Duct sizing, pressure & fans
- Duct Heat Gain / Loss CalculatorEstimate the heat gained or lost through duct walls.
- Duct Pressure Drop CalculatorFind the pressure drop along a run of ductwork.
- DuctulatorSize round and rectangular ducts, and swap between the two.
- Fan Affinity Laws CalculatorSee how airflow, pressure and power change with fan speed.
- Specific Fan Power (SFP) CalculatorCheck how much power your fans use against the allowed limit.
- System Curve & Operating Point CalculatorFind where a fan or pump will actually settle on its curve.
Ventilation rates
- Air Change Rate CalculatorWork out how many air changes an hour a room gets.
- COâ‚‚ Ventilation Check CalculatorCheck ventilation keeps air fresh enough for the people in it.
- Kitchen Extract Sizing CalculatorSize a commercial kitchen canopy and its extract rate.
- MVHR Whole-Dwelling Sizing CalculatorSize a whole house heat recovery unit for a home.
Terminals, testing & weight
- Duct Leakage CalculatorFind the leakage allowance for a ductwork air tightness test.
- Ductwork Weight & Loading CalculatorFind the weight of ductwork for support and hanger design.
- Grille / Diffuser Sizing CalculatorSize a grille or diffuser for the air it has to deliver.
- Proportional Balancing Aid CalculatorWork out target flows for balancing a ventilation system.
About these ductwork calculators
The ductwork set covers air distribution from first sizing through to testing and support: what size the duct needs to be, what it costs in pressure, how much air the space actually requires, and what the installed system weighs.
Sizing and pressure drop follow CIBSE Guide B2 velocity and pressure-loss guidance, with the ductulator giving equivalent round and rectangular sizes at a chosen velocity or pressure gradient. Ventilation rates reference Approved Document F and ASHRAE 62.1; fan laws use AMCA 201; leakage classes follow the standard air-tightness class definitions; and MVHR performance references BS EN 13141-7. Specific fan power is checked against the Approved Document L limits.
They are aimed at ventilation designers, ductwork contractors and estimators - the people who need a duct size, a fan duty or a leakage allowance now rather than after a modelling exercise.
The weight and support calculators are worth noting: they take the installed build-up including insulation and cladding and return kg/m and kN/m figures suitable for handing to a structural engineer for support design.
Frequently asked questions
What velocity should I size ductwork to?
It depends on the application and how much noise is acceptable. CIBSE Guide B2 gives typical maximum velocities by duct type and location - lower in occupied areas, higher in plant rooms and risers. The calculators let you size on either a target velocity or a pressure gradient and show the resulting figure for both.
Do the leakage calculators match site testing?
They apply the standard leakage class limits to your duct surface area and test pressure, giving the permitted leakage rate to compare against a measured result. They size the allowance; they do not replace a witnessed test.
Does ductwork weight include insulation and cladding?
Yes. The weight calculator returns bare sheet weight, insulation, cladding and installed total separately, plus kg/m and kN/m for support loading, so you can see what each layer contributes.