Getting Started

Build your first duct system in under five minutes.

What DuctStatic Does

DuctStatic calculates the total pressure loss through an HVAC duct system (straight runs, fittings, transitions) and estimates the sound, as a noise criterion (NC), reaching each room. It finds the critical path, the branch with the highest resistance, which is what the fan has to overcome. It uses the same physics as professional design tools, without the cost or complexity.

The Component Model

A system is a connected chain of components with airflow moving from the fan downstream to terminal devices. You add components from the toolbar:

Fan, the source. One per system, always at (or spliced before) the root.
Duct, a straight run with a length, shape (round or rectangular), dimensions, and material.
90° / 45° Elbow, a bend with a selectable fitting type (radiused, mitered, vanes…).
Tee, which splits or merges flow into branch and main legs.
Transition, a gradual or sharp change in size, or a round↔rectangular shape change.
Damper / FSD, balancing and fire/smoke shutoffs with a published pressure drop.
Diffuser / Louver, the terminal devices that discharge into (or collect from) a room.
Terminal Unit / VAV, a box with inlet and outlet connections and a published pressure drop.

Quick Start Workflow

Set air conditions. Enter your site altitude and design air temperature. These change air density and viscosity, which feed into every calculation below.
Add the fan. Click the Fan toolbar button. The first component you add becomes the root of the system.
Chain components downstream. Click a component, then use its + connection ports to attach the next piece (duct, elbow, tee, transition). Air flows fan → duct → fittings → terminal.
Terminate with a diffuser or louver. End each branch with a terminal device. Set each terminal's airflow (CFM) to have the flow computed from the terminals upward, or set one CFM on the fan to drive everything top-down.
Set pressures and options. Keep the default materials and fittings, or adjust each component's length, size, material, Co, or published drop in its panel.
Run the calculation. Hit Calculate. Results appear right away and the critical path is highlighted.
Check the sound (optional). Open the Sound (Prelim) tab to see each terminal's predicted noise criterion. Enable the fan's Sound Source, set a target NC on your diffusers, and switch a diffuser's self-noise to Rated NC if you have a manufacturer rating (auto-estimate is the default). See Calculation Method → Sound.
Apply a safety factor. Add a percentage buffer to the critical path loss before specifying your fan. 10–15% is typical.

Tip: You don't need an account to use the calculator. Sign up if you want to save and reload your work.

System Requirements

DuctStatic runs entirely in your browser, no installation or plugins required. Any modern desktop browser works. Mobile is supported but the diagram view is easier on a larger screen.

Unit System

The tool works in English (Imperial) units (CFM, inches, feet, in. w.g.) or SI (metric) units (L/s, mm, m/s, Pa). A toggle in the header switches between the two, and all numbers display in the system you choose.