What Extraction Rate Do You Need for a Cooker Hood?
Air changes per hour recommended for kitchens
Part F minimum rate for a ducted hood adjacent to the hob
Extra extraction to allow for open-plan layouts
Recommended duct size for most domestic cooker hoods
What Is Cooker Hood Extraction Rate?
The extraction rate tells you how much air a cooker hood can move in one hour. It is expressed in cubic metres per hour (m³/h) — sometimes also shown as litres per second (l/s) or cubic feet per minute (CFM) on imported products. The higher the figure, the greater the hood’s capacity to remove cooking vapours before they spread through your home.
Extraction rate is not the same as motor wattageMotor wattage indicates how much power a fan uses, not how much air it moves. A higher-watt motor does not guarantee a higher extraction rate.. A well-engineered fan can shift more air with less energy than a poorly designed higher-wattage motor. When comparing hoods, always check the m³/h figure, not the wattage.
It is also worth understanding the difference between the rated extraction rate and the effective extraction rate. Manufacturers test hoods under ideal conditions: short, straight ducting with no bends. Once installed with real-world ducting, actual performance is typically lower. A 20–30% real-world reduction is common, which is why sizing with headroom matters.
UK Building Regulations: Minimum Extraction Rates
Approved Document F of the Building Regulations (2022 edition, in force from 15 June 2022) sets legally required minimum ventilation rates for kitchens in England. These are the absolute floor — not a performance target.
— 30 l/s (108 m³/h) where the cooker hood is adjacent to the hob and extracts externally
— 60 l/s (216 m³/h) where no cooker hood is fitted, or it does not vent to the outside
These figures apply to new builds and material changes of use from June 2022 onwards. Importantly, Part F also now requires that recirculating cooker hoods must be supplemented by a separate mechanical extract fan venting to outside air — a recirculating hood alone is not sufficient for compliance in new dwellings.
The Part F minimums are relatively modest. A typical kitchen of 40–60 m³ will need 400–600 m³/h to achieve 10 air changes per hour, which comfortably exceeds the regulatory floor. In practice, the ACH-based calculation is the more demanding and more useful benchmark for everyday performance.
How to Calculate the Right Extraction Rate
The most practical method is the 10 air changes per hour (ACH) rule. Multiply your kitchen’s volume by 10 to get the minimum extraction rate. For open-plan spaces or frequent high-heat cooking, use 12 instead.
Example: Kitchen 5m × 4m × 2.5m = 50 m³ → 50 × 10 = 500 m³/h
Calculating kitchen volume
Measure your kitchen’s length, width, and ceiling height, then multiply all three together. For rooms with sloped or vaulted ceilings, use the average ceiling height. In open-plan spaces, measure only the kitchen area rather than the entire open floor plan — but then apply a higher ACH multiplier (11–12) to account for the greater air volume the hood must contend with.
Adjusting for your cooking style and layout
The 10 ACH figure suits a standard enclosed kitchen with moderate cooking. Increase it if any of the following apply:
- You cook frequently with high heat: frying, grilling, or wok cooking
- Your kitchen is open-plan or flows into a dining or living area
- You are fitting an island hood, which captures air from all four sides
- Your ducting run is long or includes multiple bends
If your ducted installation is less than ideal — flexible hose rather than rigid duct, or more than one bend — add 10–25% to your minimum figure before selecting a model. This gives you real-world headroom without needing to run the hood at full power.
Extraction Rates by Kitchen Size
The table below shows minimum extraction rates at 10 ACH for common kitchen volumes. If your kitchen falls between two sizes, or you cook at high intensity, use the higher rate.
