Commercial Building Duct Design

Higher velocities and efficiency considerations for commercial HVAC

Commercial HVAC systems handle larger airflows and can tolerate higher velocities than residential systems. Energy efficiency and space constraints are often more important than absolute quiet operation.

A commercial VAV system with rooftop unit, main trunk, VAV boxes, and zone diffusers

Key Differences from Residential

Higher acceptable velocities (1000-2000 FPM for mains)
Higher friction rates allowed (0.08-0.20 in.wg/100ft)
VAV (Variable Air Volume) systems are common
Galvanized steel or aluminum ducts preferred (lower friction than flex)

Commercial Velocity Guidelines

Duct Location	Velocity (FPM)
Main ducts	1000-2000
Branch ducts	800-1500
Terminal units	500-800

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Energy Efficiency Considerations

Note While higher velocities allow smaller duct sizes, they also increase fan energy consumption. Balance initial duct cost against lifetime operating costs when selecting friction rates.

Sources

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