Summary

Kitchen extraction is one of the most frequently misunderstood areas of building compliance in residential work. Many kitchen installers fit a recirculation hood (charcoal filter, no duct) and consider the job done — but this does not comply with Building Regulations Part F, which requires actual air removal to the outside. Recirculation hoods remove grease and odour but return moisture-laden air to the kitchen, failing to address condensation and humid air that causes mould growth and building deterioration.

The 2021 revision of Approved Document F introduced new requirements that significantly increased the minimum ventilation rates and added requirements for background ventilation (trickle vents) in kitchens. Understanding what is actually required — and being able to explain it to customers — is increasingly important as building control inspections become more common.

Key Facts

  • Part F (2021) extract rate — adjacent to hob — minimum 30 l/s (108 m³/h) for intermittent extract fan; 60 l/s (216 m³/h) for cooker hood
  • Part F (2021) whole-dwelling ventilation — kitchen contributes to the whole-dwelling ventilation strategy; new builds require SAP calculation
  • Recirculation hood — removes grease and odour via charcoal filters; does NOT count as ventilation under Part F; moisture stays in the kitchen
  • Ducted extraction — compliant with Part F; duct must exit to outside; grille must prevent bird/insect entry and be weatherproof
  • Minimum duct diameter — 125mm for most residential hoods; 150mm for high-output hoods or long duct runs
  • Maximum duct run — performance drops significantly with long duct runs; maximum recommended run before adding duct diameter: 3m; each 90° bend equivalent to approximately 1m of duct; use 150mm duct for runs over 3m
  • Duct material — rigid circular or rectangular aluminium; semi-rigid aluminium; flexible corrugated (only for short connections or last section); PVC rigid duct is also used but has performance concerns at some fittings
  • Duct fire-stopping — duct passing through a fire-rated floor or wall requires fire-stopping at the penetration; fire-rated duct (e.g. Specflue) in some scenarios
  • Cooker hood height above hob — gas hobs: minimum 650mm to underside of hood (or manufacturer's minimum, whichever is greater); electric/induction: minimum 450mm; typical install height 600-750mm
  • Noise — extract fans must not exceed 45 dB(A) at 30 l/s measured at 1m from the inlet; check manufacturer's data

Quick Reference Table

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Hood Type Compliance with Part F Notes
Ducted chimney hood Yes — if ducted to outside Most common compliant option
Ducted integrated (in unit) Yes — if ducted to outside Must maintain 60 l/s through the unit
Ceiling extract (island hob) Yes — if ducted to outside Needs roof penetration or long duct run
Recirculation hood No (Part F) Allowed, but does not count as ventilation
Downdraft extractor Yes — if ducted to outside Duct runs below worktop; complex routing
Extractor fan (no hood) Yes if 30 l/s minimum Can be in ceiling or wall adjacent to hob

Detailed Guidance

Part F Requirements in Detail

Building Regulations Approved Document F (2021, applicable to work in England) sets two types of requirement for kitchens:

1. Extract ventilation (Table 1.2 of Part F) Kitchens must have extract ventilation capable of removing humid air and cooking odours. The rates are:

  • Intermittent extract fan: minimum 30 l/s (108 m³/h) when operated
  • Cooker hood: minimum 60 l/s (216 m³/h)
  • The extract must discharge to outside

2. Background ventilation In dwellings with new or replacement windows, background ventilators (trickle vents) are required. In kitchens: equivalent to 8000mm² equivalent area (EqA). If the kitchen is a habitable room in an open-plan layout, the requirement increases.

3. Humidity-controlled extract Humidity-controlled extract fans (those with a built-in humidistat) can operate continuously at lower rates and intermittently at higher rates — they are an acceptable alternative to a standard intermittent fan.

Scotland and Wales: Wales follows its own version of Approved Document F. Scotland has separate Building Standards. The principles are similar but the specific rates vary — check the applicable regulations for the project location.

Cooker Hood Height and Position

Above gas hobs: the minimum clearance from hob surface to underside of hood is 650mm. This is a gas safety requirement — getting the hood too close to a gas flame risks igniting grease deposits in the hood or duct. Always check the hob manufacturer's instructions too — many specify 750-800mm minimum.

Above electric/induction hobs: minimum 450mm; typical install height 600-700mm. The clearance is less critical for electrical safety but affects extraction performance — too high and grease vapour spreads before being captured.

Canopy width: the hood should be at minimum the same width as the hob; ideally 100-150mm wider each side. A wider hood captures more cooking fumes before they escape the capture zone.

