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Open ToolFabric Duct Velocity Calculator
Free fabric duct velocity calculator for textile duct airflow, active length, surface velocity, inlet velocity, comfort checks, and early HVAC planning.
What is a fabric duct velocity calculator?
A fabric duct velocity calculator checks whether a textile or fabric air duct has reasonable inlet velocity and diffuser surface velocity for a given airflow. It converts CFM into m3/s, calculates circular duct area from duct diameter, estimates inlet velocity, then estimates active fabric outlet area using duct circumference, active length, and effective open area. Designers use it to catch high velocity, draft risk, noise risk, and poor air distribution before final manufacturer selection. It is useful for warehouses, gyms, halls, retail areas, classrooms, industrial spaces, and comfort cooling applications where textile ducting is being considered. Final design still needs manufacturer fabric data, throw pattern, pore/opening arrangement, condensation checks, suspension details, cleaning access, static pressure, acoustic criteria, and project specifications.
Inputs
Forms are empty on load. Use sample data to preview the workflow or enter your own project values.
Learn more
Formula logic, use cases, assumptions, and limits for this tool.
How this tool helps
Use this for fabric duct velocity checks before final textile duct manufacturer selection. It helps compare inlet velocity, active surface area, and diffuser discharge velocity for comfort planning.
Assumptions and limits
This tool provides a planning-level result. It does not replace detailed engineering design, approved software, manufacturer data, authority requirements, or project specifications.
Typical use cases
- Early estimation and tender support.
- BOQ sanity checking and technical review.
- Site discussion before final engineering verification.
- Comparison of alternatives using consistent assumptions.
Result interpretation
Read the recommendation, warning, and confidence sections together. A result without warnings is still not an approval; it only means the entered values did not trigger built-in planning alerts.
Quick answer for common searches
Fabric duct velocity is usually checked in two ways: inlet duct velocity and diffuser surface velocity. Use the manufacturer open-area data where available, because perforation pattern and active length can change comfort results.
Useful search phrases covered by this page
- fabric duct velocity
- textile duct velocity calculator
- fabric duct surface velocity
Next checks
Input definitions and typical values
These notes explain what each input means and which values usually produce a more reliable planning result.
Airflow CFM
Air volume flow rate. Comfort HVAC rooms often use hundreds to thousands of CFM depending on load, air changes, and occupancy.
Fabric duct diameter mm
Internal or nominal diameter used by the calculation. Use manufacturer/internal diameter for flow checks whenever possible.
Active diffuser length m
Active diffuser length. Use the fabric duct length that actually releases air, not inactive collars or blank sections.
Effective open area %
Effective open area percentage. Use manufacturer data where possible; perforated/fabric openings vary widely by design.
Target duct velocity m/s
Target duct or fluid velocity. Lower values reduce noise and pressure drop; higher values reduce size but increase losses.
Target surface velocity m/s
Fabric duct discharge surface velocity. Low values improve comfort; manufacturer selection should confirm final discharge.
Practical verification checklist
- Confirm the selected standard profile is suitable for the project location and authority.
- Replace sample values with project drawings, schedules, equipment data, or measured site values.
- Review warnings, methodology, and PDF report before using the result outside early planning.
- Verify final decisions against official standards, manufacturer data, consultant specifications, and local approvals.
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Open ToolCalculation methodology
Duct velocity = airflow / circular duct area. Surface velocity = airflow / active fabric outlet area using active length, circumference, and effective open area.
Inputs are treated as planning assumptions. The calculator shows warnings when entered values fall outside practical thresholds or selected standard-profile limits.
Version history
- v1.3.41: Added from Search Console query demand for fabric duct velocity.
Stage 2 roadmap: optional saved projects, dashboards, and shared calculation history without forcing login for free use.
Trust and verification
Every result includes assumptions, warning logic, and a downloadable report. Final engineering decisions still need qualified review, local authority approval, manufacturer data, and project specifications.
Worked example
Use the sample data button to load a realistic scenario, then download the PDF report to review inputs, results, methodology, warnings, and disclaimers in one place.