Quick answer
A ducted rangehood vents cooking moisture and grease outside, so it's the better performer and the standard MTN Kitchens recommends for most Auckland kitchens; recirculating only filters and re-releases air, used where ducting isn't possible (typically apartments or body-corp-restricted units).
The rangehood is the cheapest thing in the kitchen that causes the most arguments. A few hundred dollars of stainless and a fan, and yet it decides where your cabinetry stops, whether the soffit gets boxed in, whether the body corporate signs off, and whether the new owner cooks a steak in year one and ends up with grease streaked across the ceiling. We've installed over 2,000 kitchens out of our East Tamaki workshop across 23 years, ten-plus a week, and the ventilation question turns up on nearly every one. Ducted or recirculating is the headline. The real answer lives in the ceiling void, the wall framing, and the body corp rules nobody read.
One vents outside. One just filters and returns.
Which one you can have is often not your choice at all. It's set by the slab, the apartment stack, the external wall, and whoever owns the facade. The trick is knowing that before the cabinetry is drawn, not after the GIB is up and the painter's booked.
Key points
- Ducted exhausts moisture and grease outside; recirculating filters and returns the air to the room. Ducted wins on performance every time.
- Size extraction to the cooktop and room volume, not the brochure photo. A gas wok burner needs serious pull; an induction hob in a studio needs far less.
- Apartments and terraces are where it gets hard. Venting through a body-corp facade usually needs sign-off, and some stacks simply won't allow a new penetration.
- The expensive mistakes are the ones roughed in late. Sort the duct route, the power, and the hole through the wall or ceiling before the linings go on.
- Noise is a spec line, not an afterthought. Sone or dB(A) ratings, remote motors and duct diameter all change how loud the thing runs.
What ducted and recirculating actually do
A ducted rangehood (also called extraction or vented) pulls air up through the grease filters, then pushes it along a duct and out through an external wall or roof. The cooking byproducts you actually care about, steam, oil mist, heat, the smell of fish, leave the building. Done right, your windows don't fog, your gloss cabinet doors don't grow a sticky film, and the GIB above the hob stays paint-fresh. This is the proper job and it's what we fit wherever the building lets us.
A recirculating rangehood has no duct to outside. Air goes through the grease filter, then through a charcoal (carbon) filter that adsorbs some of the odour, and then straight back into the kitchen. It does nothing for moisture or heat, because that air never leaves the room. The charcoal filters clog and need swapping every few months to a year depending on use, and most people never do, so by year two the thing is just a noisy light fitting. We fit recirculating units where ducting is genuinely impossible, not where it's merely inconvenient.
Sizing the extraction: match it to the cooktop
Extraction is measured in cubic metres per hour (m3/h) or sometimes litres per second. The number you need is driven by two things: how much heat and steam your cooktop throws off, and how big the room is. A rule we use as a starting point is that the hood should be able to turn over the kitchen air volume roughly ten to twelve times an hour. Work out the room volume (length x width x height), multiply by twelve, and that's the rough m3/h you want on boost. A 3.5m x 3m kitchen with a 2.6m stud is about 27 cubic metres, so you're looking for something in the 300 to 350 m3/h range minimum, more if the cooking's heavy.
Then layer in the cooktop. Induction and ceramic electric are relatively clean and gentle on steam, so the lower end is fine. Gas burns dirtier and throws more heat and combustion byproduct, so push the capacity up. A serious gas cooktop or a wok burner can want 600 to 900 m3/h and a wide hood to catch the plume. The hood should also be at least as wide as the cooktop, ideally a size up: a 900mm hood over a 600mm hob catches the spill that a tight 600mm hood misses. Mount height matters too, around 650 to 750mm above an electric hob, a touch higher over gas per the appliance instructions.