Duct Routing

The duct from the cooker hood to the external grille is where most extraction systems lose performance. Key principles:

Keep it short: every metre of duct reduces airflow due to friction. Every 90° bend is equivalent to approximately 1m of straight duct. A system with 3m of straight duct and two 90° bends has an equivalent duct run of 5m.

Duct sizing by run length:

Duct Equivalent Length Recommended Diameter
Up to 3m 125mm
3-5m 150mm
5-7m 150mm (check hood specification)
Over 7m Specialist calculation; may not be achievable

Duct type: rigid aluminium round duct is best for performance. Rectangular duct fits between joists and ceiling voids but has higher resistance. Flexible corrugated duct should be used only for short connectors (less than 0.5m) and final connections — never for full runs, as the corrugations add significant friction.

Condensation in the duct: where the duct passes through a cold space (unheated loft, external wall cavity), condensation can form inside the duct and drip back into the kitchen. Insulate the duct in cold voids. Route the duct on a slight fall towards the external end so any condensate runs out rather than back.

External Grilles and Terminals

The external termination must:

  • Prevent bird and insect ingress (mesh or louvred grille)
  • Be weatherproof — self-closing flap or louvres that close when the fan is off
  • Be clear of any opening windows, doors, or air intakes (minimum 300mm separation from openings into the building)

For grilles through external walls: use a standard wall vent with back-draught shutter. Round-to-rectangular adapters are available for aesthetic brickwork grilles. Keep the external face velocity low (2 m/s or less) to prevent wind back-pressure defeating the extraction at the fan.

Flat roof termination (island hoods): roof cowl with bird guard; ensure the cowl is sealed to the roof structure and a fire-stopping collar is used where the duct passes through a fire-rated element.

Recirculation Hoods — When They Are Used

Despite not meeting Part F requirements for new and notifiable work, recirculation hoods are widely used in:

  • Flats where duct routing to outside is not practical
  • Kitchens on internal walls with no external access
  • Listed buildings where external penetrations are not permitted

In these cases, a recirculation hood may be the practical solution, but the installer should document that Part F compliance has been raised with the customer and that the ventilation strategy needs to address moisture removal by other means (e.g. whole-house MVHR, passive ventilation, humidity-controlled bathroom extract).

Frequently Asked Questions

Does every kitchen need a hood?

Part F does not specifically require a hood — it requires extract ventilation. A ceiling-mounted or wall-mounted extract fan adjacent to the cooking area, capable of 30 l/s, complies. However, a fan without a hood is generally less effective at capturing steam and grease vapour directly above the hob.

Can I duct into a chimney breast?

No. Ductless hoods (recirculation only) can be fitted in fireplace alcoves, but hoods must not be ducted into existing chimney flues unless the flue has been decommissioned and is solely used for the purpose. Active or potentially active flues create a fire and fume risk. A standalone duct through the chimney breast wall is acceptable if correctly installed.

What if the hob is on an island with no wall access?

Options for island extraction: 1) Ceiling-mounted canopy hood ducted through the ceiling void and out through the roof or soffit; 2) Downdraft extractor (integrated into the worktop beside or behind the hob, ducted below the floor); 3) Overhead pendant island hood ducted to ceiling. All require careful duct routing planning before the kitchen is installed — this is very difficult to retrofit.

Does Part F apply to a kitchen renovation?

Part F applies to new builds, and to extensions and material changes of use in existing buildings. A straightforward kitchen refurbishment (replacing units, worktops, appliances) in an existing dwelling generally does not trigger a full Part F compliance obligation, but it is best practice to bring the ventilation up to Part F standard. Installing a new extraction system always gives the opportunity to do it right.

Regulations & Standards

  • Building Regulations Approved Document F: Means of Ventilation (2021) — extract rates, background ventilation, and whole-dwelling ventilation for new and material change of use

  • Building Regulations Approved Document J: Combustion Appliances — air supply requirements for gas cooking appliances; minimum free air provisions

  • Gas Safety (Installation and Use) Regulations 1998 — minimum clearances from gas hobs to combustible materials including cooker hoods

  • BS EN 61591 — domestic cooking fume extractors; test methods and performance classification

  • CIBSE Guide A — environmental design; kitchen ventilation rates in commercial and large domestic settings

  • MHCLG: Approved Document F 2021 — full text of the regulations

  • BEAMA Kitchen Ventilation Guidance — industry guidance on compliance with Part F

  • Gas Safe Register — Cooker Hood Installation — gas safety clearances

  • kitchen layout — hob positioning constraints

  • kitchen electrics — electrical supply to extractor fans

  • bathroom ventilation — Part F requirements for bathroom extract

  • building control — when kitchen work requires building control sign-off