Yes, UK kitchens need extract ventilation to outside, or a compliant alternative, under Approved Document F. Check three things today: your extractor type and whether it vents outside, its extract rate in litres per second, and whether background vents are fitted. If an open-flued gas appliance sits in the same room, extraction must not exceed 20 litres per second unless a specialist has assessed the setup. So confirm the fan model and ask your installer for commissioning paperwork before you assume the job is finished.
TL;DR:
- Most kitchens require extract ventilation that vents outside, with a minimum rate of 30 liters per second for hoods venting outdoors and 60 liters per second if they recirculate air.
- Background vents should have an equivalent area of about 8,000 to 10,000 square millimeters and be placed at least 1.7 meters above the floor to prevent draughts.
- If a kitchen has an open-flued gas appliance, extract rates should not exceed 20 liters per second unless a specialist has approved higher ventilation levels.
- Proper commissioning and documentation are critical, with airflow tests and commissioning sheets required to prove compliance during inspection.
- For extensive projects like extensions or open-plan layouts, ventilation capacity must be increased to accommodate larger spaces, and compliance risks rise without coordinated design and oversight.
Table of Contents
- What Part F requires: extract, background and purge ventilation explained
- Numeric rules at a glance: extract rates, background vent areas and purge ventilation
- Combustion safety and Part J interaction: limits and recommended precautions
- How the rules apply to common projects: extensions, open-plan kitchen-diners and flats
- Practical compliance checklist: measurements, documents and what building control will ask for
- Commissioning, testing and maintenance: who does what and how to keep compliance valid
- Domestic versus commercial kitchen ventilation requirements
- Noise limits and acoustic performance for kitchen extract systems
- Energy efficiency considerations in kitchen ventilation design
- Practical view from Extension Kings: typical pitfalls and how an integrated build team reduces risk
- How Extension Kings helps with compliant kitchen extensions in the West Midlands
- Primary sources to consult
- Sources
- FAQ
What Part F requires: extract, background and purge ventilation explained
Approved Document F covers three distinct types of ventilation, and a compliant kitchen usually needs all three working together. Extract ventilation removes moisture and cooking pollutants at source, typically through a cooker hood or an extract fan ducted to outside air. Background ventilation, delivered through trickle vents built into window frames or walls, provides a continuous trickle of fresh air even when nobody is actively cooking. Purge ventilation clears out larger pollutant spikes quickly, usually through an openable window.
The document's underlying aim is straightforward: get moisture and contaminants out of the room, bring in enough outdoor air to keep indoor air quality reasonable, and give occupants a rapid way to clear the air after burning toast or frying with the door shut. Approved Document F (Volume 1: dwellings) sets out the extract ventilation requirements that achieve this in practice.
Placement matters as much as performance. Background ventilators should sit at least 1.7 metres above floor level, according to guidance in the Approved Document F Volume 1, which keeps draughts away from where people sit or stand. Cooker hoods are generally fitted close enough to the hob to capture steam and grease effectively, without creating a safety hazard or obstruction.
Four things to check on any kitchen ventilation setup:
- Extract type: does the fan or hood duct to outside air, or recirculate through a filter?
- Background vents: are trickle vents fitted and unobstructed?
- Purge route: is there an openable window or equivalent rapid-clearance option?
- Vent height: are background ventilators mounted at or above 1.7 metres?
Part F is performance-based rather than prescriptive. It describes example systems that satisfy the rules, but a designer can propose an alternative approach provided they can demonstrate it achieves equivalent results.
Numeric rules at a glance: extract rates, background vent areas and purge ventilation
Approved Document F sets hard numbers for extract rates, and these are the figures building control will check against. A cooker hood extracting to outside air must achieve an intermittent extract rate of at least 30 litres per second. Where the hood does not extract to outside, perhaps because it recirculates through a carbon filter, the minimum rises to 60 litres per second, according to Approved Document F.
Continuous mechanical extract systems work differently, running at a low background rate permanently and stepping up when needed. For kitchens, Approved Document F gives a continuous rate alongside a higher boost rate that should be triggered during cooking.
Background ventilator provision is measured in equivalent area, not a simple hole size. Typical guidance for kitchens and other habitable rooms calls for equivalent ventilator areas specified within a certain range, though the exact figure depends on room type and the overall ventilation strategy for the dwelling. Some decentralised mechanical extract ventilation systems use lower figures, such as 6 litres per second continuous with a 13 litres per second boost, as referenced in Scotland's technical handbook guidance, though the England and Wales figures in Approved Document F take precedence for projects in those nations.
Purge ventilation has its own benchmark: at least four air changes per hour, achievable through an openable window or a mechanical system sized to match, as set out in Approved Document F Volume 1.
The core numbers to work from:
- 30 l/s intermittent, cooker hood extracting to outside.
- 60 l/s intermittent, where the hood does not extract to outside.
- 8,000 to 10,000 mm² typical background ventilator equivalent area for kitchens.
- Four air changes per hour minimum for purge ventilation.
