Estimate single-duct-run pressure drop: Darcy-Weisbach friction (Swamee-Jain), Huebscher equivalent diameter for rectangular ducts, and fitting losses via Sigma K or a fitting schedule - with velocity, Reynolds number, flow regime and Mach shown.
Duct Pressure Drop Calculator (MEC-01) is a formula-only HVAC calculator for preliminary single-run duct pressure-drop checks. Everything it reports is computed in the browser from the numbers you type — there is no duct library, no fan database, and no project model behind it.
Nothing is computed until you ask for it: fill in the input cards, then press Calculate. See Getting started for the full flow, including what happens when you edit an input after a result is on screen.
From an airflow, a duct length, a duct size and an air state, the tool reports:
Rectangular ducts are handled with the Huebscher circular-equivalent diameter: the friction calculation runs on the equivalent circular duct, while the velocity shown to you is the real duct velocity. The method page sets out every equation as implemented, including which velocity feeds which term.
The tool covers one duct run at a time. It does not size ducts, balance a system, sum a network, select a fan, or check pressure class, acoustics or code compliance. It has no knowledge of your project standards.
The default K values are simplified typical figures published for preliminary checking
(library mvp_default_v1); they are not reproduced from a named standard, and any value can
be overridden per row. See Fittings.
Treat the output — including the PDF report — as a transparent engineering check, not an approved design or a construction document. Final duct sizing, pressure-loss assessment, fan selection, acoustic review, code compliance and construction documentation remain the responsibility of the qualified engineer and the applicable project standards.