Ductline: HVAC Duct Calculator

Every number in Ductline can show you where it came from: the equation, your own figures substituted into it, and the standard it follows. Tap any result to open the working. That matters, because a duct calculator that disagrees with the one in your other hand is worthless until you can see which of them is wrong. WHAT IT SIZES • Round, rectangular and flat-oval duct • Size by friction rate (the equal-friction method) or by velocity • Solve in any direction: size from airflow, airflow from a size you already have, or the pressure drop of either • Convert between round and rectangular at equal pressure drop with the Huebscher equation, not a rule of thumb • Whole systems: supply and return paths, segment by segment, with the critical path identified for you REAL PHYSICS, NOT A CHART LOOKUP Ductline solves the Colebrook–White equation for the actual Darcy friction factor, from your duct's own roughness and your own Reynolds number. The printed friction chart assumes galvanised steel carrying standard air at sea level. Ductline does not assume any of that. • 12 duct materials, each with its published absolute roughness — spiral, corrugated spiral, aluminium, PVC, phenolic, concrete, flex, fibrous liner • Air density and viscosity corrected for your temperature and elevation • Flexible duct compression at 4%, 15% and 30% — a sagging flex run is not the same duct as a stretched one STATIC PRESSURE YOU CAN DEFEND • Total external static pressure against the blower's rated ESP, with what is left for duct • Component worksheet: coil, filter, humidifier, balancing damper, registers and grilles • ACCA Manual D total effective length — longest supply path plus longest return path • 25 fittings with ASHRAE loss coefficients and Manual D equivalent lengths, from a conical takeoff to a 3-piece mitred elbow • Duct leakage by sealing class, from mastic on every joint down to unsealed FABRICATION, BOTH SIDES OF THE ATLANTIC • SMACNA gauge and pressure class, or EN 1505/1506/1507 sheet thickness in millimetres • Snaps to sizes that actually exist: SMACNA round and rectangular, or the EN 1506 nominal series • Sheet weight per duct, so you can price the metal before you cut it CHECKS THAT CATCH IT BEFORE SITE DOES • Velocity against the guideline for that application — a residential trunk is not a dust collection main • Terminal selection with NC noise bands • Condensation check against dew point for duct running through unconditioned space THE JOB, NOT JUST THE NUMBER • Projects, runs and segments, saved with client and notes • A one-page PDF for a run or a whole project, printing the method and every warning alongside the numbers NO ACCOUNT. NO NETWORK. NO TRACKING. Ductline is finished when you buy it. There is no sign-in, no subscription, no advertising and no analytics, and it does not need a signal — which matters, because the places you need it are crawl spaces, plant rooms and attics. Nothing you type leaves your phone. Eight languages: English, German, Spanish, French, Italian, Dutch, Polish and Portuguese. SCOPE Ductline sizes low- and medium-pressure air distribution duct. It is a design and verification tool for a competent HVAC professional: it does not perform load calculation, and it does not certify a design for permit. Fabrication tables follow SMACNA and EN; verify against the standard your jurisdiction enforces.