AMCA 201 System Effect Factor calculator

Tick the installation conditions that apply to your duct system — a short outlet duct, an elbow near the fan, a discharge damper, an inlet obstruction — and get the System Effect Factor (Pa) to add to your calculated system pressure loss, per AMCA 201-02 "Fans and Systems". Covers both centrifugal and axial fans.

AMCA 201-02 (R2011) Full standard coverage Free, no sign-up

Fan & velocities

Outlet and inlet velocities are the fan's own rated velocities at those connections (from the fan catalog), not duct design velocities.

Fan type

Air density kg/m³

Outlet velocity m/s

Inlet velocity m/s

Outlet conditions

Outlet duct shorter than optimum length (Fig. 8.2 / 8.3)

Elbow at or near the outlet (Fig. 8.4 / 8.5)

Volume control damper at the outlet (Fig. 8.7, centrifugal only)

Inlet conditions

Elbow at or near the inlet (Fig. 9.2 / 9.4 / 9.5)

Obstruction near the inlet (Fig. 9.14)

Fan near a wall, plenum or cabinet (Fig. 9.11)

Tick one or more conditions below to add them to the total System Effect Factor.

Get a full system datasheet

Link copied — it reopens with these exact inputs.

How this calculator works

AMCA 201-02 "Fans and Systems" Section 7 gives an exact equation for the System Effect Factor, not just a chart to read by eye:

SEF = C · (V / 1.414)² · ρ (Pa, V in m/s, ρ in kg/m³)

C is the "Dynamic Pressure Loss Coefficient" of a System Effect Curve (labelled F through X in Table 7.1) — which curve applies depends on the installation condition, looked up from the standard's own tables (Figures 8.2-8.5, 8.7, 9.2, 9.4, 9.5, 9.11, 9.14) rather than read off a log-log chart. Tick a condition above, fill in its specifics, and the calculator looks up the curve, computes the SEF at your entered velocity and density, and adds it to the running total. Different conditions at different locations (inlet vs. outlet) are additive per Section 7.1 — tick as many as apply.

The volume control damper condition works differently: Figure 8.7 gives a direct multiplier on the damper's own catalog pressure drop (not a System Effect Curve), so enter the damper's wide-open catalog ΔP and the calculator reports the extra loss beyond that catalog rating when it's installed close to a fan outlet.

The inlet obstruction condition (Figure 9.14) uses an adjusted, higher velocity — the standard specifies that the inlet velocity be scaled up by the unobstructed area fraction before entering the curve, since the same airflow is forced through a smaller free area. That adjusted velocity is shown alongside the result.

A few of AMCA 201's tables contain blank cells. Where a blank sits in a column the standard itself defines as the point flow is fully normalized — 100% effective duct length, or 100% unobstructed inlet area — this calculator reads it as zero SEF, per the standard's own definition. Where a blank appears elsewhere (mostly less-common axial-fan elbow combinations) it means AMCA 201 simply has no published data for that exact combination, and the calculator says so plainly rather than guessing.

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All System Effect Factor values are computed from AMCA 201-02 (R2011) Table 7.1's equation and the standard's own configuration tables (Figures 8.2-8.5, 8.7, 9.2, 9.4, 9.5, 9.11, 9.14) — not approximated from a chart. AMCA 201 itself describes System Effect Factors as "guidelines" and "approximations" based on research and manufacturer consensus, not a precision measurement for every fan. This calculator does not replace the fan manufacturer's own system effect guidance where available.