What Part F asks of your hood, and where recirculating falls short
Approved Document F, under the Building Regulations 2010 for England, sets a minimum rate of air a kitchen extractor has to move. A cooker hood that ducts outside needs to shift 30 litres a second. An extract fan mounted elsewhere in the kitchen, working without a hood above the hob, needs to reach 60 litres a second.
A recirculating hood works on a different principle from a ducted one. It draws air through a grease filter and, on most models, a carbon filter, then blows that same air straight back out into the kitchen. The carbon filter cuts some of the cooking smell, and the grease filter catches airborne fat before it settles on your cabinet doors, but neither filter takes the moisture out of the air.
That is where a recirculating hood parts company with the regulation. Part F compliance needs a kitchen extract that vents to outside, and a recirculating hood never does that: it moves air around the room. Fitted where there is no route to an outside wall or roof, it will still take the edge off cooking smells day to day, but it does not count toward your Part F obligation, and a builder or building control officer checking the kitchen against the regulations will ask where the ducted extract is.
For a new kitchen or a refit that building control has to sign off, that makes the ducting route something to settle before the cabinets go in.
Air changes, duct losses and hood height, explained
Sizing a hood by air changes
One way to size a cooker hood is to work out how many times the air in the kitchen needs replacing each hour, then choose a hood whose extraction rate meets that figure. It gives you a target in cubic metres per hour that scales with the room. A large open-plan kitchen with a low ceiling needs a different extraction rate from a small galley kitchen, even with the same hob, because the volume of air being turned over is different.
Why ducting length and bends matter
The extraction rate printed on a hood's box is measured with the fan running free. Every metre of duct, and every bend the air has to turn through, adds resistance, and that resistance reduces the airflow the hood can actually deliver once it is installed. A hood specified to just meet the Approved Document F minimum on paper can end up below it once its duct run is accounted for, particularly where the route to the outside wall or roof involves more than one bend.
This is why the run from the hood to the outside air matters as much as the model you choose. A short, straight duct keeps most of the stated extraction rate; a longer run with several bends can lose enough that a higher-rated hood, or a shorter route, is needed to still meet the figure your kitchen requires.
Height above the hob when the instructions don't say
Approved Document F sets the mounting height for a cooker hood at whatever distance the manufacturer's own installation instructions give. Where those instructions are silent on the point, the fallback is a distance of 650 to 750mm above the hob.
That range gives you room to work with, but it isn't a free choice. Check the installation instructions that came with the hood first, and only fall back to the 650 to 750mm range if they have nothing to say on the point.
Airflow and noise across the speed range
The table sets airflow and noise at the lowest and highest normal speed for two Franke hoods against the Approved Document F minimum, converted into the same unit, so you can see how much headroom a hood carries above the regulation's floor.
| Hood | Speed 1 | Top speed | Boost |
|---|---|---|---|
| Franke FDW 908 IB XS (downdraft, 900mm)Energy class A. Speeds 2 and 3 sit at 280 m³/h/49 dBA and 350 m³/h/53 dBA. Figures read from Franke's own product page, 16 September 2026. | 200 m³/h at 43 dBA (speed 1) | 440 m³/h at 57 dBA (speed 4, top normal speed) | 720 m³/h at 68 dBA (boost) |
| Franke Box Premium FBFP XS A70 (700mm)Energy class A. Speed 2 sits at 420 m³/h and 56 dBA. Figures read from Franke's own product page, 16 September 2026. | 290 m³/h at 47 dBA (speed 1) | 610 m³/h at 64 dBA (speed 3, top normal speed) | 720 m³/h at 68 dBA (boost) |
| Approved Document F minimumThe regulation sets a minimum extract rate. It does not set a noise limit at any speed. | 108 m³/h (30 litres a second) from a hood that vents outside | 216 m³/h (60 litres a second) from an extract fan elsewhere in the kitchen |
The two hood rows come from Franke's own published specification pages, read 16 September 2026. The Approved Document F row converts the regulation's litres-a-second figures into the cubic-metres-an-hour unit hood makers use, so the three rows can sit in one table. These are the two models published here.
Two things worth checking alongside your extraction figures
The height you mount a cooker hood at is set against the same worktop and appliance height stack that runs through the rest of the kitchen, so it helps to check the two together before you fix anything to the wall.