Ventilation Calculations

This page lists duct friction and pressure loss calculation tools used in ventilation and HVAC design. Select a tool to quickly check airflow rate, velocity, duct size and fitting (local) losses.

Duct Friction and Pressure Loss

Duct Friction Calculator

Pressure loss per unit length for rectangular / round ducts.

Flexible Air Duct Pressure Loss Calculation

Friction loss and pressure drop check for flexible ducts.

Grilles and Diffusers

Grille Selection

Select and check a grille based on airflow, velocity and free area.

Elbow Losses

Elbow Pressure Loss

Pressure loss using K/ζ coefficients for standard elbows.

Elbow Loss with Turning Vanes

Loss calculation for elbows equipped with turning vanes.

Tee / Cross (Diverging – Converging)

45° Branch Tee – Diverging

Loss calculation based on branch entry angle for diverging flow.

Round Tap Tee – Diverging

Diverging loss for a round tap from a rectangular main duct.

Rectangular Cross – Diverging

Loss calculation for diverging flow through a cross connection.

Rectangular Double Wye – Diverging

Loss check for diverging flow in a double-wye connection.

Heel-Tapped Elbow (90°) – Diverging

Loss calculation for 90° diverging flow with a heel-tapped elbow.

45° Branch Tee – Converging

Pressure loss and loss coefficient for converging flow.

Round Tap Tee – Converging

Converging loss for a round tap joining a rectangular main duct.

Rectangular Cross – Converging

Loss calculation for converging flow through a cross connection.

Reducers / Transitions

Rectangular → Rectangular (Supply)

Loss for parallel transitions in supply air systems.

Round → Round (Supply)

Loss for round-to-round transitions in supply air systems.

Round → Rectangular (Supply)

Loss for round-to-rectangular transitions in supply air systems.

Pyramidal Transition (Exhaust)

Loss for pyramidal transitions in exhaust systems.

Rectangular → Rectangular (Exhaust)

Loss for symmetrical transitions in exhaust systems.

Note: These tools are designed for quick checks of local losses in duct fittings. For total system pressure loss, evaluate straight-duct friction and local losses together.