| Kitchen dimensions (approx) | Volume (m³) | Min. rate — 10 ACH | Open-plan — 12 ACH | Recommended hood size |
|---|---|---|---|---|
| 3m × 3m × 2.4m | 21.6 m³ | 216 m³/h | 260 m³/h | 300–400 m³/h |
| 4m × 3m × 2.4m | 28.8 m³ | 288 m³/h | 345 m³/h | 400–500 m³/h |
| 4m × 4m × 2.4m | 38.4 m³ | 384 m³/h | 460 m³/h | 500–600 m³/h |
| 5m × 4m × 2.5m | 50.0 m³ | 500 m³/h | 600 m³/h | 600–700 m³/h |
| 5m × 5m × 2.5m | 62.5 m³ | 625 m³/h | 750 m³/h | 700–900 m³/h |
| 6m × 5m × 2.7m | 81.0 m³ | 810 m³/h | 972 m³/h | 900–1100 m³/h |
The “recommended hood size” column adds 15–20% above the 10 ACH minimum to account for ducting losses and to allow the hood to operate comfortably at mid-speed rather than maximum during everyday cooking.
Ducted vs Recirculating: How Installation Mode Affects Performance
Ducted extraction: the higher-performance choice
A ducted hood draws air through grease filters and expels it outside via rigid ductwork. Because the contaminated air physically leaves the building, ducted hoods remove both moisture and odours permanently. This makes them the better option for controlling kitchen humidity and preventing condensation on walls and ceilings.
Performance depends heavily on the quality of the duct run. A short, straight installation in 150mm rigid duct delivers extraction rates close to the manufacturer’s rated figure. Longer runs, flexible hose, or multiple bends progressively reduce effective airflow. Sizing your hood with 15–20% headroom above your calculated minimum protects against this loss.
Under Part F (2022), a ducted hood adjacent to the hob must achieve at least 30 l/s (108 m³/h) to meet the intermittent extract minimum for new dwellings. In practice, the 10 ACH calculation sets a higher bar.
Recirculating: convenient, but with real limitations
A recirculating hood filters air through a metal grease filter and an activated carbon filterCarbon filters trap odour molecules through adsorption. They become saturated over time and must be replaced every 3–6 months to maintain effectiveness., then returns the cleaned air to the kitchen. Because no duct to outside is required, installation is far simpler and the hood can be positioned anywhere.
The trade-off is significant: recirculating hoods do not remove moisture. Steam from boiling or frying is cleaned of odours but released back into the room, which can contribute to condensation. Carbon filters must be replaced every three to six months as they become saturated; a blocked filter can reduce odour removal dramatically while the airflow figure appears unchanged.
Recirculating hoods can move comparable volumes of air to ducted models, but the lack of moisture removal means they perform differently in practice. If you cook regularly or are concerned about condensation, a ducted installation is preferable. From 2022, Part F requires recirculating hoods to be paired with a separate mechanical extract fan for new-build compliance.
Factors That Reduce Real-World Extraction Performance
The figure on a hood’s specification sheet is measured under laboratory conditions: no ducting, no external resistance. Real installations always perform below this rated figure. Understanding the main causes lets you compensate when sizing.
Ducting length, diameter, and material
Every additional metre of duct adds resistance and reduces effective airflow. Keep the total duct run as short as possible, and always use the duct diameter recommended by the manufacturer — typically 150mm for domestic hoods. Never reduce the diameter with an adaptor: narrowing the duct increases turbulence, worsens noise, and can cut airflow substantially. Smooth, rigid metal duct outperforms flexible hose because the corrugated walls of flexible hose generate significantly more resistance.
Bends and elbows
Each change of direction in the duct run creates resistance. A single 90° bend can reduce airflow considerably — far more than the “10% per bend” figure sometimes cited. CATA’s own ducting guide notes that a 90° bend can cut airflow by up to 30–50% depending on the duct length and fan power involved. Where a bend is unavoidable, two 45° bends create a gentler curve and cause less turbulence than a single 90° elbow. Position any bends as far from the hood outlet as possible, where air is already moving at speed.
Filter condition
Grease filters should be cleaned every four to six weeks under regular use — most dishwasher-safe aluminium mesh filters can simply go in a dishwasher. A heavily loaded grease filter restricts airflow and forces the motor to work harder, raising noise levels while reducing the effective extraction rate. For recirculating hoods, carbon filters need replacing every three to six months. There is no visual cue that a carbon filter is exhausted; set a calendar reminder rather than waiting until odours return.
