Dairy barn fan placement: spacing, angle and height

All guides

Short answer: put the fans where the cows lie. Aim for 200–400 ft/min (about 1–2 m/s) of air over the stalls. With 48–55 inch fans, a common layout is one fan above each row of stalls every 24–30 ft (about 7.3–9.1 m), angled so each fan's air reaches the stalls under the next fan. Turn the fans on above about 68 °F (20 °C).

Why the resting area matters

Cows feel heat stress at temperatures most people find comfortable; their comfort zone is roughly 40–70 °F (4–21 °C). Humidity makes it worse: behaviour and performance are affected from a Temperature Humidity Index (THI) of about 68. Cows also gain heat while lying down and lose it when they stand, so a hot stall makes them stand longer. Fast air over the stall helps them keep lying and resting.

Target air speed

• Minimum cooling air speed in the resting area: about 200 ft/min (1 m/s).
• Some extra benefit up to about 400 ft/min (2 m/s); little evidence for going beyond that.

Spacing and angle

• The old "10 fan diameters apart" rule does not give enough air speed to enough cows and should not be used.
• Air leaving a fan widens into a cone and slows down as it mixes with still air. Cows themselves block and redirect the air, so closer spacing gives a more even result.
• With roof supports usually 10–12 ft (3–3.7 m) apart, a practical layout is a single 48–55 inch fan above the stalls every 24–30 ft (7.3–9.1 m).
• Turn each fan across the stall platform, angled to hit the stalls under the next fan in the row. Every row of stalls should have fans above it.
• In head-to-head pens, one fan can be angled across the platform, or fans can be staggered on alternating posts.
• Larger fans with a known longer throw can be spaced further apart; for example, 72-inch fans are sometimes spaced every 40–60 ft (12.2–18.3 m).
• Point fans in the same direction as the prevailing wind, or the exhaust direction in a mechanically ventilated barn.

When to switch on

Switch fans on above about 68 °F (20 °C). Cows stay heat-loaded after the air cools in the evening, so controls that turn fans off too early leave cows hot; THI-based control with an evening override is preferred where possible.

Safety and maintenance

• Fans within 7 ft (2.1 m) of the floor or working level must be guarded (US OSHA), with guard openings no wider than 0.5 in (1.3 cm).
• Poorly maintained fans can lose 20–50% of their capacity. Clean and check fans at least twice a year.
• When comparing fans, use independent test data at a realistic static pressure.

Cattle barn fans from EcoHarvest

EcoHarvest cattle barn fans are blue-housing box fans for cattle and dairy barns, hanging or on paired aisle frames, with black blades, stainless blades or full stainless. Typical size bands are 24, 36, 50 and 54 inch; air volume, power and bracket are confirmed on the written quotation. See cattle barn fans. These are not poultry tunnel wall exhaust fans — for those, see exhaust fans.

For a quote, send: barn length and width, eave height, stall layout (rows, head-to-head or not), head count, country, voltage and frequency, hanging or aisle mount, and blade choice.

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