🌾 Grain Bin Fan CFM Calculator
Calculate the exact airflow (CFM) needed for safe grain storage, aeration & drying
| Grain Type | Bu / Cu Ft | Aeration CFM/Bu | Dry-Down CFM/Bu | Active Drying CFM/Bu | Lbs / Bu |
|---|---|---|---|---|---|
| Corn (Maize) | 0.80 | 0.10–0.20 | 0.25–0.50 | 0.50–1.00 | 56 |
| Wheat | 0.80 | 0.10–0.25 | 0.25–0.50 | 0.50–1.00 | 60 |
| Soybeans | 0.80 | 0.10–0.20 | 0.25–0.40 | 0.40–0.75 | 60 |
| Canola / Rapeseed | 0.56 | 0.15–0.30 | 0.30–0.60 | 0.60–1.00 | 50 |
| Milo (Grain Sorghum) | 0.80 | 0.10–0.20 | 0.25–0.50 | 0.50–1.00 | 56 |
| Barley | 0.64 | 0.10–0.20 | 0.25–0.50 | 0.50–1.00 | 48 |
| Oats | 0.51 | 0.10–0.20 | 0.25–0.50 | 0.50–1.00 | 32 |
| Sunflower Seeds | 0.44 | 0.15–0.30 | 0.30–0.60 | 0.60–1.00 | 25 |
| Grain Depth (ft) | Corn (in w.g.) | Wheat (in w.g.) | Soybeans (in w.g.) | Canola (in w.g.) | Approx. Depth (m) |
|---|---|---|---|---|---|
| 10 ft | 0.5–1.0 | 0.5–1.5 | 0.5–1.0 | 1.0–2.0 | 3.0 m |
| 15 ft | 0.8–1.5 | 1.0–2.5 | 0.8–1.5 | 1.5–3.0 | 4.6 m |
| 20 ft | 1.0–2.5 | 1.5–3.5 | 1.0–2.5 | 2.0–4.5 | 6.1 m |
| 25 ft | 1.5–3.0 | 2.0–5.0 | 1.5–3.0 | 3.0–6.0 | 7.6 m |
| 30 ft | 2.0–4.0 | 3.0–6.5 | 2.0–4.0 | 4.0–8.0 | 9.1 m |
| 35 ft | 2.5–5.0 | 4.0–8.0 | 2.5–5.0 | 5.0–10.0 | 10.7 m |
| 40 ft | 3.5–7.0 | 5.0–10.0 | 3.5–7.0 | 6.5–12.0 | 12.2 m |
| Bin Diameter (ft) | Eave Height (ft) | Est. Capacity (bu) | Floor Area (sq ft) | Metric Diameter (m) |
|---|---|---|---|---|
| 15 ft | 18 | ~4,000 | 177 | 4.6 m |
| 18 ft | 20 | ~6,500 | 254 | 5.5 m |
| 24 ft | 24 | ~14,000 | 452 | 7.3 m |
| 30 ft | 28 | ~27,000 | 707 | 9.1 m |
| 36 ft | 28 | ~37,000 | 1,018 | 11.0 m |
| 42 ft | 32 | ~60,000 | 1,385 | 12.8 m |
| 48 ft | 36 | ~90,000 | 1,810 | 14.6 m |
| 60 ft | 40 | ~140,000 | 2,827 | 18.3 m |
Grain bin fan airflow is big deal when talking about drying, cooling or storing grain. The choice of the right fan depends on several things, like the type of grain, the depth of the bin and the airflow needed per bushel
The moisture and temperature of the grain lead to safe storage. Airflow over the aeration level of one-quarter cubic foot per minute per bushel, but under the drying amount of one cfm per bushel, gives the best safety. So it really matters to reach the right airflow.
Choosing the Right Fan for Your Grain Bin
Centrifugal fans work for natural air drying in deeper grains. They work as well as axial flow fans from 16 to 18 feet depth, and you suggest them for more than 18 feet. To reach the wanted airflow with low input horsepower in full depth, a centrifugal fan is needed.
These machines use closed impellers to press the air, which makes them efficient to push it through the whole grain column from the bottom to the top.
Some centrifugal fans have speeds in 3450 RPM for maximum airflow and in 1750 RPM for gentle treatment of grain. They also are much more silent than axial fans, which deserves thnigking because of the neighbors.
The depth of the bin affects a lot. Deeper bin requires stronger fan. For small grains you need even bigger machine, because the space between the kernels and the gaps are small.
Also the aeration duct system in the bin plays a role, especially how it blocks the air. High static pressure limits the possible fans and reduces the airflow.
Strong galvanized steel transitions help to improve the airflow through the grain and lose less pressure. Back-draft dampers automatically stop under-floor pressure spilling backwards through a dead fan. You suggest dampers for installations with several fans.
Exit ways commonly are forgotten in the drying process. Even well sized fans do not help if there are not enough exits for the air from the top of the grain column. Bins with small aeration fan in 0.10 to 0.15 cfm per bushel require four to six days to cool the grain.
Empty bin allows more airflow, which forces the engine work harder and draw more amps than full bin. If the pipeline is too broad, the moved air can overload the engine above its rated horsepower. Restricting the entry to the fan instead of the output helps to safely use it until repair.
Good fans keep stable temperatures and reduce risk of spoilage, warm spots or mold. Weather-resistant housings and commercial parts ensure their life in harsh conditions. Even soybeans can recycle fans during periods with right air temperature and humidity.
