Table of Contents:
In this article, we will look at how to design an effective air intake and exhaust system. This specific setup is ideal for larger facilities operating in two types of challenging climates:
📌If your current setup is just a hole in the wall with a simple extract fan, you might find more suitable advice here.
The system described below may seem complex, but it is actually quite simple to implement. In fact, we built the entire system on my farm ourselves! Our dampers are even operated manually without expensive automation.
Most importantly, this design is specifically tailored to the needs of oyster mushrooms—similar to the systems used on professional button mushroom (Agaricus) farms.
Let’s dive in!
Mushrooms breathe just like we do. They release CO₂ and moisture, which can quickly build up and ruin your harvest.
📌You can read more about this here.
Proper ventilation serves two key functions:
💡Required airflow depends on the amount of substrate in the room, not just the room's total volume.
A centrifugal fan (either a duct fan or a "snail" blower) is best for air exchange. The size depends on your substrate load:
The Math:
▶️ Single-zone (all blocks fruit at once): 300 m³/h (approx. 175 CFM) per ton of substrate.
▶️ Mixed-age blocks: 180-220 m³/h (approx. 105–130 CFM) per ton is enough.
📌Read more: Different types of mushroom growing systems and how they work
Ducts distribute fresh air evenly. They must be sized to maintain an internal airspeed of 4-5 m/s (13-16 ft/s).
The central duct is the largest, while side ducts have a smaller diameter (as shown in the photo).
Why use nozzles (like the plastic cups in the photo)?
▶️Nozzles create directed air jets that ensure the air actually reaches the mushrooms. They maintain a consistent discharge speed of 8-9 m/s (26-30 ft/s).
✅Place nozzles between 45 cm and 80 cm apart.
You can check the speed by placing an anemometer directly against the nozzle opening.
To make things easier, I created a practical Ventilation Guide that includes all the calculations for fan capacity and duct parameters mentioned in this article.
It is designed to help you apply these principles precisely to your own grow room.
📌You can find more details and get the guide here.
Recirculation is your best tool for saving money.
It allows you to reuse treated air, which slashes heating costs in winter and prevents sudden environmental swings.
The Setup: A recirculation pipe pulls air from the room, mixes it with fresh outside air, and passes it through a heat exchanger.
Control: This is managed by two dampers—one for fresh air and one for recirculation.
The system automatically adjusts and balances airflow based on the current load of actively fruiting blocks. You can also do this manually.
✅Pro Tip: To prevent mushroom spores from clogging your equipment, always install a G3-class air filter before the heat exchanger.
⚠️Never heat your grow room with radiators, heat guns, or stoves. These create "hot spots" and dry out your mushrooms.
Instead, use a water-based air heater installed directly inside the ventilation unit before the fan.
This ensures the air is already at the right temperature before it ever touches a mushroom.
💡It must remove the same amount of air that the intake brings in.
Its power should be roughly 90% of the intake fan's capacity to maintain a slight, stable pressure.
Many growers believe that CO₂ is so heavy it simply accumulates at the bottom of the grow room.
💡However, if your ventilation is designed correctly, this simply doesn't happen.
Take a look at this diagram - The Role of Exhaust Placement.
Humidity should be controlled within the ventilation system itself, not directly inside the grow room.
Mist or steam should be introduced inside the air ducts to ensure uniform distribution before the air reaches the mushrooms.
⚠️Placing humidifiers inside the grow room creates uneven "wet zones" and leads to condensation issues that can trigger diseases.
Ventilation must run continuously while mushrooms are growing.
Turning fans on and off with a timer is a massive mistake. This leads to constant environmental fluctuations, which directly damage your yield and mushroom quality.
The exhaust fan should always be running unless your system is in 100% recirculation mode.
✅If you need help designing a ventilation system based on these principles, feel free to contact me for advice.
Emoji guide: 📌 link | ✅ advice | ▶️ fact | 💡 important | ⚠️ warning
