Dust Collector Pipe Size Calculator - Transport Velocity

ℹ️ About This Calculator

Dust extraction ducts follow the opposite rule to HVAC ducts. In HVAC you size for low velocity to cut noise and pressure drop - in dust collection you must hold a minimum transport velocity or the material drops out of the airstream and settles in the pipe, choking the system and creating a fire and explosion risk. This calculator sizes the duct to keep material moving.

The rounding rule is what catches people out. In HVAC you round a duct up and gain a little margin; in dust collection rounding up drops the velocity below transport minimum and the duct silts up. Settled dust in a duct is not just a blockage - accumulated combustible dust is the fuel for a duct fire or secondary explosion, which is why NFPA 652/654 treat it as a hazard, not a nuisance. So dust ducts round down, accepting higher velocity and pressure drop as the price of keeping the pipe swept clean. Branch entries should be angled (30-45 degrees), never square tees, and every branch needs its own velocity check - a lightly loaded branch is where settling starts.

📐 Dust Duct Sizing (ACGIH Transport Velocity)

ACGIH / ASHRAE

Area and diameter:
  A = Q / V        (Q in m³/s, V = minimum transport velocity)
  D = √(4A / π)

Minimum transport velocities (ACGIH):
  Fine dust / fumes        : ~12 m/s  (2400 fpm)
  Wood dust / sawdust      : ~18 m/s  (3500 fpm)
  Grain / paper trim       : ~20 m/s  (4000 fpm)
  Metal turnings / heavy   : ~23 m/s  (4500 fpm)

Rounding rule (important):
  Round DOWN to the next standard duct size.
  A larger duct lowers velocity below the minimum and
  lets material settle - the opposite of HVAC practice.

❓ Frequently Asked Questions

What is transport velocity in dust collection? +

Transport velocity is the minimum air speed that keeps particles suspended in the duct. Below it, dust falls out of the airstream and settles. Typical values are about 12 m/s for fine dust, 18 m/s for wood dust and 23 m/s for heavy metal particles.

How do you size a dust collector pipe? +

Divide the airflow by the minimum transport velocity for that material to get the required area, then convert to a diameter with D = square root of 4A divided by pi. Round DOWN to the next standard duct size so velocity stays above the minimum.

Why round down instead of up for dust ducts? +

A bigger duct means lower velocity. In HVAC that is fine, but in dust collection it drops the air speed below transport velocity and material settles in the pipe, causing blockage and a combustible dust hazard. Rounding down keeps velocity high and the duct self-cleaning.

What velocity is needed for wood dust? +

About 18 m/s (roughly 3500 fpm) for typical sawdust and wood shavings. Heavier or wetter material needs more, and fine sanding dust can be conveyed a little slower, around 12-15 m/s.

Is settled dust in ductwork dangerous? +

Yes. Accumulated combustible dust inside ductwork is a recognised fire and secondary-explosion hazard addressed by NFPA 652 and NFPA 654. Maintaining transport velocity so ducts stay swept clean is a safety requirement, not just a performance one.

Free Dust Collector Pipe Size Calculator (ACGIH)

ℹ️ About This Calculator

📐 Dust Duct Sizing (ACGIH Transport Velocity)

ACGIH / ASHRAE

❓ Frequently Asked Questions

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