DuctFlow Lite — the fast, McQuay-compatible duct sizing calculator for HVAC engineers. Size round, rectangular, and flat-oval ducts with the equal-friction method — fully offline, no ads, no tracking, no account.

DESIGN A COMPLETE DUCT NETWORK
• Main ducts, branches and sub-branches with automatic airflow distribution — every new branch takes the parent duct's remaining airflow, no manual subtraction
• Automatic sizing from any two of: airflow, friction rate, velocity
• Equal-friction results matching the McQuay DesignTools reference exactly (Exact mode), or shop-floor even sizes and 50 mm metric increments (Approx mode)
• Round, rectangular and flat-oval ducts — SI and Imperial, with CFM, L/s, m³/s and m³/h

ANALYZE PRESSURE AND VELOCITY
• Total system pressure drop with critical-path detection, compared against your fan's external static pressure
• Pressure profile chart along any duct run — fitting losses as steps, duct friction as slopes
• Velocity limit warnings based on ASHRAE tables, by duct application (supply main / branch / return / exhaust) and building type
• ASHRAE fitting loss library: elbows, tees, reducers, dampers

WORK FASTER
• Built-in airflow calculator: room volume × ACH (with room-type presets), sensible load, or outlet count
• Network table — your whole duct system at a glance, with warnings and tap-to-jump
• Duct schedule report (share/print) and CSV export for Excel
• Session restore — the app reopens exactly where you left off
• Air properties with temperature and altitude correction

Built by Engineers' House for HVAC engineers, designers, and students. Several features in this version were suggested by engineers using the app — send us yours from engineershouse.org.

Engineers House

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