What math does the free ductulator use?

Darcy–Weisbach friction with the Altshul–Tsal friction factor, velocity = CFM / actual area, and Huebscher circular equivalent for rectangular ducts — the same primitives as the HVAC Duct Tools duct-engine, with flex, altitude, and Manual D system design omitted.

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Browser micro-tool

Free online HVAC ductulator

Q: Is this a full Manual D ductulator?

No. It is a simplified browser subset: galvanized roughness, sea-level standard air, stocked round sizes, rectangular Huebscher equivalence, and friction-then-velocity sizing. It does not compute ASP/TEL, fittings, flex PDCF, or full system schedules. Use HVAC Duct Tools for those.

Q: Is this ACCA approved?

No. It is a professional estimating aid based on Manual D methods. It is not ACCA approved or certified.

Size a galvanized run from CFM, design friction rate, and role velocity — or reverse-check an existing size. Simplified, attributed math from our duct-engine. For the crawlspace with no signal, take HVAC Duct Tools offline.

No account
Runs in-browser
Estimating aid
Not full Manual D

Airflow (CFM)

Design friction (in. w.c./100 ft)

Run role

Geometry

Scope: galvanized ε = 0.0003 ft, sea-level standard air, Darcy–Weisbach + Altshul–Tsal, Huebscher for rect. Stocked rounds: 4–10, 12, 14, 16. No flex PDCF, altitude, fittings/TEL, flat-oval, or ASP→FR. Math attributed to the HVAC Duct Tools duct-engine. Estimating aid for qualified techs — not ACCA approved/certified.

Crawlspace has no Wi‑Fi

Take the full ductulator offline.

HVAC Duct Tools adds flex materials, static-pressure verdicts, capacity reverse-lookups, and Manual D system schedules — free on iPhone and iPad, no account.

HVAC Duct Tools quick size screen showing a duct size result with velocity and friction rate for a given CFM — Quick Size in the app, with flex and altitude in the math.

HVAC Duct Tools details →

Common questions

Online ductulator FAQ

Is this a full Manual D ductulator?

No. It is a simplified browser subset for quick galvanized sizing and checks. ASP/TEL, fittings, flex, and full schedules are in the Duct Tools app.

What math does it use?

The same Darcy–Weisbach + Altshul–Tsal friction primitive and Huebscher equivalence as our duct-engine, locked to sea-level galvanized air. Read the friction-rate guide: static pressure & friction rate.

Is this ACCA approved?

No. Professional estimating aid based on Manual D methods — not ACCA approved or certified, and not a stamped design.