Where people get the number wrong
Two traps. First, the brochure figure is almost always the free-air rating, measured with no ducting attached. Once you add three metres of duct, a couple of bends and an external weather cowl, real-world airflow can drop a third or more. So spec with headroom. Second, people size for the hood and forget the duct. Choke a 900 m3/h motor through 100mm flexible duct with four tight bends and you've wasted your money, it'll be loud and weak. The duct is part of the spec, not plumbing detail to sort on site.
| Cooktop | Typical room | Target on boost | Min hood width |
|---|---|---|---|
| Induction / ceramic | Studio or small (under 25 m3) | 250 to 350 m3/h | 600mm |
| Induction / ceramic | Standard kitchen | 350 to 500 m3/h | 600 to 900mm |
| Gas 4-burner | Standard kitchen | 500 to 700 m3/h | 900mm |
| Gas wok / 5-burner | Open-plan living | 700 to 900 m3/h+ | 900 to 1200mm |
Duct diameter, length and bends: the part that decides performance
You can buy the best motor on the market and strangle it with bad ducting. The rules are simple and we hold to them. Use rigid metal duct wherever you can, smooth-bore, not the corrugated flexible stuff, because the corrugations create turbulence and rob airflow. Keep the diameter up: 150mm (six inch) is the standard we want for most extraction hoods, and dropping to 125mm or 100mm should be a deliberate choice for a low-output unit, not a default. Every reducer and every 90-degree bend costs you flow, so keep the run short and the bends sweeping rather than sharp.
The route is where Auckland building stock fights you. A single-storey home on a flat site, easy, straight up through the ceiling void and out the roof, or sideways through an external wall behind the hob. A two-storey with a bedroom above the kitchen, now you're routing around joists and you may need a soffit bulkhead to hide a horizontal run to the nearest external wall. A mid-floor apartment with the kitchen on an internal wall is the worst case, sometimes there's simply no honest path to outside. Always vent to outside, never into the roof cavity or the ceiling void. Dumping warm, wet, greasy air into your roof space is how you rot the framing and void the building work.
Apartments, terraces and the body corporate problem
This is where the job stops being about fans and starts being about ownership. In an apartment or a terraced unit under a body corporate, the external walls, the facade and often the roof are common property. You don't own them. Cutting a new penetration through that cladding to vent a rangehood means altering common property, and that almost always needs body corporate consent, sometimes a resolution at a general meeting, and sometimes it's flatly refused to keep the building envelope and the look of the facade consistent. We see this constantly on retrofit and upgrade work. If you're touching multiple units, our piece on body corporate kitchen upgrades walks through how that approval process actually runs.
Many apartments were built with a shared kitchen extract riser, a duct that runs vertically through the building to a fan on the roof. If yours has one, the original kitchen ties into it and you keep that connection, you don't get to add an oversized motor that overpowers the shared system, because that pushes other people's cooking smells into their neighbours' units. If there's no riser and no external wall you're allowed to penetrate, recirculating is often the only legal option you've got, and you build the moisture answer in around it. The constraints are the design driver, not the appliance you fell in love with. We cover how this and other things shift between unit types in apartment vs townhouse kitchens for developers.
Ventilation and the Building Code
In New Zealand, kitchen ventilation sits under Building Code clause G4 (Ventilation), which requires habitable spaces to have adequate ventilation, and it ties in with clause E3 (Internal Moisture), which is about keeping moisture from causing damage to the building or the health of occupants. A rangehood isn't the only way to meet these, an openable window of adequate area can satisfy ventilation in many residential situations, but a ducted hood over the cooktop is the most effective tool for getting cooking moisture out at the source, which is exactly where E3 wants it dealt with.
For a standard residential kitchen swap, you're usually working within the existing consented building and a like-for-like rangehood replacement is maintenance, not new building work. Cut a new external penetration, alter the structure, or run gas, and you may move into territory where consent or a Licensed Building Practitioner sign-off comes into play, and gas appliances bring their own certification through a registered gasfitter. For commercial cooking it's a different world again, mechanical makeup air, fire-rated ductwork and grease management under the relevant standards, which we get into in commercial kitchen compliance in NZ. When in doubt, we'll flag it on the quote rather than guess.
