Kitchen extractor fans draw fumes through filters and a capture zone, then vent or recirculate the air to cut smoke, grease, and odors.
Cooktops release steam, grease mist, fine particles, and smells. A range hood, also called a kitchen extractor fan, pulls that plume into a capture zone and moves it through metal grease filters. In ducted setups the fan sends air outdoors; in recirculating setups the fan pushes air through charcoal before the air returns to the room. Both styles lower smoke and haze, but the path the air takes is different. How do kitchen extractor fans work? In practice, the fan creates pull while the canopy holds the plume so filters can do their job.
How Kitchen Extractor Fans Work In Practice
Every hood follows the same pattern: create a low-pressure pocket near the hob, catch the plume, filter it, move it away. The list below matches the flow.
Capture Zone And Hood Geometry
The canopy forms a pocket that holds the plume long enough for the fan to draw it in. Deeper canopies and baffles enlarge that pocket. The hood sits 650–750 mm above the hob unless the maker states another height, which helps the pocket line up with the rising jet.
Grease Filter
Aluminium mesh or stainless baffles strip out oil droplets so they do not coat ducts or the kitchen. Mesh needs a wash in hot soapy water; baffles can go in a dishwasher. A clean filter keeps airflow steady.
Fan And Duct Or Recirculation
The wheel (centrifugal or mixed-flow) supplies the pressure to move air. A ducted model sends that air outdoors through smooth, short ducts with gentle bends. A recirculating model routes air through charcoal to reduce odour, then returns it indoors.
How Do Kitchen Extractor Fans Work? — Step-By-Step
- Heat from pans lifts a buoyant plume loaded with aerosols and water vapour.
- The canopy and side capture pans corral that plume under the hood.
- The fan draws air through grease filters that trap oil.
- In a ducted hood, the cleaned air heads outdoors; in a recirculating hood, it passes charcoal and goes back to the room.
- Fresh air slips in from the rest of the home as make-up air.
Quick Comparison: Ducted Vs Recirculating
This table covers the air path, what gets removed, upkeep, and best use cases.
| Type | What The Fan Does | Best Use |
|---|---|---|
| Ducted | Moves filtered air outdoors through a duct run. | Regular frying, searing, high-heat wok work, gas cooktops. |
| Recirculating | Pushes air through grease mesh then charcoal, returns air indoors. | Flats without duct routes, light boiling and simmering. |
| Ceiling Cassette | Catches the plume higher up; needs strong capture and careful layout. | Open-plan rooms with an island hob. |
| Downdraft | Pulls air sideways and down into a pop-up slot. | Design-led kitchens with limited headroom above the hob. |
| Microwave Hood Combo | Compact unit; airflow and capture are modest. | Small spaces and light cooking. |
| Inline Remote Fan | Fan sits in the loft or roof; duct carries air away. | Noise-sensitive installs where a quiet cook zone matters. |
| External Fan | Fan bolted outdoors pulls air through the duct. | Long duct runs where a strong pull is needed. |
Airflow Ratings, Noise, And Capture
Airflow (CFM Or L/s)
Marketing often lists fan flow at zero pressure. Real-world flow falls with filters, duct bends, and roof caps. Aim for a hood that can hit your local code rate while still staying quiet on a mid setting.
Noise (Sones)
Sones translate sound into a simple scale a homeowner can compare. About 1 sone sounds like a quiet fridge; normal speech lives near 4 sones. Remote or external fans trim noise by moving the motor away from the cook zone.
Capture Efficiency
Capture efficiency is the share of the cooking plume the hood actually catches. Test labs measure it using a defined burner load and tracer gas in a chamber, as set out in the ASTM E3087 test method. A deeper canopy, good overhang, and the right height raise capture even if the raw CFM stays the same.
Code Basics And Safe Heights
Most homes need a local extract in the kitchen. Intermittent extract rates differ by setup: a hood that vents outdoors can meet 30 l/s right above the hob, while a room fan on the wall needs 60 l/s. For continuous systems a kitchen needs 13 l/s on high plus the whole-dwelling rate. Hood height sits between 650 and 750 mm unless the maker states otherwise; see Approved Document F (dwellings).
