Airflow and Storage

---

When it comes to grain drying or aeration, airflow is everything. Without enough air moving through the grain mass, moisture won’t come out (or move evenly), and you risk spoilage. But to understand airflow, you need to know three connected concepts: CFM, CFM per bushel, and static pressure. 

CFM stands for Cubic Feet per Minute — it’s a measure of how much air your fan is pushing. The more CFM, the more air moves through your bin.

• A 10 HP fan might deliver ~1,000–1,500 CFM (depending on pressure)
   
• A fan rated at 2,000 CFM moves 2,000 cubic feet of air every minute — assuming no resistance

CFM by itself doesn’t tell you much unless you also know how much grain you’re pushing it through. That’s why we use CFM per bushel — a ratio that adjusts airflow based on the amount of grain in the bin.

Common CFM/bu Guidelines:

Aeration (cooling only):  0.1–0.2 CFM/bu

Natural air drying (corn, soybeans):  0.5–1.0 CFM/bu

Rehydrating or steeping:  0.05–0.2 CFM/bu 

If your CFM/bu is too low, air won’t reach all parts of the bin — and grain in the center could stay wet or heat up. Too high, and you might be wasting energy.

Static pressure is the resistance the air encounters as it moves through the grain.

Think of it like trying to blow air through a sponge. The tighter or deeper the sponge, the harder you have to blow. The same happens with grain.

• Deeper grain = more resistance
   
• Small kernels = tighter packing
   
• Fines and debris = clogged air paths
   

We measure static pressure in inches of water column (in. H₂O). This tells us how hard the fan is working to push air through the grain.

You could have a high-CFM fan, but if the static pressure is too high, the fan won't deliver that airflow. The more resistance, the more performance drops.

That’s why bin size, grain depth, grain type, and fan type all need to be considered together.

• Want more airflow? You can:
   
  • Use more or bigger fans (increase CFM)
     
  • Use shallower grain depth (less pressure)
     
  • Choose fans designed for higher static pressures (like centrifugal fans)

We built a tool that makes it easy to estimate your CFM per bushel and static pressure based on your bin, grain type, and fans. Try it here.

• Level the grain after filling
  Uneven grain can cause airflow to short-circuit around the peak.
   
• Clean out fines and broken kernels
  Fines settle in the center and create high resistance — especially in corn. If possible, core the bin to remove some.
   
• Use multiple smaller fans instead of one giant one
  Spreading airflow more evenly across the bin base helps performance.
   
• Know your fan type
   
• Axial fans move more air but struggle with static pressure
   
• Centrifugal fans handle deeper grain or tighter packing better
   
• Measure depth — don’t guess
  Static pressure is highly sensitive to grain depth. A few extra feet makes a big difference.
   
• Check your weather before drying
  Warm, dry air is best. Cold, humid air can move through the grain just fine — but may not dry it!

• Thinking one size fits all
  A fan that works on soybeans at 0.2 CFM/bu might be totally underpowered for corn at 1.0 CFM/bu.
   
• Using HP as a stand-in for airflow
  Horsepower tells you nothing without knowing static pressure. Two identical 10 HP fans could behave very differently depending on bin resistance.
   
• Forgetting bin design matters
  A short, wide bin has better airflow than a tall, narrow one — for the same fan.
   
• Overdrying by mistake
  If airflow is good but you're using poor weather or running too long, you might overdry and lose money. (Our Fan Buddy EMC tool helps with this!)