Why CFM Doesn’t Cool Cows (And What Actually Does)

11. März 2026 durch

Nancy van der Byl Coblentz

For decades, dairy farmers have been sold on one simple idea when it comes to cooling: Bigger fans. Higher CFM. Better cooling.

It sounds logical.

It sounds scientific.

And it’s been repeated so often that it feels like a fact.

But here’s the truth:
CFM doesn’t cool cows.

Cows are cooled by air speed over their body, not by how much air a fan moves on paper. Once you understand that difference, the confusion around fan size, spacing, and performance starts to disappear.

The Real Problem:
We’ve Been Measuring the Wrong Thing

CFM (cubic feet per minute) measures the volume of air a fan moves through itself per minute, under controlled test conditions. It does not describe how that air behaves once it leaves the fan or how it moves inside a barn.

What it does not measure is:

Air speed where the cow is
Whether air actually reaches the stall
Whether heat is removed from the cow’s body

Agricultural engineers have been clear about this for years:

“Achieving desired air velocity at cow level in the presence of adequate air exchange appears to be the key design challenge.” — Stowell, Gooch & Bickert, ASABE Dairy Housing Proceedings

In other words, moving air is not the same as cooling cows. Cooling only happens when air moves fast enough at the cow to remove heat.

Why Air Speed Matters More Than Air Volume

Cows lose heat primarily through convection—air moving across their body and carrying heat away. That means cooling effectiveness depends on how fast air is moving at cow level, especially when cows are lying down, where they spend 10–13 hours per day.

University and research institutions consistently reinforce this point:

“Increased air velocity is a frequently used method to reduce heat stress of farm animals housed in warm conditions. The main reason the method works is that higher air velocity increases the convective heat release from the animals.” — Bjerg, Wang & Zhang

Air speed at the cow is not a theory. It is a measurable driver of comfort and behavior.

Why CFM Breaks Down in Open Dairy Barns

Most dairy barns are not closed buildings.

They have:

Open sidewalls or curtains
Open end walls
Ridge vents
Or, in some cases, no walls at all

CFM only has meaning when air is contained and follows a defined path from inlet to outlet.

That’s why CFM is useful for:

Warehouses
Fully enclosed buildings
Tunnel-ventilated barns

In an open dairy barn, air is free to enter and leave in all directions. There is no controlled air volume to “exchange,” which makes total CFM largely irrelevant.

But one thing still matters:

How fast air is moving where the cow is.
Even outdoors, cooling is described by wind speed, not air volume. The same principle applies inside an open barn.

The Old Fan Spacing Rule—and Why It Falls Short Today

Many producers are familiar with the old rule of thumb:

One foot of spacing for every inch of fan diameter.

A 52" fan → 52 feet of spacing.

That rule came from an earlier generation of fans:

AC motors
Belt-driven systems
Low exit velocity
Designed for air exchange, not targeted cow cooling

Large blades were used to compensate for slow-moving air that lost speed quickly. Overlap was needed to avoid dead zones.

That rule was never created to cool cows. It was created to move air through buildings.

Why That Rule Doesn’t Apply to Core Cool Systems

Core Cool Systems was designed with one purpose in mind: To cool cows.

Not warehouses.
Not people.
Not general ventilation.

Core Cool uses:

Direct-drive EC motors
High torque across the operating range
Fan blades mounted directly to the motor shaft
Engineering designed for a purpose - high-speed, focused spiraling airflow

This design produces air velocity that survives distance, allowing Core Cool to deliver:

A minimum of 5 mph (7 km/h) at cow level— at 90 ft/27 m (3-phase models).

Research shows that this level of air speed is exactly where meaningful cooling begins:

“Air speeds of 200–500 ft/min (approximately 2–6 mph or 4–9 km/h) have been found to reduce heat stress markers in dairy cows, including respiration rate, vaginal temperature, and skin temperature.” — Lactanet, Ventilation and Thermoregulation

That is why older fan spacing rules don’t apply to Core Cool. 

Those rules were developed for fans that could not maintain sufficient air speed at cow level, which forced designers to place large fans very close together just to achieve minimal cooling.

Core Cool Systems units were engineered to deliver high-velocity airspeed at cow level over long distances.

Why Core Cool’s CFM Looks Smaller on Paper

CFM calculations heavily favor fan diameter. Longer blades automatically generate higher CFM numbers.

Core Cool fans are smaller—25" and 32"—so the CFM appears modest on paper.

But several unique design features, combined with a powerful EC motor, produce higher air speed at greater distances to maximize the cooling effect.

As engineering research makes clear:

“Higher air velocity increases convective heat loss even when total airflow is unchanged.” — ASABE Heat Stress Research

CFM describes the volume of air a fan can move.

Air speed at cow level determines whether that air actually cools the cow.

What Farmers Are Seeing on Real Farms

This isn’t just research—it’s what producers see every day.

“The 25-inch single-phase fan is far superior to the big fans we had before. It moves more air where the cows are and uses less power than the 52-inch panel fans we removed.” — Dairy farmer, Wisconsin, USA

And from Canada:

“The 25-inch single-phase Core Cool fan blows farther and uses much less energy than the 52-inch panel fans we were using.” — Dairy farmer, Elora, Ontario, Canada

Different barns. Different countries. Same outcome.

The Core Cool Difference—Simplified

Most fans on the market were originally designed for buildings and later adapted for agriculture. Core Cool Systems was engineered from the start for dairy farms, cow behavior, and heat stress physiology.

That’s why our focus isn't on CFM; it's on producing high-speed air at cow level, because that's critical to effective cow cooling.

We focus on:

Measured air speed at cow level
Consistency stall to stall
Cooling where cows actually live

If there’s one thing to remember, remember this:

CFM describes the volume of air a fan can move.

Air speed at cow level is what cools cows.

And cooling only works if that air consistently reaches every cow, in every stall, every day.

Air speed is the foundation of cow cooling.

If this blog challenged something you’ve always believed about fans, that’s a good thing.

If you have questions about:

Your current fans
Fan spacing
Air speed at cow level
Or whether your barn is actually cooling cows

I welcome the opportunity to talk it through with you.

Email me: nancy@corecoolsystems.com WhatsApp: +1-330-717-8852

I’ll connect you with your local Core Cool expert — and answer any questions you have about Core Cool Systems and the benefits of proactive cow cooling.   Have a FANtastic day and stay COOL.

Sources

1. Stowell, R. R., Gooch, C. A., & Bickert, W. G.

Design Parameters for Hot-Weather Ventilation.

ASABE Dairy Housing Proceedings.

https://elibrary.asabe.org/azdez.asp?AID=11625

2. Bjerg, B., Wang, X., & Zhang, G.

The effect of air velocity on heat stress at increased air temperature.

https://www.researchgate.net/publication/304624792

3. Reuscher et al.

Consistent stall air speeds in commercial dairy farms are associated with improved cow comfort.

Frontiers in Animal Science.

https://www.frontiersin.org/articles/10.3389/fanim.2024.1422937/full