Noise: the spec line people skip
A hood you can't talk over on boost is a hood that gets switched off, and a hood that's off does nothing. Noise is rated in sones or in dB(A), lower is quieter. As a feel for it, a quiet hood on a normal setting sits around 40 to 50 dB(A); push to full boost and a powerful unit can hit the mid-60s, which is loud enough to end conversation in an open-plan living space. Since most modern homes have the kitchen open to the lounge, this is not a small thing, it's the difference between a kitchen people use properly and one they suffer.
Three levers move noise. Bigger, smoother ducting lets the air move without screaming through a restriction, so the 150mm rigid duct that helps performance also helps the noise. A remote or external motor (mounted in the roof or on the external wall rather than in the hood) moves the loudest part of the system away from your ears, and it's the quietest setup we fit, worth considering on a high-end open-plan job. And simply sizing the hood with enough capacity means you run it on a lower, quieter setting most of the time instead of always flat out on boost. Good lighting under the hood matters too while you're cooking, which ties into the wider kitchen lighting plan.
Hood styles and where they suit
The duct decides the performance.
The style isn't just looks, it changes the ducting and the cabinetry. A canopy or wall-mounted hood sits on an external or internal wall above the hob and is the most common, straightforward to duct out the wall behind it or up. An undermount or concealed hood hides inside an overhead cabinet for a clean line, popular in townhouse and rental specs because it disappears, but you lose some capture area to the cabinet. An island hood drops from the ceiling over an island cooktop, looks great, but the duct has to travel through the ceiling and that locks in your ceiling void route early, no afterthoughts allowed.
Then there's the downdraught and the increasingly popular induction-with-integrated-extraction cooktop, where the extraction pulls down through a slot in the bench beside the burners and ducts under the floor or out the back of the cabinetry. They're brilliant in an island where you don't want a hood blocking sightlines, but they demand floor or sub-bench duct routing planned at framing stage and they cost real money. If you're weighing an island layout at all, size it properly first, our kitchen island design and sizing guide covers how the extraction choice feeds back into the bench dimensions.
A worked Auckland scenario
Take a developer building eight three-bedroom terraced houses in Mount Wellington, two storeys, kitchen at the rear of the ground floor on an open-plan living area, induction cooktops to keep it clean and gas-free. The kitchen sits against the rear external wall on six of the eight units, so those get a ducted canopy hood, 150mm rigid duct straight out the back wall, stainless cowl with a backdraught flap, around 450 m3/h, mounted at 700mm. Clean, code-friendly, gets the moisture straight out, and because the spec's identical across those six we cut the wall penetrations the same way every time. Consistency like that is the whole point, which is why we push for it in keeping kitchen spec consistent across 30-plus units.
The two corner units have the kitchen against a party wall shared with the neighbour, no external wall behind the hob and a bedroom above, so a vertical run is blocked by the floor and a horizontal run would need a long soffit bulkhead chasing across to the side wall. On those two we run the duct sideways inside a boxed soffit to the nearest external wall, a bit more carpentry, planned at framing so the bulkhead is deliberate rather than a patch-up. Decided at design stage, this is a non-event. Discovered at install, it's a variation, a delay and an annoyed client. That's the difference, and getting it onto the drawings early is exactly the kind of thing that keeps variations and RFIs off the kitchen package.
Nine times out of ten the ducting argument is over by the time we arrive, because nobody decided the route before the gib went up. Sort it on the plan and the install is a half-day. Sort it on site and it's a fight with a joist.
What to rough in early
Ventilation is a pre-line trade. Almost everything that makes it cheap and clean happens before the plasterboard goes on, and almost everything that makes it expensive happens because someone left it till after. Get these decided and marked up at the same time you finalise the layout, not when the hood turns up in a box.
- The duct route, end to end, from hood position to external termination, including any soffit bulkhead or ceiling void path, agreed on the drawings.
- Duct diameter and material, 150mm rigid as the default, with bends kept to a minimum and swept rather than sharp.
