Grain Aeration Airflow & Fan Size for the Bin

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.