Cooker Hoods and Extractor Fans: A Practical Guide for UK Homes

How kitchen extraction actually works

There are only two ways a hood can deal with cooking air.

Ducted extraction pulls air through a grease filter and pushes it out of the building through a duct, ending at an external wall or roof vent. Steam, smells and moisture leave the house.

Recirculating hoods pull air through a grease filter, then a carbon filter, then blow it straight back into the room. The carbon filter takes out some of the smell. It does nothing about heat or moisture, because that water vapour has nowhere to go. It ends up on your windows and, over time, in the corners of the ceiling.

Recirculating tends to be the fallback rather than the first choice. It gets used in flats where there is no external wall within reach, in island layouts where the duct run would be difficult, and in leasehold properties where you cannot cut through the facade. If that is your situation, size the hood generously and budget for carbon filter replacements.

Worth knowing before you decide: under Approved Document F, a recirculating cooker hood on its own is not treated as meeting the kitchen extract requirement. Where a hood recirculates rather than venting outside, a separate extract route is expected. That matters for new installations and material changes of use rather than for a like-for-like swap in an existing kitchen, but it is the reason ducting is worth the effort where a route exists.

The types of cooker hood and extractor fan

Kitchen ventilation covers two separate families of product, and people use the words interchangeably. Worth separating them.

Cooker hoods sit directly over the hob and are the main defence against grease and steam:

Chimney hoods are the classic wall-mounted stainless steel or glass shape, with a visible flue running up to the ceiling. Strong extraction, easy to service, and the most common choice in London kitchens.

Integrated and canopy hoods hide inside a wall unit above the hob. You only see a slim strip and the controls. Good for a clean-looking kitchen, usually a little weaker on extraction because the fan and duct are working in a smaller space.

Telescopic hoods are a variation on the integrated type — a pull-out drawer front that extends when you cook and slides back when you are done.

Island and ceiling hoods are for hobs that sit in a peninsula or island. Island hoods drop from the ceiling on a flue. Ceiling hoods sit flush in the ceiling itself, above the hob. Both need a proper duct route planned before the kitchen goes in, not after.

Downdraft extractors rise up out of the worktop behind the hob and pull air sideways and down. They suit open-plan kitchens where nothing should hang at eye level. They cost more and the ducting usually has to run under the floor.

Visor hoods are the small, cheap, angled-front units common in rented flats. They will handle light cooking. They will not handle a wok.

Separate extractor fans are a different job. These are the wall, window or ceiling fans that clear a whole room rather than a hob, and they are what most kitchens, bathrooms and utility rooms rely on for background ventilation. Axial fans are for short duct runs straight through an external wall. Centrifugal fans are stronger and cope with longer ducts and bends. Inline fans sit in the loft or ceiling void partway along the duct, which makes them the quietest option in the room itself.

A kitchen often needs both. The hood deals with the hob. The room fan deals with everything else.

What extraction rate do you need

Extraction rate is measured in cubic metres per hour (m³/h). It is the number people ignore and then regret.

The working rule is ten air changes an hour. Multiply the length, width and height of the kitchen in metres to get the room volume, then multiply that by ten. A 4m × 3m kitchen with a 2.4m ceiling is 28.8m³, so you want a hood rated at roughly 290m³/h as a minimum.

Then adjust for how you cook and how the room is laid out. Open-plan kitchens need more, because cooking smells have the whole ground floor to spread into. High-heat cooking, frying and wok work need more. A galley kitchen with a door you can shut needs less.

One trade-off to know about before you buy. Manufacturers quote the maximum extraction rate, which is the rate on the highest, loudest setting. Nobody cooks on boost permanently. Check the rate on the middle setting and the noise figure in decibels alongside it. A hood that hits its rated performance at 70dB is a hood you will stop switching on.

Buy slightly more capacity than you need and run it lower. That is the quiet setup.

Hob to hood height, and the regulations

This is the question that comes up most, so here it is directly: there is no single clearance that applies across every hood and hob. It is model-specific, and the correct figure is whatever the exact manuals for your hood and your hob say.

As a working example, some current Bosch chimney and slimline hoods specify at least 500mm above an induction hob and at least 650mm above a gas hob. Other brands and models differ, sometimes by a wide margin, so treat any figure you see online — including that one — as an example rather than a rule.