- The external penetration location and the cowl type, plus body corporate or facade sign-off if it's an apartment or terrace.
- Power at the hood position, a dedicated point at the right height, and a separate supply if a remote motor's going in the roof.
- Confirmation of recirculating vs ducted, because a recirculating hood needs no duct but does need the moisture handled some other way.
- Cooktop type and width confirmed, since that sets the hood size and the extraction target before anything's ordered.
Get those six locked and the install is a half-day with no surprises. Leave them loose and you're cutting bulkheads into finished ceilings and explaining a variation. The whole order-to-install flow runs smoother when this is sorted up front, which is the point of our what to expect from order to install walkthrough.
Ducted vs recirculating: how to actually choose
If you can duct to outside, duct. It performs better, deals with moisture, keeps the kitchen cleaner and adds value at resale because buyers notice a kitchen that doesn't reek of last night's dinner. The only good reasons to go recirculating are real ones: a mid-floor apartment with no external wall and no riser, a heritage facade you're not allowed to touch, or a body corporate that's said no. In those cases recirculating is a sensible compromise, not a failure, but you commit to changing the charcoal filters and you build in a moisture answer alongside it.
Across a development, the smart move is to standardise. Pick the hood and the duct spec that suits the majority of your units, identical termination, identical diameter, and only deviate where the building forces your hand, like those two corner terraces. Standard spec means faster installs, fewer mistakes, and trade pricing that holds across the whole job. Because we run our own East Tamaki workshop and price trade direct with no showroom markup, the saving on a repeated, well-specified ventilation detail across twenty kitchens is real money, not rounding.
Frequently asked questions
Is a recirculating rangehood ever good enough?
For a low-use kitchen, a clean induction cooktop and a unit where you genuinely can't duct to outside, yes. It catches grease and knocks back some odour. Just know it does nothing for steam or heat, and the charcoal filters need replacing every few months to a year or it stops working. If ducting is possible, ducted is always the better job.
What size rangehood do I need?
Match it to the room volume and the cooktop. As a rough start, aim to turn over the kitchen air about twelve times an hour, then size up for gas or heavy cooking. A standard induction kitchen is often fine around 400 to 500 m3/h; a gas wok burner can want 700 to 900. The hood should be at least as wide as the cooktop, ideally a size up.
Can I put a ducted rangehood in my apartment?
Only if there's a path to outside you're allowed to use, an existing shared extract riser, or body corporate consent to cut a new facade penetration. The external walls are usually common property, so you can't just drill through. Check the operational rules and ask the committee before you commit, because if the answer's no you're back to recirculating.
Where does the rangehood duct have to vent to?
Outside the building, always, through an external wall or the roof with a proper cowl. Never into the roof cavity or ceiling void, that dumps warm wet greasy air into your framing and causes rot and mould over time. It's a moisture and durability problem, and it's the kind of thing that should never pass a decent install.
Why is my rangehood so loud on boost?
Usually undersized capacity forcing it to run flat out, or the airflow being strangled by narrow, kinked or corrugated ducting. Bigger 150mm rigid duct, fewer bends, and a hood with enough capacity to do the job on a lower setting all bring the noise down. A remote motor in the roof is the quietest option if you want near silence in an open-plan space.
Does a new rangehood need a consent or LBP sign-off?
A straight like-for-like replacement in an existing kitchen is generally maintenance and needs neither. Cutting a new external penetration, altering structure, or adding gas can change that, and gas always needs a registered gasfitter. We'll flag anything on your job that crosses into consent or sign-off territory rather than leave you to find out later.
Ventilation is one of those details that's invisible when it's done right and a constant headache when it's not. Get the route, the diameter, the termination and the body corp question sorted before the linings go on, match the extraction to the cooktop, and the rangehood just quietly does its job for twenty years. Send us your plans or your unit count and your cooktop spec and we'll tell you exactly what'll duct, what won't, and what it costs, with a full trade-priced quote back within 24 hours from our East Tamaki workshop. One contract, one invoice, supplied and installed.