Should I buy a ducted or recirculating extractor hood?

Both hood types pull the plume off the hob and both catch grease in the same washable metal filter. What happens next is the whole difference: a ducted hood puts the air outside, and a recirculating hood puts it back in the room via a carbon filter. Moisture is the thing that decides it, because moisture is what makes a kitchen feel steamy and what condenses on cold surfaces afterwards.

Step by step

1. Work out whether a duct route exists at all.Look for the shortest run to an outside wall or up through the roof. An outside wall directly behind the hob is ideal. A run through a ceiling void, along a soffit, or through a bulkhead is normal. Judge it on length and number of bends, not just possibility.
2. Understand what each type actually removes.Ducted removes moisture, heat, grease and smell — everything the plume contains. Recirculating removes grease at the metal filter and smell at the carbon filter, and returns the moisture and the heat to the room unchanged.
3. Decide whether the moisture matters in your kitchen.If windows steam up, if there is condensation on a cold wall, if there is any mould behind units, or if you boil and steam a lot, the moisture matters and only ducting deals with it. If the kitchen is large, well ventilated and mostly used for frying, recirculating is a smaller compromise.
4. Price the ducted installation properly.Rigid duct, bends, a core drill through the wall, and an external grille with a backdraught flap. If it is going through a ceiling void or a roof, add the making good. This is where the cost difference between the two options actually lives.
5. Price the recirculating consumables properly too.Carbon filters are a repeating cost, typically every three to six months of regular cooking, and they are not cheap on some brands. Over ten years the difference against a one-off duct installation narrows considerably.
6. Check the hood is convertible before buying.Most hoods can be run either way with the right kit, but not all. If there is any chance the kitchen will be reconfigured later, buying a convertible hood keeps the option open for very little money.
7. If you must recirculate, buy more extraction than you think.A recirculating hood works the metal and carbon filters hard and has a lower effective performance for a given rating. Size up, and plan to open a window while cooking, which is the honest supplement to a recirculating hood.
8. Do not vent into a loft or a void, ever.A ducted hood terminating in a loft, a ceiling void or a cupboard puts several litres of water a week into the fabric of the house. It causes condensation, staining and rot, and it is one of the most damaging shortcuts in kitchen fitting.

Tips

• The external grille matters more than people expect. A fine insect mesh can add more resistance than the whole duct run — a louvred grille with a backdraught flap and a coarse mesh is the right choice.
• Going up a duct size, from 120mm to 150mm, is one of the cheapest ways to buy back extraction. Never reduce a hood's outlet down to a smaller duct.
• A hood that only ever runs on boost is undersized or badly ducted. A correctly sized installation should clear a kitchen on its middle setting.
• Run the hood on low from before you start cooking until ten to fifteen minutes after you finish. It is the single biggest improvement most kitchens can make for free.

Common mistakes

• Buying recirculating because the duct run looked awkward — An awkward duct run is usually still worth doing. A recirculating hood is a permanent compromise on the one thing — moisture — that causes the most trouble in a kitchen.
• Running a recirculating hood with no carbon filter fitted — The metal filter still catches grease, but nothing removes the smell. Many people never realise the carbon filter is a separate item that was not supplied with the hood.
• Using long flexible ducting because it is easier to install — Corrugated flexible duct has two to three times the resistance of rigid duct of the same length. It can halve a hood's real output before it leaves the kitchen.

Alternatives

• Ducted hood, rigid duct to an outside wall: The correct answer wherever a route exists. Removes moisture, heat, grease and smell from the house entirely.
• Recirculating hood with carbon filters: Catches grease and adsorbs smell, returns heat and moisture to the room. Acceptable only where ducting is genuinely impossible.
• Venting hob: Extraction built into the hob surface, drawing the plume down. Usually ducted through the floor or plinth. Removes the need for a hood over an island at significant cost.
• External or in-line motor: The fan sits in the loft or on the outside wall rather than in the hood. Much quieter in the kitchen, and it copes better with a long duct run.

Questions people ask