Where neither manual gives a clearance, Approved Document F falls back to a minimum of 650mm to 750mm above the hob. That is a regulatory backstop for when manufacturer guidance is silent, not something to aim for by default.

The practical sequence: check the hood's installation manual, check the hob's, and where the two differ, use whichever keeps both appliances within their approved installation conditions. Fit the hood higher than intended and it captures less — steam and grease spread before reaching it. Fit it lower than the appliance allows and you can breach its safety requirements.

Always check the current manual before drilling anything. Manufacturers set their own clearances and fixing requirements, and fitting outside them can affect both safety and the warranty.

Approved Document F also expects the hood to span at least the full width of the cooker, and sets the extract rates: for an intermittent system, a kitchen needs 30 litres per second where a cooker hood sits above the hob and vents to outside, or 60 litres per second where there is no hood or the hood does not vent outside. Scotland and Wales have their own equivalents, so check locally if you are outside England.

Two other regulations come up. Where there is a gas appliance with an open flue in the property, Approved Document J is relevant, because a powerful extract fan can affect how that flue clears — worth raising with a Gas Safe registered engineer rather than assuming. On the electrical side, kitchens stopped being classed as a special location under Part P in 2013, so adding a spur or socket to an existing circuit is not notifiable. Running a new circuit still is.

That is the summary. For the full sequence for setting height correctly on your specific hood and hob, including worked examples, see our page on the importance of cooker hood installation.

Ducting: the part that gets it wrong

Most underperforming hoods are not underpowered. They are badly ducted.

Four things cost you performance:

Duct diameter. If the hood has a 150mm outlet, the duct should be 150mm all the way to the wall. Reducing it to 125mm partway along throttles the airflow and adds noise. Reducers get used because a 125mm core drill hole already existed. It is a false economy.

Bends. Every 90-degree bend costs airflow — as a rule of thumb, one adds roughly 1.5m of equivalent straight duct on a 150mm run. Two gentle 45-degree bends beat one sharp corner. Plan the shortest, straightest run you can and accept a slightly less tidy route if it means fewer turns.

Flexible ducting. The concertina foil stuff is quick to fit and terrible for airflow — the ridges create drag along the whole run, and it sags between fixings. Rigid duct is the right answer. Keep flexible sections short and pulled taut where they are unavoidable.

The external termination. A vent cover with a fine mesh grille clogs with grease within months and slowly strangles the system. Use a proper cowl with gravity flaps. And check it from outside occasionally — a blocked or painted-over external vent is a surprisingly common cause of "the extractor stopped working".

Ducting through a loft space should be insulated. Warm, wet kitchen air hitting cold duct will condense, and that water runs back down the duct or drips into the insulation.

Getting a cooker hood installed properly

A hood installation is a small job with several trades hiding inside it. There is the mounting, which has to hold real weight on the right kind of wall fixing. There is the electrical connection, which needs a spur or socket in a sensible location. And there is the ducting, which is the part that decides whether any of it works.

One thing to sort out before you book anyone: whether an opening to the outside already exists. Cutting a new hole through an external wall is separate building work, and most appliance installation services — ours included — do not create new openings or enlarge existing ones as part of a standard fitting visit. If there is no duct route yet, that needs arranging first.

If a gas hob is involved, the interaction between the extract fan and the gas appliance is a Gas Safe matter, not a general handyman one.

For a step-by-step run through what a fitting day involves, what needs to be ready beforehand and where the common snags are, see our full walkthrough of cooker hood installation.

If you would rather not handle the fitting and the connections yourself, our team covers cooker hood and appliance installation in London — removing the old unit, mounting the new one, connecting it and testing it before we leave.

Replacing or upgrading an old hood

Replacing a hood is usually easier than fitting one from scratch, because the duct route and the power supply already exist. That said, a like-for-like swap is not always possible.

Check three things before you buy:

The outlet size. Older hoods often have a 100mm or 125mm outlet where modern units use 150mm. If you are upgrading to a more powerful hood, the existing duct may be the limiting factor.