Hood mounting height
Mounting height affects capture efficiency as much as raw extraction power. Most manufacturers recommend 65–75cm above an electric hob and 75–85cm above a gas hob. Too high and rising steam disperses before reaching the canopy; too low and the risk of heat damage to the hood increases. Always check the manufacturer’s specification for the model you are installing.
If you are also considering how to choose the right cooker hood style for your kitchen, mounting height requirements vary between chimney, island, and downdraft designs.
Common Sizing Mistakes to Avoid
Common mistakes when choosing extraction rates
- Using the formula on open-plan volume. Measure only the kitchen zone and apply 11–12 ACH rather than calculating the entire open floor plan at 10 ACH. The hood cannot ventilate a living room.
- Ignoring duct losses. Rated performance figures assume ideal ducting. Allow 15–25% above your minimum if you have a long run, flexible hose, or multiple bends.
- Choosing by appearance alone. Slimline decorative hoods can achieve high extraction rates, but always verify the m³/h figure rather than assuming form dictates performance.
- Confusing a quiet hood with an underpowered one. A well-engineered hood with a larger duct diameter runs quietly while still achieving strong airflow at mid speed. Noise and extraction rate are not inversely linked by design.
- Overlooking the recirculating limitation. A recirculating hood rated at 600 m³/h moves the same air volume as a ducted hood at the same rating — but it returns moisture to the room. For condensation control, ducted always wins.
- Running at maximum all the time. If you need maximum speed for everyday cooking, the hood is probably undersized. A correctly sized hood should handle normal cooking comfortably at mid speed, with boost available for intensive sessions.
Choosing the Right Cooker Hood
Once you have your minimum extraction rate from the formula, shortlisting becomes straightforward. Look for a hood rated comfortably above your minimum — not excessively so, as a very oversized hood used on minimum speed all the time offers no benefit and the motor may run less efficiently in that range.
Width and coverage
The hood should be at least as wide as your hob. Wider is better: a hood that overhangs the hob by 5–10cm on each side captures more of the rising plume, particularly at the front burners. Island hoods should be sized to extend beyond the hob on all sides where possible.
Fan speed settings
Multiple speed settings are not a luxury — they are essential for practical use. A three-speed hood lets you match power to the cooking task: low for simmering and boiling, medium for frying, and boost or high for grilling, wok cooking, or clearing a smoke incident. This also extends motor life and keeps energy consumption in check on lighter cooking days.
Energy efficiency
Look for hoods with an A or B energy rating. An efficient motor uses less electricity without compromising airflow, and LED lighting (standard on most current models) reduces running costs further. For guidance on balancing performance with noise in open-plan spaces, quieter, more energy-efficient models tend to perform better at the mid-speed settings used most often.
Noise levels
Noise is measured in decibels (dB) at maximum speed. A figure below 65 dB at full power is generally considered acceptable; below 60 dB at maximum is quiet. For open-plan kitchens or kitchen-diners, prioritise models with a low dB rating at mid speed rather than focusing only on maximum. The maximum setting is rarely used, so the mid-speed figure is a more useful guide to everyday experience.
Frequently Asked Questions
Summary: Getting Extraction Rate Right
The starting point is simple: multiply your kitchen’s volume by 10 to find a minimum extraction rate in m³/h. Choose a hood rated 15–20% above that figure to account for ducting losses, and size up to 12 ACH if the kitchen is open-plan or used for regular high-heat cooking.
UK Building Regulations (Part F, 2022) set a minimum of 30 l/s (108 m³/h) for a ducted hood adjacent to the hob in new dwellings — but the ACH-based calculation will typically demand a higher and more practical figure. Recirculating hoods now require a supplementary mechanical extract fan under Part F for new-build compliance.
Beyond the number itself, performance depends on how the hood is installed. Use rigid 150mm duct, keep the run short, avoid 90° bends where possible, and keep filters clean. A correctly sized hood running at mid speed in a well-ducted installation will outperform a higher-rated model in a compromised installation every time.