Guide
Ducted or recirculating cooker hood: which do you need?
A ducted cooker hood draws steam, grease and smells out through a duct to the outside, while a recirculating hood passes the air through grease and carbon filters and returns it to the room. Ducted hoods remove moisture and meet ventilation rules more easily; recirculating hoods suit places where ducting is impractical, but usually need a separate extract fan.
How does a ducted cooker hood work?
A ducted hood has a fan that draws cooking air through a washable grease filter and pushes it along a duct to a grille on an outside wall or through the roof. It removes moisture, heat, smells and grease from the kitchen altogether, which is why it is the more effective choice wherever a duct route is practical.
Performance depends as much on the duct as on the hood. A short, straight run of the right diameter lets the fan work properly; a long run with several bends or a duct narrower than the hood outlet cuts the airflow and makes the fan louder. Fitting the hood is the easy part; planning the duct route is where most of the thought goes.
How does a recirculating hood work?
A recirculating hood draws air through a grease filter and then through carbon filters, which absorb smells, before blowing it back into the room. It needs no duct to the outside, so it can go on an internal wall, an island or in a flat where a new outside vent is not allowed.
The limitation is moisture. Steam from cooking passes straight through, so condensation stays in the room and can lead to mould on cold walls and window reveals. Carbon filters also lose effectiveness as they fill up and need replacing at the intervals in the manufacturer's instructions, which is an ongoing cost to factor in.
What do the ventilation rules say?
In England and Wales, Approved Document F expects a kitchen to have extract ventilation. For intermittent extraction, that is about 30 litres per second from a cooker hood extracting outside, or 60 litres per second from a fan elsewhere in the room. A refit should not leave ventilation worse than it was before.
Because a recirculating hood does not remove moisture, another means of extract, such as a wall or ceiling fan ducted outside, is usually needed alongside it. In Scotland, the domestic Technical Handbook (standard 3.14) also expects kitchen extract; in Northern Ireland, Technical Booklet K covers ventilation.
What affects how well a ducted hood performs?
Most complaints about weak or noisy hoods come down to the installation rather than the hood itself. A powerful fan cannot overcome a long, narrow duct full of bends. These are the points that make the biggest difference to how well a ducted hood works in practice:
- A short duct run, with as few bends as possible
- Rigid ducting rather than long lengths of flexible hose
- Duct diameter matching the hood outlet, not reduced
- An external grille or wall vent with a backdraught flap
- A hood at least as wide as the hob, mounted at the height in its instructions
- Enough replacement air, from a trickle vent or door gap, for the fan to move air
Which type suits islands, flats and internal walls?
For a hob on an outside wall, ducted is usually straightforward. For an island, a ceiling or island hood can be ducted through the ceiling void if the joists run the right way, or a downdraft extractor can duct through the plinth. Where neither works, a recirculating hood with a separate extract fan is the usual answer.
In flats, a new vent through an outside wall may need planning permission and the freeholder's consent, so recirculating hoods are common. Check the lease, and where a ducted route exists through an existing vent, it is usually worth using. In a house, coring a new hole through an outside wall for a duct is routine work that the survey plans in.
What is a downdraft extractor?
A downdraft extractor sits behind or within the hob and rises from the worktop when in use, drawing steam sideways and down. The air is then ducted through the plinth to an outside wall, or filtered and recirculated. It keeps sight lines open over an island or peninsula, with no hood hanging from the ceiling.
Downdraft units take up space in the base unit below the hob, so drawers there are usually shallower, and the duct route through the plinth needs planning before the units are fixed. They tend to capture steam from tall pans less effectively than a hood above, so check the manufacturer's guidance on performance.
Do open-flued gas appliances affect the choice?
Yes. If the kitchen, or a room connected to it, has an open-flued gas appliance such as some older boilers or gas fires, a powerful extractor can pull combustion fumes back down the flue into the room. That is a carbon monoxide risk.
In that situation, a Gas Safe registered engineer should carry out a spillage test with the new hood running at full speed, and extra ventilation may be needed. A room-sealed boiler, which takes its air from outside, is not affected in the same way. The survey notes any gas appliances in or near the kitchen.
What does a cooker hood cost to install?
These are national guide ranges including VAT, varying by region and confirmed after a survey visit. They cover installation; the hood itself is supplied by you or priced separately. A like-for-like swap is quickest, because the duct and power are already in place, while a new route through a solid wall takes longest.
- Like-for-like cooker hood swap: £120–£240
- New ducted hood through an outside wall: £300–£900
- Island or ceiling hood installed: £300–£630
- Recirculating hood fitted: £120–£300
Questions
How often do carbon filters need changing?
Follow the manufacturer's instructions, as intervals vary by model and by how much you cook. Grease filters are usually metal and washable, often in a dishwasher. Carbon filters are not washable on most hoods and stop absorbing smells once they are saturated, so a hood that smells stale usually needs new ones.
Can a cooker hood be ducted through the ceiling?
Often, yes. The duct runs through the ceiling void between the joists to an outside wall, so the direction of the joists matters. Cutting or notching joists needs care and may need advice. Where the joists run the wrong way, a boxed-in duct below the ceiling or a different hood type may be needed.
What size cooker hood do I need?
A hood should be at least as wide as the hob, and slightly wider is better for capturing steam. Mount it at the height set out in the manufacturer's instructions, which differs for gas and electric hobs. Check its extraction rate and noise figures, and make sure the duct size matches the hood outlet.
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This guide is general information about kitchen fitting in the UK, not legal, tax, electrical or structural advice for your property. Rules differ between England, Wales, Scotland and Northern Ireland; check with your local authority or a qualified adviser before relying on it.