Combustion safety and Part J interaction: limits and recommended precautions
Extract fans do not operate in isolation. A powerful hood pulling air out of a tightly sealed kitchen can create negative pressure strong enough to drag combustion products back down a flue instead of letting them escape, a phenomenon Approved Document J identifies as a genuine safety risk. Where a kitchen contains an open-flued gas appliance, such as some older boilers or gas fires, extraction should not exceed 20 litres per second (72 cubic metres per hour) unless specialist measures are in place.
Oil and solid-fuel appliances carry similar warnings, and the safe route in most refurbishments is to fit room-sealed appliances wherever possible, removing the open-flue risk entirely. Where that is not practical, permanent combustion air vents may be required alongside the extract system.
Pro Tip: Ask your installer to confirm in writing whether your kitchen has any open-flued appliance and, if so, what extract rate the new system has been designed not to exceed.
Before signing off any kitchen extension or refurbishment with a heating appliance nearby, work through this:
- Identify the appliance type, open-flued, room-sealed, or none at all.
- Ask for a Part J check from your installer or heating engineer where an open flue is present.
- Fit carbon monoxide alarms in line with current manufacturer and building control advice.
How the rules apply to common projects: extensions, open-plan kitchen-diners and flats
Most homeowners meet these rules through one of a handful of common project types, and each carries its own wrinkle.
- Open-plan kitchen-diners. Knocking through to create one large living space usually means the kitchen's ventilation now has to serve a bigger volume of air, so expect to need extra background ventilators or a higher-capacity extract system than a single galley kitchen would require.
- Extensions to existing dwellings. Building control tends to scrutinise ventilation more closely here, because improving a home's fabric and airtightness as part of the works often reduces natural infiltration that the old kitchen quietly relied on. A system that was borderline compliant before an extension can fail once the rest of the house is sealed tighter.
- Flats and single-aspect dwellings. With only one external wall to work with, flats sometimes need larger equivalent ventilator areas than a comparable house, or a mechanical alternative such as passive stack ventilation or mechanical ventilation with heat recovery (MVHR). Where natural options run out of room, specialist ventilation design input is worth bringing in early rather than retrofitting a fix later.
Extension Kings' own project work, including an open-plan kitchen-diner rear extension in Birmingham, reflects this pattern: larger open spaces and improved airtightness both push the ventilation specification upward compared with the original layout.
Practical compliance checklist: measurements, documents and what building control will ask for
Before any inspection or handover, gather the measurements and paperwork building control will expect to see.
Measure and record:
- Fan extract rate in litres per second, both boost and continuous settings where applicable.
- Background vent equivalent area in square millimetres.
- Hood height above the hob.
- Extract terminal location, confirming it discharges clear of windows, doors and boundaries.
Collect from your installer:
- Product specification sheets for the fan or hood.
- A completed commissioning sheet (Appendix C).
- Airflow test results showing measured, not just rated, performance.
- Maintenance instructions for the homeowner or landlord.
Building control's common fail points are predictable: a missing commissioning sheet, background vents sized too small for the room, or vents and extract terminals positioned so close together that air short-circuits between them instead of ventilating the space.
Commissioning, testing and maintenance: who does what and how to keep compliance valid
Commissioning is the step that turns a fitted fan into a proven, working system, and it follows a set sequence: a visual inspection, removal of any transit packaging or protective film from the unit, measured airflow testing, and completion of a commissioning sheet submitted to the Building Control Body. Skipping this step is one of the most common reasons kitchens fail inspection even when the hardware itself is correctly specified.
Commissioning matters because a fan's rated airflow and its installed, measured airflow are often different figures. Duct bends, terminal grilles and poor balancing can all reduce the air actually moving through the system, and that shortfall is exactly what later shows up as condensation on windows or mould in corners.
- Visual check: confirm the unit is the specified model and undamaged.
- Airflow test: measure actual extract rate against the design figure.
- Commissioning sheet: complete and hand to building control.
- Handover pack: give owners or tenants the maintenance schedule and filter-cleaning intervals.
Pro Tip: Keep a copy of the commissioning sheet with your home's building regulations file, it is the document that proves the system was tested, not just installed.
Domestic versus commercial kitchen ventilation requirements
Domestic kitchens sit under Approved Document F, which sets the extract and background ventilation rates covered above and assumes relatively light, intermittent cooking loads. Commercial kitchens operate under a different set of expectations entirely, shaped by the much higher heat, grease and steam output of continuous professional cooking.
Commercial kitchen extraction typically needs to cope with sustained high-volume output, grease extraction and filtration suited to continuous use, and fire safety considerations around ducting that simply do not apply to a domestic hob and hood. Where a domestic project includes any element of commercial-style cooking, a separate catering kitchen within a let property, for example, it falls outside the scope of Approved Document F and needs its own specialist ventilation design rather than a scaled-up version of the domestic rules.
For the vast majority of homeowners, landlords and builders working on house extensions, Approved Document F remains the relevant standard, and the figures in the earlier sections apply directly. The distinction matters most for anyone converting part of a property to commercial use or adding a kitchen that will see professional-level cooking volumes.
