Grain Aeration Airflow & Fan Size for the Bin
Cools wheat
Enter grain mass and the specific airflow rate for cooling or drying to get total fan airflowin m³/hr, m³/min and CFM for your bin or silo.
Grain store & fan job
Next: run the fan to push a full cooling front through the grain (often through cool nights), check grain temperature weekly, and stop once the front has passed.
Rates are typical guides (cooling ~5, drying much higher m³/hr/t); actual fan choice also depends on grain depth and static pressure in the store.
Grain aeration airflow — key facts
- Airflow
- mass (t) × rate (m³/hr/t)
- Cooling / holding
- ≈ 5 m³/hr/t
- Near-ambient drying
- ≈ 12 m³/hr/t
- In-bin drying
- ≈ 50 m³/hr/t
- 1 m³/hr
- = 0.5886 CFM
- Run fan
- until the cooling front passes
- Check temperature
- weekly
- Privacy
- Runs in your browser; nothing uploaded
Cool grain keeps; warm grain spoils
Stored grain stays safe when it is cool and even in temperature. Aeration pushes air through the bulk to cool it and level out moisture, holding back mould, insects and respiration and stopping moisture migrating into damp, spoiling hot spots. The air it needs is set simply: total airflow = grain mass in tonnes × a specific airflow rate. That rate is small for cooling and holding (around 5 m³/hr per tonne) but much larger when you are using the fan to actually dry the grain in the bin.
This tool gives total airflow in m³/hr, m³/min and CFM from your grain mass and the rate for cooling, near-ambient drying or in-bin drying, so you can match a fan in any units. Remember that grain depth and static pressure also shape the final fan choice, that you should run the fan until a full cooling front has passed through, and that you check grain temperature weekly. Pair it with the Grain Storage Capacity, Grain Drying Cost and Storage Loss tools to keep the harvest in good store.
Size the fan
Total airflow from grain mass and the rate.
Any units
Read m³/hr, m³/min and CFM together.
Right job, right rate
Cooling, near-ambient or in-bin drying presets.
Keep grain safe
Cool, even grain resists mould and insects.
Frequently Asked Questions
What is grain aeration?+
Aeration moves air through stored grain to cool it and even out moisture across the bulk. Cooling slows mould, insects and respiration, and removing temperature differences stops moisture migrating to form damp, spoiling hot spots. It is not the same as drying — aeration conditions and holds grain in good store, while drying removes large amounts of moisture.
How is the airflow calculated?+
Total airflow = grain mass (tonnes) × specific airflow rate (m³/hr per tonne). So 200 t at a cooling rate of 5 m³/hr/t needs about 1,000 m³/hr of fan capacity. The tool reports the total in m³/hr, m³/min and CFM so you can match it to a fan's rating, whatever units the fan is sold in.
What specific airflow rate should I use?+
It depends on the job. Cooling and holding dry grain needs only a little air, around 5 m³/hr per tonne; near-ambient drying needs more, around 12; and in-bin drying needs much more, around 50. Pick the rate for what you are actually trying to do — over-specifying wastes fan and power, under-specifying leaves the job half done.
What is the difference between cooling and in-bin drying?+
Cooling pushes a small, steady flow to lower grain temperature and hold it safely without changing moisture much. Near-ambient and in-bin drying push far more air to carry moisture out of the grain, so they need far higher airflow per tonne. The right rate is the single biggest input to sizing the fan correctly.
How long do I run the aeration fan?+
Run the fan long enough to push a full cooling front all the way through the grain bulk — not just until the surface feels cool. Cooling commonly runs through cool nights or cool spells. Track the front and stop once it has passed right through; running on past that point can re-warm or over-dry the top of the bulk.
How do I know the cooling front has passed?+
Monitor grain temperature, ideally with sensors at several depths, and watch the exhaust air. The front has passed when the temperature at the far end of the airflow path has dropped to the target and stabilises. As a routine, check grain temperature weekly so you catch any warming early and can re-run aeration before problems start.
Why does grain depth and static pressure matter?+
Deeper grain and finer or trashier grain resist airflow more, raising the static pressure the fan must work against. A fan's airflow falls as static pressure rises, so two bins needing the same m³/hr can need different fans if one is much deeper. Size the fan for the required airflow at the static pressure your bin and grain depth create.
How do I convert m³/hr to CFM?+
Multiply cubic metres per hour by 0.5886 to get cubic feet per minute (CFM). So 1,000 m³/hr is about 589 CFM. The tool shows m³/hr, m³/min and CFM together so you can compare directly against fans rated in either metric or imperial airflow units.
Does this size the fan completely?+
It sizes the airflow your grain needs, which is the essential first step. Final fan selection also depends on the static pressure from your grain depth, type and condition, and the fan's performance curve at that pressure. Use the airflow here as the target, then choose a fan that delivers it against your bin's resistance.
Does this work for any grain or bin?+
Yes — enter the grain mass in tonnes and the appropriate specific airflow rate for cooling, near-ambient or in-bin drying, and it works for wheat, maize, rice, pulses and oilseeds in bins, silos or sheds. The right specific airflow rate differs a little by grain and goal, so adjust it to your situation.