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Kitchen Cooker Hood Calculator — Extract Rate & Ductwork
Calculate cooker hood extract rates per Approved Document F, air velocity and rough pressure drop in your chosen round duct, and make-up air requirements for UK kitchens.
Should be >= cooker width
Total duct length to external wall/roof
Is replacement air provision planned?
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How We Calculate This
This calculator determines cooker hood extract rates per Approved Document F, then works out the air velocity and a rough pressure drop in the round duct diameter you enter, plus the make-up air a ducted hood needs.
ADF 2021 kitchen extract rates
- Intermittent, adjacent to hob (cooker hood) — Table 1.1: 30 L/s
- Intermittent, elsewhere in kitchen (no hood) — Table 1.1: 60 L/s
- Continuous extract (high rate) — Table 1.2: 13 L/s
- Commercial range hood: not an ADF figure — size to BS EN 16282-1 / DW/172 (≈120 L/s+ shown as a placeholder)
The 30 L/s and 60 L/s figures are ADF minimums. The 60 L/s shown for range cookers is a typical manufacturer boost rate, not a regulatory requirement.
Ductwork guidance
Duct must discharge to external air, not into a loft or cavity. Use a minimum 150mm diameter rigid duct. Each 90° bend adds roughly 1.5m of equivalent straight run at 150mm (the pressure drop shown here is a rough estimate, not a manufacturer figure). Total equivalent length should not exceed the manufacturer's maximum for the hood model.
Frequently Asked Questions
Per Approved Document F 2021 Table 1.1, a kitchen intermittent extract positioned adjacent to the hob (i.e. a ducted cooker hood) requires 30 L/s (108 m³/h). If extract is sited elsewhere in the kitchen (no hood over the hob), the rate rises to 60 L/s (216 m³/h). The continuous-extract alternative (Table 1.2 high rate) is 13 L/s. Commercial kitchens typically need 120+ L/s depending on cooking intensity. A recirculating hood only filters odour/grease and does not extract to the outside, so under ADF it falls into the "elsewhere" row — a separate 60 L/s intermittent extract is still required.
Ducted hoods are far more effective as they remove moisture, odours, and combustion gases (from gas hobs) directly to outside. Recirculating hoods only filter odour and grease — they cannot remove moisture or CO/CO2 from gas combustion. ADF guidance strongly favours ducted extraction, especially for gas cooking. Recirculating hoods may not satisfy Part F for gas hobs.
A minimum 150mm diameter rigid duct is recommended for domestic cooker hoods. For longer runs (over 5m) or multiple bends, 200mm diameter reduces pressure drop and noise. Never reduce below 100mm. Use rigid galvanised or plastic duct — avoid flexible duct for long runs as it has 3-5x higher friction loss.
Yes, ducted cooker hoods extracting 30 L/s or more create measurable negative pressure, and any boost rate above ~50 L/s can affect open-flue appliances. Replacement (make-up) air must enter the kitchen through trickle vents, background ventilators, or a dedicated make-up air supply. Without adequate make-up air, the hood cannot achieve its rated flow rate, doors may slam, and back-draughting of flues can occur.
The hood should be at least as wide as the cooker, ideally 50-100mm wider on each side for better capture. A 600mm cooker needs a 600-800mm hood. A 900mm range cooker needs a 900-1000mm hood. The bottom of the hood should be 650-750mm above the cooker surface for optimal capture without head clearance issues.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.