Cooling Fans vs Drying Fans: What Your Aeration Can Really Do
Most silo fans are built to cool grain, not dry it. Airflow per tonne decides which job your fans can do — here's how to tell.
SiloSense IQ ·
Two silos can both “have aeration” and be capable of completely different things. The difference is how much air the fan pushes through each tonne of grain.
Airflow per tonne is the number that matters
Fan capacity on its own doesn’t tell you much. What matters is litres of air per second per tonne of grain (L/s/t):
| Airflow | What it can do |
|---|---|
| About 2–4 L/s/t | Cooling. The typical aeration fan. Brings grain temperature down and holds it there. |
| About 5–15 L/s/t | Slow drying. Can take a little moisture out, over weeks, in good weather. |
| About 15–25 L/s/t | Drying. Built to move a drying front through the grain in days. |
These bands are in line with GRDC grain storage guidance. To find yours, take the fan’s rated airflow from its plate or data sheet (at the static pressure it works against), multiply by the number of fans, and divide by the tonnes in the silo.
Note the “in the silo” part: the same fan on a half-full silo delivers twice the airflow per tonne.
Why cooling fans can’t dry
Drying needs a lot of air because each kilogram of air can only carry a few grams of extra water. A cooling fan simply doesn’t move enough air to shift much moisture before the weather changes. Ask it to dry and it will run for weeks, cost a lot of power, and often leave the top of the silo no drier than when it started.
What a cooling fan does brilliantly is temperature. Cooling grain below about 20°C slows insects dramatically, and it doesn’t take much air to do.
What drying airflow risks
Drying fans have the opposite problem: they move enough air to change moisture quickly in both directions. Run a drying fan on humid air and it can re-wet grain just as effectively. And because drying happens as a front moving up through the silo, the bottom dries first while the top stays wet — so the top layer is the one to watch.
Matching the fan to the job
- Cooling fans: aim for cool air, avoid humid air, and don’t expect drying.
- Drying fans: choose air by its drying power, watch the wettest layer, and stop at the target so you don’t over-dry.
How SiloSense helps
Tell the dashboard your fan’s airflow and power, and it works out L/s per tonne for the silo’s current fill, rates it as cool-only, slow drying or drying, and estimates running costs.
Aeration Manager makes cooling fans run on the right air. SiloSense IQ+ adds set-point drying for silos with drying airflow — and won’t offer drying on a fan that can’t do it.
Request a demo and bring your fan details.