Duct Fitting Dynamic Loss Calculator

Compute aerodynamic dynamic pressure drops (ΔP = C·Pv), ASHRAE local loss coefficients, and equivalent straight duct lengths across elbows and transitions.

Duct Airflow Velocity

Air Velocity V (FPM):

Air Density (lb/ft³):

Fitting Selection & Quantity

ASHRAE Fitting Type Preset:

Loss Coefficient (C):

Number of Identical Fittings:

Dynamic Pressure Drop Results

Total Fitting Dynamic Pressure Drop

-- in. w.g.

-- in. w.g. per individual fitting

Velocity Pressure (Pv)

-- in. w.g.

Kinetic Head

Equivalent Straight Duct

-- ft

at 0.10 in. w.g./100ft

Turning Vane Energy Savings: --% pressure reduction

Pressure Drop in Pascals: -- Pa

Fitting Loss Category: --

Fitting dynamic pressure losses often account for over 60% of total HVAC fan static pressure demand.

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Frequently Asked Questions

What is the local loss coefficient C in duct fittings?

The local loss coefficient C (also denoted Co or K) is a dimensionless factor that relates dynamic pressure drop ΔP to velocity pressure Pv via ΔP = C·Pv. Fittings with streamlined flow have low C (0.04 - 0.15), while abrupt turns without vanes have high C (1.0 - 1.5).

How much energy do turning vanes save in rectangular elbows?

A 90° mitered elbow without turning vanes has a C-factor of approximately 1.20 due to separation eddies along the inner heel and outer throat. Adding double-thickness aerodynamic turning vanes drops the C-factor to 0.15, achieving an 87.5% reduction in elbow pressure drop.

What is equivalent duct length for a fitting?

Equivalent duct length represents the length of straight duct of the same cross-section that produces the exact same friction pressure drop as the fitting. For example, an unvaned elbow at high velocity can have an equivalent length exceeding 60 to 90 feet of straight duct.