Noise limits and acoustic performance for kitchen extract systems
Approved Document F does not set a hard decibel limit for kitchen extract fans, but noise still matters in practice, particularly for continuous systems that run permanently at a low background rate. A fan that is too loud at its continuous setting often gets switched off by occupants, which quietly defeats the ventilation strategy the system was designed to deliver.
When specifying a cooker hood or extract fan, checking the manufacturer's stated noise output at both continuous and boost settings is worth doing alongside the extract rate itself. A unit rated for the correct litres per second but noticeably noisy at that setting is a poor practical choice for a kitchen used daily, even if it technically meets the airflow figures. This is particularly relevant for continuous systems serving open-plan kitchen-diners, where the fan runs in the background of a living space rather than a separate room.
Ducting design also affects noise. Long, straight duct runs with gentle bends tend to produce less noise than tight runs with sharp turns, and a well-insulated duct run through a loft space reduces both noise transmission and heat loss.
Energy efficiency considerations in kitchen ventilation design
Ventilation and energy efficiency pull in opposite directions unless the system is designed with both in mind. Extracting air to outside necessarily removes some heated indoor air with it, and in a well-insulated, airtight extension that loss is more noticeable than in an older, leakier house.
Continuous mechanical extract systems, running at a low background rate with boost on demand, tend to offer a more consistent and controllable approach than relying purely on background trickle vents and intermittent extraction, particularly in homes built or extended to current airtightness standards. Mechanical ventilation with heat recovery (MVHR) takes this further by recovering warmth from outgoing air before it leaves the building, though it is a bigger specification decision than a single kitchen extract fan and suits whole-house ventilation strategies rather than a single-room retrofit.
The practical takeaway for most extension projects is that improving a home's airtightness as part of the works, which is common and often beneficial for heating costs, increases the importance of getting the mechanical ventilation specification right. A kitchen that previously relied partly on background draughts through an older building fabric may need a properly specified extract and background vent combination once that fabric is sealed up, rather than continuing to lean on infiltration that no longer exists.
Practical view from Extension Kings: typical pitfalls and how an integrated build team reduces risk
The most frequent ventilation errors we see are under-sized background vents, skipped commissioning paperwork, and Part J checks overlooked when an extension brings a kitchen closer to an existing flue. Each one causes delays at building control rather than on-site problems, because the fault only shows up on inspection.
A managed design-and-build process coordinates ventilation design, Part J checks and commissioning as one sequence rather than separate trades working to their own schedules, which is the difference between a smooth sign-off and a return visit.
— Raja
How Extension Kings helps with compliant kitchen extensions in the West Midlands
The process for a kitchen extension can be managed under one team, so ventilation design, building regulations liaison and commissioning paperwork are handled together rather than chased up separately after the build.
- One point of contact from design through to handover.
- Building regulations and Part F compliance managed as part of the build, not bolted on afterwards.
- Project examples including a side-return kitchen extension in Dudley and a kitchen extension with rooflights in Halesowen.
If you are planning a kitchen extension in the West Midlands, view our kitchen extensions service or get in touch to discuss your project.
Primary sources to consult
For the current legal text, go directly to Approved Document F (Volume 1: dwellings) for extract rates and background vent guidance, and Approved Document J for combustion appliance interaction and carbon monoxide alarm advice. Amendments and clarifications are published through Gov, which is the place to check for the latest wording before relying on any printed copy.
Sources
FAQ
What are the British standards for ventilation?
UK kitchen ventilation is governed by Approved Document F under the Building Regulations, which sets minimum extract rates, background ventilator areas and purge ventilation requirements for dwellings. Separate guidance in Approved Document J covers how ventilation interacts with combustion appliances such as gas boilers and fires.
Is it illegal to have no ventilation in a kitchen?
A kitchen without any extract ventilation to outside, and without an approved alternative, would not meet the Building Regulations and could fail a building control inspection on a new build or extension. Compliance is normally checked at building control sign-off, so a non-compliant kitchen can hold up completion of a project rather than being a standalone criminal offence for existing, unaltered homes.
Do you need an extractor fan in a commercial kitchen?
Commercial kitchens fall outside Approved Document F and need ventilation designed for continuous high-volume cooking, grease extraction and fire safety, which goes well beyond a domestic cooker hood. Anyone fitting a commercial-style kitchen within a residential property should get specialist ventilation design input rather than relying on the domestic rules.
What is the minimum extraction rate for a kitchen?
The minimum intermittent extract rate is 30 litres per second for a cooker hood that extracts to outside, rising to 60 litres per second where the hood does not extract to outside air. Continuous mechanical systems use a lower background rate with a higher boost setting triggered during cooking.
What happens if a kitchen has an open-flued gas appliance nearby?
Where a kitchen contains an open-flued gas appliance, extraction should generally not exceed 20 litres per second unless a specialist has assessed and approved a higher rate. This limit exists because stronger extraction can pull combustion products back down the flue instead of letting them vent safely outside.