Air Velocity Chart — Recommended FPM by Application
How fast the air should move, surface by surface: the classic comfort-system duct velocities for residences, public buildings, and industrial plants, the residential supply/return ceilings, and the face velocities that coils, filter grilles, and louvers are selected around. All of it is design guidance — ASHRAE/Carrier- and ACCA-derived conventions, not code minimums — and scheduled equipment data overrides it.
Duct velocities by building type (FPM)
| Element | Residences | Schools & public bldgs | Industrial |
|---|---|---|---|
| Main ducts | 700–900 | 1,000–1,300 | 1,200–1,800 |
| Branch ducts | 500–700 | 600–900 | 800–1,000 |
| Branch risers | 500 | 600–700 | 800 |
Residential limits (Manual D lineage)
| Element | Recommended | Max |
|---|---|---|
| Supply trunk | 600–900 | 900 |
| Supply branches | 500–700 | — |
| Return ducts | 400–600 | 700 |
| Return grille (face) | 300–400 | 500 |
| Filter grille (face) | 250–350 | 400 |
Face velocities at components
| Surface | FPM | Basis |
|---|---|---|
| Cooling coil (DX / chilled water) | 450–550, max 550 | Moisture carryover past the drain pan above ~550; AHRI 410 rates coils at 500 |
| Heating coil (comfort-table convention) | 450–600 | Classic ASHRAE/Carrier-derived comfort table |
| Heating coil (coil-manufacturer convention) | 600–1,000, optimum ~800 | Coil-manufacturer selection guidance — two real conventions, pick per spec |
| Intake louver (free area) | ≤500 rule of thumb | Manufacturer water-penetration (BPWP) data governs the actual selection |
Velocity is the third variable — size with all three
Duct sizing balances three things: friction rate (what the fan affords), velocity (what the occupants and the coil tolerate), and size (what the building fits). A duct picked purely from the duct sizing chart at a generous friction rate can still fail this chart's velocity ceilings — check both. Velocity pressure grows with the square of FPM, so every 40% velocity increase doubles the pressure cost of each fitting; the CFM calculator and duct size calculator work the numbers for a specific run. These are conventions, not code — the mechanical code and the equipment schedule always govern.
Common questions
What is a good air velocity for ductwork?
For comfort systems: 700–900 FPM in residential main ducts and 500–700 in branches; commercial buildings run mains at 1,000–1,300 FPM and industrial up to 1,800. Returns run slower than supplies — 400–600 FPM recommended residentially. Faster moves more air through less metal but costs static pressure (which rises with the square of velocity) and makes noise.
What velocity is too high for residential ducts?
The Manual D-lineage ceilings are 900 FPM for supply ducts and 700 for returns, with return grilles kept under 500 FPM at the face and filter grilles under 400. Past those numbers occupants start hearing the system, and the static-pressure cost compounds through every fitting.
What face velocity should a cooling coil have?
Between 450 and 550 FPM, and treat 550 as a hard ceiling — above it, condensate blows off the fins past the drain pan instead of draining. AHRI rates coils at 500 FPM, which is why schedules cluster there.
What counts as a high-velocity duct system?
Roughly 2,000 FPM is the customary boundary, and 2,500+ FPM is unambiguously high-velocity — the territory of higher SMACNA pressure classes, sound attenuation, and careful fitting design. Comfort systems stay low-velocity on purpose: the noise and fan energy of high velocity only pay off where space for duct is scarce.
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