Running drying fans continuously causes spoilage, costs money

Running grain aeration fans continuously: what’s wrong with that?

The crop is in the bins and the fans are turned on. No field is so even that a little averaging isn’t important. A few too many weed seeds from near the slough and some later grain from along the ditch. Air is important to balancing the bin. Grain is cooled and conditioned and ready for short- or long-term storage. Right?

Running the aeration fan continuously has been the conventional wisdom since aeration fans came into existence.

The truth is that no one really knew what was going on and that eventually the grain would come down in moisture content. However, there also was this lingering feeling that there must be times when drying was occurring and times when it was not.

I have heard many times that one must keep their fans running because if you stop it, the moisture layer will collapse and a crust layer will form. So, maybe it is safer to just leave it on. And since we don’t really know when the conditions for drying are, maybe it is best to just leave it on.

Let’s address this issue first.

In all the data we have collected at Indian Head, Sask., since 2007, we have never seen a distinct drying layer, or moisture band. We have certainly seen the bottom dry first, and in many cases at the end of the trial run, the top of the bin is still tough, while the bottom is over-dry.

However, there is no distinct layer, or even pockets of moisture. The change in moisture from one part of the bin to another is a slowly changing continuum.

And when the fan is shut off, the temperature and moisture of the grain more or less remains constant, or at the very least, changing ever so slowly. Turning the fans off is not the culprit when it comes to creating a crust.

However, why should we leave the fans on? We don’t know when the conditions are right for drying. There was a time when this was true.

However, research now tells us that we can better manage our aeration systems and our grain inventories. We know the typical diurnal drying cycle, and using a grain calculator can tell us exactly when there are drying conditions and even conditions that create bin condensation. So not knowing when we have a drying condition is no longer a valid excuse for running the fans continuously.

Not only does it cost money to power those fans, but it actually causes spoilage.

Grain starts to deteriorate as soon as it comes off the combine. Storing grain can only slow down the spoilage process and there are two things that contribute to spoilage: higher grain temperatures and higher grain moisture.

If you run the fan continuously during the day, there is a very good chance that you will be heating and wetting the grain — the exact things that contribute to spoilage.

Instead of conditioning the grain, we are damaging it when we run the fans around the clock and for longer than necessary.

In 2009, we did some research with a bin of peas. In the first few hours of operation, the amount of water being removed from the bin was quite high.

It was not unusual to have one percent moisture removed from the grain on the first day, but at hour 21, we began to see something strange take place. The amount of water leaving the bin became negative; we were adding water to the bin.

We entered a 24 hour cycle of water being removed from the bin and then water added to the bin, in almost equal amounts. After the first 21 hours, essentially no drying was taking place.

And to make things worse, we were adding the moisture during the day, as well as heating the grain.

To see a graphic representation of this research, visit this column online at

A grain free aeration calculator is available at It is based on research at IHARF and the Western Grains Research Foundation and covers most prairie crops and conditions.

Ron Palmer is a professional engineer and former professor at the University of Regina. He is a project engineer and researcher with the Indian Head Agricultural Research Foundation. He maintains a grain drying blog at

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