Calculate airflow
Establish outdoor-air and zone airflow requirements using the inputs and method appropriate to the space.
HVAC duct design software
HVAC duct design software that carries airflow into system sizing
Design HVAC ductwork with connected airflow, equal-friction sizing, fitting losses and critical-path pressure workflows. Start with MEPFlow's free duct sizer.
Free to start. Built for mechanical design workflows in Canada and the United States.
Move from isolated calculations to a connected workflow
A single duct diameter is only one part of a real HVAC design. MEPFlow is built around the system workflow: establish airflow, size sections, account for fittings and follow the pressure path that drives fan selection and coordination.
Size round and rectangular ductwork from airflow, velocity or friction constraints.
Keep fitting losses and critical-path pressure visible as the system develops.
Connect ventilation and air-distribution decisions to downstream duct sizing.
Check individual sections instantly with the free public duct sizer.
From zone airflow to duct system
Size duct sections
Apply equal-friction or velocity constraints to round and rectangular sections while reviewing practical limits.
Follow the critical path
Include straight-duct and fitting losses so pressure requirements are based on the system path, not an isolated section.
Use cases for duct design teams
Consulting engineers developing commercial HVAC distribution systems.
Designers replacing disconnected duct-sizing spreadsheets and reference wheels.
Teams that need repeatable methods and clearer review of sizing assumptions.
Engineers working in imperial or metric units across Canada and the United States.
Related MEP tools and workflows
Free HVAC duct sizer
Solve airflow, friction rate, velocity or equivalent diameter for an individual duct section.
ExploreVentilation calculator
Calculate breathing-zone and zone outdoor airflow before sizing supply systems.
ExploreMEP design platform
See how duct design connects to plumbing, hydronics and other mechanical workflows.
ExploreFrequently asked questions
What is equal-friction duct sizing?
Equal-friction sizing selects duct dimensions so straight sections have a consistent pressure-loss rate per unit length. The final system design still needs fitting losses, the critical path, acoustics and fan pressure.
Can MEPFlow size rectangular ducts?
Yes. The duct tools support round and rectangular geometry and distinguish actual rectangular velocity from the equivalent-round basis used for friction calculations.
Is the free duct sizer a complete duct design tool?
No. It sizes an individual section. MEPFlow's broader workflow is intended to carry sizing into layouts, fitting losses and critical-path pressure calculations.
Can I use metric and imperial units?
Yes. The duct sizing calculator supports both systems while keeping the underlying calculation consistent.
Put your next MEP calculation into a repeatable workflow
Start free, test the available modules on a real project, and decide whether MEPFlow fits your engineering process.
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