Sizes a commercial kitchen canopy extract rate using BESA DW/172's hood face velocity method: canopy plan area × duty-category velocity. Then checks canopy overhang, grease-duct velocity and a makeup-air advisory against it.
Budget/approximate sizing, not DW/172's mandatory per-appliance Thermal Convection Method for final compliance design.
For design guidance only. Always verify with a qualified engineer.
About this kitchen extract sizing calculator
This free kitchen extract sizing calculator gives a budget extract rate for a commercial kitchen canopy using the BESA DW/172 hood face velocity method. It is aimed at ventilation designers, M&E contractors and kitchen fit-out estimators who need a quick canopy and plant sizing at pricing stage. Enter the canopy plan size, the appliance-line footprint beneath it, the appliance duty category and a proposed duct diameter, and it returns the extract airflow, the canopy overhang check, the grease-duct velocity check and a make-up air advisory. Everything runs in your browser. Nothing is uploaded.
How the extract rate is calculated
The extract rate is the canopy face area times the duty-category face velocity: Q = (L × D) × v, where v is 0.25 m/s light duty, 0.35 m/s medium and 0.50 m/s heavy (the DW/172 Face Velocity Method). Canopy overhang is graded against a DW/172 + HSE-verified 250 mm minimum / 300 mm recommended figure, taking the smaller of the end and front overhangs. Grease-duct velocity is Q ÷ duct area, graded against a 5–12.5 m/s entrainment band (6–10 m/s recommended). Make-up air is advised at 85% of the extract (75–95% band). This is DW/172’s approximate budget method, not its mandatory per-appliance Thermal Convection Method for final compliance design.
Frequently asked questions
Which duty category should I choose?
Match it to the heaviest appliances under the canopy: light duty (0.25 m/s) for steaming ovens, boiling pans and bains-marie; medium (0.35 m/s) for deep-fat fryers, bratt pans, ranges and griddles; heavy (0.50 m/s) for chargrills and specialist broilers. The face velocity drives the whole extract rate, so pick the band the cook line actually needs.
Is this enough for a Building Control submission?
No. This is DW/172’s face-velocity budget method, good for pricing a canopy and sizing plant early, but the specification’s mandatory route for final compliance design is the per-appliance Thermal Convection Method, which works through each appliance’s convective heat gain. Use this to get in the ballpark, then complete the full appliance schedule for sign-off.
Why does the make-up air matter?
Every litre extracted must be replaced, or the kitchen goes into negative pressure, doors slam, appliances misfire and the canopy under-performs. The advisory sizes replacement air at a typical 85% of the extract (the balance transfers from adjacent spaces), within a 75–95% band. Confirm the split against your ventilation strategy and the interlock design.