This calculator evaluates the selected comparison Qproxy=CeAv for a circular flue area A=πd²/4. Ce is an entered dimensionless factor, so the result is an airflow proxy—not a tested cowl extraction rating or a prediction of chimney draft.
Spiral Vane Cowl · Selected Airflow-Proxy Ledger
Explore selected circular-area and CeAv airflow-proxy arithmetic without treating it as a tested cowl rating or chimney-draft prediction.
Equation Used
- The selected flue section is circular.
- Wind speed is a scalar comparison input, not a resolved local velocity field.
- Ce is a user-selected dimensionless factor, not a universal efficiency or certified coefficient.
- Qproxy is simple area-times-scaled-velocity arithmetic.
- Rotor aerodynamics, wind direction, pressure, duct losses, stack effect, weather and safety are excluded.
Former extraction-rate and draft-velocity labels are narrowed to a comparison proxy and factor-scaled velocity.
Selected comparison only
The cross-section identifies wind, a generic rotating-vane cowl and the selected flue diameter. Arrow density and rotor motion are illustrative; they do not solve the external flow, pressure field or rotor speed.
What the calculator determines
Select comparison wind speed, circular flue diameter and a dimensionless factor. The calculator reports exact circular area, Ce times wind speed, and the resulting Qproxy in m³/h and cfm.
Selected proxy ledger
A=πd²/4; uproxy=Ce v; Qproxy=A uproxy=CeAv. The cfm tile is only a unit conversion of the same proxy.
Selected-input example
For v=5 m/s, d=300 mm and Ce=0.16, A≈0.0707 m², uproxy=0.8 m/s and Qproxy≈203.6 m³/h (about 120 cfm).
Proxy, not ventilator performance
Actual flow depends on tested ventilator geometry, wind direction and turbulence, rotor speed and drag, duct pressure losses, stack effect, screens, installation and system operating point. Use manufacturer or standards-based performance data for design.
Questions
Is Ce a universal cowl efficiency?
No. It is a selected comparison factor with no universal physical value.
Does zero wind mean zero chimney flow?
No. The proxy becomes zero, but real buoyancy-driven stack flow may remain.
References
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