The width of the aperture. Integrated hoods sit inside a specific cabinet cut-out. Standard widths are 60cm, 70cm, 90cm and 100cm, but the depth and the fixing points vary between brands.

The height clearance. If the old hood was fitted below the minimum height — which happens a lot in older kitchens with low wall units — the replacement may not legally or safely go in the same spot. That can mean moving the wall unit above it.

The usual reasons people replace rather than repair: the motor is on its way out and the part costs more than a new unit, the hood is recirculating and they want it ducted, or the kitchen is being refitted and the old hood does not suit the new layout. If the unit is under five years old and the problem is a specific fault, a repair is normally the better call.

Keeping the filters clean

Filters are the maintenance job people skip, and they are the reason a hood loses power over time.

Grease filters are the metal mesh panels on the underside of the hood. They catch the fat before it reaches the motor and the duct. Take them out, run them through the dishwasher on a hot cycle, or soak them in hot water with washing-up liquid and a scoop of soda crystals, then scrub gently and dry fully before refitting. Do it every one to three months depending on how much you fry.

Carbon filters only exist in recirculating hoods. They are what removes the smell. They cannot be washed — the granules saturate, and once they are full they do nothing. Replace them every three to six months. Some newer models are regenerable in a hot oven, but check the manual before trying it.

If the hood smells stale even with clean grease filters, the carbon filter is the culprit.

Cleaning a separate extractor fan is a different job with different steps, especially in bathrooms and utility rooms where the fan is often boxed in or sits inline in the ceiling. Our guide to extractor fan cleaning covers how to get into the unit safely, what to use on the fan blades and housing, and how often each type needs doing.

When the fan runs but nothing gets extracted

This is the most common complaint we get about kitchen ventilation. The motor spins, the noise is there, but hold a sheet of paper up to it and nothing sticks.

It is nearly always airflow rather than electrics — something between the fan and the outside is blocking, leaking or fitted wrongly.

Rather than repeat the diagnosis here, the full fault-finding sequence is on our dedicated page: extractor fan working but not extracting. Start there, work through the checks in order, and you will usually find it without needing anyone out.

When the extractor fan gets noisy

Rattling, humming, grinding and whining all point at different things, and the sound itself is the diagnostic clue.

Some of it is a five-minute fix. Some of it means the motor bearings have gone.

Our guide to an extractor fan making a noise matches each type of noise to its likely cause and tells you which ones are worth repairing. Worth a read before you order a replacement unit.

Landlords: what you are responsible for

If you let property in London, kitchen and bathroom ventilation is not optional maintenance. It is the front line against condensation damp and mould.

Councils assess rented housing using the Housing Health and Safety Rating System under the Housing Act 2004, and damp and mould is one of the hazards they can act on. Where they find a serious problem they can serve an improvement notice. Ventilation is one of the first things an environmental health officer will look at.

Separately, the Homes (Fitness for Human Habitation) Act 2018 requires a rented home to be fit for human habitation for the whole tenancy, and ventilation is one of the matters taken into account when deciding that. Tenants can bring a claim directly rather than waiting on the council.

Rules in this area are being tightened — the government has been consulting on extending fixed repair timescales for damp and mould to private landlords, and a Decent Homes Standard is coming to the private rented sector. Check the current position on GOV.UK before relying on any of it.

Three practical points:

Check that extraction actually works at each tenancy change, not just that the fan powers on. The paper test takes ten seconds.

Where a tenant reports mould, resist the reflex to blame drying laundry indoors. Check the extract rate and the external vent first. A blocked outside vent produces exactly the pattern of mould people assume is a lifestyle problem.

Keep records. A dated note of ventilation checks and filter changes is useful evidence if a disrepair claim ever lands.

Book a cooker hood or extractor fan installation in London

If you need a hood fitted, an old one swapped out, ducting corrected or a fan that has stopped pulling looked at, we cover it.

Our engineers work across London on cooker hood installation, replacement and extractor hood repairs. Everything is fitted to manufacturer clearances and current building regulations, gas work is handled by Gas Safe registered engineers, and our workmanship is guaranteed for 12 months. We do not create or enlarge wall openings, so let us know if a duct route still needs forming.

Book a cooker hood installation in London and we will confirm a slot, quote before starting, and leave the kitchen clean.