Guide · Extraction, light and power
What extractor airflow you need
The KÜINA team · Updated October 11, 2026
The short answer
Airflow is calculated on the volume of the kitchen, not the floor area: length × width × height in metres, multiplied by 10 air changes per hour for a closed kitchen and by 15 if it opens onto the living room. A closed 3 × 4 × 2.6 m kitchen needs around 310 m³/h; open, around 470.
The formula, and the mistake doing the rounds
The sum is this, and it fits on one line:
length × width × height × air changes the result is in cubic metres per hour (m³/h), which is the unit the hood is rated in.
Air changes per hour are 6 to 12 in a closed kitchen and 12 to 15 if it opens onto the living room, because the air to be moved is that of the whole space and because the steam escapes into a room where nobody wants it.
Work out yours
Enter your kitchen dimensions. If it opens onto the living room, tick it: it changes the answer considerably.
How much airflow your hood needs
Your kitchen dimensions in metres, with decimals if needed.
Recommended airflow
— m³/h
- Mounting height: 65–75 cm over induction, 75–85 over gas.
- Above 400 m³/h you need to let air in: a vent, a window with trickle ventilation or a door without a draught seal. If you have an open-flued gas boiler or water heater, check with the installer before buying.
- And remember the ducting: each 90° bend costs 10 %, and going from 150 to 120 mm diameter costs 25 to 40 %. Ask for a hood with some margin over this figure.
Volume times air changes per hour: 10 for a closed kitchen, 15 for an open one. It is the calculation from the section above.
Ducting eats airflow
The figure the manufacturer gives is measured on a bench with the air discharging freely. In your home the air has to travel down a duct, turn corners and pass a grille. That subtracts, and nobody mentions it in the showroom.
| What is in the run | Roughly what it costs |
|---|---|
| Each metre of rigid duct beyond 3 m | 3 – 5 % |
| Each 90° bend | 10 % |
| Flexible aluminium duct instead of rigid | 20 – 25 % over the whole run |
| External grille with bird mesh | 5 – 10 % |
| Reducing from 150 to 120 mm diameter | 25 – 40 % |
The diameter reduction does the most damage and is the most common: the unit will not take the 150 duct, so somebody fits a 120 adapter. That turns a 600 m³/h hood into a little over 400, and it gets noisier too.
- Diameter: 150 mm whenever possible. 125 only when there is no alternative.
- Rigid duct, not flexible corrugated. Corrugated is easy to fit and poor to use.
- A short run with as few bends as possible. Two bends is reasonable; four is a problem.
- An external grille with opening louvres, not a fine mesh that clogs with grease.
The air coming in, which is half the problem
A hood does not "suck up" smoke: it moves air. And to take out 600 m³/h, 600 m³/h have to come in from somewhere. In a modern flat with airtight windows that air does not come in, and three things follow: the hood is noisy, it does not pull, and the doors become hard to open.
And there is one case that is not about comfort but about safety: if the home has a gas boiler or water heater with a natural flue, a powerful hood can reverse the draught and pull combustion gases into the house. This is not theoretical and it is regulated.
- If the hood exceeds 400–500 m³/h, provide an air inlet: a vent, a window with trickle ventilation or a door without a draught seal.
- If there is an open-flued gas boiler or water heater in the same home, check with the gas installer before choosing the hood. A safety device that cuts out on detecting depressurisation may be required.
- With a room-sealed boiler, which draws its air from outside through a concentric flue, this problem does not arise.
Height, noise and what you actually notice
| Figure | What to look at |
|---|---|
| Height above an induction hob | 65 – 75 cm |
| Height above a gas hob | 75 – 85 cm |
| Hood width | Equal to or wider than the hob. 80 over a 60 hob is better |
| Noise | The dB(A) at the speed you will actually use, not the lowest |
| Grease filter | Metal and dishwasher-safe |
| Carbon filter | Only for recirculation; replaced every 6–12 months |
Two things matter more than power: that the hood covers the hob, because no amount of airflow catches steam escaping sideways, and that you can use it without it bothering you. An 800 m³/h hood that sounds like a hairdryer gets used on speed 1, and then the 800 is irrelevant.
Recirculation: when yes and when no
A recirculating hood filters grease through a carbon filter and returns the air to the kitchen. It removes neither steam nor smell: it leaves them cleaner, indoors.
| Situation | What to do |
|---|---|
| There is a duct to outside | Vent outside, no hesitation |
| Closed kitchen, no duct | Recirculation, with the carbon filter kept up to date |
| Open kitchen, no duct | Before deciding, see whether a duct can be run: €400 – 900 |
| Old flat with no flue | Out through the facade or a light well, if the building allows |
A hob with built-in extraction is the alternative that works best when there is no duct, because it draws at pan level, where the steam is, rather than waiting for it to rise. It comes in ducted and recirculating versions.
Questions we get asked
How many m³/h does an extractor need?
Multiply length × width × height of the kitchen in metres and the result by 10 if it is closed, or by 15 if it opens onto the living room. A closed 3 × 4 × 2.6 kitchen needs around 310 m³/h; open, around 470.
Is it calculated on the floor area?
No, on the volume. It is the most repeated mistake: ignoring the ceiling height leaves the calculation at less than half.
How high should the hood go?
65 to 75 cm above an induction hob and 75 to 85 above a gas one. Lower and you hit your head; higher and it stops catching the steam.
Does a recirculating hood remove smells?
It removes grease, not smell or steam. In a closed kitchen that is bearable; in one open to the living room it is very noticeable, and it is worth pricing a duct before resigning yourself.
Shall we look at it with your kitchen on screen?
An hour in the showroom, your kitchen on screen and the price fixed the same day. No commitment, and no follow-up calls unless you want them.
