AMCA Standard 99 — Fan Arrangements
AMCA Standard 99-16 establishes a common industry language for describing how a fan’s wheel, shaft, bearings, and motor are arranged and mounted relative to one another. Rather than relying on manufacturer-specific terminology, engineers, specifiers, and end users can reference a standardized arrangement number to communicate a fan’s mechanical configuration precisely and consistently across the industry.
AMCA recognizes 10 standard arrangements. Arrangements 4, 7, and 8 are direct-drive configurations, in which the motor drives the fan shaft directly or through a coupling; Arrangements 1, 3, 9, and 10 are belt-drive configurations, using sheaves and belts to transmit power from the motor to the fan. Axial fans generally follow layouts similar to Arrangements 4 and 9. Selecting the right arrangement has a direct bearing on installation footprint, maintenance access, bearing life, and overall fan longevity, making a clear understanding of these configurations essential when specifying or servicing a fan.
Standardized fan configurations describing how the motor, wheel, and bearings are mounted relative to each other.
1 · Arrangement 1 The impeller is overhung on the shaft, with bearings mounted on a pedestal. Used for both belt & direct drive fans. Suitable for high-temperature and bulk-material applications.
| 2 · Arrangement 2 Similar to Arrangement 1, but the bearing pedestal is mounted directly on the fan housing rather than a separate base.
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| BELT DRIVE | DIRECT DRIVE |
3 · Arrangement 3 The impeller sits on the shaft between two bearings, one on either side of the wheel. Because the bearings are in the airstream, this arrangement suits dry-air applications.
| 4 · Arrangement 4 The fan wheel is overhung and mounted directly on the motor shaft, eliminating fan bearings for a compact, economical design. Motor sits on a motor pedestal; best suited to moderate temperatures. Variants include 4V, 4F, and 4H.
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| BELT DRIVE | DIRECT DRIVE |
7 · Arrangement 7 Bearings sit on both sides of the fan wheel, which hangs on a shaft between the two bearing sets. A motor pedestal is included, with the motor and fan shaft joined by a coupling.
| 8 · Arrangement 8 Includes both a motor pedestal and a bearing pedestal, with two bearings supporting the shaft (both on the drive side) and the wheel overhung on one side. The motor connects via a coupling — a slightly costlier option due to the extra components.
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| DIRECT DRIVE | DIRECT DRIVE |
9 · Arrangement 9 Bearings are mounted on the fan pedestal, with the motor mounted on the side of the fan and connected via a belt drive.
| 10 · Arrangement 10 Similar to Arrangement 9, but the motor is mounted inside the bearing pedestal. Most often used in light industrial applications.
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| BELT DRIVE | BELT DRIVE |
5 · Arrangement 5 MANUFACTURER VARIANT Offered by some manufacturers as a variant of Arrangement 4. The fan wheel overhangs the motor shaft, and the motor is flange-mounted directly to the fan casing.
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| Note: Drive type indicates whether the fan wheel is driven directly by the motor shaft (Direct Drive) or via belts and sheaves (Belt Drive). |
Ultimately, the right arrangement is dictated by the specific application, the operating environment, temperature, available footprint, and access required for inspection and maintenance. Referring back to this standardized set of configurations ensures that fans are specified, installed, and serviced correctly, supporting reliable performance and a longer operating life.