cap | 85% | 30 s every 15 min |
| Wood Ear | 92% | 25 s every 16 min |
FAQ
How do you calculate air changes per hour for a grow chamber?
Multiply the fan flow per hour by the share of time the fan runs, then divide by the chamber volume. One air change moves as much air as the chamber holds.
How many fresh air changes do oyster mushrooms need?
A University of California grower guide lists 4 an hour while pins form and 4 to 6 an hour while fruiting, with carbon dioxide under 600 ppm.
Does fresh air lower humidity in a mushroom chamber?
Yes. Room air is drier than fruiting air, so each air change lowers humidity for a while. Short fan bursts give humidity time to recover.
What are signs of too little fresh air?
Long stems, small caps, and oyster clusters that look like coral or trumpets. More fresh air fixes it.
Sources
- UC Agriculture and Natural Resources, Cultivating Mushrooms on Small Family Farms
- SARE and FungiAlly, Growing Oyster Mushrooms
- Shroom Labs grow profiles