Choosing The Right Size And Style
Match The Hood To The Hob
Pick a width that equals or exceeds the hob width. Add extra overhang for an island to help catch cross-drafts. If you own a tall stockpot or cook with a wok, a deep canopy pays off by holding the plume.
Balance Flow And Noise
Run the lowest setting that keeps steam out of your face. A backdraft damper in the duct stops cold air entering when the fan is off. Look for smooth rigid duct, few bends, and a short run to keep noise down and flow up.
Make-Up Air
Strong fans pull air from somewhere. In a tight home, plan a make-up air path so doors do not slam and the boiler or fireplace stays safe. A trickle vent, an undercut at doors, or a dedicated make-up kit can do the job.
Filter Care And Charcoal Replacement
Grease mesh loses flow as oil builds up. Wash mesh monthly if you fry often; quarterly if you steam and simmer more than you sear. Baffle plates drain oil into a trough; empty and clean it to avoid drips.
Charcoal inserts do not remove moisture. Swap them every three to six months in a busy kitchen. If smells linger even with fresh charcoal, the load may be too heavy for recirculation and a duct route would serve you better.
Extractor Fans In Open-Plan Rooms
Open layouts add cross-draft from people moving, doors, and HVAC. Open kitchens need care. A larger canopy or a higher capture rating helps. Keep tall pots under the deepest part of the hood and turn the fan on a minute before heat goes on so the flow is already stable.
Installation Basics That Pay Off
Duct Design Rules
- Use rigid round duct where you can; keep flex duct short.
- Pick a diameter that matches the collar on the hood; upsize for long runs.
- Limit bends and use large-radius elbows.
- Seal joints with foil tape, not cloth duct tape.
- Terminate with a roof or wall cap that has a damper and bird guard.
Mounting Height And Clearances
Read the manual for gas vs electric clearances. Many hobs allow a lower mount for electric and an upper mount for gas. The range from 650 to 750 mm is common where no other rule is given.
Switching And Boost
A simple rule works: start low before you light a burner, step up during searing, then leave the fan on for a few minutes after the flame goes off. Some hoods add a timed boost and an auto shut-off to make this routine easy.
Real-World Sizing Guide
The table below groups common layouts with a practical target flow and notes. Size up if you cook smoky dishes or use a griddle pan often.
| Layout | Target Flow | Notes |
|---|---|---|
| 60 cm wall hood over electric | 180–250 m³/h (50–70 l/s) | Quiet on low for simmering; boost for frying. |
| 90 cm wall hood over gas | 300–480 m³/h (85–135 l/s) | Extra depth aids capture. |
| Island canopy 90–120 cm | 400–700 m³/h (110–195 l/s) | More headroom and cross-drafts need a higher target. |
| Downdraft behind hob | 300–600 m³/h (85–165 l/s) | Works best with pans near the slot. |
| Recirculating under-cabinet | As high as noise allows | Focus on charcoal upkeep; expect less odour aftercare. |
| External roof-mount fan | 400–900 m³/h (110–250 l/s) | Quieter at the cook zone; plan make-up air. |
Care, Cleaning, And Odour Control
Pop the mesh out and wash it in hot water and a mild degreaser. Rinse and dry before refitting. Wipe the canopy baffles and the tray under them. A monthly wipe stops sticky build-up that would whistle or buzz later.
For smell control in recirculating mode, fresh charcoal is the lever you have. Set a calendar reminder for the swap. If you only steam rice and boil pasta, filters last longer; burger night shortens that span.
Common Mistakes To Avoid
- Mounting a hood too high, which lets the plume escape.
- Using long, crushed flex duct that robs flow.
- Forgetting a backdraft damper.
- Installing a powerful hood with no make-up air path.
- Expecting a recirculating unit to remove humidity.
- Skipping filter cleaning.
When A Pro Site Visit Helps
If the duct run needs a bend around beams, or you plan a remote fan, a site visit saves time. A technician can measure pressure drop, set the correct duct size, and confirm a safe route past flues and soffits.
Bottom Line On Kitchen Extractor Fans
Now you can answer the question, “how do kitchen extractor fans work?” The fan creates a low-pressure pocket, the canopy holds the plume, filters remove grease, then the system vents outdoors or returns air through charcoal. Pick a size and layout that match your cook style, keep filters clean, and the kitchen stays clearer and cooler.